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Patrick Dixon
2005-08-19, 02:39
I'm think about re-boxing my modified SB2 in a metal (ally) box. I will probably ground the box (although I suppose I don't have too since there are only low voltages involved), and I'm wondering what effect this will have on wireless reception. Obviously the external antenna will be unaffected, but there's an internal one too.

Anyone got any thoughts or experience they could share?

Is the existing (plastic) box zinc sprayed, since that seems to work OK?

seanadams
2005-08-19, 08:25
I'm think about re-boxing my modified SB2 in a metal (ally) box. I will probably ground the box (although I suppose I don't have too since there are only low voltages involved), and I'm wondering what effect this will have on wireless reception. Obviously the external antenna will be unaffected, but there's an internal one too.

Anyone got any thoughts or experience they could share?

Is the existing (plastic) box zinc sprayed, since that seems to work OK?

The antennas won't work in a metal box. It should work fine with a single antenna though.

You could also look into getting some "pigtail" cables to bring the connector(s) our to the back panel.

The connection on the card is called "MMCX" and the back panel is called "SMA" (reverse polarity SMA to be specific). Some googling should turn up a few choices as these cables are used a lot by antenna hackers.

seanadams
2005-08-19, 09:09
Sorry, meant to say "UFL", not MMCX for the internal connector (MMCX was for SB1's 802.11b card). UFL is also known as IPEX.

Something like this should work. Just drill a hole and screw into the back panel:

http://www.netgate.com/product_info.php?cPath=21&products_id=144

Patrick Dixon
2005-08-19, 09:55
Sean, many thanks.

If I ever get it done I will post some pictures for you. I have made a few mods to the audio circuitry though, and comparing it to the standard SB2 is like chalk and cheese. Decent though the standard SB2 is, the mods make it a real giant-killer. Shame you're not closer or you could come for a listen! (Plenty of room for parking here).

Robin Bowes
2005-08-19, 11:35
Patrick Dixon wrote:
> Sean, many thanks.
>
> If I ever get it done I will post some pictures for you. I have made a
> few mods to the audio circuitry though, and comparing it to the standard
> SB2 is like chalk and cheese. Decent though the standard SB2 is, the
> mods make it a real giant-killer. Shame you're not closer or you could
> come for a listen! (Plenty of room for parking here).

Patrick,

Care to share with us what you've done?

R.

Patrick Dixon
2005-08-20, 00:56
Robin,

I sprinkle loads of fairy dust on my soldering iron tip and then get stuck in ;)

I'd say my mods fall somewhere between the simplicity of the Red Wine Audio mods and the butchery of the 'hacksaw' approach. I've reworked the PSU (using Andy Weekes' fabulous SuperRegs), the clock and the output op-amp, and upgraded some of the component types. I need to rebox it now, so that it's in two matching boxes.

If you're in the UK and reasonably located wrt Bristol, email me and maybe we can arrange a listen.

firstname dot lastname @at-view.co.uk

Robin Bowes
2005-08-20, 06:32
Patrick Dixon wrote:
> Robin,
>
> I sprinkle loads of fairy dust on my soldering iron tip and then get
> stuck in ;)

Heh.

>
> I'd say my mods fall somewhere between the simplicity of the Red Wine
> Audio mods and the butchery of the 'hacksaw' approach. I've reworked
> the PSU (using Andy Weekes' fabulous SuperRegs), the clock and the
> output op-amp, and upgraded some of the component types. I need to
> rebox it now, so that it's in two matching boxes.

I have about 4 SuperRegs that I had intended to use on my Art DI/O ADAC
but having heard the SB2 I've decided that I'd be better of using them
in the SB2.

What have you done to the PSU? I seem to remember, from some schematics
Sean/Dean posted, that a couple of SuperRegs would do the trick - one
for the DAC and another for the output stage. Although, I'd probably
take the audio out directly from the DAC chip and bypass the opamp.

And the clock - I thought the SB2 has remarkably low jitter. Did you see
much improvement after the clock mod? What have you done to the clock?

> If you're in the UK and reasonably located wrt Bristol, email me and
> maybe we can arrange a listen.

