PDA

View Full Version : PC Power supply?



Simon
2005-05-16, 07:18
I have a spare PC power supply with various 5v outputs, would this be better than the standard one provided with SB2?

Regards
Simon

cliveb
2005-05-16, 08:44
I have a spare PC power supply with various 5v outputs, would this be better than the standard one provided with SB2?
PC power supplies are switched mode, which are not generally thought of as the greatest type for powering audio equipment. But then again, from the size of the thing, I suspect that so is the SB2 wall-wart. So whether the quality of the power coming from the PC supply would be any better is anyone's guess.

But one thing's for sure: unless it's one of those expensive fanless power supplies, it'll be a heck of a lot more noisy than the (silent) SB2 wall-wart. One might argue that the additional background noise of the PC supply's fan could be enough to mask any improvement you might get if it gave a cleaner feed.

There's only one way to find out, of course: try it and see if they sound different, and if so which one's better. But before you do, double check with Slim Devices that you won't do any damage. I'd assume that since a PC power supply is regulated, you'll be OK, but don't take my word for it. And whatever you do, don't get the 12V and 5V supplies confused!

max.spicer
2005-05-16, 09:03
PC power supplies are switched mode, which are not generally thought of as the greatest type for powering audio equipment. But then again, from the size of the thing, I suspect that so is the SB2 wall-wart.
What's a wall-wart?

Max

cliveb
2005-05-16, 10:04
What's a wall-wart?
Sorry, that's an Americanism. Although I'm British, I sort of assumed it was the most widely understood terminology.

A "wall-wart" is a power supply with built-in mains plug, the sort of thing we tend to call a "power brick" here in the UK.

Christian Pernegger
2005-05-16, 12:38
Are there battery based power supplies? I should think something that
runs its output off battery and keeps recharging that should be pretty
much perfect for audio equipment. Something like a online-type UPS
with DC output.

C.

Mike Hanson
2005-05-17, 02:34
I should think something that runs its output off battery and keeps recharging that should be pretty much perfect for audio equipment. Something like a online-type UPS with DC output.
Actually, batteries don't provide their exact voltage. It usually starts out a bit high, and then fades over time. Also, the chemical reaction that occurs in the batteries creates noise, analogous to "bubbles". At least that was what Naim determined, when they researched using batteries instead of regulated supplies.

I'm build a pre-regulated, linear supply for my SB1 and SB2. We'll see how that helps out.

-=> Mike Hanson <=-

Phil Leigh
2005-05-18, 10:22
Mike - I'd be keen to know how you get on with your home brew SB linear PSU - are you planning on including any mains filtration or will it be straight x-former/bridge/smoothing caps job? Any exotic parts planned?
Regards and best of luck,
Phil

Neil Sleightholm
2005-05-18, 14:07
I have a spare PC power supply with various 5v outputs, would this be better than the standard one provided with SB2?One thing to bear in mind is that switch mode PSUs have a minimum power rating which means that they won't work unless you draw the minimum current. From my bad memory I think this is 0.5A but it may be more.

Neil

Mike Hanson
2005-05-19, 04:13
Mike - I'd be keen to know how you get on with your home brew SB linear PSU - are you planning on including any mains filtration or will it be straight x-former/bridge/smoothing caps job? Any exotic parts planned?
I'm actually concentrating my efforts on the regulation stage. The initial prototypes are leaving the transfomer, rectifier and initial smoothing to an unregulated, linear wall wart. I've purchased a couple of these from a local surplus store, rated at 12VDC and 2A. Once I get done with the regulation stage, I may replace the wall wart with my own raw supply.

I'm taking this approach to keep the transformer away from the audio gear, while the supply regulation is very close to the load. Even if I do my own raw supply, it will still be positioned away from the regulation stage.

I'm using a tracking pre-regulator arrangement, in which one regulator sits on top of another. IOW, the first regulator's "ground" is the output of the second regulator. The first then feeds its output into the intput of the second regulator. This enables the first regulator to have a quiet ground (because it's really the regulated output of the second regulator). The second regulator has a smoother input supply (the output from the first regulator). I know it seems almost like pulling yourself up by your own bootstraps, but it really does work! :)

For regulators, my initial testing has been with basic Fairchild LM317T adjustable regulators. However, I'll probably end up using a low dropout-voltage LD1085V. I'll use a scope to see which configuration "looks" quieter, as well as do listening tests (because if it doesn't sound better, then what's the point?).

For capacitors, I'm just using a bunch of 10uF electrolytics, although I'm probably going to add/replace some of them with 1uF and/or 100nF tants.

You can read the ongoing saga (quite a learning experience for me) at http://www.pinkfishmedia.net/forum/showthread.php?s=&threadid=10540.

-=> Mike Hanson <=-

Phil Leigh
2005-05-19, 11:00
You can read the ongoing saga (quite a learning experience for me) at http://www.pinkfishmedia.net/forum/showthread.php?s=&threadid=10540.

-=> Mike Hanson <=-
Mike,
Great thread!

I'd like to try your dual reg circuit once you've perfected it.
Any chance you could draw a circuit diagram and post it when tested & working - I'm sure other SB owners would be interested...
Regards
Phil

seanadams
2005-05-19, 11:28
You can read the ongoing saga (quite a learning experience for me) at http://www.pinkfishmedia.net/forum/showthread.php?s=&threadid=10540.


I would have posted this there but there's a delay for account activation... I wanted to share some details about the itnernal power supply configuration in Squeebox2 which are really important to understand if you're trying to get better performance through modding.

The DAC and line-out power supplies are internally regulated by LDO regulators U12 and U13 (5V and 9V respectively), and these in turn are powered by 14VDC which comes from the display's power supply (a step-up voltage multiplier configuration which generates 55VDC and 11VAC from the 5VDC input).

Not to spoil the fun of designing an external supply, but these 5V and 9V power supplies are SO far isolated from the wall-wart input that it's hard to imagine (let alone measure) how changing the input supply would make a difference. In fact, the way we get such good measurements for SNR and THD+N is attributable almost entirely to this power supply configuration (the PCM1748 DAC is a good one, but all modern DAC chips are good and it's frankly not the most difficult part of the system to design). I tested three different DAC chips and all performed similarly - the variance in different configurations was all in the power supply and op-amps.

