SB3 volume output lower on left than right channel

[Glenn2]

Just coming here to say thanks for the schematic. Fixed my SB3 yesterday. Both channels were down. I'd been using it with a DAC for ages and hadn't noticed. On a whim I'd decided to compare to the built in DAC and that's how I found the issue. Probably some kind of OCD kicked in and I couldn't leave it broken even though I normally use the S/PDIF out!

Firstly I replaced C16/C20 (10uF Elna Silmic II) but fitted them the opposite way to the polarity markings on the board (and the originals).
I checked the output via the headphone socket and all was now good. When I reassembled it I was dismayed to find the lineout was still bad on the right channel even though the headphone output was now fine! C23, the coupling cap between the opamp output and the jack, was also bad...

Took it apart again, replaced C21/C23 (again Elna Silmic II but 47uF instead of 10uF).

I can understand C16/C20 going bad as they were fitted back-to-front, but I don't see why C23 would go bad. This makes me worry about the longevity of the other caps on the board...

I also took the advice of Martin Clark (not for the first time) and changed C15 from 1uF to 100uF (I used a Panasonic FM for this).

http://www.pinkfishmedia.net/forum/showpost.php?p=571002&postcount=1

All working good and sounding great!

[iPhone]

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Resistors and inductors as well as air transformer usually don't degrade with age. But almost ALL capacitors age whether they are being used or not. Anybody that has a 20 or 30 year old Amplifier with a larger power supply will eventually find out about dried out electrolytic PS caps whether they are being used daily or stored in a closet going bad. Some caps start degrading after only 1000 hours of powered use and following that once they degrade as little as 20 percent will fail. Many caps only have an operational life of 10,000 to 100,000 hours of use, so they could start degrading and going bad in less then a year and a half of being constantly left on.

[slimjimbo]

right channel down on my SB3

Thanks for this thread, my right RCA channel is barely audible. I will be swapping both C16 and C20 and reversing the polarity from original.


Can someone confirm please that these are suitable:

This is the exact one mentioned by someone previously.

https://www.ebay.co.uk/itm/390758777696?

This is the same package as the original part, and looks like it will be easier to solder in.

https://www.ebay.co.uk/itm/351554609760?

thanks

[Glenn2]

Thanks for this thread, my right RCA channel is barely audible. I will be swapping both C16 and C20 and reversing the polarity from original.


Can someone confirm please that these are suitable:

This is the exact one mentioned by someone previously.

https://www.ebay.co.uk/itm/390758777696?

This is the same package as the original part, and looks like it will be easier to solder in.

https://www.ebay.co.uk/itm/351554609760?

thanks

Yes they will work fine.

The signal coupling caps can have a large effect on the sound though because the audio signal passes right through these.
Why not use some good quality audio ones? Your e.bay links are UK so if you are UK you could use Hifi Collective. That's where I got mine from. I used Elna 'Silmic II'. They are among the best for signal coupling, commonly used in these positions in Marantz CD players amongst many others.

https://www.hificollective.co.uk/catalog/elnas035-10uf-elna-silmic-electrolytic-capacitor-p-4346.html

I would buy at least 4 though. If my experience is anything to go by, you might have to replace C21/C23 as well, if not now then later. All 4 values are 10uF although for C21/C23 I used 47uF which is a more usual value to find in such a position (a larger value here moves the bass rolloff frequency down).

https://www.hificollective.co.uk/catalog/elnas075-47uf-elna-silmic-electrolytic-capacitor-p-6216.html

These are the 4 most critical capacitors in the box for sound quality of the analogue outputs.

By the way, I found it difficult to remove the old ones. I think my tip was too big (ooer, missus) and in the end I used the last-resort method of just twisting them off. This is generally frowned upon but I was about to give up anyway. I grab the cap with long-nosed pliers and push down into the board as I twist so as not to pull up the pads, twisting in the same direction until they just fall off. Worked fine on all 4 caps without problems. The wires inside the cap are very thin and you are effectively ripping them out of the cap. Careful where the remnants go when you clean up the pad. Not suggesting you use this method but as a last resort it worked for me (there are youtube vids showing SMD cap removal like this).

Good luck.

[slimjimbo]

Fixed

Thanks for the comments, even though I ignored them

I went with the surface mount option https://www.ebay.co.uk/itm/351554609760? because they looked easier to use. And it's only a cheap system in my workshop so I didn't want to start A/B testing the channels for sound quality improvements.

I didn't try twisting them off, maybe I should have. On the first one I damaged the track a bit, but it seems OK after I soldered the part on. Then I changed the part on the working channel at the same time on the basis that the original part is incorrectly biased and liable to fail.

And it all works now.

[Glenn2]

And it all works now.

That's the important thing!

[jazzjohn]

Changed C16 and C20

Hi all,

Thanks for taking the time to post thoughts and solutions for the low output issue. In my case, both channels were both low and about the same. I checked both caps in circuit and, sure enough, both were a very low value. Replaced them with ceramic (non-polarized) 10 mfd caps, 1206 size, X5R 25 volt units and output is back to normal now.

Thanks again!