An idea maybe already executed? Wanna collab?

[TimWaldvogel]

I have an idea of taking something like cot50:electra distortion with adjustable bias with a decent amount of fixed output and pushing a jfet or mosfet into Overdrive.
I like the idea of a silicon transistor gain stage pushing a jfet/mosfet into overdrive. Maybe the sound equivalent of the COT50 below noon. Very light clean breakup.
Where i don't know where to start on the 2nd gain stage. Any idea on where to start? Reference from another circuit with two gain stages?

[CynicalMan]

I'm interested. Keep in mind that the loading of the diodes on the transistor is a component of the distortion. If you remove the diodes, then you won't get the electra sound as much. Here are some similar designs:

http://sites.google.com/site/distorque/home/projects/atomic-overdrive-ii
http://www.runoffgroove.com/peppermill.html

[TimWaldvogel]

That sounds like Good starting point. This morning I experimented on breadboard with the lpb-1 layout from the Beavis audio site. Which just has a couple resistor changes. Not sure why it's different then the other schematics but it is a lil different. I used a 2n3904.

I experimented with input cap and diodes to ground after the output cap. The best input cap so far was .147 uf. (parallel basically 1.5) and actually believe it or not I liked using only one 3mm red LED. I need to confirm the cathode orientation. But from the sound of things it was only clipping high end.
Tonight/tomorrow I MAY change it to an Electra type distortion setup and see if that changes anything. I think with minimal diode clipping, and a trim pot or fixed resistor in place of the potentiometer. I also have thought about a resistor/capacitor to ground with the diode to soften the clipping to that out a amp on the edge of breakup sound. I figure with the right output feeding the jfet (j201/mpf102) we can get musical overdrive as the end result.

Opinions from all angles are welcome.

[CynicalMan]

So, what kind of sound are you going for? Are there any overdrives that you've used that are in the ballpark?

Also, how is this overdrive going to be different from other designs? Will there be new innovations, or will it just be a personal tuned OD?

Just curious about where this is headed. 

[TimWaldvogel]

The primary goal is dynamic overdrive using a SIMPLE transistor circuit. I feel like all the nice dynamic overdrives are consisting of a jrc4558d and Are TS based. I want a simple transistor od that people would enjoy to use

[WGTP]

Check ROG for the Peppermill and Fetzer Valve to get a Mosfet or JFET second stage. 

[Scruffie]

I'd probably go Fetzer -> Electra, get a nice high input impeadance and push the clipping harder, add a clipping blend & or Pregain (at the output of the Fetzer) pot so you can dial in how hard it's hit as well.

But that's just like... my opinion.

[CynicalMan]

The primary goal is dynamic overdrive using a SIMPLE transistor circuit. I feel like all the nice dynamic overdrives are consisting of a jrc4558d and Are TS based. I want a simple transistor od that people would enjoy to use

In that case, you should try out the circuits I posted. The bjt-fet circuit kind of circuit you're looking at would be quite similar to them in terms of dynamics and clipping. They're already tweaked and tested, so you can get an idea of what kind of sound you'll end up with.

[TimWaldvogel]

When you push silicon diodes don't they tend to get fizzy and fuzzy?
I thought a major keypoint in jfet overdrive tone was a large signal hitting a jfet causing it to overdrive? What if we used the 2nd stage from the peppermill after a clean silicon transistor boost? Maybe using higher threshold diode clipping so the signal is only lightly compressed and clips very lightly. That way we are not in a real OD territory until the jfet sees signal in front.

[TimWaldvogel]

Ok I'll check them out

[Gus]

Here is an adjustable bias booster, it is kind of like a RM as posted, you can adjust the input cap.
http://www.diystompboxes.com/smfforum/index.php?topic=93052.0

Why the COT?  If you look around here there are other boosters.

I posted sims of a circuit like the LPB with a gain control not long ago

You don't need jfets for high input resistance plus you need to select the Jfet or adjust the circuit.  There are ways to make JFET more drop in but you have to understand how to design.

Look at the bootstrapped circuits I posted.

Nice one transistor circuit is the NPN boost ver2. that is a design I shared the other day.  It has been built and testing has started.

The minute man posted the other day is a two stage circuit.
http://www.diystompboxes.com/smfforum/index.php?topic=92997.0

Other two stage circuits have been posted and there is stuff in the schematic section the gallery and the web.

There are things to know about when using diode clipping.  You can make a nice opamp diode circuit.

Here is a hint you need to understand how to adjust the gain and EQ of the circuit.  You need to understand high pass and low pass filters and/or EQ networks.

The EQ and gain control of mult stage gain circuit was posted about years ago at AMPAGE and IIRC R.G. and M.H. have posted about this

[petemoore]

  Overdriving the Jfet input or NPN input is probably possible with either order of the two circuits.
   NPN>Diodes will distort with guitar pickup source, adding boost will increase the intensity and generate more harmonics.
  Somewhat the same is true with the Jfet last in chain, boosted by the distorted NPN>Diodes output, but the output won't be compressed as much as when coming from the clipping diodes.
   In both cases an interstage attenuator [volume pot] will allow the second stage to exhibit it's non-linearities to a lesser or greater degree, and can be made to create controllable amounts input or output related distortions...depending on how it is set up.
  Suggestions: Board one of the circuits, breadboard an other...consider test-jig box or boxing part of the circuit to allow rearranging the effects order before commiting to final circuit installations...tended to cut down on debugging/circuit failures while still allowing ease of tweeking. Once the first circuit is set up nicely, the second circuit should have enough 'more' to work with, and the result will probably require some tweeking as far as gain attenuating and voicing because more than enough gain could be on tap to make second stage get hit very hard with signal, it's output many times greater also.
   It could be set up to be similar to a TS except with discrete components, [ie boost/voice, but only clip once...] however, since multi-stages are being built why not go for a little bit of distortion from each stage.

[TimWaldvogel]

my head has been swimming with ideas all day at work and ive been playing with my breadboard just to figure how i wanna do this. im trying to setup the first npn stage to be something i definitely like that way when i work my way towards the jfet stage i can know its the 2nd gain stage creating something i do\dont like and adjust accordingly. so far im like the lbp-1 esc circuit with 3mm red leds in series with a resistor value of roughly 20k to ground, the resistor softens it up but keeps it clipping. tomorrow i need to go by the proper trim pot value to be able to bias the jfet. hopefull rat shack has it, i only have a 100k trim and idk if ill be able to bias it as easily as i would with a 50k