Fix amplifier crackle

[vaio-fx]

I have a Denon PMA 520 amp, from 1988, it is a great amp and I can't afford a decent enough replacement right now. I was wondering if it would be possible to fix it. When you play music through a PC it is fine for most of the time, however on other sources such as iPod the problem occurs more frequently. Basically you will be playing music and either the left or right channel or sometimes both (more often the right) will start to go all crackly - you cant hear any of the song, just this crackle, after turning the volume up and down quickly and playing with all the levels etc, it kind of like un pops and works again. Any idea if this is fixable?

 

[01001010]

Get a new amplifier and disconnect those speakers.

 

[vaio-fx]

I put the 6ohm ones back with their propper amp. I'm simply running 2x 100W 8ohm speakers on it, that is below the amp's stated power. I googled the problem and apparently its common on old amps but is fixable, I don't know enough though to be able to fix it.

 

[J03]

I get a bit of crackle sometimes, but then then i kinda.. wobble the Input Selector knob, it fixes it. It's a bad contact, in my case.

 

[vaio-fx]

The way which seems to work best for me is to change the balance to whichever channel is crackling, blast up the volume and then it seems to make like a poppoing noise and goes back to normal. I can put up with it as sometimes it won't do it for ages, but others it will do it constantly and out of both channels.

 

[root]

what is the rated load and impedance of the amplifier, and what speakers do you have connected.

when you say crackle I guess you mean that it starts to go fuzzy and petters out to nothing?

is this still happening as much or has removing the 6ohm speakers from the equation helped any?

 

[berry120]

Changing the impedance of the speakers is unlikely to help with these symptoms.

It sounds to me like you've either got a duff transistor or a dry solder joint, perhaps both. They are perfectly fixable, but you have to know what you're doing and what to look for - I really wouldn't recommend poking around with a soldering iron unless this is the case! If not you could do a lot of harm and pretty much no good, both to the amp and yourself...

 

[root]

I was thinking that if the impedance was too low that he might load the amp too much or perhaps draw too much from the supply rails for the power supply to cope.

the amp is a fairly simple class A amp, (I think from a few google searches).
I'm guessing that there might be a separate filtered supply for the left and right channel,

and probably that there may be some kind of thermal protection on either the supply or the amp...

if there was too much current going to the speakers this would likely trip one of these and the sound would peter out to a crackle. this would be more true of the power supply than the power amp failing I think. but that' depend on how/what the crackle appeared.

 

[berry120]

Completely valid logic there root, I wasn't trying to undermine you on that I was more going on the principle that running 6 & 8 ohms should be a small enough difference not to cause any symptoms such as the above. If the amp has been overdriven and that's what's causing it then I'd generally expect no sound or a constantly distorted sound anyway rather than intermittent crackling - though of course as you rightly point out, it is possible. I'd just say it was relatively unlikely.

 

[vaio-fx]

Hi thanks for the responses. The 6 ohm speakers are no longer connected. I tried running two pathetic tiny 8 ohm supposedly 50W speakers on this amp and once again the crackling came so I'm convinced its nothing to do with which speakers are connected (although i realise the 6 ohm ones are overloading it). The amp has done this on all different variations of speakers in the past but it seems to be getting worse. If I get some time I may go look at some amps today.