Friday, 10 February 2012

Wampler Plexi-Drive

In the words of the maker Brian Wampler, this was designed to sound "sort of like a cross between a "Marshall 18®" and a "JTM45®", and those who have purchased the Plexi-Drive agree that it's very accurate! The bass boost toggle switch adds fat, full bottom end which is very useful in lower gain or lower volume (bedroom practicing) applications. For band volumes, cutting the bass out a bit really helps the tone cut through perfectly."


Some people experienced popping which can be due to the input being connected directly to the first JFET gate.  This is a modified version which adds an input capacitor and anti-popping resistor.



Geiri's demos of his dual build with Les Paul and Strat:


Posted by at 11:09
Tags: , , , ,

130 comments:

  1. Geiri15 February 2012 at 00:56

    Hey, thanks so much for the layout! I'm gonna try it out. I was wondering what to remove to skip the switch and just stick with it stock ?

    Thanks!

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  2. IvIark15 February 2012 at 02:04

    Well the switch came with the original (the first pic is the stock circuit), but if you don't want to include it just omit the Sw1a and Sw1b wires (obviously) and the 2n2 cap above Q1.

    D1 is a reverse polarity protection diode, and you can omit that entirely without affecting the pedal audibly. In fact I really don't like parallel protection diodes when they're used without fuses because in the event of reverse polarity, they basically explode which isn't going to do the pedal much good anyway. It seems like an unimportant inclusion for people using batteries or dedicated daisy chained power supplies anyway to me, but I included it because it was in the original scheme.

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  3. Geiri15 February 2012 at 15:26

    Awesome, thank you for this and all the other layouts. You have no idea how grateful I am for all this work of yours!

    By the way, do you know the insides of a Lovepedal Kanji ? I think it was a limited thing and I wouldn't be surprised it it was just a modified Eternity or something. Just wondering if you know anything about it. ProGuitarShop used to have them and I remembered by the videos that they sounded quite good.

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    1. IvIark15 February 2012 at 15:45

      You're very welcome. I haven't seen a schematic unfortunately but I've seen a gutshot and it looks like a typical TS type pedal with a switch to swap the input capacitor, and one to switch between diodes. If I ever get a confirmed schematic I'll do a layout

      Delete
    2. Geiri15 February 2012 at 15:51

      Thanks!

      Delete
  4. Anonymous11 May 2012 at 20:04

    Would the switch be on-on?

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    1. IvIark11 May 2012 at 20:12

      It's single pole single throw so it's always 1 contact, 2 lugs, 2 position, on or off (contact make or break). You could use a SPDT switch though and just use one of the "throws" and so the centre and one of the outer lugs.

      Delete
    2. Anonymous11 May 2012 at 20:18

      Hmmm It's just I have a box of switches and I can't tell which is which, just some are 3 positions and some are 2 positions (3 lugs)

      Ahh think I got, so I just use middle and outer lug on a 2 postion switch?

      Or just buy some more? lol

      Delete
    3. Anonymous11 May 2012 at 20:20

      Like these?
      http://www.ebay.co.uk/itm/SUB-MINIATURE-SPST-ON-OFF-TOGGLE-SWITCH-PACK-TEN-/370570248244?pt=UK_Trains_Railway_Models&hash=item5647b54034#ht_2095wt_1187

      Delete
    4. IvIark11 May 2012 at 20:48

      Yes they would be fine mate, but at that price you'd probably be better getting some 2 position SPDT which will then have two uses (SPST or SPDT) and you should be able to pick up 10 cheaper than that.

      Delete
    5. Anonymous11 May 2012 at 21:20

      Oh right.. pennies dropped. I have loads of SPDT's.. I'll use them.
      I'll have take a swing at this tomorrow :0)

      Delete
  5. Anonymous12 May 2012 at 15:04

    I've built this, sounds amazing but my tone has no effect? I notice it goes from board to tone 3. And tone 2,3 and vol 1 to ground? would that have anything to do with it?

    (I built the anti popping one)

    ReplyDelete
    Replies
    1. Anonymous12 May 2012 at 15:15

      I've tried running the tone 3 to lug 1 with no change too

      Delete
    2. IvIark12 May 2012 at 15:23

      I just checked and it's actually Tone 1, with Tone 2 and 3 connected to ground. Oops, sorry. But that's definitely how it is in the schematic. Tone 1 connects to the 10n with the other side of the cap going to the 15K and Volume 3 junction which looks right on the layout.

      Delete
    3. Anonymous12 May 2012 at 15:43

      I've just changed the pot with no change? it's like the tone is completely bypassed. Everything else works as it should.

