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Thanks, Tom, for bearing with me  ;D It seems, this PT thing is a pandora's box. Well, off to the breadboard. I already killed a few, so what the heck ...

By the way (and a bit off-topic): If I want to phase-reverse the Stompflo modulation signal, will an inverting opamp buffer suffice?
To help Rob to be more clear... :icon_wink:
<DC gain occurs when you don't have cap in series with R2.   So in this case it would be wise to keep C.>
C "isolates" DC path to GND through R2 (also called Gain resistor) hence there is no gain for DC in this branch..
But DC appears through R3 (feedback resistor) which resistor value doesn't mind at all in this case 'cause it only acts as a wire (like just in voltage follower/buffer).
R2 has an open leg for DC so it can be safely omited..
For such a non-inverting arrangement, DC gain is unity..
Pictures / Re: Pictures!
« Last post by Benoi31 on Today at 04:50:05 AM »
Isn't it meant to use top mounted jacks?
Pin 6 is the VCO control pin. It seems to be the case (Princeton Tech don't actually tell us this) that the current drawn from this pin to ground sets the VCO frequency and hence the delay time. There are various ways to get modulated control over that current, including vactrols or basic LED/LDR, FETs, or current sinks. The Jenny Greenteeth BJT can be regarded as a very basic current sink. But note that only one of the transistors is there for modulation - the other one is to prevent the chip latching up at start-up. The PT2399 can be fussy about having a low resistance on pin 6 initially and if the resistance is too low, the VCO clock doesn't start-up correctly.

Pin 2 is completely different. It's supposed to be a 2.5V reference voltage for the internals of the chip. For some reason I don't understand, modulating that voltage also alters the delay time.

That's all I know.
Yeah, wrong schematic, sorry. I stand corrected.
Thats pin6 in the vomit comet mate.
pin3 is Gnd
Different layouts, different techniques:

Some feed the LFO signal into pin 6

some seem to prefer pin 2

while some use pin 3 - I forgot which circuit that was, but it exists  :icon_frown: Ah! This one:

Why? What are the differences? Could some of you PT2399-experts shed some light on this?
Building your own stompbox / Re: MN3207 + MN3102. How to test
« Last post by temol on Today at 03:25:30 AM »
Quick update.

The ICs are OK. Now it's time to breadboard the cabsim again and make it work with a DL. Thank you all for your help.

Building your own stompbox / Re: Help with DOD250-type OD
« Last post by Wadey86 on Today at 03:10:16 AM »
OK thanks for clarifying that
Building your own stompbox / Re: Help with DOD250-type OD
« Last post by Rob Strand on Today at 03:02:23 AM »
Thought - should the 9v power and the signal ground be separate things? I'm having trouble visualising how the circuit would get to the guitar that way... Then again I'm new at this.
The -ve side of the 9V supply and signal ground must be the same.  Normally the battery -ve connects to the signal ground via the input socket.
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