Pedals squeal at high settings

[lethargytartare]

Hey folks! I'm new to building pedals, and ran into something odd.  I built two based on the materials at GeneralGuitarGadgets.com -- one is the Brown Sound in a Box and the other is the Smash Drive. In both pedals, if you turn up the dials too high, you start to get a steady squeal that get's progressively louder as you turn up further. I'd say it's feedback, but it's not related to any actual output -- I get it through headphones and amps alike. So maybe it's just feedback in the circuitry itself?

What intrigues me is that it's not just the gain or volume that causes it. The Smash Drive has a gain and three tone dials -- you can turn the tone pots down and the gain up to inhibit the feedback; or the gain down and the tone pots up. It's odd. But the other thing is that I don't see this in commercial pedals, even when jacked all the way up -- so is this a component problem, or is is that these just have a higher output range and are more susceptible to the feedback? Just looking for some debugging help.

Cheers!

ltt

[Paul Marossy]

It's perfectly normal for high gain pedals to SOMETIMES squeal, that's called oscillation. They can go into oscillation without any input at all. There are commercial effects that will do the same thing, such as a Boss Metal Zone, etc. Perhaps the commercially manufactured pedals have a little more thought put into them as to how to prevent oscillation, but things also depend greatly on your amp, how the controls are set on it, the type of room you are playing in, how microphonic your guitar pickups are, etc., etc.

[aaronkessman]

keep the leads inside your pedal as short as possible. also, try to keep high-signal output leads away from the lower amplitude signal leads. I had the same problem in my rat, but i cleaned it all up and the problem is gone.

[lethargytartare]

heh...I just recognized your name...so, you actually built the BSIAB as well.  Although you made your own layout, they should be largely the same as far as the circuit goes (I built mine JUST before it was replaced by the BSIAB 2 on generalguitargadgets.com)...can I ask if you ran into the oscillation issue?  That I get the noise through headphones confuses me.  But the other question is -- is there anything I can do to fix it?  Is there anything I should read up on that could give me a place to start (i hate just asking for help in solving it before I've done any of the work first).

Hey -- is there any chance I could talk you into sharing a photo of your completed circuit board -- I know the layout wouldn't be the same, but I think I can compare the two ok.  When I built mine I didn't have the bill of materials, so I had to guess on a couple of the cap types (I know I got the values right, but I guessed on the types) -- could that be a source of the problem?

ltt

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For a laugh, here it is:



I was excited to get it into a usable box for my guitarist to try out -- he loved the tone, so now I'm just trying to rein in the oscillation (The Oscillation Formerly Know As Squealing), and put it in a new box (which I'm gonna make out of steel stud material).

[lethargytartare]

Gotcha...I do have a lot of extra wiring in those that I should be able to clean up and arrange better.

Thanks!!

keep the leads inside your pedal as short as possible. also, try to keep high-signal output leads away from the lower amplitude signal leads. I had the same problem in my rat, but i cleaned it all up and the problem is gone.

[Paul Marossy]

The length of the wires - that's a good point that I forgot to mention, partly because it has never been a problem for me personally. I don't have any squealing at all with my BSIAB. Sorry, but taking out the PCB to take a picture of it would be a real PITA.

Your headphones must be microphonic or something...  

[lethargytartare]

n/p  I should really neaten up the wiring before anything else...

[Paul Marossy]

I should really neaten up the wiring before anything else

There's a good chance that will fix your problem.

[Joe Davisson]

Try putting a large (100uF) cap across the battery leads.

[Paul Marossy]

Try putting a large (100uF) cap across the battery leads.

That's a good thing to try as well. Although, isn't that approach usually used in Fuzz Faces and similar circuits to lower the battery impedance in order to prevent motorboating? I have seen that on things like the Black Cat OD-1 as well.

[col]

Exactly the same thing happened on my foxy lady. I will try shortening the leads. As soon as you hit the strings the screeching stops and then builds up once a note dies away (which takes forever with this pedal). The pedal sound so good I always use itlive but I have to be very careful with the screeching to prevent it becoming noticable in a live context. It sounds very similar to feedback but is produced even when a guitar is not plugged in and dies down slightly once one is,

Col

[aaronkessman]

yup. thats exactly what happened with mine. i just tidied it up a bit, not even TOO much, but it was enough.

[Davide]

I'm fighting again a strange oscillation in my HMP.. i can make it oscillate not only with some freq knob's regolations.. it oscillates also if i turn my guitar volume knob down... only at max or min i dont have problems... how can it be possible ?

[lethargytartare]

Sorry to have to ask -- by "across the battery leads" do you mean just wherever the two ends of the battery snap leads are connected?  I have one on my board (the ground) and one connects to the DC jack (red) -- can I just bridge those two points with the cap?

I dramatically neatened up the pedal, and the oscillating may have improved, but I was still getting it at high levels -- although now I don't get it when I'm just playing directly through headphones.

I saw one guy used shielded wires for the long runs between the switch and the jacks -- does that help?

Comments and suggestions greatly appreciated!!

ltt

Try putting a large (100uF) cap across the battery leads.

[lethargytartare]

and for the record, I just noticed that the BSIAB II description specifically notes that the ver 1 had oscillation problems, so I'm gonna try this cap and call it a day.  The thing has so much output that I think I'll just deal with keeping it within certain limits.

[Paul Marossy]

Hmm... I really have never had any oscillation problems with the BSIAB I. I suppose whatt might matter to some degree is the variability of the JFETs themselves. I must have a good combination of them going or something...

[lethargytartare]

It's been a while, but I figured I should put up the final notes on my original question.

For the Smash Drive, the suggestions from here were dead-on -- in a box with nice short leads, the oscillation disappeared.  And it's a great pedal.

For the BSIAB, nothing cured it -- the cap, short leads, etc.  So it's just a ball-buster now -- sounds fantastic, but you just have to get creative with the settings, and maybe with a booster or eq elswhere in the chain to get more of its potential out.

Since building these two, I've also been better about starting with shorter leads...haven't had any such incidental problems again.

Thanks again for the help guys!

ltt

[Samuel]

This keeps coming up and I can't help but feel that the standard switches we use for everything are a big part of the problem - no matter how clean your wiring is, no matter how much shielding you use along its length, at the switch you are bringing the input lead within a couple millimeters of the output lead, and with no shielding...

[guile]

This keeps coming up and I can't help but feel that the standard switches we use for everything are a big part of the problem - no matter how clean your wiring is, no matter how much shielding you use along its length, at the switch you are bringing the input lead within a couple millimeters of the output lead, and with no shielding...

I second that and confirm. My dual Timmy works fine without the usual 3pdt switches.

[antonis]

It's just a necro or it took you 8 years to realize it..??