Wampler - Plexi-Drive  [traced]

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indyguitarist
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Post by indyguitarist »

whosyourdaddy wrote:no worries I've solved the problem, I overlooked C6, thought it has one strip space between terminals. :slap:
now it sounds great, plexi sound it is. :applause:

here are voltages if anyone needs them: (supply 9.02V)
Q1: (DSG) 3.65V 0.36V 0V
Q2: (DSG) 5.37V 0.24V 0V
Q3: (DSG) 3.76V 0.35V 0V

DON'T do it this way. You MUST sort through jfets to get a bias as close to 4.5 - 5v max as possible. This will allow to keep the drain resistors the same.

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Post by whosyourdaddy »

I've thought of that as well, I'm going to try that for sure. (using fet matcher, which I left - somewhere) ;)
soon :)
thx

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Post by grrrunge »

indyguitarist wrote:DON'T do it this way. You MUST sort through jfets to get a bias as close to 4.5 - 5v max as possible. This will allow to keep the drain resistors the same.
That's very nice to know ;) How would one go about matching them?
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Post by azrael »

bah, I would rather just make different drain resistors, hahaha.
Makes for less work, I think.

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Post by whosyourdaddy »

ok, these are my new voltages:
Q1: (DSG) 4.59V 0.29V 0V
Q2: (DSG) 4.78V 0.28V 0V
Q3: (DSG) 4.95V 0.27V 0V
picked 3 from a set of 10, and that's tight.
(just install socket on Q1 and measure drain voltages on all of them)

not a big change in sound, sounds a bit clearer (tube-ier maybe)
I also think that it would be much easier to just change those drain resistors.

it's a wrap :cheers

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indyguitarist
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Post by indyguitarist »

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.

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Post by azrael »

Hmm....that's a good point...

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Post by grrrunge »

indyguitarist wrote:DON'T do it this way. You MUST sort through jfets to get a bias as close to 4.5 - 5v max as possible. This will allow to keep the drain resistors the same.
Yes! Thanks again ;) The pedal sounds clearer all over, and it's not farty on lower gain settings this way. My Q1 is 4.51V. Q2 ad Q3 around 4,7V. Highly recommended!
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Post by DahakaNishoba »

Built one following the vero layout....suonds amazing and clear but
MASSIVE POP from the switch....anyone xperienced the same problem ? tried with larger resistor at input/output no luck at all
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Post by DahakaNishoba »

changed 3 swithches and switch wiring (on millenium bypass now)
changed pulldown resistors
changed electros
checked all the cuts/joints......even passing cutter between lines...

this is STILL seriously popping......both in on/off and the bass switch......

:(
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Post by grrrunge »

I just recieved the following question in my PM-inbox:
britmusic wrote:Hi,

It really looks like you know what you doing here and you know this pedal inside and out. I have a stock Wampler Plex-Drive and wanted to know two things if you could help me out here.

1. Would there me anyway to bump up the mids just a touch by way of a toggle switch so I could bounce between the stock Plexi Wampler tone and a modified mid bump tone?

2. I was thinking about replacing the 47uf and 470uf caps (the big ones) in the curcit with real mustard caps if I can find the smallest value uf, pf, or n. Do you think this would make any difference at all in tone and in a good way?

Thank you very much,
Brit


Subject: Wampler - Plexi-Drive
grrrunge wrote:
indyguitarist wrote:DON'T do it this way. You MUST sort through jfets to get a bias as close to 4.5 - 5v max as possible. This will allow to keep the drain resistors the same.
Yes! Thanks again ;) The pedal sounds clearer all over, and it's not farty on lower gain settings this way. My Q1 is 4.51V. Q2 ad Q3 around 4,7V. Highly recommended!
I answered the following. Maybe someone else could chime in with something more clever to add?
grrrunge wrote:Thanks a lot. Those first words were very kind :)

If i were you i would post the question in the plexidrive thread though. Wampler Pedals are made by Brian, who goes under the handle indyguitarist on this forum. He's usually very kind and helpful with questions regarding his products. I mean - who would be better to answer this, other than the guy who invented it?

To answer question number 1: Mid humps in a simple form are usually accomplished by carefully filtering out the bass and treble (like Ibanez' Tube Screamer, BOSS SD-1 etc), rather than actually boosting the mids. Putting something like this on a single switch seems like quite a bit of trouble to me ;) Not that it can't be acomplished though...

Question 2: I don't really know much about mojo parts, and - if anything - exactly what makes them do stuff in a nicer way than non-mojo equivalents.
I don't really think the 470uF cap is going to affect your sound at all. It's just there for power filtering, and is completely out of the signal path. It's placed across 9V and ground, acting like a battery, smoothing out noise and ripple in the incoming power from an external 9V adapter.
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Post by indyguitarist »

DahakaNishoba wrote:changed 3 swithches and switch wiring (on millenium bypass now)
changed pulldown resistors
changed electros
checked all the cuts/joints......even passing cutter between lines...

this is STILL seriously popping......both in on/off and the bass switch......

:(
Well, the schem posted is from an older version.
The popping is most likely from the jfet at the input. stick a cap in front of it (.022 should do) making sure you have a 2.2M before the cap and a 1M after the cap (closest to jfet). This should help quite a bit.

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Post by Ghandi »

could it be that c3 and c4 have to be exchanged with another?

somehow it seems to me more plexi like to use the 2n2 cap (Super Lead) or parallel with an 22nF cap (Bluesbreaker) after the first jfet stage
and use the 470pF as the treble bypass cap on the gain pot, just like in a real marshall... :hmmm:

cheers
ghandi

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Post by lukatosh »

Today i made this PCB based on the schematic posted on page 2... It would be grat if anyone can check if works!.. i'm planning to build it next week.

Here are the files!

Saludos desde Chile!
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PlexiDrive.rar
Plexi drive PCB, lay and Part list
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Post by lukatosh »

i just received the materials to build this pedal... But i've read that the schematic is from an older version of the pedal... anyone have an actualized schematic?

i'll be posting the building process

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Post by lukatosh »

nobody have a newer schematic?? Thanks!

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Post by lukatosh »

Hello!

Well... I built this today!!

i Used the layout that i posted a while ago... But, i have some problems!!

The first thing that i note was that the tone pot was backwards... so i flip it and now it's ok... but... the tone is not too much affected...

When i lower the gain pot to its minimun... there is no sound comming out the pedal

when i turn it up... it distorts the singal, but very little :(

what can be wrong?

please!! i need help :(
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Plexy drive layout.png
Plexy drive layout.png (20.79 KiB) Viewed 3330 times

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Post by RnFR »

read through the thread again. did you measure your drain voltages?
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Post by lukatosh »

I don't have a multimeter....it just broke down yesterday :(

But... i bought a bag of 10 j201. i tried them in different arrangements, and the same... low distortion and when i turn down the gain pot... there is a little signal coming out the pedal

i can't even use it as a clean booster :(

i'll try to get a multimeter at university to report the drain voltages...

thanks so mucho for your time and help!

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Post by lukatosh »

today i measured the voltages... drain are between 4.5 - 5 v....

but the same.... when i lower the gain de sound goes off....

i rechecked the components :(

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