music, guitars & other obsessions

SMPS Test

After reading some threads on diyaudio, diystompboxes and AX84, I decided to try some DC-DC converters to if they would work in guitar amps. Functionally, of course, they would but how would they sound, that’s what I wanted to find out… The biggest complain from users (or just speculators), was SMPS are noisy as the switching noise gets coupled into the audio circuit, well we are about to find out yea or nay.

I ordered two DC-DC converters, one 25W and the other 120W, both use TL494 PWM for control, MOSFET push-pull switching, step-up transformer, pretty much text-book design. The switching frequency is 70KHz. The larger unit has the MOSFET mounted on medium size heat-sink, the smaller one has none.

So how did they work? Quite well, actually. I removed the PT HV and the tube rectifier from the Otto amp, and hooked it up to the converter, first the larger one then the small one. Below are some shots of the units in action.

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Both converters worked just fine, I was surprised the smaller one worked without breaking a sweat, the switches did not even get warm after half an hour of playing. The noise level was about the same as the old supply, I was not able to detect any switching induced noise even when I put my ear right next to the speaker. Since the test was run with the lab supply, I could not try the amp in the studio, so further tests will be done after I get some wallwarts to supply the voltage.

Some shots of the converter to give an idea of their sizes.

120W Converter

25W Converter

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