If you want to improve power supply cleanliness, an external 5V linear supply might make some difference but I doubt it - the real place to focus would be on the internal regulators and that 14VDC supply. The thing about linear regulators though, is that they perform MUCH better when they're physically closest to the load. Resistance and noise introduced between the supply and the load limits the precision. Maybe replacing U12 or U13 with some really expensive high-precision regulator ICs, or replacing the 14VDC feed (filtered through R29 and C55) with a dedicated linear supply instead of coming off the display. The thing is, I tried this when I was testing SB2 using a THD+N analyzer, and the performance was actually a couple of dB *better* when using the internal 14VDC supply compared to using an external linear benchtop supply. I'd attribute this not to the external lab supply being not as good, but simply to it being farther away.

So SB2's power supply, while not expensive, is not a POS either. I spent a great deal of time using specialized equipment, testing dozens of circuits to optimize it. It's unsafe to assume that any change to more exotic power supplies is going to improve it, as the system is already delivering better-than-datasheet measurements from the DAC.

Phil Leigh
2005-05-19, 12:25
Sean,

This is fantastic stuff and I seriously doubt many other manufacturers would go to such trouble to explain this detail to their customers.

I agree that the SB PSU is not a POS...It's just an obvious place to look for improvements after we've wasted thousands on DAc's , cables, snake oil etc.

Everybody who has heard my SB2 system has been impressed and I know 8 people who've bought an SB2 as a result - and I''m not going to stop promoting it because I honestly believe it's the best things that's ever happend to my music listening and I did sell my expensive Linn CD player as a result...


If I'm reading you correctly, you don't think there's much audio performance mileage in improving the SB PSU?. You may well be right - after all, you guys designed it and what do I know?

But, I'd like to waste my own time and money trying. I'd also like to try an I2S connection from the SB to my DAC but that's another story!

Your product achieves a fantastic price/performance ratio. I'd just like to see if we can push the envelope a little further - without getting into "silly money" territory. This is the audiophile (how I hate that term) forum after all.

Best regards
Phil

Triode
2005-05-19, 15:21
Assuming you are looking to use an external dac, the psu that matters is the digital rail rather than the analogue one discussed by Sean.

I think the internals of SB2 do some dc-dc conversion for the digital rails - so there is probably quite a lot of issolation between the dc supply and the external power, so a new external power supply may not give the benefits you expect.

Having said that, the power rail for a clock oscilator impacts jitter. [Hence the expensive audiophile add in clocks which spend lots on clean power rails.] But to make a real difference you probably need to mod the internals of the SB2, rather than adding a new external power rail..... But any benefit will depend on your dac too. If it does any clever reclocking it is probably relatively insensitive to what it fed into it. And the output of SB2 is already very good.

Adrian

Mike Hanson
2005-05-20, 02:36
If you want to improve power supply cleanliness, an external 5V linear supply might make some difference but I doubt it - the real place to focus would be on the internal regulators and that 14VDC supply. The thing about linear regulators though, is that they perform MUCH better when they're physically closest to the load.
That's fantastic information! Thanks, Sean. Yes, I had intended to put the regulator circuit as close to the load as possible. This extra information that you've provided has forced me to rethink my approach. I was planning to use an external DAC, although even that's not made in stone. (Is anything? ;) ) I assume this would circumvent any benefits I would achieve by regulating the DAC and audio-out circuits in the SB2.

Triode suggested looking into the PS for the digital rail, but the benefits of that may also be negated by the fact that I was expecting to use a Benchmark DAC1, which is supposedly immune to less-than-perfect S/PDIF streams.

BTW, I've got both an SB1 and SB2, along with both a Benchmark DAC1 and Scott Nixon Chibi Saru non-oversampling DAC. One combo will go downstairs in my main system, while another will remain in my office. The Chibi Saru definitely benefits from a superior supply, so I will need to continue to work on that. Supposedly the audio-out on the SB1 is also greatly improved by an external supply, so I'll also need it for that. Perhaps I'll end up with the stock SB2 through the Benchmark DAC1, and highly tweaked supplies for the SB1 and Chibi Saru. Or maybe I'll use the SB1 to feed the Benchmark, and use an SB2+PSUs alone, and find another use for the Chibi Saru. We'll see...

Thanks again for the post. It gives me lots to chew on.

-=> Mike Hanson <=-

robinbowes
2005-05-21, 01:12
I'm actually concentrating my efforts on the regulation stage. The initial prototypes are leaving the transfomer, rectifier and initial smoothing to an unregulated, linear wall wart. I've purchased a couple of these from a local surplus store, rated at 12VDC and 2A. Once I get done with the regulation stage, I may replace the wall wart with my own raw supply.

I'm taking this approach to keep the transformer away from the audio gear, while the supply regulation is very close to the load. Even if I do my own raw supply, it will still be positioned away from the regulation stage.

I'm using a tracking pre-regulator arrangement, in which one regulator sits on top of another. IOW, the first regulator's "ground" is the output of the second regulator. The first then feeds its output into the intput of the second regulator. This enables the first regulator to have a quiet ground (because it's really the regulated output of the second regulator). The second regulator has a smoother input supply (the output from the first regulator). I know it seems almost like pulling yourself up by your own bootstraps, but it really does work! :)

For regulators, my initial testing has been with basic Fairchild LM317T adjustable regulators. However, I'll probably end up using a low dropout-voltage LD1085V. I'll use a scope to see which configuration "looks" quieter, as well as do listening tests (because if it doesn't sound better, then what's the point?).

For capacitors, I'm just using a bunch of 10uF electrolytics, although I'm probably going to add/replace some of them with 1uF and/or 100nF tants.

You can read the ongoing saga (quite a learning experience for me) at http://www.pinkfishmedia.net/forum/showthread.php?s=&threadid=10540.

-=> Mike Hanson <=-

Mike,

You might like to investigate Andy Weekes' Super Regulator (ALWSR).

