Sound of recap?

abarson · #1 10-18-2010, 11:14 AM

Can anyone describe what an amplifier that needs to have its capacitors replaced sounds like?
My Tubeworks RT-3300 has developed a lot of white noise, even with nothing plugged in, which leads me to believe that the filter caps are breaking down. What is the typical life expectancy of the electrolytic caps?

craig.p · #2 10-18-2010, 12:48 PM

Experience has shown me that electrolytics can begin breaking down as early as a quarter century or so, but this is one of those things where the watchword is "it depends." As in how good they were to begin with, how conservatively they're being used, how hot they're being allowed to get, how many hours are on them, etc. etc. etc.

However, power-supply filter caps breaking down usually causes hum (usually 120 Hz) to be injected into the signal. Would I say that's always the case? No. But your problem almost sounds like a noisy transistor or tube. On that amp, is it possible to switch back and forth between a solid-state section and a tube section?

The good part of your problem is that it's fast and easy to troubleshoot, i.e. minimal tech charge.

Mr. Foxen · #3 10-18-2010, 02:30 PM

Bad filtering caps gave my amp a frying eggs sort of sound, like not really constant.

The time is pretty highly dependent on use, conditions and quality.

Greg Clinkingbeard · #4 10-18-2010, 05:05 PM

I'm not familiar with that amp, but it sounds like a bad tube. Try that first.

abarson · #5 10-19-2010, 11:43 AM

Switching between the solid-state and tube preamplifiers doesn't affect the noise: it's always there. The power section is solid-state, not tube.

I'm torn between getting this amp fixed (eliminate noise, bad pots) and investing in a Promethean.

craig.p · #6 10-19-2010, 01:59 PM

I'd get it fixed since in the condition it's in now it's basically a brick and worth about as much. Once it's fixed you can sell it and be able to say it's been gone through, bad stuff replaced, etc. etc. I really don't see this as an expensive fix. Maybe 1-2 hours of tech time plus whatever the bad part(s) cost. I'm assuming this is a standard/legacy circuit and not one of the new switching types.

abarson · #7 10-19-2010, 08:07 PM

I just got back from a local shop to try out a pair of Acme B2's with my gear, and the noise wasn't really apparent. Now I'm really confused!

McWood · #8 10-19-2010, 08:48 PM

Disclaimer: I don't know what i'm talking about! i apologize in advanced for the following.

How does the load of the Acme's compare to the cab you've been using? Power rating? How's your speaker cable doing?

Would it be possible that the old cabs impedance has gone wonky or is mismatched to the head and is the source of the noise? Would a mismatched impedance of the Acme's somehow attenuate the noise?

abarson · #9 10-19-2010, 11:53 PM

McWood,
I understand your chain of thought, no worries!
My cab is a single 4 ohm 15" neodymium. The B2's are each 4 ohms, daisy chained to appear as 2 ohms. The RT-3300 is rated to handle a 2 ohm load. FWIW, the RT-3300's 350 watts still aren't enough for those powerhog B2's.
Knocked all the crud out of the pots with some Caig Deoxit, good stuff!

I'm starting to suspect my cab, and will investigate further tomorrow.

Alex1984 · #10 10-20-2010, 11:47 AM

I wouldn't say it's the impedance. I'd think it's probably the fact that the sensitivity of ACME cabs are so much lower than most, so noise isn't as audible on them.