[DuCKy!]

Hey guys,

So I've wired up my dual gang ALPS switched pot for my little CMoy amp. Worked like a dream at start. However after a while there's a little "pop" on the right channel, which then the volume decreases on the right, but increases on the left.

I have to turn the amp off with the pot or it'll stay like this. Also, once that has happened, the "pop" and its following situations arise after a certain rotation of the pot, and has to be turned all the way down (off) to reset it again.

I've tested adjusting the volume from my source but it doesn't seem to affect it at all, so I'm thinking it's the pot. I've re-soldered it already, double checked groundings for it. Still seems to play up.

All components of the amp seem to be normal (no overheating etc).

Any ideas guys? Is there a chance that I might have destroyed the pot somehow?

Thanks

 

[tangent]

I don't actually see how a pot can suddenly change its setting while the amp is just sitting there. Drift, yes. Be bumped, yes. Jump in a predictable way all by itself, no.

This sounds like some other problem, like oscillation.

Have you tried removing the amp's battery for 5-10 seconds instead of turning the amp off with the pot's built-in power switch?

What gain level have you set your amp to, and which op-amp did you use?

 

[DuCKy!]

Thanks for the reply Tangent.

I've just found what the problem is...
I tested my amp with some cheap earbuds with an oscillator and a frequency generator.

Output on both channels are fine, nice and clean.

Came back home, tested it again with the earbuds, worked fine
Plugged my 555's in, and pop.

My headphones = dead?

 

[DuCKy!]

I've also checked the DC Offset on the output lugs. Seems to be minimal...

So I'm not too sure why it does that?
As mentioned before, I can increase the volume through my source (computer) and it won't pop at all. Only when I increase it through the pot on my amp.

 

[DuCKy!]

I've also checked the DC Offset on the output lugs. Seems to be minimal...

So I'm not too sure why it does that?
As mentioned before, I can increase the volume through my source (computer) and it won't pop at all. Only when I increase it through the pot on my amp.



Oh, by the way, I'm running the CMoy amp after my EMU1212m soundcard from my computer.
I've just realised that, plugging my headphones straight into my onboard soundcard, it does not pop with the increase of volume. Tried it with my brother's iPhone, doesn't pop as well.

I've tried another pair of random sports headphones i had lying around on the amp, no popping. So it seems to only do it, on my Sennheisers, through the amp.

 

[tangent]

What power supply are you using? If it's a wall supply, is it isolated?

Try measuring the amp's quiescent current while this happens, and compare it to the no-load case.

 

[DuCKy!]

I'm just running it off a 9V battery.

Will check and calculate the quiescent current later when I get a chance.
I'm still stumped as why it only happens with the 555 and not on other headphones?

 

[tangent]

Simply put, the load matters. Different headphones have different resistances, inductances and capacitances, and that's all important in determining whether a circuit oscillates or not.