Wampler Plexi-Drive on the Breadboard

[Ben Lyman]

This just in: The magic is back! Sorry for the sloppy diagram but I think it represents everything from the breadboard into my Plexi-Drive pedal.
I'm not sure if there is something I need to add or subtract around the joining of the two via the boost switch.


Frank_NH- I just saw your post, ya two OD's is pretty special. Here's some combos I've tried in the past with memorable results:
TS9 into SD1
SD1 into RAT
2x TS9
2x SD1
Blues Driver into Red Llama
Any combo of the above

Other than that, for me it's always been SD1 into Marshall stack 

[anotherjim]

Neat.
I think you could lose Q4 without changing any character. Keep everything up to Q4 base and connect right to the op-amp + input. So Q4, C16, R22 & R23 go. Then you have same impedance & same gain and a few less bits.

My TS driving a Jfet was a bit lame. Kept one in front, added one after. So I added feedback diodes to the after FET a la BMP and pretty cool if somewhat metal. Between gate & drain, diode pair in series with 100n at the moment and a 2n2 or 1n across the lot to cut the hash. FET by itself doesn't really make enough voltage gain to exercise the diodes, but driven by the TS it do. It removes the clean pick attack you get in the distortion from the TS, which doesn't sit right with me for some reason.

.

[Ben Lyman]

Thanks Jim, I've been wondering about the buffer and whether or not it has a significant impact on the tone of my SD1. Easy enough to skip it on the breadboard and see what happens.

So you think R19 and R1 are in the right places?

Should I be concerned about my boost switch making any noise the way I have it planned?

This is sounding good so far:

[anotherjim]

Should I be concerned about my boost switch making any noise the way I have it planned?

Good that you ask, Ben. I missed that bit.
As drawn, you have a mix of cases where there's either 0v or VB (from U1 output) at the bypass switch. You can only have one, and since the input is referenced to 0v, it has to be 0v.
So the TS stage should be treated just like a stand-alone circuit between the bypass, with an extra coupling cap and pull-down after R27/C19.
C6 and the extra TS coupling cap could both be 220nF film caps I think, thanks to the high impedance into Q1.

[duck_arse]

with your opamp gain and 3 following fet gain stages, you might avoid minor disaster by adding another R//C supply filter, between your current +9V (keep that for the dirty, dirty opamp) and the R6//R11//R14 point. maybe 1k and 47uF ??

[Ben Lyman]

Thanks again guys.

Jim, that all makes sense. How about this? I've added C16 and R22, 2M2 good for it?

Duck, I'm not sure what you mean, 1K series resistance with my +9v going to the 3x 15K r's in the Plexi?

[anotherjim]

R22 can actually be anything over 100k I think. But if you already have 2M2 on the BOM, 2M2 it is.

Duck means the FET stages should have their own power filter. So there's a 47u supply cap on the +9v feed to the drain resistors and 9V there is fed via 1k from R2/C1.

[Ben Lyman]

Ok, got it, thanks. I see now that if it were viewed as a stand alone pedal, it makes sense to use a 100K for R22, I think some pedals without volume controls even use a 47K to ground at the output but I can change it easy enough, I'll go with 100K.

For Duck's idea, ya that's kinda what I thought he meant, I just thought putting a 1K in series was kinda a lot of resistance for the power. I've never used more than 100r tops for that spot.
So it should look something like this then?

That's from R2/C1, I thought maybe it would come from D1/R2, so parallel to R2, no?

I guess I thought maybe this:

[anotherjim]

Either.

The second (star form) if either feed causes high current pulses, but neither should here.
The first (Daisy chain) means the last feed benefits from the previous filter, but loses that benefit if the first feed takes excessive current. Again, it shouldn't do that here.
Pick the easiest layout.

A higher feed resistor gives better filtering with a smaller capacitor. I think "rule of thumb"  less than 1/10th of the circuit resistance. 3x 15k in parallel. 5k. So 1k is fine.

[Ben Lyman]

Thanks again Jim, I've started a layout so I'll just use whichever fits better.
As for two footswitches with two LED indicators, will this be OK?

[anotherjim]

Yes, the circuit is very well isolated from LED activity done like that.

[Ben Lyman]

great thanks Jim. I got a good looking perf layout going and I am about to start planning the box layout. The only wild card in the equation will be how the two react when sharing an enclosure, so far it's just been booster on the breadboard into the completed Plexi pedal, I'm going for it anyway. I might skip the battery snap on this build and go with just DC power jack only, make a little extra room to work and fit the extra switch, etc.

Looks like this is the final plan but I can't decide how many toggles (S1, S4) I really want on the extra 47uF OD boosters, either two separate or one DPDT.
C17 (47n) can go to ground or VB with no change in sound as far as I can tell. 

[Ben Lyman]

It's alive! I wired the bypass switch to take out everything including the boost so it's kind of like my old Fulldrive II, not like the Wampler Plexi-Drive Deluxe which allows you to use the boost feature independently.

I could just as easily do that but I wanted to start with it this way because I didn't really like the idea of pushing two buttons to bypass it after playing in boost mode.

It has the standard bass boost toggle and also a 3-way toggle for the extra 22uF caps.

[rutabaga bob]

Way t'go, Ben!  Nice job!

[Cozybuilder]

Nice one Ben!

[Ben Lyman]

Thanks guys, I couldn't a done it without you!

[anotherjim]

Brilliant job Ben.

Does exactly what it says on the tin.
Which is a figure of speech, since I see it don't say anything yet, but if it did, what it does is what it would say... err, something like that anyway...