# Deofol Whistle



## yanivt (Feb 4, 2019)

Project name
Deofol, Okko Diablo Plus


Description of the problem (What does it do?  What does it _not _do?)
Pedal creates a loud high pitch whistle when engaged. Replaced the transistors and had the same result. The pitch of whistle changes when the gain/level knobs are turned but always exists. Q1 seems microphonic when knocked.

List any modifications/component substitutions
Zero mods. Used Siliconix J201 through hole from reputable source.


If applicable, did you hard-wire the 3PDT switch or use a Bypass Board?
Hand wired both switches.


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## Robert (Feb 4, 2019)

This fix seems to be working for everyone who has tried it.  

Basically you need to:

Disconnect lug 2 of the Gain pot from the PCB and insert a 39K resistor in series with the lug / PCB pad.
Add a 10nF capacitor from the gate of Q3 to ground.


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## yanivt (Feb 10, 2019)

Did the mod as recommended.
Worked like charm. GREAT sounding drive pedal. Thank you.


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## geekmacdaddy (Feb 10, 2019)

Hi *yanivt*. Directions say disconnect lug 2 of gain. You left yours connected and threw the resistor in, correct?


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## Robert (Feb 10, 2019)

It looks like he clipped it out and completed the connection with the resistor.


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## geekmacdaddy (Feb 10, 2019)

Robert said:


> It looks like he clipped it out and completed the connection with the resistor.


awesome. thank you! definitely next on the list. very impressive pedal.


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## yanivt (Feb 10, 2019)

Robert said:


> It looks like he clipped it out and completed the connection with the resistor.


Exactly!


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## fritz (May 8, 2019)

hello, I've tried the fix as mentioned above. even though whistling disappears, to me it's not a way to go, since the tone color changes too much.

could someone please post target jfet voltages for this build.

any alternative fixes? bias trimmer?


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