Fuzzdog Wrecktifier (Wampler Triple Wreck clone) Whistles At High Gain Settings

[rmjlmartin]

Hi everyone, and thanks in advance for your help.

I built a Fuzzdog Wrecktifier pcb, which is a clone of the Wampler Triple Wreck. I built it as the 9v only version (without the charge pump), and with the Boner Boost instead of the original boost, which I've heard described as "Tubescreamer-style". The build document is available here- http://pedalparts.co.uk/docs/Wrecktifier-v2Black.pdf

It mostly works and sounds great. I've attached a gut shot.

The problem it has is that, with the treble above 12:00, and the gain above about 3:30-4:00, it makes this weird whistle. you don't have to actually be playing anything for it to do it, just simply turn it on and turn the gain and treble up. I think I can still hear something faintly with the treble turned down, so I'm guessing that the treble control is filtering off the whistle as you turn it down.

I've gone over the circuit with an audio probe, and the first place it can be heard plainly in the circuit is pin 7 of IC1, but I think I can hear something faintly on pins 1 and 2. The voltages at IC1 are-
pins 1, 2, 6, 7- 4.36v
pins 3, 5- 2.96v
pin 4- 0
pin 8- 8.6v

I've tried swapping all of the op amps, but it didn't make any difference.

Does anyone have any suggestions of where I should start? To be honest, I'll probably never  actually turn the gain up that high, but it'll bug me if I don't figure it out. lol Someone suggested changing the value of the resistor that controls the maximum amount of gain so that it just won't ever get turned up that high. That might well be an acceptable option. Which resistor would that be?

Thanks!

[zombie_rock123]

This could be completely wrong but I seem to recall having something buffered infront of them quiets them a little, have you got a buffer to hand at all?

[jubal81]

I remember the same thing, though I never built one. Circuit opens with a buffer, though.

One thing I notice is the Bias resistors, like R3, look kinda low at 470K. Not sure how much current that opamp needs, but upping those to 1m or 2m2 could help.

[thesmokingman]

consider shielded wire for all signal wiring to and from the daughterboard

[rmjlmartin]

Thanks! That does help.

I'm a little embarrassed to admit that I discovered that I missed C33, since it's in the middle of the list between the original boost parts and the charge pump parts, both of which I was leaving out. I added it in, and went ahead and added the charge pump, too, to see if it made a difference, and neither changed anything. It still whistles, at both 9v and 18v.

But, I grabbed a random Boss pedal and put it on front of the Wrecktifier, and the whistle is gone.

So the buffer obviously made a difference.

Any thoughts as to why? Or where exactly the whistle is coming from? I'm somewhat new at diy pedals, and I'm trying to learn as much as I can about how they work and how to deal with problems like this.

Is there an easy way to add an input buffer to the pedal? Or will I just have to make sure I run a buffered pedal in front of it if I plan on diming the gain?

[Willybomb]

I don't know much about why a buffer works, but in my experience sticking a buffer in front of a high gain pedal fixes it 9/10 times.  I've done this with a Seventh Heaven, Brown Betty, BE-OD, and a number of others I can't recall.  It didn't work with my Boneyard, but putting a ~160k resistor to ground from the footswitch effect in lug fixed that one.

[rmjlmartin]

Just an update here-

I now have access to a real Triple Wreck, and it makes the exact same whistle at the same settings. So I guess there's nothing wrong with my build. I also tried several other guitars with it, including one with EMG's, and the EMG-loaded guitar is the only one that doesn't make the whistle without a pedal with a buffer in front of the Triple Wreck/Wrecktifier. I assume that's because the active pickups probably have a built-in buffer?

Which leaves me with the question- Is there an easy way to add a buffer inside the pedal? I doubt I'll worry about it on this one, since the original does it, too, and I'll probably never turn it up that high anyway, but it would be nice to know for future reference.

And, if this thread doesn't go any further, thanks to all of you that took the time to offer your help. I really appreciate it.

[thesmokingman]

for buffered bypass, place the buffer between the input jack and the footswitch daughterboard's input. if you want to keep the pedal true bypass, place the buffer between the daughterboard's output and the motherboard's input.