Microhponic sounding noise and a lot of feedback when playing BSIAB2

[davidjnichols]

I'm having a ton of high, microphonic sounding feedback when playing my BSIAB2.  I just finished building it the other day.  It's built exactly like GGG.  The only mod was the added contour knob.  The only time I don't hear it is when the gain knob is at like 15%.  I've tried messing with the bias trimpot to no avail.  Would swapping out the J201's in Q3 and Q4 help?  I understand those are kind of high noise, and the pedal has a ton of gain, so I wouldn't mind losing some by going to a lower gain transistor if it would take away the microphonic sound when I play.  I know there have been a lot of threads about noisy and squealing BSIABs, but I was unable to find a definitive solution to the microphonic sound.  It also causes my Les Paul to feedback like mad the second I take my hand off the strings, but I assume that's just because it's such a high gain pedal.

I know I've been posting a lot about my pedal issues and problems lately.  I'm not trying to be a mooch and only take and not give back. I just don't have a ton of electronics knowledge yet.  You guys are incredibly helpful and your collective knowledge is stunning. Thanks for being awesome!

[aron]

This sounds like microphonic pickup feedback. Are these single coils? Does it happen with the les Paul? If not, then you just have to back down the gain, turn the treble down or maybe even pot the pickups. I hate that microphonic feedback too! Darn tele and mustang! :-)

[deadastronaut]

hi david,

you could try 2n5457's...for a bit lower gain.

i assume the input is shielded?...

[davidjnichols]

It does sound like microphonic pickup feedback!  But I think it's something else.  It acts the same on all my guitars (humbuckers, single coil/p90).  The input is shielded, yes.  I have some 2n5457's laying around, so I'll swap out the transistors this afternoon and see if it helps.  Thanks!

[Paul Marossy]

This sounds like microphonic pickup feedback.

+1

What kind of power supply are you using? Does it do this when operated with a battery?

[davidjnichols]

This sounds like microphonic pickup feedback.

+1

What kind of power supply are you using? Does it do this when operated with a battery?

I usually use a 1-spot daisy chain, but it acts the same with the daisy chain and the 9v battery.

[Paul Marossy]

This sounds like microphonic pickup feedback.

+1

What kind of power supply are you using? Does it do this when operated with a battery?

I usually use a 1-spot daisy chain, but it acts the same with the daisy chain and the 9v battery.

So that rules out the power supply as being a possible cause. What amp are you using? Maybe it feeds back very easily.

[davidjnichols]

This sounds like microphonic pickup feedback.

+1

What kind of power supply are you using? Does it do this when operated with a battery?

I usually use a 1-spot daisy chain, but it acts the same with the daisy chain and the 9v battery.

So that rules out the power supply as being a possible cause. What amp are you using? Maybe it feeds back very easily.

I'm using a Peavy Classic 50.  I have never had issues with feedback from the amp.  I usually have to work to get the amp to feedback.  I have two identical Classic 50's. I tried the pedal on both and got the same results.

[Paul Marossy]

Check the lead dress in your pedal then. Do you have long wires running in parallel? Sometimes that can cause a pedal to squeal like a pig going to the slaughter.

[aron]

> I usually have to work to get the amp to feedback.

When it does feedback, does it have the same microphonic feedback? If so, it's just too much gain - sometimes it's unavoidable.

[davidjnichols]

> I usually have to work to get the amp to feedback.

When it does feedback, does it have the same microphonic feedback? If so, it's just too much gain - sometimes it's unavoidable.

No, the feedback I get from this amp is very musical.  The feedback from the pedal is hidden under the chords and notes while I'm playing.  Almost sounds like I have a bad reverb on (but has no decay after I mute strings). 

[Paul Marossy]

the feedback I get from this amp is very musical.  The feedback from the pedal is hidden under the chords and notes while I'm playing.  Almost sounds like I have a bad reverb on (but has no decay after I mute strings).

That tells me that the pedal itself is oscillating. Could be something as simple as two wires very closely running parallel to eachother and you get a feedback loop via parasitic capacitance, can easily happen in a high gain circuit.

[aron]

It does sound like it's an internal problem. Like everyone else said, check the wires etc...

[Paul Marossy]

I remember one post at another forum I was paid to moderate for a little while where a boutique pedal guy with uber neat wiring had a squealing problem - there were a bunch of wires running parallel to make a pretty layout, but it caused problems with oscillation. I told him the same thing. He re-routed some wires and the problem went away. The funny thing is that he had no idea why it was happening!

[amptramp]

Shielded wire is your friend.  For audio frequencies, the shield should be grounded at one end only.  For RF, ground at both ends.

You don't mention what tpe of chassis you have, but cast aluminum such as the Hammond 1590 or 1550 should be best.  If you have plastic, all bets are off.

[davidjnichols]

Got slammed with life stuff this weekend, but I'm hoping to open up the BSIAB and tinker tonight or tomorrow.  Thought you guys might enjoy a pic of the finished enclosure though.  It turned out really well, especially the two 3mm red LEDs! 

[davidjnichols]

the feedback I get from this amp is very musical.  The feedback from the pedal is hidden under the chords and notes while I'm playing.  Almost sounds like I have a bad reverb on (but has no decay after I mute strings).

That tells me that the pedal itself is oscillating. Could be something as simple as two wires very closely running parallel to eachother and you get a feedback loop via parasitic capacitance, can easily happen in a high gain circuit.

I think you're on to something.  The wires aren't obnoxiously long, but they could be shortened.  They are also all coming out parallel to each other from the pots.  Very nice and neat looking but also very parallel.  I'll move them around this evening and see if that makes any changes.  Thanks!

[amptramp]

The picture explains the problem.  You are picking up the sounds of Satan calling you to join him.  Oscillation is caused by the same phenomenon that makes ghosts repeat their last day, every day, but since the oscillation is electronic, it repeats quicker, at audio speeds.

[Paul Marossy]

I think you're on to something.  The wires aren't obnoxiously long, but they could be shortened.  They are also all coming out parallel to each other from the pots.  Very nice and neat looking but also very parallel.  I'll move them around this evening and see if that makes any changes.  Thanks!

It's been my experience that as little as 1/8" of space between wires can make the difference. Yeah, it's good practice to make wires are short and direct as possible, to try and not to run long wires from different parts of the circuit in parallel, and to keep them at right angles where they have to cross over eachother.

The picture explains the problem.  You are picking up the sounds of Satan calling you to join him.  

Ha ha, I had a similar thought when I saw the pedal.  

[davidjnichols]

The picture explains the problem.  You are picking up the sounds of Satan calling you to join him.  Oscillation is caused by the same phenomenon that makes ghosts repeat their last day, every day, but since the oscillation is electronic, it repeats quicker, at audio speeds.

I literally LOLed!