Build Your Own Clone Message Board

Hello,
I purchased a two knob MKII fuzz clone several years ago and I finally got around to building it.
It works great but I am unable to get the voltage on Q3 collector down to 4.5 volts.
The lowest I can get is about 6.4 volts, and as the notes decay it sputters a slight amount, and sounds over biased.
My question is:
What resistor can I change to bring down the voltage to vintage spec ?
At the moment the range on my bias trimmer goes 6.4 volts on the low side to 9.1 on at max.

Thank you in advance.

Dan.

Could we please see photos of the build? They need to be LARGE, well-lit, well-focused shots of BOTH sides of the PCB and all of the jack and switch wiring. Otherwise, we're just guessing at potential problems....

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

ok,
I am attempting to add pics
hope this works,
based on what I found on the Fuzz central website ,
I think the resistor is the 470 ohm
Fuzz Central recommends tweaking that resistor to 1k-1.2k for more gain.
I am hoping that will also reduce the voltage going to Q3 collector ???

Thanks for your input

more pics

Feel free to increase the resistor value that you mentioned, but don't expect that to significantly change the bias voltage on the Q3 collector. Your best bet to achieve that is to increase the value of the trimpot from the stock 25K to 50K; this will give you a greater voltage range on that adjustment and should allow you to get the voltage down to the 4.5V range. If that doesn't improve the sound of the pedal, you may want to work through this process, which takes very little time with a low component count circuit like this one: viewtopic.php?f=9&t=52188

Incidentally, that's the ESV 2-Knob Bender, not the ESV Fuzz.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

ok,
Thanks for the info. I have the resistor on hand, I am thinking of lifting one side of the 470 and just tacking on the 1.2k on the underside ( for test purposes ) since I do not have a trim pot on hand.
the pedal works fine, as is I am just trying to get it to what stock specs show for Q3

I referenced the pedal as the MKII , oops ops


Again,
thank you

Dan.

I would recommend using a much higher resistance to replace the 470R. That resistor and the trimpot are in series, so your maximum combined biasing resistance is ~25.5K at the moment. The chance that an extra 0.5K - 0.7K will get your voltage down to 4.5V is very slight. I'd try a 22K resistor, giving you a max. 47K resistance.

You may find reading through this thread, discussing the same basic subject, to be useful in understanding what's going on in this part of the circuit: viewtopic.php?f=51&t=48093

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Thank you so much for the reply, and link.
I guess I am not the only one with bias troubles .

These NOS germanium transistors are notoriously variable and often cause problems like this. They sound great when running optimally, but silicon transistors are so much more stable and consistent.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Before changing the resistor value, try swapping the transistors around.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I had previously tried a different set of transistors that I had purchased from Small Bear and the pedal wouldn't work
I swapped the supplied transistors and the voltage went up to 7.4ish volts.

I have ordered a 100k trim pot , so I will patiently wait for that


thanks
Dan.