Wampler Black 65 with trimmers and boost mod

[MAO]

Update: Corrected layout and link/cut pictures

I'm sure this is old news by now, but like what I read on other's posts, I also wanted to replace the boost toggle switch with a boost stomp switch for leads. Thing was, I felt there was too much of a volume difference between the 2 modes.

So I finally added a boost volume pot. Since I only wanted to reduce the volume of the boost mode, not increase it, I replaced 1/2 of the voltage divider (the 240k resistor tied to ground) with a 250k linear pot.

This worked out even better than I had hoped, not only am I able to dial back the volume of the boost mode, I found that the new boost pot and gain pots work really well together, adding new versatility to this excellent pedal. Fully clockwise, the boost pot is essentially the original boost toggle setting.

I had also considered using a 250k trimmer as a set and forget for the boost mode, but for one thing, that wouldn't have allowed for the original full boost mode. Given the added versatility with the boost pot, the trimmer is no longer a consideration.  

I further modified my modified IvIark's layout to accommodate the 250k boost pot and a 3PDT boost stomp switch. I also added 2 CLRs for the LEDs and a 9.1 zener to better stabilize the bias of the J201s when using different power supplies.

Verified by me:



Here's a rough draft of the 1590BB faceplate



 

[Muadzin]

There are at least 4 links in different positions (and lengths) on the two layouts.
The one next to the top left trimmer
The one above the bottom left trimmer
The one next to the bottom left 1M resistor (also two cuts missing on right layout)
The one next to the right bottom 47u cap

I guess the right layout is still the one you used on your original layout without boost mod.

[MAO]

Shoot, you are correct, Sorry about that.

Inexcusable, won't happen again.

pictures have been updated 01/12/15

Mike

[Muadzin]

I've built this layout and I propose some changes in the trimmers and the links underneath them. If you use cermet trimpots from Tayda (as I did) pins 1 and 3 will be in the middle, not in the corners as presumed on the layout. Meaning you will have to move the links that are in the middle underneath the trimpots as on the layout a hole backwards or you will have a have a major problem. There is room for it for the trimpots for Q1 to Q3. There is no room however for the trimpot of Q4 though, so I had to be creative and raise it a little. Not the most elegant solution though.

I also propose that the values for the trimpots be changed from 20K to 50K. 20K works fine if you use regular J201's. But mine turned out to be goddamn fakes. No gain whatsoever with the gain pot maxed. Damn you Polida!!! Damn you straight to hell!!! I got some SMD mmbfj201's with adapter boards from chromosphere and those work. Glorious gain to be heard. But to bias them 50K's probably work a lot better

[MAO]

Thanks for the feedback on both the cermet trimmer footprint and trim pot values. Wish I would have seen this sooner.

I'm not exactly sure how the footprint differs from the cheap 6mm trimmers Tayda sells. Which ones did you buy?

And FWIW I just built another one using this layout, this time with SMD J201s and could not properly bias some of them with the 20k pots.  50k would be better as you suggested.

I will update the layout with the changes once I get a look at the other trimmers.

BTW, how do you like the boost pot rather than the toggle?

     

[Muadzin]

I used these trimmers:

http://www.taydaelectronics.com/potentiometer-variable-resistors/cermet-potentiometers/3362p.html

As for the boost pot, some extra control is always nice. Although I do seem to like it fully cranked as I'm a moar gain kind of guy. Which if I'm correct is the stock setting of the boost switch of the original.

[traktop]

I did same mod to mine, but left the trimmer inside setting the boost volume to match the normal volume. Then I just used the old on-on switch to select between normal boost volume and reduced boost volume.
I always felt this pedal lacking from gain. The gain pot always remains fully cranked, but I just get a tiny break up when using the normal setting. When engaging the boost I get a little more, but nothing remarkable, (it sounds great anyway...), so the gain pot remains barely usable on 3/4 of the running.
I matched all the j201s with trimmers and all the drains reads about 4.10v.
Should I try new transistors¿ (got them from Tayda).
Cheers, Gilberto.

