oscillation with boss builds

[induction]

JaviCAP wrote

So, the only difference left, is the 100k resistor from output cap to ground. NO really sure about of the role that this resistor play in the buffer

That's just a pulldown resistor. It prevents pops if the buffer is switchable, and provides a bias point (ground) for the output signal.  

[JaviCAP]

Thanks Induction :)

Yeah, Kinski, when I have to add the buffer in a pedal that it' supposed not to have it, i place it after the 3pdt, so only gets engaged when the pedal is on.

Now, I have no fucking idea why the Klon buffers stops the squeals, and the Buffer 1 is not able....

J.

[Frank_NH]

When I get the chance I'm going to breadboard the Klon buffer and will experiment with putting a capacitor in series with the 100k resistor at the output of the op amp.  I think that will do the trick.  I'll need to try different cap values to determine one that kills the squeal and doesn't roll off the high frequencies too much (start with 1 nF).  

I'd also like to try the Cornish buffer at some point...

[Surgeon]

I just finished putting a centaur (klon) buffer in my bd2 and hm2. It did stop the squeal in the bd2 but introduced a lot of noise.
It did absolutely nothing in the hm2... I used the tl071 version btw.

[IvIark]

Try using shielded wire for your input and/or output wire and see if that sorts it.  I've seen more cases of oscillation caused by crosstalk than anything else.

[Surgeon]

I'd never doubt your instinct but since the squealing goes away with a buffered pedal before the two offenders I'm thinking the problem isn't crosstalk...

[IvIark]

Possibly not but you don't know whether changes in impedance could affect cross talk, that could be what the buffer cures which would explain why a buffer hasn't worked for some people.  At the end of the day it's another common cause of oscillation and if you make allowances for it then at least you can cross that one off the list.

[Surgeon]

all good points of course!

[Beaker]

I learned the hard way about crosstalk. One of my very first builds was a Fuzz Factory in a 1590B. After testing the built up circuit out of the box, which worked perfectly, I crammed all the pots and wires into the enclosure, and fired it up. WHIIIIIIINE!. So I took it all out again, tested again - worked perfectly, put it all back in, and got the same result.

I ended up repeating this a total of SIX TIMES, before I twigged what was going on. After carefully separating my signal and power wires, I finally got it working without whining and squealing all the time.

Now I always make sure I have good separation, my board input an output wires go down one side of the box, and I use two core plus ground shielded wire to run from the footswitch to the jacks. This sits on top of the board input and output wire.

On the opposite side of the enclosure, I have my power socket, LED, and the battery snap, and all the battery, power socket and indicator LED wires run down this side.

If a power line needs to cross or pass next to a signal line, try to make sure that they cross each other at 90 degrees, rather than have them run alongside each other. Running your power lines around the very edge of your enclosure also helps a lot, as it keeps them as close to ground as possible.

[Surgeon]

Thanks beaker, great points. I do make sure of all of this as you do...

[Surgeon]

I don't know if anyone's still looking into this but I just put some shielded wire in both pedals and here are the results:

- HM2: Cured the oscillation

- BD2: Didn't do a thing. Guess it's back to a buffer with this one, although I'm not happy with the noise level so far...

[Frank_NH]

Thanks for the information, Surgeon.  That's how we learn - I didn't think that my OCD squealing was caused by lack of shielding, but I may go ahead and rewire my test rig's input and output with shielded Belden wire.  Can't hurt...

I abandoned the OCD mainly because I thought it wasn't really anything special as an overdrive...

[Surgeon]

Yeah, I figured someone might find the info useful.

I sold my original BD2 a while ago 'cause I never bonded with it (I know it's a highly-regarded pedal), to me it's way too bright and sterile... I'm really debating whether I should just gut this one and use the enclosure for something else entirely. I just built it again for the "it'll be fun to build and I'll have it again if I ever change my mind about it with time" factor.

And I know what you mean about the OCD. I haven't even built one, the soundclips never impressed me. We all have different tastes of course but I still belive that true "HOlyCRap that's an awesome pedal that will make everything sound amazing" pedals don't exist and the few that get raved about so so much are usually mostly hype... a few exceptions exist of course (the Timmy comes to mind, I do find this one pretty amazing through everything), but that's my general belief when it comes to overdrives.