'Crackle' through audio output when volume slider is actuated.

[Cookeh]

Evening,

I've started noticing, with increasing frequency, that whenever I move the volume slider on my Pioneer SA770 amp, there is a very audible 'crackle' through the output device, be it speakers or headphones. This crackle can often be accompanied by a partial (L or R sided) or full loss of audio as the volume is being changed. It's a bit irritating, but other than that the amp functions perfectly. It tends to occur mostly when moving the slider to lower volumes, from 2 down to 0, for example. It is from 1984, so its getting on a bit tbh, but its 100W per channel, quad channel amp and I love the sound and power. Any ideas as to the cause?

I've ruled out interference, I've ruled out any issue with speaker/headphone, any connection from or to the amp.

Cheers!

 

[rids57]

Sounds as though the volume potentiometer is either worn out or dirty. If you can get at the pot it might be worth a squirt of switch cleaner, otherwise you're looking at a new one.

 

[Kei]

Deoxit D5 should sort that out. Apply a small amount directly to the slot and then slide it back and forth to work the cleaner/lubricant in. (you will need to remove the front panel to access the pot properly) Cheaper alternatives are electrolube SWC or ambersil contact cleaner. If none of the other switches or pots make any noise when used, you may as well leave them be.

A service manual can be obtained here. May help with some dismantling, plus if it won't clean up you will know what part to buy in order to replace it. (although it's likely to be difficult to source a perfect fit replacement)

 

[Cookeh]

Thanks chaps, some good info there - the manual is handy (think I found it ages ago whilst trying to do some research into the amp and forget about it since)!

One slight issue, that manual, and ones from other sources all state its 50W per channel, but the specs on the back of my amp clearly state 100W per channel, 400W total. That's the only external difference I can find, do you think its a different model or a slight change in spec mid-production. Either way, would I be correct in assuming the internal layout be the same?

So close with the year too, must have gotten that mixed up with my floorstanders