SB3 volume output lower on left than right channel

[cutandaweb]

In my Squeezebox touch december/2010 the volume output is different also.

[eCo]

This exact problem has now happened to my SB3 as well. I'll give this fix a try. Thanks for the info.

[Stu-e]

I just had a quick look at the SB2 schematic Sean posted earlier and I am very concerned about the decoupling caps C7 and C39. The schematic symbols for the caps imply they are polarized and studying the circuit they are fitted with incorrect polarity. This will probably cause low frequency popping or rumble noises and eventually premature failure of the caps.

The inverting opamp buffer circuit has an input reference of 5V connected to the cap negative pin. The output of the DAC is somewhere between 0V and 5V connected to the cap positive pin.

I'm going to open my SB3 and check this out for myself. I think I've got a faulty power connector anyway which I can fix while I'm there.

Stu-e

[Stu-e]

Yup
C16 and C20 are reverse biased on my SB3.
I'll start a new thread

Stu-e

[eCo]

I'm happy to report my SB3 is now fixed. Though only the left channel was affected, I replaced both c16 (R-Channel) and C20 (L-Channel) with new 10uF/16v caps (Vishay 097 RLP 7) as I concur with Stu-e's assessment about polarity.

Accordingly, I soldered the new caps in with the negative lead towards the pcm1748 - opposite to the schematic and the original caps orientation. The procedure was quite simple, but some soldering skill and an iron with a micro-tip are helpful.

This thread will undoubtedly come in handy for electronics' savvy consumers of SB3's who've yet to experience what appears to be a likely failure mode.

[swaf]

Hi, I have a queation.

I seem to have more or less the same problem, one channel that is substantially lower in volume, and recently it has stopped working at all. However, I do not have a SB2 or 3, but a SB reiceiver. I haven't been able to find the SBR schematics anywhere, could it be possible that the same fault still exists in the SBR, although it has been designed and built approx 5 years after the SB3?

So I opened it up and I think I identified the caps. On them is printed 10/16s./9J9" so I think these are the 10 uF / 16V caps you were speaking of. The positive side is directly connected to the dac. Perhaps they used the same circuitry as in the SB2/3 here?

I haven't measured anything yet, but the suggestion to measure RMS to ground before and after the cap when playing a sine wave seems to make sense.

In the mean time, if anyone could provide me with a SBR schematic I'd be very grateful.

EDIT:

So I measured. I got 4.7V from the DAC's output signal on both channels. I got 0.8V output from the output caps on both channels. All seems fine so far. But one RCA connector measures at 0.8V, the other 0.1V. How is this possible? The components are very small and it's hard to see what happens to the signal after the output cap without schematic, probably an LP filter? But I don't think I see an opamp in there. Probably one of the smaller R or C's of the filter are defective, but this is nearly impossible to replace, they are so small. So I'm thinking of connecting both channels directly to the output, bypassing any defective component there might be, but also bypassing the LP filter. Good idea? Any other solutions?

Then there's only the question of which cap to use. Same value (10uF) as the stock ones, or a different value?

[swaf]

Ok, so I did some reading. I read the spec sheet of the Wolfson DAC. The output caps seem to be correctly oriented. So that isn't the problem. For future reference, I'm going to describe what steps I'll undertake to fix my problem and what their results are.

I'm pretty sure one of the mini components that make up the LP filter has failed, which is the reason why one channel is dead. My output caps are fine. Now I was wondering if that LP filter is really necessary. According to the spec sheet: in most cases, no. The DAC already has a built-in LP filter.

Quick fix is to bypass the filter and go directly from the output cap to the RCA connector, so that's what I'll do, once I have my mini soldering iron, still looking for a good one. I can solder, but I've never soldered anything that small.

Since I need to solder anyway, I was looking if there's a way I can change the output caps to something better (note that the spec sheet says to use high quality C0G caps, which the stock ones aren't). There are not many threads about modding the SBR, but there's one monster thread that I half read, and from what I gather it's not as easy as it seems. It requires constant tweaking and listening to the changes you made. While I like such a kinds of projects, right now I lack the time, and more importantly the audio equipment of high enough quality to actually hear such minor changes. And all I really want is to have my stereo sound back.

So, I'll simply bypass the LP filter and keep on using the stock caps. I'll let you know how that went in just a few days.

[Appalachik]

I have a similar problem... I own 2 SB3s and an SB2. One of my SB3s is outputting about 20dB less on the right channel. I have substituted the other Squeezeboxes into the system to confirm the fault. The faulty squeezebox outputs fine via headphones. I run this system in my recording studio through a Focusrite Audio interface, using toslink and configuring MixController to use ADAT as an optical SPDIF, routing the output either to my Tannoy main monitors, or to an Adam 2.1 monitor/sub setup. The setup lets me mute individual output channels, where I noticed another odd thing... muting the right channel works fine, but muting the left channel only diminishes its output somewhat, so it can still be heard. Seems odd to me and may be part of the same problem? Any ideas? If there is a full schematic of the SB3 available, I'd like to check it out and show it to my resident electronics wizard as he will most likely be able to fix the problem.

Thanks! Jenna

[fieldwolf]

Hi,

I have a Slimdevices SB3 classic which appears to have developed the same fault where the Left channel output is significantly lower than that of the Right.

I see eCo resolved this buy replacing Capacitors C16 (R-Channel) and C20 (L-Channel) with new 10uF/16v caps (Vishay 097 RLP 7).

As an electronics beginner, I take it that requires me to purchase new capacitors, solder out the old ones and solder in some new?

In which case, could anybody help to confirm the below 2 links the ones I need?

http://www.farnell.com/datasheets/415423.pdf
http://www.vishay.com/docs/28308/097rlp7.pdf

and so purchasing them from here is probably an ok bet?
http://uk.farnell.com/vishay-bc-comp...rad/dp/1165518

eCo suggests soldering the new caps in with the negative lead towards the pcm1748 so I'll go for that.

For anybody experiencing the same problem but not wanting to open or solder their unit, am I right in saying that you could use the SPDIF or Toslink digital outputs and hook those up to a digital optical to rca analog converter that you can find on ebay?

I believe that bypasses the DAC in the SB where the fault but you would then be only as good as the quality of DAC you buy? I see ones from £10 to £100 so plenty of options there....but for those who just want their SB back in working order that should work?

Apologies for resurrecting an old thread and many thanks if anybody is able to get back to me.

[ralphy]

For anybody experiencing the same problem but not wanting to open or solder their unit, am I right in saying that you could use the SPDIF or Toslink digital outputs and hook those up to a digital optical to rca analog converter that you can find on ebay?

I can confirm that the SPDIF out works for me on an SB3 with this problem.