      Delete
    4. IvIark12 May 2012 at 16:08

      I just checked if anyone else had mentioned problems with the tone control but couldn't find anything, and the PCB layouts that people have done seem to have done it the same way too. Maybe something like the "Stupidly wonderful tone control" would be better in this, ie the 15K connection to Tone 1, Tone 2 and 3 connecting to Volume 3, and the cap going from Tone 2 to ground. Like the top example here:

      http://www.muzique.com/lab/swtc.htm

      But I'd have to build it up to have a play.

      Delete
    5. Anonymous12 May 2012 at 16:17

      Hmmm It's bizarre and a shame as it could've sounded among the best.. I've checked over and over and as everything else is working perfectly, I can't make out what could be wrong. I don't really want to dump this as it sounds nice but OCD and impatience will get the better and it'll end up scrapped.

      Thanks anyway mate...

      Delete
    6. IvIark12 May 2012 at 16:27

      Just put it to one side. You don't have to throw it immediately, wait until I get to experiment and then there may be a decent mod for the tone which you like. It's better being left in a drawer for later than going in the bin. I've got tons of boards all over the place that I built but didn't bother boxing, one day I may revisit some, but I'd never dump anything!

      Delete
    7. Anonymous12 May 2012 at 17:20

      Just to note, I took out the 10nf cap with no difference to anything. Not sure if that's relevant but thought I'd mention it.

      Delete
    8. mirosol13 May 2012 at 00:30

      All my problems with this build (from one norwegian's layout) were about JFETs, so i'm not going to be much of a help here either...

      Delete
    9. Anonymous13 May 2012 at 10:41

      Ok, Mirosol. Thanks anyway. I've usually binned it by now but it really does sound good and the problem seems to minor as I'm getting effect signal coming through. I'll hold on a little longer.

      Delete
  6. Anonymous12 May 2012 at 20:41

    Ok,Wheres Jeremy Beadle and his camera?! because this is taking the effing piss now!. I've rebuilt this from complete scratch and I got the same results!? lol.. I've even un soldered the tone pot completely and it still sounds the same? ...I've tried the 'tone 1' wire on all lugs and even just frantically prodded it all over the place, it's dead? nothing. It squeals if I prod the gain lugs and thats it?!

    wrong component value? (on my part)

    ReplyDelete
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    1. Anonymous13 May 2012 at 14:20

      Ok, it's totally dead now and I've had enough of it. It's binned. A shame but that was really winding me up.

      Deep breaths.....

      Delete
  7. OCD28 September 2012 at 07:35

    Plexi Drive - Diode?

    D1 is a reverse polarity protection diode, can anyone give me a designation for it.

    thanks.

    ReplyDelete
  8. OCD28 September 2012 at 08:12

    can i use a 1N4001 ?

    ReplyDelete
  9. johnk7 October 2012 at 02:46

    just built this one today. it works perfect..... AND MY TONE CONTROL DOES TOO ;-). looking at the layout and schematic, i don't know how it couldn't.

    BTW, it sounded great with just a random trio of J201's that i grabbed from my inventory. then i went thru about 40 J201's until i found three of them that have a drain voltage from 4.48-4.53V and it sounds even better.

    ReplyDelete
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    1. IvIark7 October 2012 at 02:56

      Thanks for the feedback John. Did you do any mods on it to make it bass friendly?

      Delete
    2. johnk7 October 2012 at 03:19

      i changed the bass switch cap to a 4n7 (i tried a 10n and a 22n but they all sounded nearly the same as the 4n7). with the bass switch in, it makes a nice bass distortion pedal.

      Delete
    3. johnk7 October 2012 at 08:13

      here's a couple of pics of my plexidrive build. i ended up using two 220u caps in parallel foir the PS filter since the original has a 470U.

      http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/Plexidrive/Plexidrive-01.jpg

      http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/Plexidrive/Plexidrive-02.jpg

      Delete
    4. IvIark7 October 2012 at 11:16

      Nice job John

      Delete
  10. kod2nd31 October 2012 at 02:32

    Is it possible to use 2n5457s or 2n5458s? might be running out of J201s and i have loads of the 2n545xs.

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    1. kod2nd31 October 2012 at 02:40

      And is the 2.2M resistor a dropdown? Am i able to put a 1M resistor in its place?

      Delete
    2. IvIark31 October 2012 at 08:58

      Yes to all of the above

      Delete
  11. kod2nd1 November 2012 at 04:03

    This comment has been removed by the author.

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  12. kod2nd1 November 2012 at 11:43

    Sounds amazing...

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  13. kod2nd2 November 2012 at 15:07

    Does changing the drain resistor values(to get 4.5ish Volts) affect the usable range on the gain knob?

