Leak delta 30 volume spike on right channel on switch off

[pockets]

Hi, as in title my issue is volume spike on one channel when switching off ,the unit is a recent purchase , have swapped out all cards and still does the same , also swapped out R C34 1000 uf cap for known good one from another unit still the same ,have recently swapped in a new to me volume pot and pretty certain its wired in correctly , one thing that i did do was accidently short c6 mains filter cap to chassis as it moved within the bracket , and blew a fuse ,could have happened then , dont know if the issue was there before as had to turn off unit at the mains and the test speaker may have been in the left chann which has no issue on switch off . Quiescent current is set to 40ma on both channels.

[pockets]

Anyone in the Newbury area willing have a look at it ? or could give some advice maybe on possible issue .

[pockets]

Think, ive located the issue, seeems to be the replacemrnt volume/onoff pot is faulty, have dissamembled and cleaned , it doesnt volume spike anymore but the balance is uneven so have asked for a decent replacement from the seller and its on its way .

[pockets]

259 views and not one comment , cliquey here or what

[Silicon]

The symptoms had me 'stumped'.

I could not think of a fault that would affect only one channel in this way.

When you swap power amplifier boards you should adjust the quiescent current in the output transistors each time.

Have you checked the stage gain of the preamplifier and power amplifiers to make sure the imbalance is not 'outside' the volume control.

[pockets]

I swapped over the wires going to each pot on the control and the fault shifted from right to left , so presume that shows the problem is with one of the tracks , when I dismantled and cleaned the parts I noticed one of the tracks is quite worn where the contact fork runs ,think before I cleaned and tweaked the contacts it was going between the end of the track on switch off and touching the centre solder pin causing the spike , will report back when I fit the replacement pot. thanks for reply .

[Radio Wrangler]

It's quite common for ordinary grade stereo volume pots to have poor balance at low levels, so some swapping until you find a good one is maybe the best you can do. Many of the later Japanese amoplifiers had an attenuator button. It looked like a handy convenience for when your phone rang etc, but it was really a way around volume pots with wandering balance at low levels.

Bad wear on volume pots at the low end is an inevitable penalty of including the on/off switch on them. Every time the user turns the amp on or off the volume control slider gets grated across this section. The other penalty is in routing AC mains wiring close to the low level audio signal path and risking hum pick-up from it.

Once fixed, it's worth just leaving the amp turned on at the volume control and using some external power switch to turn it off, improving longevity.

Relying on an external power switch also helps because a lot more pots are available without built-on switches and you have a better chance of finding something good.

People on this forum tend not to wade in if they can't see anything definite that they can contribute. It gives a better signal to noise ratio on the forum. You found the dodgy pot yourself. Before that, although there were several possible causes of pops and bangs as you turn off, there weren't any clues in the posts that steered to any specific cause.

David

[Ted Kendall]

Just to reinforce David's point, generally people don't post here unless they believe they have something useful to say. We're pretty helpful in intent, believe me.

I'll just mention that there has been a recent thread in this section where the OP asked a question, received several helpful replies, and hasn't been back since his one post...

[knobtwiddler]

Wandering channel balance at high attenuation is something that affects some of the most expensive pots ever made. I use an R+S analyser that makes it very easy to watch channel balance across the frequency spectrum over a range of 120dB, so it really enables you to sort between pots. A client in Japan returned an item to us, where we replaced the £80 pots with £12 Alps, because he was bothered by the expensive pot's drift at high cut.

TKD actually make a pot that is limited to 50dB in range. The tracks look as if they've been laser-trimmed to my eye. It goes from 0dB when fully open, to -50 at nearly full CCW - if you move a fraction off, it cuts to full short-0V. TKD's normal pots (100dB-plus range) have mediocre channel balance beyond -50dB, which explains why they made the 50dB taper with its trimming. I suspect this is a byproduct of their track printing technique, whereby limited ranges can be tightly controlled, but not more than 50dB or so. Alps tracks are carbon, and don't seem to have the limitation.

[pockets]

Yes , but people could've at least made some suggestions or asked for more info , but i'm not that bothered really and thanks for peoples recent comments, the imbalance is quite pronounced so would've had to adjust balance to compensate , even then the volume on one side was a little too high , hopefully the replacement pot will be the answer , will report back once fitted .

[pockets]

Arrived and fitted , now works as it should .