Snap, Crackle, Popp

[Joe Popp]

My 2204 circuit is crackling and popping like it has a bad pot. I changed the pots. I cleaned the tube sockets. I changed all of the tubes. The sound will go away when the master volume is down. It will also go away when I pull V2. I have a bunch of vintage NOS parts in the amp and guessing it is resistor or cap. Any guidance would be appreciated. The amp worked like a charm and was super quiet after I did the Larry grounding but I had not played it for a while and now at a rehearsal it's the cracklemeister. Thanks as usual Metroamp dudes...

[spaceace76]

Is the crackle random? does it happen at a constant rate?

can you provide a clip or something more specific to compare the sound to?

it's tough to diagnose an amp just by ear unless you have experience troubleshooting. Most likely you have a cap that isn't blocking DC, and letting random bits of DC current into the signal path.

the symptoms of not hearing the sound when the master is down or when v2 is pulled says that something is getting into the signal path that shouldn't. Does it go away if you pulled V1 or V3? If not then you may have answered your own question, replace V2 signal caps and see what happens.

It's really hard to test for leaky caps. You need a voltage/current supply similar to the amp's in order to see it happen with a meter. In the circuit itself, if you know where DC should and shouldn't be, you can get a basic idea of where the problem stems from.

Best of luck

[Haze13]

If you have strange noise while turning the gain pot, than it can be 22nF cap before the first treble picking circuit (470k + 470p).

[Joe Popp]

Thanks for the replies guys!

Spaceace76: The crackle is random. It sounds sort of like a scratchy pot but with some extra pops.

It does not go away when V1 is pulled.

It does go away when V2 or V3 is pulled

I will swap some caps and if it persists I will post a clip.

Thanks again.

Joe

[Joe Popp]

Found it!

The tone stack treble cap was bad.

I had an old Radio Spares 560pf (there are two as you can see, it was the one to the left) installed.

Super quiet again!

So much for NOS.

Thanks for the help guys.

Joe

[neikeel]

Just saw this.

You diagnosed this yourself at the beginning - goes away when you pull V2 so either second gainsatge issue or tonestack/cathode follower. Was the cap new or a pull?

[Joe Popp]

Neikeel:
It was supposedly NOS and it had full leads. It appeared to never have been soldered before.

I swapped them both out with Cornell-Dubilier 500pf NOS I had laying around and the amp is back to being amazingly quiet.

Those Radio Spares micas are harder and harder to find. I paid $35 for the bad one!

It was an odd problem as it sounded like the Pre, Master, Treble and Bass pots were bad. All of these are of course in the signal path of that cap.

Joe

[spaceace76]

Glad you found the issue quickly. Sometimes that first instinct and symptom are the biggest tipoff. Crank it up and enjoy!

[Joe Popp]

Thanks Spaceace76!
Cranking has ensued!

[matttornado]

I just had this happen to me two times in one week! The type of caps were silver mica 500pF. both bought new about 7 years ago.

[SteadyEddie]

I just had this happen to me two times in one week! The type of caps were silver mica 500pF. both bought new about 7 years ago.

Happened to a buddy of mine as well. I thought that mica caps were more, I don't know, robust against this kind of thing but apparently, leaky mica is not uncommon.

[Joshabr1]

Damn that is the coolest 2204 ever. Frigging great work on that build man ! Props to your skills.

[jimmyride]

Dude, thanks for this thread. I've just fixed my amp thanks to you trouble. I was lucky to have bought some of these caps some time ago. I use NOS Lemcos.