I've got several of his PCBs - I've just not got round to building them yet. I'm going to build my Art DI/O DAC into an RB850 amplifier chassis, using the amps original transformers and capacitors, but replacing the rectification with FREDs. The DI/O needs +/- 15v, +5v digital, and +5v analogue so I'll be building 4 regulated supplies.

I notice he's a SB owner (he posted on the plugins forum about AlienBBC).

R.

Andrew L. Weekes
2005-05-22, 02:34
Not to spoil the fun of designing an external supply, but these 5V and 9V power supplies are SO far isolated from the wall-wart input that it's hard to imagine (let alone measure) how changing the input supply would make a difference. In fact, the way we get such good measurements for SNR and THD+N is attributable almost entirely to this power supply configuration (the PCM1748 DAC is a good one, but all modern DAC chips are good and it's frankly not the most difficult part of the system to design). I tested three different DAC chips and all performed similarly - the variance in different configurations was all in the power supply and op-amps.

At risk of opening myself up to the usual subjective vs. objective stuff posts like this usually degenerate into, have you actually tried the Squeezebox with an external linear supply and listened to it?

I've actually built a sample supply which a number of people have tried with their SB's and SB2's and all have reported an improvement when using it.

The thing with PSU's is that the effect of them is hard to resolve at the output of the device in question, yet their effects sonically are clear to hear. Witness the large number of audio manufacturers devoting great efforts to power supplies, some have even built an upgrade route just on PSU changes alone, and charge large premiums for the privelege. The simplistic noise measurements really don't tell the whole story, there's a big clue in the word 'linear' though ;-)

When I get a minute, I'll take some measurements of the SB wall-wart supply vs. a good linear one and post the results here - I may be able to do that today, I guarantee the wall wart will be orders of magnitude away from an external linear supply.

You are right though, in that much bigger gains are likely to be had from the internal supplies, especially if they are sourced from a non-linear supply (lots of potential for nastiness here too - an internal non-linear PSU being powered rom an external non-linear PSU mixing nicely together!) the basic THD or noise doesn't tell the whole story either, the harmonic structure of that distortion makes a far greater difference audibly.

My current regulator design exhibits something in the order of >160dB line rejection and a wideband noise floor of circa -135dBv when optimally implemented, yet changes to the raw supply ahead of it (capacitor types etc) are still clearly audible, yet are unresolvable based on simple FFT measurements at the o/p of the regulator.

Effects such as impedance characteristics, harmonic makeup of the raw supply noise etc. make a substantial difference sonically, despite being buried in the noise floor at the output of the reg.

I'm building a complete 5V PSU at present - it will be interesting to see if I can resolve anything at the o/p of the SB2.

Certainly at present, great though the SB2 is, it's a fair distance removed from either my CD player or turntable, sonically.

Frustrating yet fun!

Andy.

Fabrice Rossi
2005-05-22, 09:58
Andrew L.Weekes a écrit :
> At risk of opening myself up to the usual subjective vs. objective
> stuff posts like this usually degenerate into, have you actually tried
> the Squeezebox with an external linear supply and listened to it?
>
> I've actually built a sample supply which a number of people have tried
> with their SB's and SB2's and all have reported an improvement when
> using it.

Was it a double blind test? With the ABX methodology? If not, this kind
of testimony is interesting but has no _scientific_ value.

> The thing with PSU's is that the effect of them is hard to resolve at
> the output of the device in question, yet their effects sonically are
> clear to hear. Witness the large number of audio manufacturers devoting
> great efforts to power supplies, some have even built an upgrade route
> just on PSU changes alone, and charge large premiums for the privelege.

Yeah, right. Don't you think this might be a kind of sophisticated and
legal rip off? The problem is that in wine testing (for instance), their
is a strong culture of double blind tests. Top wine testers can
recognize wines in a amazing way (including the vintage) in a double
blind test (or, at last, in a blind test). In the audio world, as ABX is
difficult to set, there is no such culture. If you buy a wine journal,
you'll find in almost every issue a double blind test with sometimes
quite funny outcomes. In all audio journals I've read, I've never ever
read the results of an ABX test. And of course, those journals compare
cables, power supplies, and so on.


> Frustrating yet fun!

In a way.

Fabrice

Patrick Dixon
2005-05-22, 10:52
I don't actually think the wine analogy is a very good one: tasting wine is something that's only done in very small quantities (for obvious reasons); listening to music is something that many people like to do for several hours at a time. My experience is that very small differences that you hear in an AB comparison, often translate into very significant differences over a longer period of time. If you find yourself wanting to listen to more music (and more varieties of music), then I think that's a pretty good indication that your music reproduction system is doing something pretty good.

There are plenty of areas where scientific testing is playing catch-up rather than dictating the 'correct' methodology, and I happen to think music reproduction is one of them - because it's not just a 'simple' matter of electronics, acoustics and anatomy - the brain gets involved too.

But then if you want to be sceptical, it's no skin off my nose - I just think if you're more open-minded you might have something to gain.

Andrew L. Weekes
2005-05-22, 11:15
It only took one post though, better than normal ;)

The idea is presented as interesting, not as science. Why don't you try it yourself?

I won't argue debate any further in the interests of others viewing, since these debates always end up as diametrically opposed views, neither side willing to change or acccept the opponents view. I have plenty opf statistical evidence for the audibility of PSU changes yet, like anyone else, can provide no *proof* since by definition subjectively assessed criteria cannot be proven, one can only provide statistical evidence.

I have a slightly unsual viewpoint on this as I've spent many years developing linear power supplies simply because the difference they can make has been a surprise to me and others and I've yet to reach a point where I've hit an audible limit. I do this for myself, not to make a living from it, so have no vested commercial interest, beyond the similarly open-minded DIY'ers that I help out along the way.

Along this path there have been many measurements internally within the PSU that have directly correlated to sound, yet many of these won't resolve using conventional measurement outside of the PSU in the manner expected.

As an example, subjectively the impedance the PSU sees looking back into the raw supply is audible as a subjective response change, as is the impedance looking back from amplifier to PSU as a whole (bassy, bright etc.) yet this isn't resolvable as a response error at the output of an amplifier.

On the basis of a quick experiment earlier the comparison between the SB2's SMPS supply and an external linear, low noise, wide bandwidth supply is audible to *me*.

