Crate GT1200H - Mod rhythm channel for more laid-back distortion

[bobanahalf]

I picked up this Crate GT1200H from craigslist. I'm getting to know it a little, and it turns out to be a fuzz-filled monster. Perfect for the metal-head I was 20 years ago, but that was 20 years ago.

These days I'm thinking more about the blues than head-banging, and I'd like to re-tool this amp a little to get me there. I know the warm, middy tone of the blues is ever-elusive from SS amps, but I'm after it. Cleanish and warm from note to note, breaking up a little when you get into the cords.

What this means is that this amp gives me a lot more distortion than I'm really looking for. The most obvious option is to just keep the gain down around 1 or 2, but where's the fun it that? I figure it would be a lot more interesting to dig around in this guy, trying to tweak it's overdrive section into something I'm a little happier with.

I've got a schematic, and I understand some of it, but by no means all of it. (I'll attach it if I can figure out how.) And I've got half a notion that I'm just talking about switching out a resistor or capacitor. but I'm not sure which one to go after.

Does anyone have an idea where I should start? Or any recommendations on a book that would get me going?

[Jazz P Bass]

Well, for a start, Crate has provided you with an excellent 'roadmap'.
If you look at the Test Points, you can see how they square of a nice sine wave on the distortion channels.
My first stab would be the 'Solo Channel".
IC2/A.
The 3.3v back to back zener diodes are a prime suspect for squaring off the sine wave.
I am not into modding but there is an aweful lot of info on pedal sites.
You should also look into how a dual supply opamp works.

[bobanahalf]

Hi there, JazzP.

The part I'm most interested in, I think, is the chain between TP2 and TP4. Based on how I'm selecting my channel, I wouldn't expect to be into the solo channel yet. I'd like to clean up the overdrive section a little first.

I guess you're right: since I'm really dealing with preamp, I could check out how folks tweak their stomp boxes. Good pointer.

[J M Fahey]

You have an *excellent* metal machine.
"Modding" it for Blues would mean stripping it in full and building "something else".
You won't get what you want by tweaking a couple parts here and there.
Even worse, The Blues sound is the *hardest* one to get on the SS world.
That said, and before you go buy some Cyanide at the chemist's, I suggest you use the clean channel only, and build a Marshall Blues Driver clone, the project is available if you Google it.
As those who tried the original pedal said: "it provides a very acceptable imitation of Eric Clapton'r "Bluesbreaker" (JTM45) amp sound"
Any pedal to get SRV sound or similar? Forget it. Sorry.

The *only* SS amp (that I know of) which provides a warm, sweet, elastic, punchy Blues sound is the Roland Blues Cube, but it's a *very* different project altogether, with tons stacked FETs to provide dual slope wave bending, a PSU "un-stiffener" to provide Sag, and 1000 other little tricks to enhance the illusion.

[BowerR64]

I have one of these and i wanted a more crunch on the yellow (rhythm channel) it had crunch but there was a fine line between crunch and to much gain for this channel IMO

I started at R7, i was going to try it in steps first R7 then R3 i didnt need to move past R7 though i just took out R7 and put in a jumper wire and the gain rolled back enough that the window for both the Solo channel and the Rhythm channel were good enough. This way its still a "Metal Machine" but i can get some decent crunch out of it as well.

I kinda like this amp, not bad for a Solid State Crate amp. I got mine off my local craigslist for a set of old burstbucker pro pickups and $25. i couldnt pass it up.