Soviet-ish Distortion+

[drew.spriggs]

After much messing around, I'm almost at the end of this one.



Cliffs:

• Distortion+ish with NOS almost Soviet parts (all components from Tesla in the early 90's except for diodes which are D18 germaniums).
• Component values based around what I could get in suitable parts - different min/max gains, different rolloff frequencies, etc but still in the same spirit.
• Mod cons - reverse polarity protection, IC decoupling, stability caps in the feedback network, quality jacks/switches, etc.
• Eyelet board I designed/CNC'd mounted with stainless steel hardware.
• Enclosure is a custom job I had a friend whip up - 2mm steel, pressed inserts for mounting.

Jobs left to do:

• Mount the TO99 IC - planning on using a uA709 which may require input/output compensation networks (will be hidden on the back of the board).
• Repaint the enclosure as the hammer coat I used must have not dealt with our temperatures too well.
• Mount the 9v lamp indicator.
• Figure out wtf I'm going to call/label this.
• 

 

[drew.spriggs]

Alright, TIL about input/output compensation networks.

Output was easy - a small value cap from pin 5 to out. Tried a few values while I had a sig gen/scope on, and about 47pf everything seemed to come good - about 3x the output and much less noise than without it.

For the input, most examples of circuits I could find had 1k5/1n so went with that - marginal increase in output but didn't really change as I tried a few different values. Left it on there.

I've also changed the clipping diodes to series pairs of 1D507's as she was pretty light on the output - we're maxing about 1v out with these diodes which isn't a lot of output, but enough.

Plugged it in and it sounds FANTASTIC. I am going to try and get the pot taper a little closer to reverse log as the log I've got really bunches the gain up at the end - I'm only losing min gain range so not too concerned.

Still need to come up with a name for it!