Issue adding buffer to Boss HM-2 clone - please help

[themachinerages]

Hey all,

I have a high-pitch squeal / oscillation on my Boss HM-2 clone on the last 25% of the volume pot sweep.

http://2.bp.blogspot.com/-dMh-yFDJ23I/U4PQZhso-SI/AAAAAAAAHfI/PayAmAfwZ90/s1600/Boss+Heavy+Metal+HM2+with+mids+control.png

Thanks to a suggestion from Reddit, I tested with a buffer before the pedal and the squeal disappeared. I had the buffer circuit attached into my test box and sent the output into the HM-2 clone. The two were daisy chained via the same power supply and connected via patch cable.

Next I tried adding the buffer to the pedal. I swapped the input of the HM-2 on the 3PDT with the input to the buffer. I took the output of the buffer and soldered to the input of the HM-2 circuit. I soldered the 9V and ground for the buffer to the DC jack.

But the squeal is still there! I removed the buffer from the circuit and back to the test box and the squeal disappears again.

I am using the TagboardEffects off-board wiring style if that could affect anything.

Any help is greatly appreciated! I am so confused

[Ciaran Haslett]

Dimi had success here with a Carvin Legacy.

You may also try using shielded cable for all your Inputs/Outputs, keeping the wires short and away from the circuit etc.  This can help with oscillation.  Good luck

[Travis]

I have an original HM-2 and also built a clone. Both of them have the same squeal with all knobs maxed out, but I have noticed that this is feedback which will change as you move around the room, not an oscillation like a Fuzz Factory.

Try moving your guitar around or move around the room and see if it's actually just feedback. This is an extremely high gain circuit so with the knobs maxed you have enough gain to get constant feedback which sounds like oscillation

[themachinerages]

Thanks for the response!

@Travis -  I have an original HM-2 as well and another clone I built and neither have this feedback / oscillation issue. Moving the guitar around the room doesn't affect the squeal.

@Ciaran Haslett - Maybe I'll try that one instead but I am mostly wondering why the buffer would stop the squeal when hooked up to my test box but not when I add it to the enclosure. The signal path is no different as far as I know.

[Ciaran Haslett]

Don't discount your wire dressing.  Some high gain circuits can bleed signal back into its input if the wiring is messy/unshielded.  This could well explain your problem, cramming 2 separate boards into one enclosure.

[themachinerages]

@Ciaran Haslett - Thanks for the reply! I will try this out tonight. Would using shielded wire for the input of the buffer be enough? If not, what other wires should I replace with a shielded cable?

I am going to try using a piece of standard instrument cable

ie: http://www.parts-express.com/Data/Default/Images/Catalog/Original/100-297_HR_0.jpg

I hope this is sufficient

Thanks!

[Ciaran Haslett]

I'm afraid it's a case of trial and error man.  For safety I'd probably just shield every input/output wire.  Remember to ground your shielded wires only at one end though.  Doesn't matter which end.

[themachinerages]

@Ciaran Haslett - Thank you for all the advice! I'll report back once I've had a chance to try this out

[lasermonkey]

Hmm, I had squealing issues with an HM-2 build (with the controls maxed) but it was cured by sticking a Klon buffer in front, on a separate board. I didn't need shielded cable.