Request for help debugging Black 65 - with recommended debug info list provided

[m4j0rbumm3r]

All right, my job here is to be candid, clear and neat. I realise that your time is valuable. I've run out of ideas after many attempts to find the problem on several days, with ample clearing of my head in between.
Here goes:

2.Name of the circuit =
Wampler Black 65

3.Source of the circuit (URL of schematic or project) =
Vero from: http://tagboardeffects.blogspot.com/2012/08/wampler-black-65.html
Edit: schematic http://www.newtone-online.nl/forum/index.php?action=dlattach;topic=6816.0;attach=10352;image

I based my build on the vero.

1.What does it do, not do, and sound like?
It produces the guitar sound, but the volume is very low. All controls (switches and pots) seem to do what they are supposed to do. With all pots maxed out and the pedal in boost mode, the gain is around unity as compared to bypass. With boost disabled, the guitar signal is extremely low, although I was able to hear it with my amp turned fully up. With the effect on, the sound produced is nasal and unpleasant, with little (but some) break-up. The tone controls work. Turning treble all the way down and bass all the way up makes for a somewhat more tonally balanced output as compared to bypass, although this is clearly not normal for this pedal. If anything, it is supposed to sound fat, with little use for the higher bass settings.


4.Any modifications to the circuit? Y or N
Yes, not to the board/vero, but to the boost switch and gain control wiring:
I replaced the original 2PDT toggle by a 4PDT stomp-switch. Half of this 4PDT is wired as suggested in Mark's vero, the other half is wired to switch between gain pots. That is, I have 'cloned' the original gain pot, and made the footswitch select between the two. The wires from the board labeled 'to gain 2' and 'to gain 3' are wired to the middle lugs of the 4PDT switch. Each of the two gain pots has its lug 2 and lug 3 connected to a side of the 4PDT switch, such that the board is either connected to lug 2 and 3 of the 'clean gain pot'*, or to lug 2 and 3 of the 'boost gain pot'. Lugs 1 of both gain pots are wired to the board where it is labeled 'to gain 1', with no switch in between.

* although I talk of 'clean' and 'boost', the clean mode is not supposed to be all that clean, but rather to have an edge; a pushed sound.

Visually, it would be something like this:

Lugs of the 4PDT:

[10 11 12]
[  7  8  9 ]
[  4  5  6 ]
[  1  2  3 ]

connected to:
1: ground, as suggested in vero
2: board, as suggested in vero
3: edit: input and 4, as suggested in vero
4: edit: input and 3, as suggested in vero
5: board, as suggested in vero
6: board, as suggested in vero
7: clean gain pot lug 3
8: where gain 3 should connect on the board according to vero
9: boost gain pot lug 3
10: clean gain pot lug 2
11: where gain 2 should connect on the board according to vero
12: boost gain pot lug 2

My simple mod seems to work. The switch does switch between clean and boost. Also, the gain pots seem to do what they are supposed to do, i.e. only one works at any time, and it then does control gain. The effect as a whole just lacks volume and low end.

5.Any parts substitutions? If yes, list them.
Yes, the 5k6 resistors that connect directly to the transistor drains are replaced by 25K trimpots so I can adjust the bias. Many people report that drain voltages should be between 4 and 5 Volts, with 4 V being dirtier and 5 V being cleaner sounding.

6.Positive ground to negative ground conversion? Y or N
No

7.Measure the following:
Voltage at the circuit board end of the red lead = 8.61 V (this is after a polarity protection diode which creates a drop from the original 9.19V)
Voltage at the circuit board end of the black lead = 0.0 V

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Edit: oops, I reported S for G and G for S earlier, changed that now:

Q1
G = 0.00 V
S = 0.13 V
D = 5.04 V  which is as low as I can get it with the 25K trimpot

Q2
G = 0.00 V
S = 0.31 V
D = 4.13 V  

Q3
G = 0.00 V
S = 0.31 V
D = 4.01 V  

Q4
G = 0.00 V
S = 0.27 V
D = 4.13 V  

If there is any other voltage that may provide insight, I'd obviously be happy to measure and report it.

Finally, a summary of things I have tried over the past week:
- Biased the JFETs as close to recommended voltages as I could get them
- Checked and rechecked my component values against the vero
- Checked that the big (electrolytic) caps are put in the right way
- Checked correct functioning of the switches
- Checked, rechecked and re-rechecked the location of all components, track cuts and connections on the board against the vero
- Visually inspected all solder joints, and reheated a few that looked less than perfect, to no avail
- Looked hard for any bridges or shorts, didn't find any.
- Swapped around the J201s in position Q1 and Q4, which didn't produce a better sound
- Edit: I also measured max resistance of all the pots to make sure I didn't swap any; they matched the vero instructions/comments.

To anyone who has read this far, thanks for your time and effort!

[pappasmurfsharem]

 I don't think a 4pdt can do what you are wanting

Since 2poles are dedicated to the boost.  would need a separate 3pdt to switch the gain pots since they are wired like a voltage divider (requires 3 lugs) not a variable resistor(requires 2 lugs)

A 4pdt should look like this with all the lugs horizontal

1-4-7-10
2-5-8-11
3-6-9-12

Since lugs 1-6 are used to switch boost

To switch the gain pot you would need a 3pdt

Note: all lugs horizontal

1-4-7
2-5-8
3-6-9

From board:
Gain 1 to lug 2
Gain 2 to lug 5
Gain 3 to lug 8

From pots:
Pot A1 to lug 1
Pot A2 to lug 4
Pot A3 to lug 7

Pot B1 to lug 3
Pot B2 to lug 6
Pot B3 to lug 9

The way you have stated the 4pdt is wired your gain 1 connections aren't connected to anything


EdiT:
Just reread your post looks like you have lugs 1 connected to the board directly.
Hmmm......

