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Clapton Mod - Distortion - from where


Chuck Bryden (cbryden)
Username: cbryden

Registered: 12-2006
Posted on Thursday, December 28, 2006 - 04:41 pm:   

I am curious about doing this mod.

The simplest answer is probably try it and undo it if i don't like it. (or have it done and undone).

I play a 4x10 65 (tube PI) into a weber attenuator. I use it on high power, and I love the sound when the master is on 10 and the pre is anywhere from 4-8. Around 8 is where the preamp starts to get dirty if I have the master down.

My question is, does the clapton mod cause more distortion from the preamp circuit, does it cause a higher signal into the phaser inverter causing (apparently from andrew's work) phase inverter clipping or would it cause power amp clipping?

The even harmonic distortion created before the preamp clipping occurs is truly beautiful and natural. I'd love to be able to dabble more in that area.
Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Friday, January 12, 2007 - 10:04 pm:   

The Clapton mod increases the preamp gain and there are some other cool mods to go with it.

Ed Goforth (ed_goforth)
Username: ed_goforth

Registered: 06-2006
Posted on Friday, January 12, 2007 - 10:34 pm:   

The modded Paul C. mod for the Musicman PI smooths out the tone, fattens up the tone and takes out any harshness and is more stable. The Clapton Mod I like is putting a 25k treble pot with the push/pull switch on the back (these can be purchased from different suppliers) to parallel another 4.7k resistor across R-32. This drives IC-7 more to push the first stage of the 12AX7, when pulled out and is stock when pushed in. The Clapton mod schenatic shows another 1uf cap paralleling C-18, but I did not notice much difference with my amp doing the extra 1uf, so I did not use it. I also swapped out the 2k middle pot to a 10k pot, for more mid/gain control, it really helps fatten/warm up the overedrive without sound honky like some amps with treble shift switches. The effects loop works good if you take the send after C-35 (.047uf), not C-34 (.047uf) that was shown on the Clapton schematic. The effects stay cleaner this way after C-35 (just off the master volume wiper cap) and also attenuates the signal going to the effects, sending effects from C-34 will overload the signal going to the effects and garble the clarity of the effects, coming off the top of the master volume, there is no attenuation. Also changing the IC's with Browndog adaptors to use something like a LF356 sounds great! The Brite switch mod is cool, but I stayed with the stock brite switch circuit. New filter caps is the next thing I will be doing and should really sweeten this amp and tighten up the low end. Possibly change out the speakers.