valve distortion

Posted: Tue Feb 01, 2005 9:45 am

Mr Sebatron

I have a question for you.

Last year I got a local tech guy to build me a custom 2 channel valve distortion unit. While in testing phase, its sounded absolutely amazing on really hi gain. While building it he decided to swap the output transformer for a cheap one, claiming it would help the distortion... but I have found that their is a characteristic buzzing effect on certain high gain settings (not a nice one in most cases), and the unit as a whole destroys bass, though thats not surprising...

Just wondering if you (or anyone else here) could give me your learned opinion on this, as I'd like him to try a higher quality transformer.

BTW I'm probably gonna get one of your VMP 2000's soon... would love a stereo deuterium but dont think finances will allow.

Posted: Tue Feb 01, 2005 11:38 am

Not that I work for Sebatron, but having had a lot of experience with valve amplification for guitar I can confirm that a lot of manufacturers take great pride in the quality of the output transformers and therefore can only presume they contribute to the quality of the tone obtained, as does power valve distortion as opposed to preamp valve gain, which may not be so applicable in your case.

YOu could look at the websites of Rivera, Soldano, and THD to get some more thoughts on this.

Posted: Tue Feb 01, 2005 12:09 pm

Hi

I should post more info on the unit then: it uses power amp distortion, not preamp distortion (which is only nice at moderate levels), with one input gain stage and an output/power gain stage. I've had it a while now, even with the cheap output transformer it makes a lovely addition to drums and synth sounds when used as an aux effect, really nice hi-end fizzle. But the frequency range seems to be limited, I assume by the choice of output transformer.

Posted: Tue Feb 01, 2005 12:22 pm

Certainly if it's a guitar amp or power amplifier with a definitive output stage to drive low impedances , yes there may be significant colouration from the output transformer.
As a line level unit however, the tendancy would be to swing towards a more transparent output trasformer or one that would inherently produce a certain' warmth ' or fuzz in the lower spectrum as opposed to the buzz that you may be talking about.
That may well be the clipping points of the transformer brought on by its own limitations or sick resonant points in the frequency response in which case the higher quality transformer may be the only option.
Sometimes setting up a careful ' Zobel Network' around the primary or even the secondary may improve things a little.Negative feedback from the seconday may also be an option.
I suggest replacing just one transformer and running some objective A/B tests between the two channels to confirm any speculation.

Cool

Posted: Tue Feb 01, 2005 7:00 pm

this is fascinating, let me know what happens.

Posted: Wed Feb 02, 2005 5:08 am

will do, hope to do this soon! Mr. Green

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