Have you tried disconnecting the gain pots from the 4 pole and wiring 1 pot up as per the layout?

EdiT 2:

You sat you have switch 3 and 4 wired together AND to the board?

Where on the board is it wired, I don't see anywhere that they should connect to the board directly just the input

[m4j0rbumm3r]

Originally, gain lug 1 is supposed to connect to the board, where it goes to only a 68K and then to ground. That 68k is just there to prevent zero gain with the pot turned down, I think. I figured I could just as well hook up two gain pots' lug 1 to that same 68K which goes to ground. Connecting them both to ground should also work I guess, though perhaps changing the gain range slightly.

It is true that my boost switch does not cut the connection to lug 1 of the disabled gain pot. I thought it shouldn't matter, as there is 'nowhere for the signal to go' in that direction. That is, the disabled gain pot is a dead end; its lugs 2 and 3 connect to nothing at the foot-switch. However, this is certainly not the time for me to act like mr. smarty pants, as I'm the one staring at a fairly simple circuit that I can't get to work.

I'll try what you suggested and take out one of the pots, reverting to the verified original. If it doesn't help, I can continue debugging the original and put my mod back in once I get it to sound good.

Thanks for helping out.

[pappasmurfsharem]

I noticed after I reread from what I can tell your pot wiring should be fine.

Check my second EdiT though.

Also I'm confused why have them linked anyway surely it would be more beneficial to have a second switch abreast so you can have your two gain channels with the one and a separate boost switch

[m4j0rbumm3r]

EdiT 2:

You sat you have switch 3 and 4 wired together AND to the board?

Where on the board is it wired, I don't see anywhere that they should connect to the board directly just the input

I believe that is what was meant in the instructions at the bottom of the vero.

As I understand it, the boost switch is meant to insert Q1 and its housekeeping in front of the rest (Q2 through Q4). Boost disabled means input signal goes straight to Q2 and onwards.

When the boost is enabled, input to sw3 connects to sw2, and signal enters the board where wire to sw2 hooks up. Also, sw5 and sw6 are connected in this throw of the switch. This is to route the output of Q1 in front of Q2 and the rest of the circuit. Although input signal is also on sw4, this is the unconnected side of the switch in this throw.

When boost is disabled (the other throw of the switch), input signal on sw3 is unconnected, but input signal on sw4 now connects to sw5, which leads it to Q2 and onwards.

Does that make any sense?

[pappasmurfsharem]

Yes.that's what it is supposed to do.

You just said "board and sw3 and 4" which itself isn't correct it ends up going to the board through either sw2 or sw5 just the wording was confusing as sw3 and sw4 don't directly connect to the board.

I'm out of ideas at this point however, maybe verify all resistors color codes to the values required

[m4j0rbumm3r]

Also I'm confused why have them linked anyway surely it would be more beneficial to have a second switch abreast so you can have your two gain channels with the one and a separate boost switch

This is not a bad idea, but I suppose that mod would require three footswitches on a pedal that originally has only one footswitch plus a toggle.

What I had in mind were two things really:
A) I can fit two stomp switches on a modest size enclosure, so I won't have to flip the boost switch by hand. This I know has been done before and those DIY-ers seemed very happy with it.
B) Why not add a gain control so I can set the gains for the boost enabled and disabled modes independently? I might want a fairly low gain tone without boost and then switch to a max-gain sound for a solo. At least I'd get the option. In the original version, I'd have to first flip the boost toggle and then change the gain pot, play my lick, then again change gain and flip back into boost disabled. It keeps the pedal small, but it's not the most versatile way if your using it on stage.

Note that the normal mode (which I misnamed 'clean' in the above) is supposed to have nice break-up at higher gain settings.

Edit: I've corrected my first post regarding the switch wiring. It was nonsense to write sw3 and sw4 connect to board. Sorry about that and thanks for pointing out the mistake.

[m4j0rbumm3r]

At last, I fixed it! Man, it sounds sweet now 

After a good night's sleep I went over all the solder joints again. Found a joint of a 0.1uF cap in the signal path (C5 in the schematic) that looked somewhat suspicious. Resoldered it, et voila! This really was a pain to find with all the funny JFET bias and gain pot mod stuff distracting me from the basics. Also, the cap lead apparently wasn't entirely disconnected, as the pedal did produce sound - just horrible sound - before the fix. It was a sneakey high resistance solder joint that didn't look all that bad IMO. Well, just goes to show what poor workmanship can result in.

One more good thing to report: my dual gain pot mod works like a charm. My build has six knobs (level, gain1, gain2, treble, mids, bass) and two footswitches (bypass and boost). For my purposes, this is the perfect compromise between size & complexity on one hand, and tweakability / flexibility on the other. I can dial in the right amount of gain for the non-boosted tone, do the same for the boosted tone, and then stomp between these favorite settings during playing. 

Papasmurfsharem, thanks for your time and effort in helping me debug this thing. It's much appreciated.

[pappasmurfsharem]

No worries just wish I could have been more useful