has anyone built this - jcm800 emulator

[StephenGiles]

Where is the circuit diagram?

http://www.diystompboxes.com/smfforum/index.php?topic=64038.0 fourth posting

Of course, my computer filing beat me for a minute - many thanks!

[DougH]

putting that 22n coupling cap before the volume, makes the volume act like a variable high pass filter.

It shouldn't be variable. End-lug to end-lug, the pot will have a fixed resistance between that cap and ground.

[dschwartz]

putting that 22n coupling cap before the volume, makes the volume act like a variable high pass filter.

It shouldn't be variable. End-lug to end-lug, the pot will have a fixed resistance between that cap and ground.

but snyder said he put it before the volume pot, and i´m sure he meant "coupling" and not "decoupling" cause mentioned that blocked DC through the pot..that way it is a variable filter.

[DougH]

If it goes between the drain of the last JFET stage and the "hot" end lug of the volume pot, with the other end lug grounded and the wiper going to output, it will be a fixed high pass filter.

[dschwartz]

If it goes between the drain of the last JFET stage and the "hot" end lug of the volume pot, with the other end lug grounded and the wiper going to output, it will be a fixed high pass filter.

you´re right 

[DougH]

No need to blush.

Filters with variable pieces stuck in and around them can be confusing sometimes. Best way to read them is left to right as the signal flows through the circuit. Looking from the left, the signal "sees" a series cap and fixed shunt resistor. It doesn't "see" the wiper and therefore the wiper doesn't affect it. The pot wiper just taps off a portion of the signal from the "fixed" resistor. The reason you can say that is because the wiper (being the output) is most likely tied to a high impedance load (1M typically) when it is plugged into the input of an amp. Since this is so much higher (10x) than what is between the wiper and ground (100k max) it will have a negligible effect. It's a large resistor in parallel with a small one, so for all intents and purposes, as far as how it will affect the audio and etc, you can neglect it. Therefore you can pretend it's not there and if the wiper is not connected to anything (infinite or at least very high resistance between it and ground) the wiper has no effect on the HPF formed by the pot and cap.

This is one reason I strongly suggest people learn to read schematics instead of layouts, folks. (Not that you weren't doing that, but it just gives me a chance to stomp on my soapbox again... )