Variable Buffer and Pedal Idea

[rocket88]

just some food for thought on something on my mind. so most of us use a buffer that has a fixed output, but what if you wanted to have a variable output on a buffer, so you can actually boost the output into another pedal.

by using a buffer, you can control the input impedance, the JFET can create a tubey sound, and if you can control the output then you can drive a second stage with a trimmer in the circuit, and drive a second stage creating a mild overdrive.

for those that don't know, i've been chasing the germanium boost dragon for while, specifically since i heard the phat phuk b, which seems to be based on this principle. now the trick is were would the trimmer go? if it comes completely after the circuit as a voltage divider, then you would get a set max output that wouldn't "boost" the signal into the second stage which wouldn't provide enough to really drive it. and as i read it the way to control the max output is with the resistor on the source leg of the JFET, so then would it make sense to make this resistor the trimmer?

also, since a buffer is usually meant to be clean or neutral if you will, what could you do to make the have a more "tubey" sound?

cause here's the idea i have in my mind. what if you take the variable output buffer and run it into something like an Electra powered by a Ge transistor instead of Si. theoretically, by increasing the output from the buffer could drive the Ge of the Electra into a mild, and warm overdrive, just adding a tad of distortion and be sorta open and tube like in tone.

another thing. i've noticed that there are some pedals that will use a PNP Ge transistor while the circuit is negative ground. i have not found much about how you can do that without the use of a charge pump/inverter, so how can you do that? again, going with the circuit idea in my head, since there are much more PNP Ge transistors that have great usable hfe's, with low leakage it would make more sense to find a way to effectively use them in an negative ground circuit.

[rocket88]

Found this discussion over at DIYSB that seems to have some interesting information about a similar concept, at least as far as JFET buffer adding "tubeyness." so it seems my idea is possible, the question is how.....

http://www.diystompboxes.com/smfforum/index.php?topic=55928.0

[alex.s]

You should have a look at the Fallstaff overdive/treble boost designed by Jon Patton. The logic behind it seems to be somewhat similar to what you are talking about and it's all explained very well in the build document.

Jon's page HERE
Jon's build document HERE
Mark's vero layout HERE

Have a look on Jon's website should you want to have a crack at it as last time I checked he had PCBs for it going for dirt cheap because of a tiny missing link which is very easily done with a component leg, worth a look!

Hope that helps in giving you ideas!

[inefficiency]

I built an MXR micro amp a while ago and if you keep the volume at minimum, ie no boost - it seems to act like a buffer.

Not sure if it actually does, but it seems to to my ears.

[rocket88]

hmmm, interesting concepts. i checked out the Fallstaff overdrive/treble boost, but it's a little different then i was thinking, but very similar. the build notes did give a little help and insight, so definitely a big . the micro amp, i have to investigate a little bit more, as it might be a way to accomplish my goal in a different manor.

by checking both of these options out, i think i can focus my thoughts into two questions:

1 - how can i vary the output of a buffer? would it be a simple attenuator or could/would i need to replace one of the  source resistor with a trimmer?
            - isn't the SHO a variable output buffer not really a booster?

2 - since buffers a usually "neutral" sounding how can i get one a little a little tubeyness? what i mean by that is make it sound more warm and open sounding like you're playing with a tube amp.

any ideas?

[Silver Blues]

I'd be inclined to just replace the source resistor with a 10K pot for variable output. I think that'd work.

[rocket88]

that's kinda what i was thinking, so i'll have to hit the breadboard and see what that adjustment does to the output. if that works, then i have to work on the way the buffer sounds to try and get it warm and open sounding, which i figured will be the most difficult part....