OD stage development

[uneumann]

I recently spent a fair amount of time pursuing and tweaking a preamp overdrive stage. It's a bit different from most, so perhaps the story is of general interest. The schematic is below to give you an idea of where I wound up. The details are too lengthy to post here, so they're posted - here - where you'll also find scope pics, spectra, and actual audio clips.

Comments or pointers to similar adventures into OD design are welcome. This could be a good thread for collecting comments or ideas about how to approach the problem of OD stage design.

[nickb]

Thanks for sharing your work and ideas.

I'll have to go and built one to play with now...

[Mike Sulzer]

It is very interesting how the intermod spectrum changes with capacitor vs. no capacitor. A tube is a field operated device. If you change the output waveform it is because the grid-cathode voltage has changed, and I think the only thing that can do that in this case is the time dependent flow of grid current and the resultant charging of capacitance associated with the grid circuit. So I wonder what the spectrum is like when such charging is prevented (or greatly reduced) by another method, such as stabilizing the dc current with a huge cathode resistor to a negative supply? I have the amp that can be used to check this. (What I need is the time.)

I recently spent a fair amount of time pursuing and tweaking a preamp overdrive stage. It's a bit different from most, so perhaps the story is of general interest. The schematic is below to give you an idea of where I wound up. The details are too lengthy to post here, so they're posted - here - where you'll also find scope pics, spectra, and actual audio clips.

Comments or pointers to similar adventures into OD design are welcome. This could be a good thread for collecting comments or ideas about how to approach the problem of OD stage design.

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[Malcolm Irving]

Great article and nice sounding clips. I hope to try that circuit. It would be interesting to see how it goes if you have two of those OD stages in cascade (for those folk who want more distortion).