'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!

 

[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