One Knob Fuzz v2 – What to do with the A/B pads?

[Anonymous]

After having completed a Sunn T (with help from folks on this forum), I went and ordered my second kit – the One Knob Fuzz v2 (Colorsound). Per the description on this site, the PCB has the A/B pads “for further modification.”

Before I get too far in putting it together, I was curious if there are any examples of anyone doing something interesting with the A/B pads.  I understand there’s nothing that <span style=”text-decoration: underline;”>needs</span> to be done with the A/B pads, but I like to tinker with stuff (usually to my own detriment).

I’ve searched all over the interwebs, and this forum, but haven’t found any examples of how to make use of the A/B pads.

In looking at the schematic, it seems like the A/B pads would, if jumpered, bypass C3 (220n) just before the volume pot:

Anyone know what purpose C3 serves?  Wasn’t sure if one could add a switch between A/B and have different capacitors selectable for C3, and what different values would do to the signal.   Or if C3 just plays some sort of role with respect to something like impedance, and has no impact on the audio signal.  In which case, I’d guess the A/B pad is just an easy way to add a different circuit into the board.

In any event, would love to hear what folks think could be done.

[Anonymous]

C3 serves an important purpose.  It blocks DC voltage from reaching the VOL pot.  The stock value of 220n is high enough to pass all guitar frequencies.

You missed the BUILD NOTES that described inserting a DPDT “TIGHT” switch between A and B.  Install a 22n cap on one side of the switch and remove the 220n cap from C3 and install it on the other side of the DPDT switch.  When the 22n cap is selected, some of the bass frequencies will be filtered out giving a “tighter” tone.  Enjoy!

[Anonymous]

Thanks, Wilkie.  I now remember seeing the provision about a “Tight” switch and being confused as to what it was, and so promptly forgot about it!  : )

Having built my own speakers and crossovers, you’d think I’d have better understood how capacitors filter audio signals, but I guess the values are so different I didn’t make the connection.

As I use down-tuned guitars (C-standard) and would like to use the pedal for Bass as well, I’m thinking I’ll just leave C3 at 220n.  Unless folks think that filtering out more of the Bass signal is good for Bass – though that seems counterintuitive.

[Anonymous]

BTW, I’d greatly appreciate anyone pointing me to a schematic how the “Tight” switch would be wired.

I personally find understanding these switches to be challenging.

In the “Beginners Guide to Components” document, there is a link to a posting on switches:

http://www.guitarpcb.com/apps/forums/topics/show/12495344-understanding-switches
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But the link seems to be broken.

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[Billy]

Use a DPDT on/on switch Bill don’t populate C3

Wire the switch centre lugs to the A and B pads and your two capacitors to each of the two outer switch lugs like this

Regarding the link you’d need to insert .webs into the URL

http://www.guitarpcb.webs.com/blah/blah/blah that takes you to the old site forums etc, I don’t know if it’s still being hosted though

[Anonymous]

Billy beat me to it!  Here’s my drawing.

[Anonymous]

Bill and Wilkie, thank you both!!!  The switch wiring certainly looks simple enough, not sure why I couldn’t visualize it. : )

[Author]

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