But hey, if you and others are totally happy where you are that's absolutely fine by me, I'm not an evangelist; I contributed to a thread in an area I have years of experience in, nothing more, nothing less and I shall contribute no more, unless asked!

In response to my previous post though, attached is a calibrated plot of the output noise of the SB2's SMPS supply, compared to a low noise discrete linear one. There's a sea of noise and discrete output spectra that is common to the non-linear behaviour of almost all SMPS PSU's. The potential for these to have an impact within any audio device is huge in my view, these spectrta are very likely to worsen, as they intermodulate through the non-linearities inherent within the internal electronics.

When you factor in the line rejection of the internal reg's (which isn't constant and degrades rapidly with frequency) and the PSRR of the internal IC's (again degrading rapidly with increasing frequency), the referred to input degradation which comes with the output op-amp if it has any gain, I very much doubt that the suppies as they stand get to full 24 bit performance levels across the entire audio band.

More may be revealed if I ever feel the desire to prod around internally, which might be interesting as the load presented to the supply by the Squeezebox is not going to be benign.

As with all this stuff, it's food for thought, do with it what you will (which includes ignoring it) :-)

Regards,

Andy.

Phil Leigh
2005-05-22, 11:37
I was hoping (obviously in vain) that we could avoid the ABX/double blind bs on this forum...

Andy - please keep posting and please advise (via personal email if necessary) of a linear PSU design for the SB2. I'm not fussed about analogue performance of the SB2 as I use an external DAC (with its own separate linear PSU)but I have a suspicion that the digital output of the SB2 can be improved (even though IMHO it is already good - Sean!)

Best Regards
Phil

Triode
2005-05-22, 12:01
Is this turning into an audio modding board?

The only thing I would say, is that if anyone is seriously interested in modding and building a linear psu, may want to consider taking it direct to the relavent rail(s) inside rather than just an external psu.

I'd be interested in any before and after measurements you do of the internal rails with your external psu Andrew.

[And I definately agree power supplies impact audio quality - I wouldn't have spent so much on exotic PSU capacitors if not, but that's another story...]

Fabrice Rossi
2005-05-22, 12:42
Patrick Dixon a écrit :
> I don't actually think the wine analogy is a very good one: tasting wine
> is something that's only done in very small quantities (for obvious
> reasons);

Au contraire (being French, I had to answer this ;-). The analogy is
perfect, because wine _drinking_ is not wine _tasting_. When you taste wine:

1) you spit
2) you wash your mouth with water and spit again

One of my friend do this for a living and she can taste more than one
hundred different wines in a couple of hours. I can taste around 30
different wines in the same amount of time without getting drunk (at
all) and without loosing my taste.

> listening to music is something that many people like to do
> for several hours at a time. My experience is that very small
> differences that you hear in an AB comparison, often translate into
> very significant differences over a longer period of time.

Absolutely the same thing for wines (remember, I'm designed by centuries
of evolution to like wines).

> If you find
> yourself wanting to listen to more music (and more varieties of music),
> then I think that's a pretty good indication that your music
> reproduction system is doing something pretty good.

And it's a pretty good indication your wine producer is doing something
pretty good...

> There are plenty of areas where scientific testing is playing catch-up
> rather than dictating the 'correct' methodology, and I happen to think
> music reproduction is one of them - because it's not just a 'simple'
> matter of electronics, acoustics and anatomy - the brain gets involved
> too.
>
> But then if you want to be sceptical, it's no skin off my nose - I just
> think if you're more open-minded you might have something to gain.

That's funny because I only complain about the lack of scientific
_observation_ not the lack of scientific _explanation_. A that's exactly
why I used the wine analogy and not a technical one. I'm not claiming
that fancy PSU will not improve the sound, I'm simply saying that if ABX
cannot prove it, then it does not.

Fabrice

Fabrice Rossi
2005-05-22, 12:51
Andrew L.Weekes a écrit :
> It only took one post though, better than normal ;)

My pleasure ;-)

> The idea is presented as interesting, not as science. Why don't you try
> it yourself?

Well, the only ABX testing I can do right now is between compression
methods. I've not the specialized hardware needed to do proper ABX
comparison.

> I won't argue debate any further in the interests of others viewing,
> since these debates always end up as diametrically opposed views,
> neither side willing to change or acccept the opponents view. I have
> plenty opf statistical evidence for the audibility of PSU changes yet,
> like anyone else, can provide no *proof* since by definition
> subjectively assessed criteria cannot be proven, one can only provide
> statistical evidence.

Please, read my post again. As I said, I'm not claiming that PSU cannot
change the sound you hear, I'm saying that only ABX can prove it (in a
statistical sense).

<...>

> On the basis of a quick experiment earlier the comparison between the
> SB2's SMPS supply and an external linear, low noise, wide bandwidth
> supply is audible to *me*.

How did you test it?

> But hey, if you and others are totally happy where you are that's
> absolutely fine by me, I'm not an evangelist; I contributed to a thread
> in an area I have years of experience in, nothing more, nothing less and
> I shall contribute no more, unless asked!

Why not?

> In response to my previous post though, attached is a calibrated plot
> of the output noise of the SB2's SMPS supply, compared to a low noise
> discrete linear one. There's a sea of noise and discrete output spectra
> that is common to the non-linear behaviour of almost all SMPS PSU's.
>
> When you factor in the line rejection of the internal reg's (which
> isn't constant and degrades rapidly with frequency) and the PSRR of the
> internal IC's (again degrading rapidly with increasing frequency), the
> referred to input degradation which comes with the output op-amp if it
> has any gain, I very much doubt that the suppies as they stand get to
> full 24 bit performance levels across the entire audio band.

So it seems you have scientifical evidence, don't you? Thanks for these
information.

Fabrice

Fabrice Rossi
2005-05-22, 12:57
Phil Leigh a écrit :
> I was hoping (obviously in vain) that we could avoid the ABX/double
> blind bs on this forum...

Just for fun, could you explain why ABX/double blind is bullshit?

