Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

March 29, 2024, 01:13:23 AM

Login with username, password and session length

Recent Posts

 

acoustasonic pro buzz

Started by rwooley, November 15, 2014, 10:42:03 PM

Previous topic - Next topic

rwooley

Hello all,
I have an acoustasonic pro amp that I love. It has recently developed a significant buzzing sound, even when no instruments are plugged in. My first inclination was to think it was my filter caps, as I understand they will do this with age and have had this problem with another amp. However, I can get it to almost disappear by smacking the top of the amp. It will go away for a while, then come back. If I understand correctly, all filter caps do need replaced every 10 years or so. This amp is easily that old, so maybe I should just do this anyway. But, I've also read that transformers are another typical cause of buzz, and the fact that I can get the buzz to change with a light smack makes me think that it probably would not be the capacitors.

I can't really afford to take this to an amp tech right now, and I'm confident I can fix the problem with a little support. I have done plenty of soldering, including replacing the filter caps in another amp. Anyone have any advice? I"m attaching the schematic in case that helps.

Roly

Quote from: rwooleyI can get it to almost disappear by smacking the top of the amp.

Then it isn't the filter caps.

Thanks for the circuit, that's helpful, but five will get you ten this will be an "off-circuit" problem.

Quote from: rwooleyIf I understand correctly, all filter caps do need replaced every 10 years or so.

You understand the mythology correctly.  "Replace the caps!" has become the standard parrot cry of the clueless to any and every amp fault, and as we constantly demonstrate around here, it is wrong at least nine times out of ten.  Caps (like everything else) do fail, but not nearly as often as many people think (but then "many people" normally aren't working amp techs).

The electrolytic filter caps in my homebrew workhorse Twin-50 are at least 45 years old and still going just fine.  Electro's do age, but we still only replace them when they test faulty - i.e. with good reason.  In this case the sensitivity to a "smack on the head" points in a different direction.

Quote from: rwooleyI've also read that transformers are another typical cause of buzz

And that isn't the direction.  Could I ask what forum you are getting this rubbish from?

Loose transformer laminations can cause a mechanical/acoustic buzz, i.e. one you can hear coming directly from the amp itself, not via the speakers.  It has always been uncommon, very minor, and certainly no cause for replacing a transformer.  Because of the way transformers operate it is next to impossible for a transformer to inject an electronic buzz into the amp signal circuits.


As techs we don't guess, we diagnose.

Since the buzz is mechanically sensitive we first need to eliminate some possible mechanical causes.

Q. Is the buzz controlled by (any) of the front panel controls?

Q. If you insert a shorted plug into "Stereo Fx Rtn R" does it stop the buzz?
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

Chimed in to say exactly the same (thanks Roly ;) ) and add:
is it buzz (imagine a bee) or hum ? ( imagine a deep, dark organ tone or yourself saying "hmmmmmmmmmmmmmmm" with both ears covered)

But the most important doubt is whether they respond to any control.

g1

  The fact that it responds to you smacking it means it is likely an intermittent connection.
  As Roly mentioned, this rules out defects of the capacitors themselves.  However, their solder connections could cause the problem you have.  Often resoldering the filter caps corrects this type of problem.

Enzo

My advice is resolder the filter caps, they are otherwise likely just fine.