Well, I'm in the UK but alas live just north of York so Bristol is a
little out of range!

Cheers,

R.

Patrick Dixon
2005-08-20, 06:58
I have about 4 SuperRegs that I had intended to use on my Art DI/O ADAC
but having heard the SB2 I've decided that I'd be better of using them
in the SB2.I've only used one - but I'm going to try two next.


What have you done to the PSU? I seem to remember, from some schematics
Sean/Dean posted, that a couple of SuperRegs would do the trick - one
for the DAC and another for the output stage. Although, I'd probably
take the audio out directly from the DAC chip and bypass the opamp.I'm still using the opamp - although not that exact type!


And the clock - I thought the SB2 has remarkably low jitter. Did you see
much improvement after the clock mod? What have you done to the clock?Jitter can never be too low - see Sean's post for some hints.


Well, I'm in the UK but alas live just north of York so Bristol is a
little out of range!Shame - if I'm ever heading that way I'll let you know.

Robin Bowes
2005-08-20, 07:50
Patrick,

Sorry if this sounds a little blunt...

I could keep replying, asking for ever more detail, but you seem to be a
little reticent.

Would you care you share with us what you've done, or do you have
reasons not to do this?

Thanks,

R.

Andrew L. Weekes
2005-08-28, 12:22
I think the SB2 would be worth your attentions, mine is sounding bloody marvellous at present, to the point I now feel it's little different, and possibly slightly better, than my main CD player (which cost a 4-figure sum)!

Having heard Patrick's last week, with super-reg's installed it sounded amazingly good.

This is all still without actually using any of my super-reg's (yet) in mine as I need to do a re-box to allow this, I do have one used as an external linear supply replacing the standard wall-wart though.

The things I've done to mine, in some approximation of sonic importance are: -

1) Added a linear regulator (3-terminal at present) to the 'HCU04 (currently fed from the internal 14V)

2) Disabled the 12MHz clock and the SPDIF from the 'HCU04

3) Routed the clock directly to the DAC

4) Added an external linear supply (5V)

5) Changed the analogue decoupling electrolytics for polyester film caps (with 0.5R in series)

6) Changed the output op-amp for an AD8066

7) Re-jigged the o/p stage to be a 2-pole Bessel filter and using polystyrene caps in place of the ceramics

8) Changed the coupling electrolytics between DAC and op-amp and op-amp o/p for Elna Silmics

9) Changed the op-amp bias voltage decoupling for a film cap

1-4 are by far the biggest winners in my view, and I'm certain there are large gains to be had from much better reg's all around, my intention being to replace all the analogue supplies with super-reg's (14V, 5V, 3.3V) once I get the box drilled and ready to receive the SB2!

I'll then examine whether the internal switchers cause any problems, now they are isolated from the critical analogue /clock functions.

Andy.

Triode
2005-08-28, 12:56
Andrew,

Any views on the noise spectrum of Nicads/NMHi batteries? I am speculating about a battery psu for the HCU04. As I am only interested in digital out I am wondering whether this is a way to go. I'm Currently using a simple linear reg for this.

Adrian

Yannzola
2005-08-28, 16:00
Andrew,

Any views on the noise spectrum of Nicads/NMHi batteries? I am speculating about a battery psu for the HCU04. As I am only interested in digital out I am wondering whether this is a way to go. I'm Currently using a simple linear reg for this.

Adrian

You should get in touch with Vinnie at Red Wine Audio, SB2 battery mods are his specialty. http://www.redwineaudio.com/SB2_Mods.html

y.

Triode
2005-08-28, 16:45
Sean - any chance you could confirm the family of the Xilinx chip. I just want to check it doesn't have any problems with input voltages above 3.3V (should be fine if interfaces to 5V or 3.3 V logic which I think it does based on the datasheets I've looked at)

The thing I want to try is is 3x 1.2V cells to the HCU04....

Andrew L. Weekes
2005-08-29, 03:05
I'm not a big fan of batteries, under most real-world loads they are always worse (noisier, lower bandwidth, poorer transient performance) than a *well-designed* linear regulator BUT they are possibly easier for the average DIY'er to get reasonable results from, hence the appeal, I guess.