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    1. IvIark2 November 2012 at 17:23

      Well the gain control here is like the Big Muff and sits in between the drain of Q1 and gate of Q2. So biasing Q1 would affect the gain range you get, but it is pretty much a moot point when the most important issue is biasing the JFET correctly so the gain sounds better. With that in mind the JFETs should be biased with the gain control in the position which it is likely to spend most of its time, and so most people would want to dime the gain when biasing.

      Delete
    2. kod2nd3 November 2012 at 01:51

      Makes sense, but what does "dime" mean? all the way up?

      Delete
    3. kod2nd3 November 2012 at 01:55

      Facepalm. Dime = 10. I get it lol

      Delete
  14. kod2nd7 November 2012 at 04:37

    and.. one more question, if i want more gain, is it possible to swap the 1k resistor connecting Gain-1 to ground for a higher value?

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    1. IvIark7 November 2012 at 08:27

      That's a minimum gain resistor which determines how much gain you will get in the counter clockwise position of the Gain pot. Decrease it for less, increase it for more.

      Delete
    2. SmoothAction30 December 2012 at 02:16

      Sounds just like the demos, smooth build. Thanks Ivlark

      Delete
  15. Anonymous24 January 2013 at 14:28

    Revisited this one. rebuilt and BINGO!.. I have no idea what gremlins were at play months ago but nice little pedal once done...

    ReplyDelete
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    1. IvIark24 January 2013 at 14:44

      Yay! I reckon your son was desoldering things when you were asleep! :o)

      Delete
  16. Jason Ballantyne4 February 2013 at 17:02

    Killer circuit. Great power amp emulation. Knocked a Catalinbread Dirty Little Secret off my board.


    http://i203.photobucket.com/albums/aa227/axe_34/IMG_6119_zps7d4cb331.jpg

    http://i203.photobucket.com/albums/aa227/axe_34/IMG_6120_zps99fe72ed.jpg

    http://i203.photobucket.com/albums/aa227/axe_34/IMG_6121_zpsd44822e1.jpg

    ReplyDelete
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    1. IvIark4 February 2013 at 19:07

      Excellent stuff, thanks for the pics Jason

      Delete
    2. Fever van Roode27 December 2013 at 05:26

      Jason you have serious Gear Acquisition Syndrome (GAS) based on your photo bucket album... Jeezzzz...

      Delete
  17. fede.90k11 February 2013 at 08:15

    Here's mine!
    The best pedal i've ever played :)

    http://www.youtube.com/watch?feature=player_embedded&v=StWDKkXlqXs

    ReplyDelete
  18. Jens Lindell15 February 2013 at 12:23

    Hi mark. Just buildt this one and have a copule of questions
    On q1 and q2 i have about 4,5 and 4,8 and the last one 4,8 is that enugh to make it blaffy sounding ? Witch it is. Is the drain v to much. And i have no reading on q3 ist 0.00 on all pins. Or os that my problem. Cnat realy find anything wrong ist easy enough. So
    1 is the drain to much?
    2 should i have volatge on q3?
    Ithink if i know the answer to this i would be able to fix it
    Ok thanks

    ReplyDelete
    Replies
    1. IvIark15 February 2013 at 12:55

      You should set the voltage to what sounds good to you rather than concentrating on the voltage measurement, but 4.8V sounds close enough to me anyway. The problem is undoubtedly the 0 volt reading on Q3. If it has no voltage on any pins then it isn't passing a signal so that needs investigating.

      Delete
    2. Jens Lindell15 February 2013 at 15:36

      hahah as always i missed a resistor from v to q3 it runs perfect.
      Had it up against carl martins new plexi-drive singel channel pete thorne and i must say the sound very simiular. The carl martin had more gain and the wampler more bottom end but very alike
      thanks again mark

      Delete
  19. Jarrett Trezzo18 February 2013 at 06:08

    This comment has been removed by the author.

    ReplyDelete
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    1. johnk18 February 2013 at 06:12

      if it's only doing it on one string, it sounds to me like it's your guitar and not the pedal.

      Delete
  20. Jarrett Trezzo18 February 2013 at 06:10

    Also, I was thinking about doing these Wampler ones with trimmers to set the drain voltage. How would I go about putting these on the board?

    ReplyDelete
  21. Ludo27 February 2013 at 20:33

    Hello, just built this one and had some troubles with the bias settings. I had just bought a bag of 4 j201 so I had to manually set the drain voltage for Q1, Q2 and Q3 via different resistor values on my breadboard. I used 10k for Q1 and Q2, and 7.4k for Q3 in order to have my drain voltages sit in the 4.5-5V range.

