SB3 uncontrolled full scale output bug - still a concern?

[dmsmit1]

I recently bought an SB3. It is connected to an Adcom stereo preamp, then to a Parasound amp. The sound is very good. I expect it would be even better with the SB3 going directly to the amp, but noticed a post about a bug that can result in the SB3 sending full scale output, which could possibly blow the amp or the speakers (especially if the signal is clipped either from the SB3 or from the amp). The Slimdevices CEO even warned that connecting directly to the amp is not recommended.

Is that bug/issue still a concern?

[ezkcdude]

I think you should be careful, if you're not using some attenuation b/w the SB3 and the amp. I don't have a preamp, but I do use passive attenuators. In fact, I just ordered a Parasound amp (the A23) off Audiogon, and will use it without a preamp. The problem you may encounter, if you choose to have no attenuation, is that the SB3 volume will have to be very low, maybe below 10 or 20, in order to keep it from being loud. I'm not sure about the bug issue, but even still, I would suggest at least using some passive attenuation.

[95bcwh]

I recently bought an SB3. It is connected to an Adcom stereo preamp, then to a Parasound amp. The sound is very good. I expect it would be even better with the SB3 going directly to the amp, but noticed a post about a bug that can result in the SB3 sending full scale output, which could possibly blow the amp or the speakers (especially if the signal is clipped either from the SB3 or from the amp). The Slimdevices CEO even warned that connecting directly to the amp is not recommended.

Is that bug/issue still a concern?

Dmsmit1
I am thinking of doing exactly the same thing, connecting the analog output directly into a power amp! Your message did make me worry a little bit, are you saying that even if we play the SB3 at low volume, signal clipping will still cause the SB3 to send full output into the amp? Can you point me to the message where this bug is being discussed?
Sorry I wasn't able to help you instead I'm asking for help! I'm an absolute newbie in this.

Thanks
barry

Thanks
barry

[dmsmit1]

I recently bought the A23, after 22+ years using a Haffler 220. Very nice sound.

The A23 has adjustable input levels - knobs on the back, separate for left and right, so not useful as volume controls (use the Adcom for that). Need an accurate meter if you want to ensure L/R balance.

Turning down the input on the A23 may provide enough protection from a malfunctioning SB3 connected directly to it, the problem is how to determine the right setting on the amp. If too low, then the full potential of the amp will not be realized, when desired. If too high, the amp or more likely the speakers (tweeters) could be damaged.

[dwc]

search for "white noise" or "white noise death" in the general forum.

I think it can still happen in rare cases, and some kind of attenuator should be used.

-Dan

[dmsmit1]

Barry,

The title of the post was "Extremely loud "white noise" from Squeezebox?!".

URL:
http://forums.slimdevices.com/showthread.php?t=19309&highlight=white+noise

[95bcwh]

Thanks Dan & dmsmit1 for pointing me to the right direction.

As I read those threads, it does seems to me that although this "white noise" thing rarely occured, but the consequence can be extremely severe. However, I also noted that it seems like Slimdevices had then introduce a Preamp volume control function that will help to lower the risk, please correct me if I'm wrong.

[Skunk]

Quoting ezkcdude <ezkcdude.246oob1141540501 (AT) no-mx (DOT) forums.slimdevices.com>:

> <
> To paraphrase the Good Book, let those without sin cast the first stone!<
> <

Those stores are legal, and their wares legal, becasue it's assumed that's the
only copy of that disc in existence. The letter of the law (Audio Home
Recording
Act of 1992) allows backing up to cassette, and it's assumed you'll
destroy the
cassette when you sell the original disc. Even though the sticker says 'mp3 is
not a crime', it may not be the whole truth. I'm not 'like mike' ie AL, but my
understanding is based on this c:net article:
http://reviews.cnet.com/4520-10165_7-5798512-1.html?tag=tnav

If I like a cd, I keep the original. If I don't I sell it, and yes
delete it. My
squeezebox is too cool to have bad albums on it anyway. If I love it, I
want that
artist/label and everyone associated w/ the album down to the engineer
and cover
designer to get their credit due. If I sell a copy of the cd, that's one less
person buying it from a big box (store). That's one less jo*nt willie
can smoke,
or one less p*le some exec can snort- but that's none of anyone's business.

Our business of ripping and the hypocrisy's surrounding it shouldn't be
anyone's
business either, but that might change, so why flaunt our hypocritical
behavior?
It's bad enough SD is ranked 6th in google for 'ripping to flac'. FLAC
will become
a bad word soon <guessing>, and a 'flac ripping ring' sounds absolutely
hedonistic.

FWIW I agree used stores can be shady too, I sometimes see promotional
material
that should have never been bought/sold, and sometimes even ask if I
can have it
for free- and why not???- just to start an argument. Maybe I have a problem...

Let's create a new 'Godwin's law' based on Good Book references.
http://en.wikipedia.org/wiki/Godwin's_law

[Skunk]

Quoting ezkcdude <ezkcdude.246qzn1141543501 (AT) no-mx (DOT) forums.slimdevices.com>:

>
> I think you should be careful,

indeed. sorry about the mispost

[Patrick Dixon]

Is this in Bugzilla anywhere?