I've nothing, absolutely nothing, against _strange ways_ to improve the
sound reproduction. If it can be improve by putting a half empty crystal
glass of salty water on my loudspeakers, I'll do it. However, I'm always
puzzled by this kind of anti-scientific point of view. The scientific
method does not require scientific explanations. They come after,
sometimes. Fortunately for us, the drug industry is using a valid way of
assessing the performances of its product, while the way it produces new
drug is quite a mystery.

Fabrice

Andrew L. Weekes
2005-05-22, 13:04
Andy - please keep posting and please advise (via personal email if necessary) of a linear PSU design for the SB2.

I'll have more to say once I've completed the unit I'm currently building, but in response to the comments above re: the best results being obtainable inside the Squeezebox, the non-invasive method I've chosen currently can, in my view, acheive big benefits, just with a bit of lateral thinking.

The solution I'm currently working on is a two-box one, such that one contains the raw supply with the relastively noisy mains stuff in one box, followed by another box containing the high quality regulation, remote from the mains and as close as possible to the Squeezebox.

The idea being to get the regulator as physically close to the squeezebox as is humanly practical, without delving inside it. the regulator (which is a discrete circuit) then feeds the SB2 via as short a cable as is practical, little more than a couple of inches.

This keeps the loop area to a minimum and brings most benefit from the ultra-low output impedance of the regulator (which is at lest an order of magnitude below that of a three-terminal type, along with having lower noise and wider bandwidth) this would otherwise be lost, due to the cable impedance.

You could trial something similar, just using standard 3-terminal adjustable reg's, like the LM317 / LM1086 or, if you can get them, the higher current, but obsolete, LT range (LT1085 / 4 etc.).

In my case I have plenty of voltage head (due to the transformers I had around), so I have a pre-regulator in the mains PSU box, feeding the final regualtor.

I've just spent an hour listening to this, in comparison the SB2 supply is much harsher on the ears - subjectively the noise floor seems higher (in that less subtle detail is apparent in the mix) but most obvious is there is a harsh edge to the treble, that's tiring for me to listen to. The linear supply eliminates this, so much so I'm going to plug it into the main system later and see how close it gets to the CD player, 'cos it sounds rather enjoyable.

Regards,

Andy.

Andrew L. Weekes
2005-05-22, 13:15
I wanted to share some details about the itnernal power supply configuration in Squeebox2 which are really important to understand if you're trying to get better performance through modding.

BTW, I wanted to thank Sean for the incredible openness he's shown here relating details about the SB2's internals - it's unusually refreshing to see such stuff, given the normal secretive behaviour that goes with much of the audio world!

It should save a whole bunch of reverse engineering for those that want to delve inside - I'd strongly agree with his view that the 14V supply is likely the most critical one to address, sonically.

Thank you,

Andy.

Andrew L. Weekes
2005-05-22, 13:38
Just for fun, could you explain why ABX/double blind is bullshit?

I know I said I wouldn't get involved, but since you do seem genuinely open-minded (and I may have mis-interpreted your response) I'll make a comment, if I may ;-)

I wouldn't say it's bullshit myself, simply mis-applied to the job in question. The problem for me with ABX is it doesn't take into account the way we hear music, which is not through some short-term effect in the ear, but a longer term effect in the brain.

For most of us music is all about emotions; dancing, singing, happy, sad, angry, agressive, soft etc. That's the whole raison d'etre for it's existence and why musical artists do what they do. To break it down to simple measurement is like digitising a great painting and assessing the range of colours or the contrast etc :) Our ears know nothing about the emotional effect music has on us, that process happens in the brain.

Some of the best scientific work in this field comes from Hugo Fastl and the late Eberhard Zwicker - their publications and work are ammassed in Psycho-acoustics - Facts and Models, which isn't exactly light bedtime reading, but is fascinating nonetheless.

The ABX test forces us into trying to listen for a difference, usually in an inherently short-term fashion, by rapid switching. Thsi is not how we listen to music, which is a long term event by comparison.

The reason is that hearing takes place in the brain, not in the ears.

Hearing is related to data processing in the brain and makes use of enormous amounts of previously stored data and complicated adaptable data processing schemes. Therefore hearing fundamentally makes use of the long term memory were all those data sit.

Hearing is only partially related to the gathering of audio data in the ear and the primary storage of those data in sensory memory, which is short term.

Now in a rapid switching DBT you want to make an "objective" test by deleting the huge data processing part of the hearing equation which is related to long term memory, because the rapid switching prevents the long term memory from being activated. Take out this "subjective" part of hearing and what's left is the "objective" part related to short term memory, ain't that true?

No.

Take out the data processing part and nothing serious is left of
hearing: no dataprocessing in the brain means no audio image reaches our consciousness which means no conscious judgement can be made.

The curious thing is that in such a DBT you STILL want the test person to make a conscious *subjective* judgement (a judgement on personal experiences is by definition subjective).

So you want the test persons to give their subjective judgement on the data collecting process in the ear plus short term sensory memory storage process. But nobody can do that.

The subjective judgement canonly be made by our consiousness, and our consiousness has no knowledge of the early processes of hearing.

It's one of the reasons that level matching is deemed so critical, since that is one of the few things the early processes of hearing can determine - remove it and the tests differences often vanish.

To that end, I DO believe that double blind testing can work, but that it has to be inhernently long term - the comment Partick made earlier, about whether you are glued to the seat listening to music that engages you, or would rather be watching the TV, is the best measure by far in my view.

I think that if one allowed the listener to listen to each item for a long period (and here I'm thinking several days per item) then it's possible that a DBT, or an ABX could be made to function reliably. So I'm not anti science at all, but I do believe that the way it is often proposed is fundamentally flawed.

So why don't I try it out?

Simply because using the long term evaluation, the results become obvious; whether a particular change is better or not becomes obvious, simply owing to the amount of music I listen to - if i find myself still up at 2 in the morning when I have work the next day, it's usually a good sign ;)

NealG
2005-05-22, 23:37
I count myself as one of those ‘open-minded DIY'ers’. I don’t have Andrew’s experience in PSU design but I am conversant in electronics and have a strong experimental side to audio. It was Andrew’s postings on PinkFish that made me experiment with a simple linear supply for the SB1, here the audible benefits are undoubted to my ears. I have also found that the SB2 benefits as well from a linear supply, I have no doubt that improving it would make the SB2 even better, perhaps with one of Andrew’s super regulators.