    However, I think I have a problem with the gain control. When the 500k pot is turned all the way down, I have no sound at all. Also the volume is very very low when the gain is just turned up a bit. The 1k resistor on Q1, which ensures minimal gain, is correctly connected to ground + lug 1 of the gain pot. I don't know if it's the normal behaviour of the Plexidrive...

    Could the overall gain of the effect be affected by changing the 15k default value for bias resistors ? When the gain is cranked all the way up the sound is overdriven but it seems a little anemic to me. Please correct me if I'm wrong but Q1, Q2, Q3 gain can be roughly calculated by dividing the drain resistor by the source resistor value ? So with 15k it would be a gain of 15/1 ~= 15 for each j201 but with 10k it would be ~10 ?

    ReplyDelete
  22. metalman221055 June 2013 at 05:54

    Hi! Thanks for the layout, I have a couple questions regarding the tone and gain pots on this; all I have in stock are 1Mlog and 50Klog for the gain and tone respectively, will it matter if I double the stock values on the layout? If so, do I need to change any other component values to compensate for the higher pot values? (I'm a noob at pedalbuilding and so far have only gone by the "paint-by-numbers" method haha)

    Thanks in advance!

    ReplyDelete
  23. metalman221055 June 2013 at 05:56

    Also, I have a butt-load of 2N5457's, I was going to try those instead of the J201's, dunno if that makes any difference to the pot changes I mentioned above

    ReplyDelete
  24. JaviCAP28 July 2013 at 02:03

    Well, I have the same Tone problem that Vince had, and the same I've found in the Stone Grey (sames sytem).....don't know what's the fuck with this problem but is a general one. Maybe it's related to the gounding of the tone pot. I¡ve done ground -> tone 2-3 -> vol 1

    Will have to try a different way

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    Replies
    1. JaviCAP28 July 2013 at 11:00

      Well, problem solved. The tone was working, but simply, a 10nf cap was no enough. I replaced it with a 47nf, and now is a real tone control.

      With 10nf was very subtle... so subtle that was useless :P

      BR

      Delete
  25. Unknown9 August 2013 at 11:33

    Hi,
    Built this in a a dual build:
    http://imageshack.us/a/img842/3030/k2sf.jpg
    I had to replace the drain resistors with trimpots, so I could bias the fets properly.
    I went for the original version and seem to be ok with popping so far, but I have only tested it on a smaller amp, to check it was working OK. Hope I won't get a pop when I use it at higher volumes with my band.
    Also, I used 2 on/off/on DPDTs, and mounted 2 bass caps offboard instead of one onboard. I mounted a 2n2 and a 1n5 on the lime side, that I use with softer gain settings, and a 1n5 and a 1n on the lemon side, that I use with higher gain settings. This allows me to switch from no bass to mellow bass or more present bass on both channels, with more bass available on the softer gain side. :)
    Thanks for the layout!

    ReplyDelete
  26. Unknown24 August 2013 at 12:38

    Hi,
    Say I want to replace the bass toggle switch with a pot, so I can really dial in how much bass I need... What value would you recommend?
    Also, I was thinking using an audio pot, with the signal coming in via lug 3, and out via lug 2. Should lug 1 be connected to ground, left as is, or linked to lug 2?
    Thanks in advance
    Fred

    ReplyDelete
    Replies
    1. JaviCAP24 August 2013 at 21:08

      Hi,

      You can't replace the switch with a pot, because the switch just drives in a 2n2 cap into the circuit, so, no pot (resistor) can't replace it.

      Second question: One wire to lug 3 and other to lugs 1-2, or just to lug 2, and leave unconected lug 1.

      BR

      Delete
    2. Unknown25 August 2013 at 19:50

      Arf... Too bad... :-(
      Thanks for the reply, JaviCAP.

      Delete
  27. Jacob Bundren31 August 2013 at 23:56

    Love this thing!

    http://instagram.com/p/bMw7M6B5K8/

    ReplyDelete
  28. Doron Barness5 September 2013 at 14:53

    Can the PS cap be replaced with anything between 100uF and 470uF?

    ReplyDelete
  29. Doron Barness13 September 2013 at 08:28

    OK....got it...sounds great with the 22nF input cap but any thing above sounded great too. If you ever wanna play bass on this pedal better put a larger 220nF or even a 1uF cap in there.
    The TONE control is a bit too subtle and that's a pitty for such a great pedal.
    The J201 FETs were tested from a lot of about 40 and I tried everything from 4V to 6V and I believe the best crunch I got resembling the strength of the YOUTUBE videos was around 4.7-4.8V on all 3. I guess 5V would be OK too but 4.5V was a bit weak.
    the PS cap could be anything from 100uF to 470uF

    ReplyDelete
    Replies
    1. mirosol13 September 2013 at 16:03

      Swapping the input cap alone for more bass doesn't quite help as the bass boost switch will cut it right after the first gain stage. One would need to up the 470p and 2n2 caps too.
      +m

      Delete
  30. chadster28 September 2013 at 12:53

    Just built this , decided not to use the trimmer layout as I plan to build some of the other samplers which don't have layouts with trimmers. I matched my j201 before building and after tweaking the resistors I have all biased at 4.5v .sounds great , can't wait till tomorrow when I can crank the volume and test it properly. Thanks for these great layouts.

