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Buzzy tone?

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3/12/2004 5:07 AM

Buzzy tone?

I'm at a bit of a loss as to what is happening with my Liverpool clone. I had a go at recording it today, and the results were terrible. The amp sounded buzzy.

The problem isn't apparent when you play though the amp normally, but when you listen with hearing
protection, and particularly when you record the amp, the buzzy tone comes very apparent.

I did try Paul Ruby's zener diode crossover distortion mod, but the problem must be elsewhere in the amp.

Any recommendations?

Yours Sincerely

Mark Abbott.

3/13/2004 5:24 AM
Jack Koochin	Hi Mark, If your ears aren't hearing it without headphones, and it sounds good just guitar and amp, wouldn't that mean that the electronics in the recording/monitoring/headphones circuitry are introducing the buzz? This also includes mics, etc. Jack

3/14/2004 4:39 PM

Dear Jack

Thanks for your reply, the buzziness is in the tone of the amp.

When I listen to the amp it sounds pretty good though I can hear slight buzziness.

When I employ the Ken Fischer technique of using some form of hearing protection (to remove the highs) the buzziness in the mids and bass is noticeable.

When I mike the amp up, it's all apparent.

I have tried removing parts of the circuitry, and I feel that the problem has to be in the P.I. or the output stage.

I was wondering if anyone has come up against this sort of thing in the past?

Thanks for your help.

Yours Sincerely

Mark Abbott.

3/16/2004 4:53 PM
Geoff Gross	You probably know this already, but have you experimented with different mic posisitons? It may not directly affect teh buzzy tone, but I have found that I almost always prefer the off-axis mic, usually around 45°away from the cone centerline. It may help tame some highs, which would help mask the buzz a bit. Geoff

3/23/2004 11:36 PM

Mike positions don't change the fact he hears the buzz in the room.

A scope would make tweaking this amp a lot simpler. However, you did manage to build it and can easily tweak it just by ear.

Most buzz and fizziness comes from spikes on top of the signal. These give it edge and cutting quality, but also that buzz if it is too present. If you adjust some of the interstage attenuation so LESS signal gets to the grid, buzz will reduce.

Another quick fix that smooths things out nicelyt is a plate cap. this can take three forms: The first is literally a tiny cap across the plate load of the second/third/or last stage. The second way to install it is to hang it off the coupling cap from the plate, to ground. The third way is to connect it across the plate and grid of a middle or later stage. Some amount of grid-stop resistance is nice, to turn the cap/grid-stop into a low-pass filter.

In each of these cap tries, the value is probably 100pF or less. Set by ear. Don't get zapped.

Have fun
Kevin O'Connor

3/26/2004 10:16 AM
km	hate to jump on a thread but-im having similar problems with my amp--the top end "fizz"--mines a high gain/similar to SLO or marsahall amp.i tink i only have one or 2 470pf in there...I think i will try to add a few of these small caps throughout the circuit to test

4/5/2004 3:56 AM
Bradster2k	Wow what a weird coincidence, I was recording a Marshall 2204 this weekend that was doing that same thing. By itself sounded quite good and the buzziness was barely distinguishable, but recorded it was very apparent and annoying. (JMP 2204 w/o mods) Thanks for the tips Kevin.

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