I have only witnessed this once in normal use, when I unplugged a lamp transformer from an adjacent mains socket.

This lead me to suspect that a noise spike on the mains supply had disrupted the Xilinx RAM configuration somehow, and if so it's potentially an issue for CE conformity.

My experience with FPGAs is predominately with antifuse technology (eg Actel), so I don't know if is this is a common Xilinx type problem.

[dwc]

Thanks Dan & dmsmit1 for pointing me to the right direction.

As I read those threads, it does seems to me that although this "white noise" thing rarely occured, but the consequence can be extremely severe. However, I also noted that it seems like Slimdevices had then introduce a Preamp volume control function that will help to lower the risk, please correct me if I'm wrong.

I had white noise through the digital output. The preamp volume was already developed by then, but it does not affect the digital outputs. So the preamp volume control did not stop or limit the noise.
Secondly, there's no guarantee that the preamp volume control would limit the output on the analog outputs.
-Dan

[95bcwh]

Dan,
Can you help me to understand just one last thing, which still doesn't make sense to me. I keep reading that the volume control on SB3 is "digital". If it's "strictly digital", doesn't it mean when we lower the volume, the analog output voltage should remain unchanged, because all we do is changing the amplitude of the digital signal?

After reading so many posts, it now seems to me that SB3 has three different volume control:

(1) The volume control done via the remote is actually an analog volume control, which will change the analog output voltage from 0 to 2.1Vrms (full-scale)?

(2) We can adjust the digital volume on the web interface which does not change the output voltage?

(3) We can further adjust the analog volume via the preamp volume control function on the web interface, which will change the analog output voltage from 0 to 2.1Vrms?

I put question marks on all the above.. because I am not sure of the answer at all.

Thank you for your patience.
Barry

[dwc]

Barry,
I believe you have it right, and I'm sure others will jump in and correct any misconceptions. I'm not an ee, but here is what I have come to understand via following Sean's (and other's) posts.:

There are independent volume controls for the digital and the analog output connections.

1. The analog outputs have a 2-stage volume control. One stage is the "preamp volume" attenuation you set in the player settings, and this setting is meant to limit your max output voltage so that you can run direct into a power amp w/o a preamp. This setting is not adjustable from the remote control, and is generally set according to your amp's input voltage requirements and your desired maximum listening level. The units of measurement for this control are in DB of attenuation, but can be converted to actual voltage with some formula that's floating around but I don't have handy atm. (sorry)

The other volume control is the standard volume control used from the remote control which operates from zero up to the maximum you have set in the preamp volume.

2. The "digital" volume control affects the output level from the digital outputs. It can be set to "fixed" (at full output) which decouples it from the remote's volume control. By default it not fixed and will vary along with the analog standard volume from zero to 40.

3. If I set the digital volume control to "fixed" I can vary the analog output volume without affecting the digital output level.

4. Preamp volume attenuation does not affect the digital output level.

5. When digital volume is set at 40, or is set to "fixed" - then no resampling takes place. The SB3 digital outputs the source pcm signal unchanged. If you limit the digital volume then the SB3 will resample in order to lower the digital output level.

-Dan

[dwc]

Courtesy Robin Bowes:

dBu measurement is referenced to 0.7746v (often rounded to 0.775v), i.e.:

dBu = 20log10(v/0.7746v)

where v is the rms voltage, 0.775v in this case (rounded from 0.7746v).

[JJZolx]

I recently bought an SB3. It is connected to an Adcom stereo preamp, then to a Parasound amp. The sound is very good. I expect it would be even better with the SB3 going directly to the amp, but noticed a post about a bug that can result in the SB3 sending full scale output, which could possibly blow the amp or the speakers (especially if the signal is clipped either from the SB3 or from the amp). The Slimdevices CEO even warned that connecting directly to the amp is not recommended.

Is that bug/issue still a concern?
Yes. I'd be wary of connecting a Squeezebox directly to a power amp without a volume control. The issue is the fact that the SB employs a software volume control, so there's always the prospect that a bug or glitch will cause the Squeezebox to lose control of the volume level. Unlike most hardware volume controls, it's always a possibility when its done in software.

[Jenks]

Its always difficult squinting as circuit boards but it seems to me that both volume controls are digital - one affects the digital output level and the other affects the digital level entering the DAC. There might be a variable shunt after the DAC chip but I can't find anything between the DAC chip and the output jacks that looks like it might control volume.

[dwc]

Its always difficult squinting as circuit boards but it seems to me that both volume controls are digital - one affects the digital output level and the other affects the digital level entering the DAC. There might be a variable shunt after the DAC chip but I can't find anything between the DAC chip and the output jacks that looks like it might control volume.

Jenks, Search a bit on it or PM Sean, I think he has explained somewhere in tech terms how the different volume controls work.

[JJZolx]

Jenks, Search a bit on it or PM Sean, I think he has explained somewhere in tech terms how the different volume controls work.
It's a digital volume control for both the analog and digital output. Which means it's controlled by the SlimServer software plust SB firmware.