Wampler - Plexi-Drive

induction · Post by **induction** » 03 Jul 2013, 15:39

I'll just remind you of this:

indyguitarist wrote:
azrael wrote:bah, I would rather just make different drain resistors, hahaha.
Makes for less work, I think.
That's one way, but it'll change the gains and eq a bit. It won't be an accurate clone.

Nicht Bernd · Post by **Nicht Bernd** » 03 Jul 2013, 17:06

hmmm????

indyguitarist · Post by **indyguitarist** » 12 Jul 2013, 17:08

askwho69 wrote:Or just biased it with a potentiometer to 4.5-5v, then measure the potentiometer's value with DMM and put the closest resistor.

Don't do that unless you want it to not sound accurate.

Nicht Bernd · Post by **Nicht Bernd** » 13 Jul 2013, 10:11

OK, if Indy says so...

induction · Post by **induction** » 09 Oct 2013, 18:45

Been playing with this on the breadboard. I bought a bag of 100 J201's from Tayda and sorted them for this and for the Black 65. Out of 100, exactly one biased at 4.7V on the Black 65 (the rest were over 5V), and none biased over 3V on the Plexi-Drive. I don't know if "fake J201's" can explain this, since they bias too high for the Black 65 and too low for the Plexi-Drive. Maybe these circuits favor the outliers, and mine fall right down the middle. Or maybe there's more to it than that, I don't know.

I wondered if there was a way to bias the transistors by connecting the gate resistors to a voltage divider instead of ground and/or swapping both the drain and the source resistors, but nothing I simmed worked out.

Anyway, with a trimpot, I found that 11k drain resistors would get my closest J201's to 4.7V on the Plexi-Drive. I tried both 10k and 12k resistors, and it sounded anemic. I put the original 15k drain resistors back in and it came to life and sounded much, much better. My only complaint was that is sounded a bit muffled, I assume this is because of the mis-biasing, but again, I don't really know. I found that replacing the 25k A tone pot with a 500k A pot brings up the available treble to acceptable levels. With this pot dimed it sounds identical to disconnecting it altogether, and since its just a variable resistor, the lower end of the pot travel gives the same sounds as the 25k pot. I also found the 2n2 cap on the bass switch was too overwhelming, but a 1n cap sounds great.

All in all the modified circuit sounds very nice. I don't know if it sounds identical to the genuine Wampler, but it definitely sounds Marshally, and I'm happy with it.

Just thought I'd share.

batak_man · Post by **batak_man** » 07 Dec 2013, 07:30

finish build this pedal in breadboard and i like it
have some confuse with this pedal
when i max the gain the vol increase to (to loud)
so if i play with full gain, the vol max at 8 o'clock, more than that the vol to loud (if i compare with clean sound from amp):scratch:
i follow the schema from the earlier page

when i compare to the ori from youtube, the ori plexi not like this

is this normal, or i do some mistake?

or can someone tell me what should i do?

imnotgay · Post by **imnotgay** » 07 Dec 2013, 19:44

try audio taper pot

batak_man · Post by **batak_man** » 08 Dec 2013, 05:30

imnotgay wrote:try audio taper pot

your mean log pot?

alexradium · Post by **alexradium** » 08 Dec 2013, 08:45

You can't hear exactly through yt.
Anyway the current production plexidrive is not the same as the schematic floating around here.
Plus Mr Sampler has made various revisions of each pedal so what is "right"?

imnotgay · Post by **imnotgay** » 08 Dec 2013, 10:51

yep..

batak_man · Post by **batak_man** » 10 Dec 2013, 05:35

i see in plexi gutshot has more elect. capacitor
hmm.. i think he use it to boost gain in q1 andq3 (just a stupid guess)

btw thx for reply

alexradium · Post by **alexradium** » 10 Dec 2013, 08:41

Exactly,that's why maybe it sounds more gainy in videos.

andregarcia57 · Post by **andregarcia57** » 16 Jan 2014, 11:58

J201 of tayda really are not reliable, where they can find good J201 4.5va 5.0v with 15k?

Nocentelli · Post by **Nocentelli** » 16 Jan 2014, 12:25

That's a big problem with this kind of design: I'd love to build another Velvet fuzz (which has a plexi drive stage) but only three of my 15+ J201s came anywhere near 4.5v with a 15k. I used a 15, 18 and 12k but the rest are useless. I don't fancy buying an expensive big batch to find only a couple of candidates, so I'm seriously thinking about getting a load of SMD and trying them. They're cheap, so if it's a disaster, it's not a waste of too much cash.

andregarcia57 · Post by **andregarcia57** » 16 Jan 2014, 13:38

Nocentelli wrote:That's a big problem with this kind of design: I'd love to build another Velvet fuzz (which has a plexi drive stage) but only three of my 15+ J201s came anywhere near 4.5v with a 15k. I used a 15, 18 and 12k but the rest are useless. I don't fancy buying an expensive big batch to find only a couple of candidates, so I'm seriously thinking about getting a load of SMD and trying them. They're cheap, so if it's a disaster, it's not a waste of too much cash.

I'm also seriously considering buying J201 SMD. where to find them Nocentelli?

Nocentelli · Post by **Nocentelli** » 16 Jan 2014, 14:06

I think the parts number is MMBFJ201. They're available at mouser, digikey, farnell and other big electronics parts online places. They don't always appear to be much cheaper than the through-hole types for individual pieces, but you can get 100 for £10 at Mouser [edit - Farnell UK seems to do them for 13p each individually, so it seems well worth hunting around online].

copachino · Post by **copachino** » 11 Feb 2014, 18:01

what a horror to work with j201 a have a bag of 30 and only three are close to 4.5-5v, ut im still gated, i ant figure out the problems i use the correct schemactic values, i only change the 220pf cap for a 100pf cap.

Mbas974 · Post by **Mbas974** » 05 Oct 2014, 17:24

Hi ! I built my clone of this wonderfull pedal.

But to my taste it sound really too dark... I'd like to have the Tone pot full open like in 12 o'clock position ( or at least less dark sound )

What I should change ?

induction · Post by **induction** » 05 Oct 2014, 18:52

Mbas974 wrote:Hi ! I built my clone of this wonderfull pedal.

But to my taste it sound really too dark... I'd like to have the Tone pot full open like in 12 o'clock position ( or at least less dark sound )

What I should change ?

Increase the tone pot.

I replaced the 25K tone pot with a 500K A. Works well. Read more here.

jalmonsalmon · Post by **jalmonsalmon** » 06 Oct 2014, 16:35

I am not sure about buying a 100 x SMD 201's since it would be a pain to test them unless I missed something here

I suspect I am being just lazy but I can see me doing it LOL Spend a couple hours soldering those little SMDs on a conversion pcb and then having at it... I have seen a layout for this pedal on IvIark's site that has trimmers for biasing but as stated before, using the trimmers will not yield an accurate clone.
Any one try out SMDs for this one? You would think out of 100 SMD fairchilds, you could get a lot of working jfets vs buying the so called fakes from Tayda... thoughts?

Wampler - Plexi-Drive [traced]