[MAO]

Hi, did you use this layout?

If so, I would suggest you 1st set the "new" boost control fully clockwise, which is essentially the same setting as the original Boost toggle switch on.  Then compare both your normal mode and boost mode to this video.

https://www.youtube.com/watch?v=D1jiV68MdR0 

Brett demonstrates both modes with different settings on the gain knob.  Mine sounds just like this video.

If yours has less gain in the Normal mode, and you have verified the components are the correct value, then I would have to suspect there may be an issue with one or more J201s. Most likely Q2, Q3 or Q4

And if so, you can try this. If your lucky and only 1 J201 is the issue, this should help you find it. Q1 (in this layout) is only needed for the Boost mode, so you can remove it when using just the Normal mode, and then rotate it through the other positions to see if your Normal mode comes alive. If so, you will have found the culprit. Of course you will need to re-bias for each new position. Hope that makes sense.  

FWIW I have had good luck with most of the J201s I had purchased from Tayda in the past, however there were a couple that were way out of spec. But I have also had the same occasional issue with the SMD versions I have recently purchased from Mouser. In both cases, I had the adjust the trim pots to the extreme to get them to bias correctly, or couldn't even get them biased properly with the 20k trimmers in this build. I've had the best results with the J201s that biased with the trimmers somewhere in the middle range, neither extreme.  

If it helps, and your not in to much of a rush, I could test 4 of my J201s in my '65 build and send them to you. They would be the SMD package soldered to a tiny breakout board and will fit this layout without issue.

And last, if yours does sound like the video and your not satisfied with the Normal mode's gain, I'll have a suggestion to deal with that too.

Let me know,
Mike

[Muadzin]

traktop wrote

I did same mod to mine, but left the trimmer inside setting the boost volume to match the normal volume. Then I just used the old on-on switch to select between normal boost volume and reduced boost volume.
I always felt this pedal lacking from gain. The gain pot always remains fully cranked, but I just get a tiny break up when using the normal setting. When engaging the boost I get a little more, but nothing remarkable, (it sounds great anyway...), so the gain pot remains barely usable on 3/4 of the running.
I matched all the j201s with trimmers and all the drains reads about 4.10v.
Should I try new transistors¿ (got them from Tayda).
Cheers, Gilberto.

You can still get J201's from Tayda?

Chances are they're probably fakes. Unless they are from a really trustworthy seller I no longer bother with through hole J201's. Especially everything being sold from the far east is fake in my opinion. And those of trustworthy sellers like Smallbear is hideously expensive. I much prefer SMD J201's with adapter boards. Those at least you can get in large quantities without breaking the bank.

I had several batches of fake J201's in my pedals and those had me underwhelmed in the gain department as well. Even with the gain fully open I was barely getting any distortion. Then I swapped them for SMD J201's and suddenly I had angry mobs with bleeding ears and pitchforks and burning torches outside my door.

[traktop]

I used the old layout.
Finally, the J201s were from banzai not tayda... I bought those from a seller in my town with success before, they are just a little more expensive. I will try swapping Q1, but if the problem with fake ones is that they go out of range, mine are biased as the original thread suggested. When their drains measure under 3.5 volts it gets dirtier, but in a bad way, (thinner and earspliting), but anything above seems too clean compared with the videos. If It still is not working, maybe Ill contact with you to get some of them, thanks.
Anyway, I would be interested on hearing your thoughts about getting more dirt from the original
Cheers, Gilberto.

[induction]

If your pedal doesn't sound like the original, my suggestion is to ditch the bias trimmers and use the original resistor values. Swap J201's until you find some that bias correctly with those resistors, which is what Wampler does. This is a giant, expensive PITA, I accept, but there's no way around it that I can see. I had to sort through roughly 100 J201's to find 4 that worked in this build. They were not fake, as they all tested within spec. But this particular circuit wants J201's that fall very near one end of the spec range. Other J201's can be perfectly within spec, but still not bias correctly in this circuit. Some of the ones that didn't work on this circuit were perfect for the Tweed '57, the Plexi-Drive, or the Pinnacle.