I think its possible to design a good SMPS, Linn do but it must come at a cost, something that the rather low cost off the shelf wall wart item could never emulate IMHO. From my experiments with tube amps where I have far more practical experience, the PSU is key to the overall sonic and measured performance of the amp, especially with SE design, you are listening to the PSU. I don’t see why the SB should be any different.

cliveb
2005-05-23, 01:37
I realise that I'm a bit of an outsider in this debate, but I'd like to make a comment. Let me begin by declaring my own personal position: I believe that ABX is a valid way of establishing whether there are any sonic differences between components, where by "sonic difference" I am referring only to the actual soundfield generated in the listening room.

Andrew makes some very valid points about ABX testing and the listening process. The fact that the listener's response is an emotional one and occurs over a long time period is certainly true. But I think he misses an important issue. The listener's emotional response is determined not only by the physical sound that is produced: other non-sonic factors influence things enormously, such as the listener's current state of health, their general mood, and the visual/tactile appeal of the equipment in use. My feeling is that, apart from transducers such as microphones/loudspeakers/etc, the current level of performance achieved by modern competently designed audio reproduction equipment is sufficiently high that these non-sonic factors have a greater influence on the listening experience than the actual soundfield.


To that end, I DO believe that double blind testing can work, but that it has to be inhernently long term - the comment Partick made earlier, about whether you are glued to the seat listening to music that engages you, or would rather be watching the TV, is the best measure by far in my view.

I think that if one allowed the listener to listen to each item for a long period (and here I'm thinking several days per item) then it's possible that a DBT, or an ABX could be made to function reliably. So I'm not anti science at all, but I do believe that the way it is often proposed is fundamentally flawed.

This method cannot work, because over the long term, the non-sonic factors will change radically. Your health will change from one day to the next; you may have had a row with your spouse/partner/children; and so on.

Where the ABX detractors make their mistake is in attributing their perception of a difference to purely sonic reasons. If the equipment sounds different, then a short-term ABX will show it. If you get a negative result in an ABX, then the differences in sound fields generated are probably beneath the threshold of audibility. But that doesn't stop you genuinely perceiving a difference over the long term, due to your emotional response to the equipment.

NealG
2005-05-23, 01:59
Clive, I have to disagree, the same reasons you give also apply to short term A / B listening. One's personal health and mental state will also affect the listeners perception, with short term listening the 'risk' or 'error' is greater for the listener. A 'snapshot' is not an accurate measure unless you can perform it over many samples and over a longer time period, thats why I agree with Andrew that long term listening is better, it will average out the 'errors'. This debate will never be resolved, it's been done to death many many times before, best to agree to disagree, IMHO.

Andrew L. Weekes
2005-05-23, 03:03
This method cannot work, because over the long term, the non-sonic factors will change radically. Your health will change from one day to the next; you may have had a row with your spouse/partner/children; and so on.

Actually I am in total agreement with you in that your personal mental and physical state do have a significant and even dominant impact on what you perceive, but would argue that over the long term my experience is that as an evaluation method it works.

The 'off days' are a problem, but they are always outnumbered by the good days, which means I am able to make an accurate judgement.

The fact is that the 'off days' result in everything sounding 'bad' but on the 'good days' one can make an accurate judgement - bad stuff doesn't suddenly become good, in my experience, just because I feel great.

The only area where I disagree is that the curent state of audio design is one where the human element dominates, I profoundly (but respectfuly) disagree here.

As it curently stands, for example, the SB2 is not something *I* could be happy listening to for my daily musical fix, but I have little doubt it can become one, based on brief experiments thus far.

In fact I'm *really* hoping it will, I like the in your face, radical two fingers it sticks up to the overpriced, underperforming mass that curently is the 'high end' or whatever you'd like to call it.

Again my experience here is everyones expectations are different - there's almost no absolutist 'right' answer for everyone, we all have different levels of what is sufficient to press our musical buttons, and different things bother different people. I accepted this a long time ago, hence my total lack of evangelism with regard to this, I found a lot of people who like what I do, but am happy to accept that as many others may hate it with avengeance!

So back to the ABX thing, I have no problem with anyone who uses that to evaluate their changes, but for me it's not a lot of fun or very effective in my view - I'd rather just listen to (and hopefully enjoy) music! Just please don't try and convince *me* that I cannot be hearing what I hear, when I'm happy that you are totally happy with your position. I'll continue to present my experiences, which anyone may test in any manner they see fit.

Good discussion anyway, it's nice to see such reasoned participation against the backdrop of what these discussions so often degrade into.

:-)

Andy.

Fabrice Rossi
2005-05-23, 03:49
Very interesting post, Andy.

Andrew L.Weekes wrote:
> I know I said I wouldn't get involved, but since you do seem genuinely
> open-minded (and I may have mis-interpreted your response) I'll make a
> comment, if I may ;-)

My response was a bit strong, because I'm quite annoyed by the fact some
hifi gear cost a lot and then you are supposed to buy a lot of fancy
stuffs (like high end PSU) to get the most out of them. It seems to me
that more care should be exercised by the designers of this gears. For
instance, if you pay 1000 $ for a DAC, it should include a nice PSU.
When I see the very careful design that has been done for the SB 2 that
costs almost nothing for such a good product, I'm really thinking about
rip off for some other products.

> I wouldn't say it's bullshit myself, simply mis-applied to the job in
> question. The problem for me with ABX is it doesn't take into account
> the way we hear music, which is not through some short-term effect in
> the ear, but a longer term effect in the brain.
>
> For most of us music is all about emotions; dancing, singing, happy,
> sad, angry, agressive, soft etc. That's the whole raison d'etre for
> it's existence and why musical -artists- do what they do. To break it
> down to simple measurement is like digitising a great painting and
> assessing the range of colours or the contrast etc :) Our ears know
> nothing about the emotional effect music has on us, that process
> happens in the brain.

I guess we agree on that. And this applies also to wine, tea, coffee and
a lot of other things.

