Tricks to decrease brightness of Tchula circuit?

[harmaes]

I've build the Tchula (electra like) circuit on a veroboard and it's working quite nicely. I used a 2n5089 after comparing it to 2n5088 and some other transistors. Higher HFE (600-650) seems to work best in this circuit.

I noticed that the first cap in the circuit is 22n and I increased it to 33n, 47n and 68n which reduced the higher peaks somewhat. If I'm correct the 22n is the input cap and the 100n the output cap? I now have the output cap at 100n and the input cap at 33n which sounded best with my strat IMO and still was open enough with a LP.

Did you experiment with this circuit and what values did you come up with?

Here's the schematic: https://www.freestompboxes.org/download/file.php?id=32230

I also tried some diode combinations for clipping and ended up with a germanium/1n4148 combination and 2x BA283 on a switch.
A zendrive BAT41/BS170(2n7000) clipping sounded almost identical to the BA283 diodes. Asymmetrical 1n41480 had slightly more lows. The BAT46 in the schematic sounded too raw for my taste and the bias pot at it's max starts farting out IMO.

 

[Feral Feline]

“Tricks to decrease brightness of Tchula circuit?”​

Check out the Stupidly Wonderful Tone Control and its variants.

The SWTC could be an internal trimmer or pot with external control-knob, whichever suits.

 

[harmaes]

So the SWTC would be following the Out in the schematic of the Tchula? I heard that adding a volume control at the end is too interactive with the circuit? I can experiment with a tone pot and resistors to see how it behaves at the end of the circuit.

I normally roll off the volume on a strat or tele to about 8 anyway and that already improves the behavior of the Tchula circuit. I dislike a high setting on the bias control which is activated by the 2nd “boost” switch.

 

[harmaes]

I experimented a bit with tone and volume and IMO it's best to leave the Tchula circuit as is. The tone somehow reduces some of the lows and the volume doesn't really work well. I prefer to use the volume and tone on my guitars.

I've also created a small veroboard with 6 different clipping options which I'm still experimenting with. I'm using a 6 point rotary to go from the default BAT46 to germanium and germanium/1n4148 combinations to BA282. The last ones make it a great clean boost and the others provide variying levels of hair.
Should I make some sort of faraday cage around the clipping vero board to reduce the light high squeeling noises I noticed being increased when adding it? I haven't build the Tchula circuit into a pedal enclosure so I'm probably waiting to see if that removes it. Is that something that's done sometimes to tape a diode switching veroboard and put copper or alu foil around it to ground?

 

[spi]

In my COT50 (same circuit pretty much), I added a 47n cap in parallel to the clipping diodes to tame the highs a bit.

 

[harmaes]

In my COT50 (same circuit pretty much), I added a 47n cap in parallel to the clipping diodes to tame the highs a bit.

I’ve been experimenting with different caps (22n, 47n and higher) and noticed that a 22n cap works well with 2x BAT46 diodes to tame the highs/fizz.

With the other diode combinations I tried and liked: 2x1n60, 1n34a+1n914, 2xBA282, 2xyellow leds, 2x1n34a+1x 1n914 (asym) and 2x1n270 I noticed that the filter caps have much less impact to the tone, 47n or higher only barely take away fizz?
Is that because the filter is parallel (across) the diodes and the higher voltage ones are clipping far less so the cap doesn’t have much signal to filter?

Would be cool if someone can explain this! Are there some more areas in the Electra based circuits like Tchula to filter?

 

[phi1]

I will 2nd the recommendation to SWTC at the end. If you’re concern led or find through experimenting that the series resistance affects the tone, you can use a buffer before and/or after the SWTC to isolate this effect. But, if the item next in line (amp or pedal) has high input impedance, the series resistance of the SWTC probably won’t have much impact.

I don’t know as I would try to filer anywhere else in the circuit. It’s typical for dirt pedals to filter highs out After clipping. This is because the act of clipping generates higher harmonic content. So most designers find it easier to remove harshness but not sacrifice clarity by filtering highs after clipping, instead of before. (Of course you may find something different). On the topic, it’s typical for dirt pedals to filter bass out Before clipping. For reference, Timmy is the perfect example of this, the way the bass and treble knobs are implemented.

Edit: I see you tried some tone & vol controls, but not sure how a SWTC would affect bass.