    ReplyDelete
  31. Unknown11 December 2013 at 06:23

    Any suggestions on a cap value substitution for the bass switch? I'm looking for something in between. The 2n2 sounds a little "woofy" to me but it's too wimpy with it switched out. Otherwise it sounds great!

    ReplyDelete
  32. Unknown12 March 2014 at 14:20

    Hello Everyone, built this Pedal today and it sounds killer. Took me a while to notice that the J201s I bought needed to be directed the other way round. I think I should mention that...

    Thank you!

    ReplyDelete
  33. Unknown29 April 2014 at 17:40

    Please, what i do with the +Led output if i don't want to use 3PDT switch?

    ReplyDelete
    Replies
    1. IvIark29 April 2014 at 18:05

      Just ignore it, and you can ignore the 4k7 resistor too. If you want to use conventional true bypass wiring you won't able to have LED indication though, or if you really want LED indication but only want to use a DPDT stomp then you'll need to use millennium bypass, which you'll find a layout for via the search box above.

      Delete
  34. BB2 May 2014 at 05:17

    Might seem like a dumb question, i have no knowledge of electronics but can you tell me where the output is on the board? or does the volume 2 to output go to the foot switch?

    ReplyDelete
    Replies
    1. dbat692 May 2014 at 08:36

      Hi BB

      The output comes from pin 2 of the volume pot - that the goes to the stomp switch

      Delete
    2. BB2 May 2014 at 13:33

      Do you know what is the best type of wiring for the foot switch?

      thanks

      Delete
  35. Unknown25 June 2014 at 00:08

    This comment has been removed by the author.

    ReplyDelete
    Replies
    1. Unknown25 June 2014 at 03:08

      One more question,

      When you are biasing the J201s to get the 4.7vs, are you supposed to be playing through the Plexi or do you ground the input?

      Delete
    2. IvIark25 June 2014 at 08:04

      You don't need to be playing, that won't affect the bias in a significant way, so just tweak and measure

      Delete
    3. Unknown25 June 2014 at 14:11

      Thank you,
      Since I matched the J201s, now each measuring 6.43v at the drains, can I simply tweak the 10R resistor to get the 4.7Vs.on all 3 J201s?

      Many replace it with a 5k trimmer?

      Delete
    4. IvIark25 June 2014 at 14:54

      Yes that would make more sense, they won't need individually biasing if they are matched like that

      Delete
  36. Unknown26 June 2014 at 03:46

    Thanks Mark, swapped out the 10R with a 1k trimmer, biased all 3 @ 4.7 and it sounds great! Going to leave the trimmer in place so I can tweak some more if the mood strikes.


    ReplyDelete
  37. Unknown13 July 2014 at 00:33

    I'd like to add MIDS to my circuit. everything sounds great with it but it could use a bit more in the middle. Having a mid-toggle would be very nice! What component(s) should I change? Thanks.

    ReplyDelete
  38. John28 July 2014 at 19:42

    Wampler clone's done. Great sounding, thank you for this awesome layout.

    I was first a bit disappointed cause my orange rocker 30 sounds considerably darker and have a very naturally middy voicing, both together were much aggressive to me
    So i plug a 7 band equalizer to fix the problem.

    Maybe I should put a switch or a pot more to avoid using an equalizer but I don't know where ?

    Any idea please ?


    ReplyDelete
  39. LikeaGlove5 October 2014 at 06:52

    Simple question.. I used a 20 k pot for tone as it's all I could find, however running at almost open.. What can I change (without replacing the pot) the add more treble or add more range? Cheers :)

    ReplyDelete
  40. Unknown9 November 2014 at 21:25

    This comment has been removed by the author.

