What's going on here?

[Boy Howdy]

I have a Vox Straight Six tube overdrive pedal. It sounds really good. When I first got it I thought that it would have some clipping diodes producing the bulk of the distortion. But I can't hear any evidence that there are any. It sounds like the real deal! I do know that it's a true high voltage pedal (200 volts), but every single-tube preamp I've made (high or low voltage) produces very little distortion. This thing has gobs! And it sounds great! How are they doing this with only one tube?

https://www.gear4music.com/us/en/Gui...itar-Pedal/UET

[J M Fahey]

I am quite certain they have a high gain stage *before* the tube and drive it balls to the wall.

As in 100X or more before even reaching the first tube grid.

Of course, since the clipping/distortion comes from the tube itself, thatīs the flavour it acquires.

[g1]

This doesn't show anything about how the circuits work, but does show some waveforms on a scope. Sounds pretty good too.

[J M Fahey]

Thanks.
Thatīs a typical overdriven triode waveform: flat clipped on top, because it smashes against +V rail; rounded on bottom because tube saturation caused by poor emission with very low plate voltage is not such a sharply defined event.
Of course top peak can reach +V but bottom will never reach ground.

Of course, completey different to hand drawn waveforms shown on most (98%) pages explaining "tube sound"

[Boy Howdy]

Yeah, I'm actually thinking about doing my own video for the pedal. Every single one I've seen has been terrible. The pedal sounds much better than any of the videos for it would lead you to believe. I don't think there's a single video that uses a Strat. Maybe that's the difference. It sounds great with a Strat.

I wondered about whether there is a solid state booster stage before the tube. But in my experiments building my own preamps, that approach didn't get it at all. A booster before the tube yielded a pretty crappy sounding distortion.

Gar Gillies did some strange things with his various Stinger circuits in his Garnet amps. I don't have a clue about how all of that worked. I wondered if maybe Vox had incorporated some of those strange tricks.

It'd be nice to see a schem of course. Good luck with that, I can't even figure out how to get into the pedal!

Edit: I just re-watched G1's video. I had forgotten (...blocked out?) that there is a transistor stage before the tube.

[Chuck H]

Thanks for locating that video g1 Definitely confirms Juan's prediction.

Very good sounding pedal I think.

I wondered about whether there is a solid state booster stage before the tube. But in my experiments building my own preamps, that approach didn't get it at all. A booster before the tube yielded a pretty crappy sounding distortion.

Gar Gillies did some strange things with his various Stinger circuits in his Garnet amps. I don't have a clue about how all of that worked. I wondered if maybe Vox had incorporated some of those strange tricks.

There are no "strange things" or special tricks really. Some of it has to do with limiting LF going in as the gain is increased and then filtering some of the hash. That, along with setting up the OD stage to respond the way you want it to. Bias, possibly some voltage sag with a resistor in the HV supply, etc. will change things like symmetry in a dynamic way. Finding the recipe (or knowing how to get there) that sounds good is the only trick.

[Boy Howdy]

https://gjikaamplification.com/gjika-gainmaster

Check this out. Tune in at 3:10 to hear the pedal into an absolutely clean amp. That pedal has only one tube. How you reckon he's doing that? I've only been able to get that with two tubes.

[Boy Howdy]

Here's a Stinger schematic: https://elektrotanya.com/garnet_stin.../download.html