> Some of the best scientific work in this field comes from Hugo Fastl
> and the late Eberhard Zwicker - their publications and work are
> ammassed in Psycho-acoustics - Facts and Models, which isn't exactly
> light bedtime reading, but is fascinating nonetheless.

Do you have complete references, I'd like to read this kind of work.

> The ABX test forces us into trying to listen for a difference, usually
> in an inherently short-term fashion, by rapid switching. Thsi is not
> how we listen to music, which is a long term event by comparison.

Well, you are not forced to do rapid switching when doing ABX. This is
the way many people are reacting to ABX because they feel pressured, I
think. But you really can spend one hour (or more, of course) listening
to A, same thing for B and then again X.

And by the way, this is the same thing for wine. Wine tasting has almost
nothing to do with wine drinking. However, it is a accepted way of
judging wines (more on that latter).

> The reason is that hearing takes place in the brain, not in the ears.
>
> Hearing is related to data processing in the brain and makes use of
> enormous amounts of previously stored data and complicated adaptable
> data processing schemes. Therefore hearing fundamentally makes use of
> the long term memory were all those data sit.

You should be careful with this sort of statement. With non invasive
brain monitoring, it is indeed possible to test what part of the brain
(short memory, long memory, etc.) is used to perform a given task. I
don't know if this kind of experiments have been conducted for hearing,
but this could be done and this statement (critic hearing uses long term
memory) can be tested (I do believe that you are right). If this has
been done, I'll be pleased to have references.

> Hearing is only partially related to the gathering of audio data in the
> ear and the primary storage of those data in sensory memory, which is
> short term.
>
> Now in a rapid switching DBT you want to make an "objective" test by
> deleting the huge data processing part of the hearing equation which is
> related to long term memory, because the rapid switching prevents the
> long term memory from being activated.

That's simply not true. The only explanation we have for the amazing
performances of professional wine tasters is that they are indeed
relying on long term memory to recognize wines and to compare the one
they are tasting with the huge library of smells and tastes they have in
mind. I don't have references, but I'm almost sure some brain imaging
experiments have been done on this. And the nice thing is that they do
it very very quickly. Trained wine tasters can identify several
different wines in one minute.

Long term memory can be recalled very quickly. So the problem is here to
store A and B on this long term memory. Several minutes of careful
listening will do the trick. Remember that you don't have to do rapid
switching, you can listen for a long time to A, then to B (and then back
to A, etc.).

> Take out this "subjective" part
> of hearing and what's left is the "objective" part related to short
> term memory, ain't that true?
>
> No.
>
> Take out the data processing part and nothing serious is left of
> hearing: no dataprocessing in the brain means no audio image reaches
> our consciousness which means no conscious judgement can be made.
>
> The curious thing is that in such a DBT you STILL want the test person
> to make a conscious *subjective* judgement (a judgement on personal
> experiences is by definition subjective).
>
> So you want the test persons to give their subjective judgement on the
> data collecting process in the ear plus short term sensory memory
> storage process. But nobody can do that.
>
> The subjective judgement canonly be made by our consiousness, and our
> consiousness has no knowledge of the early processes of hearing.
>
> It's one of the reasons that level matching is deemed so critical,
> since that is one of the few things the early processes of hearing can
> determine - remove it and the tests differences often vanish.
>
> To that end, I DO believe that double blind testing can work, but that
> it has to be inhernently long term - the comment Partick made earlier,
> about whether you are glued to the seat listening to music that engages
> you, or would rather be watching the TV, is the best measure by far in
> my view.
>
> I think that if one allowed the listener to listen to each item for a
> long period (and here I'm thinking several days per item) then it's
> possible that a DBT, or an ABX could be made to function reliably. So
> I'm not anti science at all, but I do believe that the way it is often
> proposed is fundamentally flawed.

How long do you need to learn a piece of poetry? I don't think that you
need days, a couple of hours will suffice for some short poem. If you
already are very familiar with some music, I think you can "learn" the
way it is reproduced by a device in a couple of hours or less, and then
compare this (using long term memory) with the way it is reproduced by
another device.

> So why don't I try it out?
>
> Simply because using the long term evaluation, the results become
> obvious; whether a particular change is better or not becomes obvious,
> simply owing to the amount of music I listen to - if i find myself
> still up at 2 in the morning when I have work the next day, it's
> usually a good sign ;)

Well, well, well. I think you are familiar why the reason why double
blind tests are used for drug testing. The placebo effect (which
demonstrated beyond reasonable doubt). The mind is so strong that it can
boost your immune system enough to heal you if it believe that the water
pills you are taking is indeed a drug (so blind tests are needed). Even
more, it can guess the reality of the pills being a drug by analyzing
the body language of the medical staff (so double blind tests are
needed). So maybe ABX double blind do not work, but then nothing does.

Fabrice

cliveb
2005-05-23, 06:29
Clive, I have to disagree, the same reasons you give also apply to short term A / B listening. One's personal health and mental state will also affect the listeners perception, with short term listening the 'risk' or 'error' is greater for the listener.
Surely the chances of a listener's health/mental state changing will be lower over a shorter period of time? If you carry out a comparative test over the course of days, there is virtually no chance at all that these non-sonic factors will remain constant. But if you do a test over the course of a few hours, they are less likely to change. And since the purpose is to try and do some sort of scientific test, you have to try and eliminate as many external variables as you can.

Of course, an intensive ABX test is rather stressful, and many people would argue that this in itself is a non-sonic factor that overwhelms any differences one would otherwise notice in a more relaxed environment - hence the large number of negative results. It may be this issue that you're referring to when you say that the 'risk' is greater in short-term listening. As far as I'm concerned, this is the only valid criticism one can level against ABX, because everything else it sets out to do seems pretty logical to me.

cliveb
2005-05-23, 06:43
So back to the ABX thing, I have no problem with anyone who uses that to evaluate their changes, but for me it's not a lot of fun or very effective in my view
And it's also a heck of a lot of hassle to set up properly if you're trying to compare things like PSUs.


Just please don't try and convince *me* that I cannot be hearing what I hear, when I'm happy that you are totally happy with your position.
Hey, I would never do that, because it is tantamount to telling people they are lying. My position is one of trying to come to some understanding about why people (including me) do genuinely hear differences between equipment which cannot be distinguished under ABX conditions. There's no shame in allowing oneself to be influenced by external factors: it's only human nature, after all.