    ReplyDelete
  41. Unknown16 November 2014 at 14:09

    A question: Why are the fets underbiased?? I did not like the sound and biased the fets to the point where it must theoreticaly must by: 0,6x9Volts and a little bit more, so 5,5 volts. It sounds much less harsh to me.
    Second: The first layout is drawn from the schematic that you can find on the net. In this circuit drawning there is no iput cap! I think this is wrong. You can not skip this cap! The 1 Mohm resistance between the gate and earth wil force a very little DC offsett on the gate. When you have no cap. and you plugin your guitar or switch the plexidrive on, the 1Mohm resistance will be parralel to your guitar resistance ( 2 to about 10 kohm!) At that moment the very little voltage at the gate will drop to zero!! Thats why there is a plop. Theoretically the first ampstage is not proper working then. This circuit is the only Wampler drawning without a input cap. Brain Wampler is an excellent electronics engeneer (in spite of the most boutique pedal copy makers), so I think in the original circuit there will be a input cap. Just my thoughts

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    Replies
    1. mirosol16 November 2014 at 14:49

      Your thoughts are almost on spot, but wrong. The original does not have an input cap. Check any guitar amplifier schematic and you'll see there is nothing but resistance between the input jack tip and the preamp tube grid. There are other JFET pedal designs in the wild that are also "missing" the input cap. So omitting it isn't exactly an engineering error.
      If i was to build or design one, i would most certainly use an input cap, but with JFET or tubes it's not mandatory.
      +m

      Delete
    2. mirosol16 November 2014 at 14:52

      On a side note, i did draw a modified version of this, with input cap and with trimmers for each gain stage. With that layout the FETs can be easily tuned by ear. Which is usually way better method to bias JFETs in comparison to some known voltage.
      +m

      Delete
    3. Unknown16 November 2014 at 17:56

      Thanks for your input. I have a hughe amount of amp schematics and Yes the Fender and many copy's of the Fenderamps (even Marshall was a copy of the Fender design) do not have an input cap. Many other more modern tubeamp designers do have that cap like Borgner, Trace elliot, Peavy, Ampmaker aso. Mind you that Leo Fender was a radioservice man and not a tube amp designer. Pick a tubeamp design web and you see they all have an input caps to isolate the gridresistance from everything that is before that stage. http://www.valvewizard.co.uk/Common_Gain_Stage.pdf f.i. The fact that there are no input caps in many amps is that they copyed from old Leo. I looked at all the wampler jfet design available on the net and they all have the input cap.

      Delete
    4. mirosol16 November 2014 at 23:45

      What about Voxes and Laneys? I don't think those are fender copies.
      +m

      Delete
    5. mirosol16 November 2014 at 23:52

      Plus there are no Wampler factory schematics around, so there is a chance the schematics you refer to have been modified by adding an input cap. On a side note - check all of the JFET designs at Runoffgroove.com.
      +m

      Delete
  42. Unknown13 December 2014 at 08:17

    Take a look at the Fender tonestacks. That was a very bad design! Take a look at the tonestacks of the Marshall/Vox/Laney's and you see they are almost the same bad design. Let's go on topic: You have two almost the same pedals: one is plopping an make bad klicking noises when you engage it and the other is death quite. Which one is the good design???

    ReplyDelete
  43. Dimi Nalbantov15 February 2015 at 16:55

    This comment has been removed by the author.

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  44. Doron Barness7 April 2015 at 20:08

    Starting to build this one now. Anybody has a list of mods to somehow implement some of the new features of the new DELUXE version?
    I just thought of maybe adding a switchable top boost on top of the switchable bass boost, and a switchable pre-gain boost to add that extra hair.

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  45. Unknown26 April 2015 at 14:15

    Oke, I build during the last years this pedal and many more with JFets in it. Instead of the drainresistance of 15 kOhm you can place a trim resistor. I always build these with a trim resistor of 100kOhm. Then adjust the drain voltage to about 5 Volt (Usupply 9 V) as everybody tells. But.. the pedals I build sound never so nice as the real one's I hear on YT! Made many changes in the schematic but all of them sounded nice but not good. Especialy this Plexidrive laks a lot of drive. I kept the pedals on the shelf and did not use them, till yesterday! I was trying again to make the plexidrive like I hear on YT. But nothing helped till I turned the trimpots on a drain voltage of 2,5 Volt. And voila the Marshall was in da House. Big Big screaming marshall tone's. I have 9 diff. stompboxes and I have down-drained them all to 2,5 Volts (drain to ground voltage!) and it works. I have beatiful sounding boxes now. Go ahead and try this.

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  46. Frederik Erikson16 May 2015 at 21:57

    This comment has been removed by the author.

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  47. pavonepedalfx1 July 2015 at 22:06

    Hello guys.
    I made the circuit and plays really well. The only strange thing is that to get an acceptable distortion, I had to increase the values ​​of the relative strengths of the Drain Q1-2-3 from 15K to 100K, arriving to obtain a voltage of about 4.5V.

    Now I wonder: is it possible to get this tension must reach resistance so high? Maybe I of J201 defective?
    I saw then that there is a layout with the trimmer from 50K to set the tension, but would be insufficient trimmers from 50K in my case.