So why not just use the trimmers? The problem is that the biasing resistors set the gain of the jfet stage, so when you use a trimmer to dial in the bias, you change the gain and EQ of that stage. Wampler designed this pedal with very specific gains in mind, and then chose his J201's in order to get that gain. If you twiddle your trimmer until you get the bias you want, and the resulting resistance ends up outside tolerance of the original resistor value, then you have changed the gain enough to have a noticeable effect on the sound of the pedal. If you end up with too low (IIRC) resistance in the trimmer, the gain will be too low, and the pedal will sound too clean. If you end up with too high resistance, the gain will be too high, and the pedal will sound too dirty. In some high-gain circuits (like the Pinnacle for example), this may cause oscillation. The further the resistance is from the original resistor value, the more obvious the sonic change will be.

Of course, if your pedal does sound like the original, but you would like more gain anyway, there is an obvious solution: Choose J201's that require bigger drain resistors to bias correctly. Just watch out for oscillation.

This logic applies to all of Wampler's other J201 amp-emulation circuits equally well.

[MAO]

Thanks for the information!

That probably explains some of the oscillation issues I had with the Pinnacle.

 I seem to recall Brain posting something similar on another site regarding drain resistors and their effect on the EQ.

Tractop, would you post the resistance values of the drain resistances when you have the J201s biased at 4 volts? (Which I believe was measured on an original '65)

I had mine biased at 4.5v, unfortunately my '65 is out on loan right now, but I'll measure the same when I get it back.

My "gain" suggestion was regarding the boost control mod, let me know if still interested once you have the base sound sorted out. It probably won't be necessary once you sort out the biasing/drain resistors as Induction advised.

[Beaker]

I have to agree with everything Induction has said on this issue.

The more you have to deviate from the optimum resistance in order to bias your JFETS correctly, the more effect it will have on the sound of the pedal.

The gain range tolerance of JFETS is really quite large, but if the pedal demands a very small tolerance within the gain range, then you just have to accept that.

It's almost certainly why some of these pedals are so expensive to buy - think of it from Wampler's point of view - having to buy literally thousands of JFETS, just to get enough with the correct range of values in order to build a production batch. I don't know what the average failure rate is for this, but from what others including Induction say, 90% is not unreasonable. That means you can only make two and a half pedals for every one hundred JFETS you buy!

(Of course those "failures" will still find a use elsewhere, but even so, that is a lot of money, time and effort expended.)

And that is when you are buying the genuine article from reliable sources.

So, as Induction says, use trimmers and accept that the altered resistance caused when biasing can change the sound.

Or you can use the original resistors values, and choose only the correct gain JFETS - just be prepared to buy a lot in order to do this.

Alternatively, take Muadzin's route and buy SMD JFETS. At least their far greater consistency gives you a fighting chance of success, without breaking the bank!

Ultimately, these issues are the main reason why I avoid building some of these pedals.

[traktop]

My wampler 65 is on loan as well. I lent it to the other guitarist in my band that has a black face twin and sounded more transparent than played on my hiwatt dr-103. I will take a look to the trimmer resistance next week and will let you know, but I think that I swap the 100 ohms resistor that comes right after Vcc by a trimmer as well, (kind of a general electricity faucet...), then I did a fine tune to the transistors with more trimmers, (I seem to remember that I didn´t use a drain trimmer with Q4, just used the 5,6k original resistor).
Cheers, Gilberto

[traktop]

I see... I just thought that I could match gain and sound characteristics of the original pedal transistors by matching transistor drain voltages, but it seems that there is more stuff involved.
Thanks for the explanation.

[MAO]

I got my '65 back today. Here are the trimmer (drain resistors) measurements.

Q1 5k2
Q2 6k
Q3 5k3
Q4 5k3

So I got lucky they are not to far off the stock 5k6 drain resistor values.