Boneyard grounding issue?

[CK1]

Hey all,

I have a very nice Boneyard pedal here that I'm loving so far, but there is this crazy high-pitched squeal going on any time I run medium to high gain (or use hot pickups).  

I saw this thread, and my issue seems to be similar, though I haven't tried it with active pickups yet:  http://www.madbeanpedals.com/forum/index.php?topic=2290.0

I think I've at least narrowed it to the input jack in some capacity.  When it's on the highest gain setting, it squeals like a 12 year old girl at a Justin Bieber concert.  If I reach inside the pedal and touch the tip of the input cable, about half the volume of the squeal disappears.  If I do that AND touch the part of the 1/4" plug that's outside the enclosure at the same time, it goes away entirely.  Literally nothing happens when I do the same to the output jack.  

Any ideas, mates?

[nzCdog]

rofl...  

When it's on the highest gain setting, it squeals like 12 year old girl at a Justin Bieber concert.

sig'd!

[CK1]

rofl...  

When it's on the highest gain setting, it squeals like 12 year old girl at a Justin Bieber concert.

sig'd!

[k.rock!]

How about grounding the input jack? I know it should be grounding with your case, but maybe hooking up a wire from input sleeve to output sleeve might help? Im thinking the issue is ground related and there's a possibilty that somehow ur input is not being grounded properly...


-Kaleb

[madbean]

You might want to consider using shielded wire. It's an awfully high gain pedal, and shielded wire on the input and output may help reduce or eliminate the whine. Also, using a smaller value of gain pot will reduce unwanted oscillation. What values did you start with?

[CK1]

The pots are the same values as the MB document, so hopefully there's not an issue there.

I attempted to connect the input and output sleeves with alligator clips just to see, and it did nothing.

I'm actually having what appears to be the exact same issue 'audioware' is having as listed in this thread:
http://www.madbeanpedals.com/forum/index.php?topic=2290.0

As per his suggestion, I tried using an active pickup guitar and the squeal disappeared completely (even with all buttons on and every knob all the way up)!  He mentioned trying shielded cable and it not helping, so I would guess that I'm in the same boat.  So, now I'm really stumped...

[madbean]

Okay, that seems to be an input impedance issue then. Try raising R1 to 2M2 or 3M3 to see if it solves the issue with single coils.

[madbean]

Or--use a socket and try it with no pulldown resistor at all. That could be it.

[madbean]

Check that---hold on. Try this: socket R1 but leave it off. Now, take a 1k resistor and solder a wire to one lead. Clip the other lead short and stick that in the R1 hole (the one above the input). Now, disconnect the input wire from your 3PDT and instead hook the other end of the new wire to it. What you've done is eliminate the pulldown and substituted a 1k series resistor instead.

See if that works. If it does, then I will explain why

Sorry for the multiple messages.

[CK1]

Thanks for the reply, MB.  I didn't have my soldering iron at my computer (I've been checking the pedal here), but I did have a bag of components handy, so I just started trying things with R1.

After a few attempts, it seems that if I put a 10k resistor in parallel with the 1M resistor that's already in R1, that the whine goes away entirely.  I didn't have a free hand to strum my guitar to see if the frequency response changed, but it seems that R1 is the issue. 

So now the question is, what's the best course of action?  Since a 1M and a 10k in parallel are almost 10k anyway, shall I just swap that resistor?  Or should I do your last suggestion instead?

[madbean]

Did you try it with no resistor? IIRC, I added R1 as an option, but looking back at the stock schematic there is a 1k series resistor at the input which I omitted. That 1k forms a low pass filter with the 330pF to ground, which might reduce or eliminate the high pitch whine.

It could be that no pulldown was used in the stock version to instead allow the Vb bias resistor (also 1M) to set the input impedance of the input gain stage. The added pulldown actually reduces the overall input impedance because it is parallel to the biasing resistor (since Vb is virtual ground). That's why I thought raising the overall value of R1 would bring it closer to the stock 1M input impedance.

Somewhere in here lies the solution. My guess is make into the stock unit by eliminating the pulldown and adding the 1k series resistor.


All of this was not a concern when I initially worked up the project, mainly because I had suggested using a 470R resistor off the inverted input of stage one instead of 47R and I suggested lower value pots. However, after releasing it some folks had mentioned that their builds were fizzy sounding at that 47R worked a lot better for them. So, given that the change from 470R to 47R increases the overall gain of that stage GREATLY, it isn't surprising that some other issues like this have come up.

Frankly, I don't understand how the Plexitone does so much gain without more noise and oscillation problems. The gain is so ridiculous I think it would cause a lot of problems with different set-ups. Maybe that's what we are seeing here...or maybe most people use humbuckers with this thing. I really need to get a guitar with humbuckers! It's also possible that the use of the charge pump instead of an actual transformer like the Plexi might be exacerbating the problem. But, the only way to test that is to completely remove the charge pump portion and try the thing with two batteries to create the +/-9v this thing uses to simulate the transformer's role more accurately.

Anyway, sorry for the rambling...I'm kinda jacked up on goofballs for a migraine today, ha ha.

[CK1]

You're a trooper for replying to this while you have a migraine!

I didn't try it with no resistor yet because I don't have that one socketed and I didn't have my iron handy at the time.  I'm going to pull it this evening and see what I get (no extra sockets lying around, though, so I guess I'll just have to do a jumper wire). 

I'll try that first and see what I get, but I plan to also add the 1k resistor as well.  Is the only acceptable way to add it to do what you previously suggested?

[CK1]

Just to clarify, you mean attach the other end of the 1k resistor wire to the 3PDT, right?  Since R1 is socketed (at least theoretically in my case), everything is still connected, then.  Just making sure I'm understanding.

[madbean]

That's right. The 1k essentially replaces your input wire (for experimentation purposes). R1 is connected between the input and ground.

[CK1]

Removed R1 completely, but still got massive squealing. Then, tried removing the input line to the 3PDT and running a 1k resistor there from the first connecting point of R1, and no dice, still squealing.  

Going back to my first attempt, I started changing resistor values for R1 just to see what I'd get.  1K alone worked great, except I lost at least 50% of my input level.  I just tried running a 10K and 1M in parallel, and that works as before, with maybe 85-90% of gain level (and some loss of highs).  

I'm going to experiment some more and see if I can come up with something, but feel free to chime in if you have any other ideas.