Chalumeau mods

Bricksnbeatles

Well-known member
What mods are most worthwhile in your opinions? I've been looking for a cool pt2399 based effect to build for my 23rd birthday next month, and last night I settled on the Chalumeau.

First off is the matter of gain- If I understand correctly, the gain of the 386 in the circuit is 200, due to pins 1 and 8 being tied directly together. that should mean that c2 and r2 are completely redundant in this circuit, as they'll only set the gain if pins 1 and 8 aren't shorted together. c2 and r2 should give the gain of the non-fuzz version of the Clari(not) if you cut the trace between pins 1 and 8. of course, you could always cut the trace, populate r2 and c2, and connect a spst between pins 1 and 8 if you want both versions of the circuit, but why not take this in a different direction and just do a gain pot? If we cut the trace between pins 1 and 2, and then also leave c2 and r2 unpopulated, then we should be able to wire up a 1KΩ pot between pins 1 and 8 for a continuously variable gain between (I think, I'm doing mental math rn) 40 and 200. any thoughts or corrections here? I haven't double checked my calculations yet...

Next is the mater of delay feedback. more on that soon...
 

Betty Wont

Well-known member
I put a clean boost on the fuzz lift switch to give it enough juice to trigger in "clean" mode. The delay feedback mod is easy, but due to the extreme pitch shifting, it is pretty much unusable as an echo.
 

Bricksnbeatles

Well-known member
I put a clean boost on the fuzz lift switch to give it enough juice to trigger in "clean" mode. The delay feedback mod is easy, but due to the extreme pitch shifting, it is pretty much unusable as an echo.
Since I plan on doing a pot instead of a fuzz lift switch, maybe I’ll just add an LPB to the front end. As for the feedback mod— unusable isn’t in my vocabulary ;) (plus with the modulation turned mostly down, it should be marginally normal)
 

Bricksnbeatles

Well-known member
Also can anyone who’s built this describe what the tracking knob does? Every demo I’ve seen adjusts at least one other knob when they adjust the tracking so it’s hard to see exactly what it does
 

Bricksnbeatles

Well-known member
Yep. Take a look at the schematic, @Bricksnbeatles. It essentially controls the signal routing to the LED, which affects the LDR tied to the DEPTH control.
Ok yeah I see, it’s sort of controlling the envelope depth, like the range knob on an envelope filter (or well, the range knob on some envelope filters, or the sensitivity knob on other envelope filters, or the depth knob on some envelope filters because sometimes range and sensitivity do other things because envelope filter parameter naming is extremely inconsistent 😂)
 

Bricksnbeatles

Well-known member
Just occurred to me I could very easily omit having a switch to remove the feedback circuit by simply modding a C50k pot to be ‘no load’.
That should free up some real estate
 

Bricksnbeatles

Well-known member
Any thoughts on which LDR is best for this circuit? I’ll probably socket it just so I can try ‘em all out, but I’m in a rush to finish this up and don’t have time to test each type out.



I’ve got about a dozen of each, so I can cherry pick the best-spec one, but not sure what range is best for the circuit
 
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