Gallien Krueger 250ML overdrive pedal?

valdiorn · May 14, 2009, 07:57:14 PM

differnt usage of the same device. The method described by the wiki utilizes the PN-junction of a JFET to create clipping, the way it's done here is by using the current-limiting qualities of JFET's n-channel to create a non-linear resistor.

Edit: See my post on FET clippers here

sm3000 · May 14, 2009, 10:29:41 PM

Pretty interesting issue that is being brought up. Are there any pedals that use this type of circuit? If I wanted to put together a Gallien Krueger 250ML overdrive pedal which JFETs should I use?

sm3000 · May 17, 2009, 07:09:22 PM

Anyone can suggest me an equivalent for the dual jfet used in the amp? Maybe two J201?....

anchovie · May 17, 2009, 07:52:05 PM

Quote from: sm3000 on May 17, 2009, 07:09:22 PMMaybe two J201?....

Try them! Breadboard first if you're worried.

Bear in mind that if you make this as a pedal it's not going to sound exactly the same anyway if you run it into a clean amp, as you'll have the GK tonestack followed by the tonestack of your amp.

sm3000 · May 18, 2009, 02:20:18 PM

Yeah I'll try it! Do you suggest me to put everything on perfboard with diy layout? I've never drawn a layout!...

Just for reference the J406 / J412 is wired like this:

N/C-------N/C
S----------G
D----------D
G----------S

anchovie · May 18, 2009, 03:06:17 PM

I'd suggest you get a solderless breadboard so you can plug in components and jumper wires. Not just for this circuit, but for many others in the future! They're great for tweaking circuits to make them "just right" for your ears, and for trying experiments such as "what happens if I replace this cap with a higher/lower value?".

nelson · May 18, 2009, 03:34:15 PM

ooooo, variable symmetry soft clipping.

sm3000 · May 19, 2009, 01:15:34 PM

Quote from: anchovie on May 18, 2009, 03:06:17 PM
I'd suggest you get a solderless breadboard so you can plug in components and jumper wires. Not just for this circuit, but for many others in the future! They're great for tweaking circuits to make them "just right" for your ears, and for trying experiments such as "what happens if I replace this cap with a higher/lower value?".

don't you think that using a breadboard would be to messy for such circuit?.. I'll try on prefboard but if anyone on the board feels like helping me design the layout on diy layout or eagle would be extra sweet!

sm3000 · May 20, 2009, 04:18:57 AM

Let's see..I'm still working on it of course....but is it correct so far?

I got to the point of the opamp U6 meets U9

the pinout of the FETs I will use is:

flat side
| | |
D S G

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Gallien Krueger 250ML overdrive pedal?