Plexi-2203 Marshall wantobe

[printer2]

You guys are a bright bunch. Figured I'd pass this by you also. They guy at work wants a 15W Plexi but from hearing some of the guitar he likes I think he really wants a higher gain model, more of a 80's-90's sound. So I started to mess around with the Plexi schematic and came up with this with the thought of using a 500k pot I have with a dual push-pull switch on it. While the hi gain position is not 100% true to the 2203 circuit I think it might be a good compromise. The schematic has the switches in the Plexi position.

While the 500k pot should be a 1M, it is harder to come by 1M's with the switch, I think it loading the first stage more would be less detrimental than after the second stage. In 2203 mode I am going to loose signal after the second stage with the 470k and 220k combination already, normally there would be a pair of 470k's. The first stage is also loaded with the other 220k resistor, the price I have to pay for using two switches and wanting the Plexi circuit to remain true to its roots with the 470k mixing resistors.

Also on the 2203 the coupling cap after the first stage is a 0.022uF while the Plexi value is 0.0022uF. I think the reduction of bass should not be a detriment in high gain. Other than that just tune the PI for 6V6's or maybe some EL84's. At least that is the theory. OK, now tell me where I am going wrong.

[printer2]

OK, iteration #2. Took some of the suggestions and tried to fit them with my goals. First off and foremost I want this to mimic a Plexi. With the normal and bright channel you kind of want to jumper the inputs. Also need the mixing resistors and 500p cap on the bright channel, good call I missed that trying to switch the input stages in series only using two switches. I came up with a fairly bizarre way of accomplishing it, not all together happy about it as it requires the user to know they can not plug into the normal channel when they are in series. Oh well, at least it will not hurt anything. The Plexi bright channel has a 0.002uF coupling cap and I think it after the first triode will somewhat make up for the treble bypassed resistors in the 800 series amps. Might be worth trying out.




Just for those that are interested, used this as a guide.

[sluckey]

Have you seen this...

http://home.comcast.net/~seluckey/amps/misc/Marshall_Dual_50.pdf

[printer2]

Nope. Looks cool. What do you use to do you layouts?