    Then I would ask you to increase a little 'can I increase the gain still resistance from 100k to obtain a lower voltage on the Drain of Q1-2-3 (maybe listening ear to the result)?

    And finally, the tone control works well in close but even when the tone knob is fully open, the overall sound seems a bit too gloomy and dark. What I would do to get more brightness general?
    Sorry for the English .....
    Thanks

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    Replies
    1. pavonepedalfx30 April 2016 at 16:57

      Problem solved. I replaced the J201 with 2N5457 and now all OK. I think the J201 was defective. I have about 40, and they all have the same defect. With 2N5457 I had no trouble calibrating the bias voltage and the pedal now is perfect.

      Delete
  48. Anonymous28 October 2015 at 01:26

    Quick bias question: If I build this up on the breadboard and leave the stock 15k on Q2/Q3, then install a 20k pot to Q1, bias it to 4.7ish volts, can I just do that through Q2/Q3. Or does Q1 bias impact Q2/3 where I need to tweak them all together to get them all dialed in to 4.7ish? Thanks!

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  49. Wellu Leppälä5 January 2016 at 14:59

    This comment has been removed by the author.

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  50. Wellu Leppälä5 January 2016 at 15:00

    I read somewhere that Velvet Fuzz is supposedly very close to this design? I am new to effect building, but it is incredibly fascinating.

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  51. Boris27 January 2016 at 11:06

    Hi
    Can someone explain to me the function of ceramic capacitors on the circuit?
    Thank you

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  52. Unknown27 January 2016 at 14:44

    The 47 pF to earth is in conjunction with the 1M res. a high rolloff filter. The 470pF is a kind of low pass filter.

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  53. ZanBon2 April 2016 at 11:15

    Anyone has been around the plexi deluxe? Can't seem to find anything about it in the usual forums!

    ReplyDelete
    Replies
    1. Doron Barness3 April 2016 at 19:05

      Looking for the same thing also.....waiting.....waiting.....

      Delete
  54. Unknown20 June 2016 at 21:19

    Plexi Drive deluxe please???!!!! Anyone??!!

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  55. Unknown9 December 2016 at 12:25

    This comment has been removed by the author.

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  56. Unknown6 March 2017 at 02:55

    Is the modified layout verified? I can't get any sound out of it, when I use 15k resistors on the drains I get .9 volts on the drains, when I try to bias them on breadboard I find a 1.5k should get me within 4.5-5 volts, but after installation I get 9 volts on the drains, maybe my Jfet are bad? I have re-flowed and checked the layout a hundred times, 3 weeks at it, I am about to rebuild it using the first layout without a pop resistor

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  57. Unknown9 April 2017 at 23:33

    Hey guys
    Does anyone have the diagram for the Wampler plexi drive deluxe?

    ReplyDelete
  58. Ray12 June 2017 at 00:46

    Need help troubleshooting... awesome layout and information, by the way. I have verrrry low volume out of this thing, and no gain. I have to turn my amp up to 9 to get anything out of it...I normally have my amp on 1 or less.
    Looking at this schem : http://1.bp.blogspot.com/-rAWTuUNK1aM/TxDYkVflb9I/AAAAAAAAAg4/V81eRfQXHMY/s1600/plexi-drive.PNG , I have deduced that I have
    1. 4.5 v to Q3 drain
    2. no signal to Q3 gate
    3. no signal past R7 (10k resistor feeding Q3).

    Any more help is greatly appreciated.

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    1. Ray13 June 2017 at 13:21

      This comment has been removed by the author.

      Delete
  59. Ricky Sheaves26 July 2017 at 21:40

    Apologies for the necro-comment here, but thought I'd share a tip:

    I've made several of these over the years and find that biasing isn't too challenging as long as you can get a handful of JFETs with very similar characteristics. Simply replace the 10ohm resistor with a 10k trimpot, and you can bias all three at once. Load 3 JFETs in, adjust the trimmer until you're near 4.5v on at least one of the JFET drains. If the others are out of whack, swap them out with the others in your bag until everything is in the ballpark. This way, you can also experiment with hot or cold biasing the whole circuit in one go.

    This has worked well with J201, 2N5457, and 2N5458 for me.

    Cheers!

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  60. Travis27 July 2017 at 01:32

    In my opinion by doing that you are not "biasing" the FETs but you are doing what a "starve" control would do.

    Changing the supply voltage is different to biasing the JFETs. For example, if I power this pedal with a 9V supply, then switch to a 18V supply, I really didn't change the "bias", I just changed the power supply.

    I think you will find that you can just forget about that trimmer because the fixed drain resistors are actually biasing the FETs in a way that you apparently like.