Fabrice Rossi
2005-05-23, 07:05
cliveb wrote:
> NealG Wrote:
> Of course, an intensive ABX test is rather stressful, and many people
> would argue that this in itself is a non-sonic factor that overwhelms
> any differences one would otherwise notice in a more relaxed
> environment - hence the large number of negative results. It may be
> this issue that you're referring to when you say that the 'risk' is
> greater in short-term listening. As far as I'm concerned, this is the
> only valid criticism one can level against ABX, because everything else
> it sets out to do seems pretty logical to me.

I question the validity of this criticism, again with the wine analogy.
I've witnessed blind testing of wines by some highly trained sommelier
and they do operate under _very_ stressful condition. This is in general
a competition for some title like best sommelier of the world, the tests
are extremely difficult (like recognizing completely a wine, including
vintage), they have very limited quantities of wine to taste, and yet
the tests are passed by those professional sommeliers. And remember the
wine tasters do not have to test for differences, they have to recognize
a wine they might have tasted years ago.

So I don't understand how the ABX test could prevent people to hear
differences that they claim to hear in other conditions. I won't claim
that any one in this forum is not hearing was he says he is, but I claim
that under proper ABX double blind test, he should hear the difference.

Fabrice

NealG
2005-05-23, 08:13
But for me that's the problem IMHO Fabrice, "....under proper ABX double blind test, he should hear the difference."

What is 'proper'? As Andrew pointed out it's not a natural way to listen, it creates a false environment. I struggle to understand how we can apply a scientific test to what is a purely subjective and emotional event. No two people perceive visual or audible stimuli in the same way, yes, the sound may be the same reaching the ear but the listener’s perception of it will be different. I also feel that there will be a level of pressure on the listener to identify a difference. Does that not happen with wine tasting? Two people may recognize the taste of the same wine and recognize/identify it correctly but do they actually perceive exactly the same flavor?

Should we also say ‘better’ instead of ‘difference’? Hmmmm, maybe not as it’s a test but there again it’s a personal and emotional event to which I can’t help thinking you can’t apply such stringent rules………

Setting up of such tests would also be a nightmare, getting levels and balance correct for instance would take great care.

What I meant by 'risk' earlier is with taking 'snapshots' or 'samples'in time of a listening experience when the measuring tool IE: the listner is not at his or her receptive 'best'. The worse case would be that at each 'sample' the listner percieved the least or 'worst' result. Averaging the test out over several days may well eliminate this but aren't we back with subjective long term listening in this case?

Anyhow a good discussion that I am learning from.

Fabrice Rossi
2005-05-23, 12:46
NealG a écrit :
> But for me that's the problem IMHO Fabrice, "....under proper ABX double
> blind test, he should hear the difference."
>
> What is 'proper'? As Andrew pointed out it's not a natural way to
> listen, it creates a false environment. I struggle to understand how
> we can apply a scientific test to what is a purely subjective and
> emotional event. No two people perceive visual or audible stimuli in
> the same way, yes, the sound may be the same reaching the ear but the
> listener’s perception of it will be different. I also feel that there
> will be a level of pressure on the listener to identify a difference.

Difficult question. I in fact don't know if reasonable experimental
settings (on a scientific point of view) will be accepted by many
audiophiles. I suggest to give the listener the device A for a long time
(let's say a week) and the same thing for device B (both with complete
identification). And then, we just remove all identification means and
ask for the listener which one he prefers, or which is which. He/she can
listen as long as he/she wants. A bit theoretical, isn't it?

> Does that not happen with wine tasting? Two people may recognize the
> taste of the same wine and recognize/identify it correctly but do they
> actually perceive exactly the same flavor?

Indeed. I guess this is because we don't have correct words to describe
the actual taste and smell of a wine. It's very frustrating in the
beginning when you're told that this wine smells chocolate and you only
smell alcohol. With some training, you can identify some specific
flavors and odors, but I think no one perceive a wine the same way.
However, this does not prevent recognition and quality judgments.

> Should we also say ‘better’ instead of ‘difference’? Hmmmm, maybe not
> as it’s a test but there again it’s a personal and emotional event to
> which I can’t help thinking you can’t apply such stringent rules………

I would stay to difference rather than better. If you listen to rock
music for instance, I don't think you can say more than "this way of
reproducing the sound suits me better than this other way", because
there is no such thing as a natural sound when you are listening to an
electric guitar. Of course, with jazz or classical music, this is
another story and there are in way some references (live performances).
I'm always puzzled by some people who claim that this sound device
sounds very natural but never listen to jazz or classical music, or have
never attended to a live performance. But even so, difference is more
neutral.

> Setting up of such tests would also be a nightmare, getting levels and
> balance correct for instance would take great care.

Absolutely. But in some situations its easy. For instance, if you have 3
SB2, you can easily set up an ABX test for a fancy PSU (you need two of
those ones). On the other hand, implementing an ABX test for
loudspeakers seems more difficult.

> What I meant by 'risk' earlier is with taking 'snapshots' or
> 'samples'in time of a listening experience when the measuring tool IE:
> the listner is not at his or her receptive 'best'. The worse case would
> be that at each 'sample' the listner percieved the least or 'worst'
> result. Averaging the test out over several days may well eliminate
> this but aren't we back with subjective long term listening in this
> case?

Yes we are. But even so, it think you might figure out something in this
kind of setting (long term hearing test) as long as every thing stays
double blind.

> Anyhow a good discussion that I am learning from.

Me too. I especially enjoyed the discussion about short term memory vs
long term because this was really something new for me and its very
convincing. But all the discussion was very interesting.

Fabrice

Mike Hanson
2005-05-24, 05:51
You might like to investigate Andy Weekes' Super Regulator (ALWSR).
I've been in frequent contact with Andrew, and he's been exceedingly helpful in guiding me along the path to power supply nirvanah. I don't expect my designs to rival his, but for now I'm having fun playing with him. In the end, I'll probably get some of his units, just to see what I can see.

-=> Mike Hanson <=-