Added to the inconvenience of charging and maintenance, they'll never be my first choice, I've certainly never acheived state-of-the-art performance with them. I've never tried NiMH, but have no reason to suppose their chemistry makes them any better than NiCD for audio.

Andy.

joshk
2005-08-29, 07:34
Andrew,

What do you mean by lower bandwidth for batteries? I understand your other two points, but I am not grasping this one.

Mike Hanson
2005-08-29, 07:47
It doesn't maintain voltage (and/or supply current) for some frequencies as well as others. For example, it might handle the big, slow surges of LF, but not the fast, finesse of HF.

-=> Mike Hanson <=-

Triode
2005-08-29, 13:42
Well it was worth a play, but I agree with Andy's view - at least NiMH batteries aren't as good as a linear regulator and appropriate smoothing caps.

I tried 3 AA cells to power the HCU04 which is acting as spdif buffer and oscillator for the 11.29 Mhz clock [12 Mhz clock lifted]. On a scope I can clearly see noise at the clock frequency on the spdif output in this configuration - indicating supply impedance. With a linear regulator and a couple of Oscon caps this is much less noticable. Sound wise the linear reg has more focus too. [NB you can only see clock noise once the 12 Mhz crystal is removed so the clock and spdif signals are in phase]

Adrian

Andrew L. Weekes
2005-08-30, 03:01
What do you mean by lower bandwidth for batteries? I understand your other two points, but I am not grasping this one.

D.C. power supplies are often considered as simply DC, i.e. thay have no AC content, but of course the reality is this is never the case.

For a PSU that experiences a dynamically changing load, as most do, it's response to this is important.

In an active regulator, it is attempting to keep it's output constant, based upon the changes it measures through it's (internal or external) feedback connections.

The load placed upon any power supply will have an inherent bandwidth, i.e. it will be making current demands upon that power supply, in relation to it's own internal activity. In the case of something like an audio amp, the demands placed upon the PSU will be related to the audio frequencies it's dealing with, primarily, in the case of digital they will be related to clock speeds and edge transitions, which can generate very high frequency demands on a PSU.

The reality is one can never deal with very high frequency demands actively, only through passive means, like decoupling etc.

The bandwidth of a PSU therefore needs carefully defining, in order to ensure it is capable of meeting the demands of the loads placed upon it, and keeping the supply within the design criteria. For feedback based regulators one needs to define these bandwidths very precisely to ensure that the system is stable and performs as expected. The regulator can affect the system being powered, but equally the system can affect the performance of the regulator, in a critical manner - it's for this reason it's much harder to do stuff actively.

For batteries, the ability of the system to respond to transient (and by definition higher-frequency) demands, is related to the ability of the battery to maintain a constant DC potential, which is related to the internal impedance of the cells and the chemical reaction that goes on internally.

A chemical reaction is, by it's inherent nature, slow in comparison to the demands of either an audio, or particularly, a digital system. It also tends to be ill-defined in terms of response to a transient demand, which from my perspective makes batteries a poor choice unless care is taken to limit the demands placed upon them, which ususally requires active circuitry after them, to acheive this.

Andy.

occam
2005-08-30, 06:21
I'm not a big fan of batteries, under most real-world loads they are always worse (noisier, lower bandwidth, poorer transient performance) than a *well-designed* linear regulator BUT they are possibly easier for the average DIY'er to get reasonable results from, hence the appeal, I guess.

Added to the inconvenience of charging and maintenance, they'll never be my first choice, I've certainly never acheived state-of-the-art performance with them. I've never tried NiMH, but have no reason to suppose their chemistry makes them any better than NiCD for audio.

Andy.

Why in heaven's name, in the context of the SB2, would one compare a raw battery to a linear regulator? Isn't this why the good Lord, in Her infinite wisdom, gave us capacitors? Isn't the proper comparison between a 6v SLA and your toroidal transformer & rectifier bridge? What precludes us from adding those charming Pannasonic FC/FMs or Nichi HE after both? As our basic requirement is a 1 amp, 5Vdc supply, for batteries one presently has to choose a 6v 12a SLA and regulate down.