    You may like the sound of the circuit with a starved supply, in that case you could just use a 5V regulator and forget about trimmers altogether

    Just my 2 cents

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    Replies
    1. Ricky Sheaves27 July 2017 at 11:45

      Thanks Travis. Good point. And yeah, that is doing what a starve control would do. But maybe I am missing something...

      If one builds this circuit and finds that all three 15k fixed drain resistors had to be changed to, say, 18k (maybe even with three trimmers) in order to get ~4.5v on the drains for their set of *matched* JFETs, have they "biased" the transistors, or "starved" them, one by one? (This is a real question ... not being a punk!)

      And I get what you mean with the regulator, but the required voltage would be dependent on the characteristics of the set of matched JFETs, or need to be adjustable. In which case, a trimmer seems easier IMO. In this specific application, I guess I don't understand the difference: we're just trying to get the drains to read 4.5v, and there is nothing else drawing power from that supply rail. So, maybe I am missing something obvious?

      Of course, all of this is moot if your JFETs require different fixed drain resistor values.

      P.S. Technically, I think we use the word "bias" a little loosely in general sometimes ... this being one of those times ;)

      Delete
  61. Unknown9 May 2018 at 20:10

    Tried building the modified version of this again, still a dead circuit. No signal past Q1. I have all drains at 4.5v

    ReplyDelete
  62. andrewsrea3 September 2018 at 23:50

    Ivlark: great build - thank you!

    Tested last night, worked like the Youtube videos. A really nice pedal, took me about 5 or 6 hours. I used 50K variable resistors for the drain-bias, which came out to about 6.5K each to achieve 4.9v between the drain and gate (a little higher than half-voltage from supply sounded the best).

    I love Wampler's designs.

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  63. oshun23 January 2019 at 06:13

    cant find my mistake. when gain turned to 0, there is no sound - it works almoust like a volume knob. and on max it doesnt sound like plexi - very low gain

    ReplyDelete
    Replies
    1. oshun23 January 2019 at 06:14

      (4.5V - at all drains)

      Delete
    2. mirosol24 January 2019 at 17:41

      Sounds like the behaviour i had with "aliexpress" J201s. They seem to bias correctly, but do not give out the gain they should. To get something usable out of yours (whether you have bad J201s or not), try replacing the 10R resistor with a 50K trimpot. If that doesn't work, then leave the trimpot in place and lower the three 15K resistors to 10K or lower. Won't be as great as the idol, but you might get something usable out of it.
      +m

      Delete
    3. oshun11 August 2021 at 21:54

      thank you! i will try

      Delete
  64. Andyroid20 February 2019 at 01:08

    All of my drains are at about 1.2V and the pedal sounds like crap. I got my J201s from China so they are obviously not J201s. If I reduce the drain resistors to get 4.5V, can I expect it to sound right?
    I've been making valve amps for years and I would not expect an ECC82 to sound like an ECC83 if I simply adjusted the plate resistor to achieve the same plate voltage. Are transistors a bit different in this respect? Cheers

    ReplyDelete
    Replies
    1. johnk20 February 2019 at 02:18

      you need to get it set to 4.5 volts. some of the chinese J201's just don't work properly but it's worth a try. i've had some that work just fine.

      Delete
  65. Louis K7 June 2019 at 04:47

    Hi IvIark,

    This is the best pedal that i feel the harmonics perfect. Thank you :)

    I want to ask if there is a way to decrase the gain? Also after %50 of volume i have a terrible hum (noise) I had tried 2n5457s but nothing has changed.

    Do you have any suggestions?

    Thanks, regards.

    ReplyDelete
    Replies
    1. Louis K7 June 2019 at 05:44

      Sorry i forgot. My Drain voltages are:
      Q1: 3,22
      Q2: 7,05
      Q3: 5,07

      Is everything seems ok with J201s?

      Delete
  66. Boris5 May 2021 at 20:16

    Hello,
    Can someone explain to me what the two 15K resistors are for with the 2.2NF capacitor going to ground, located just before the tone and volume.
    Thank you.

    ReplyDelete
    Replies
    1. IvIark5 May 2021 at 20:58

      It's 2 low pass filters in series, with the tone control altering the frequency response of the second filter. It is probably more apparent in the schematic

      https://1.bp.blogspot.com/-rAWTuUNK1aM/TxDYkVflb9I/AAAAAAAAAg4/V81eRfQXHMY/s1600/plexi-drive.PNG

      15k & 2n2 gives a corner frequency of around 4.8KHz
      15k & 10n gives a corner frequency of around 1K but I'm not sure how that interacts with the tone control

      Delete
  67. Boris5 May 2021 at 21:11

    Thank you for the answer.
    I understand the principle at the start of the circuit, but there I had a doubt :)

    ReplyDelete

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