Carlsbro 2 Knob Fuzz

[anders]

Here is a verified layout of a rare bird, Carlsboro 2 Knob Fuzz. Not much info on this one and it's not a tonebender variant.



I don't have any OC71 transistors so auditioned several others. AC128 were very hissy with an unpleasant decay, SFT306 were a bit better but still some gating. Tried some russian trannies  like MP16B and MP21D - Viola!. Great stable fuzz sound with long sustain. The Attack pot is more like a tone or presence control. Counter clockwise it is quite comressed and bordering to Big Muff territory and clockwise it opens up, gets louder and brings in higher mids.



I did an NPN version as well, and with MP38's it rips.

Cheers

[Travis]

I just drew a layout for this last week too!! Pretty interesting circuit.

The OC71 tends to be low hfe. You're probably looking at hfe around 40-50 here

[anders]

Interesting indeed. Yes, I settled on MP16B for all three slots with Hfe 50-60, so low gain trannies with low leakage seems to work best here.

Would love to see your layout at the main site soon, this is a forgotten gem IMHO.

[kelnz]

Late to the conversation ....
I just built this with some low gain Matsushita 2SA102BA germaniums. Super happy with the result, it works ridiculous well with my set up.
For what it’s worth I took the following measurements
Q1; 42hfe, 100uA leakage, collector voltage -1.03V
Q2; 44hfe, 100uA leakage, collector voltage -4.24V
Q3; 44hfe, 40uA leakage, collector voltage -1.017V
Battery measurement 9.2Vdc
As I have mentioned the 2SA102’s; If buying off ebay confirm the complete part number. I bought 10 x 2SA102 that turned out to be 2SA102AA's with an average gain in the teens i.e hfe 13 to 24! You want 2SA102BA’s as this is the correct gain sub class for this effect.

[Addy Bart]

An NPN layout would be great if you have it to share.

[HamishR]

I just happened to have done one from Anders' excellent layout above!  I have some MP38s I might try with this.  Not verified yet.

Or of course you can just use Anders', as it has been verified.  All you do is reverse the polarity of the diode and the electrolytic caps.  That might be safer!

[Addy Bart]

Awesome, thanks! I’ve also got some low gain MP38s waiting to be used somewhere, so this should do nicely.

[G.G.]

I built an NPN version of Anders' layout yesterday and it sounds great! I used GT404D for Q1 & Q2, and an MP38A for Q3. Three GT404s sounded really good at some settings but the decay was a little spitty and they sounded slightly mis-biased. Three MP38As also sounded good overall but more saturated and compressed. The MP38A in Q3 cleaned up the decay but kept the presence I liked in the GT404s. Thanks for the layout!

[cjonesplay]

The layout by HamishR has a mistake on the link/cut section. The holes/links are not right. I got halfway through building before I even noticed it, hope it doesn't happen to someone else

[HamishR]

Sorry - only just noticed this!  Here is a corrected layout.  D'oh!

[Mulekicker]

I think you need a wire for volume 1 going to q3 emitter. The row just above the 9v connection.

[Mulekicker]

Yep. Built it with the vol 1 wire (won't work without it). Verified and it sounds great! Used mn38a's with hfe in the mid 50's for all 3. Thanks!