Tactical Fuzz - Not Cleaning Up, Trim Pot Issue?

[apierz]

I recently finished a build of the Tactical Fuzz. It sounds great as a fuzz, but it doesn't clean up no matter how low I set the volume on my guitar (which is my main reason for wanting to build this pedal).

I couldn't find instructions for how to set the internal trim pot in the build documentation. Another post on this forum suggested setting the bias knob to noon and setting the internal trim pot to get a reading of 4.5v. If I set my bias knob at noon, I can only get a max reading of 3.7v across the trim pot testing holes, even with the trim pot fully clockwise. If I set my bias knob to around 10 o clock I can get a reading of 4.5v if I max out the trim pot, but it still doesn't clean up even my my volume as low as I can get it.

I'm using 2N1308 transistors. My TC-1 gives me these values (Vbat = 3.61v):

Q1:
hFE=410
Ie=2.8mA
Ube=137mV
ICE0=0.24m

Q2:
hFE=373
Ie=2.6mA
Ube=144mV
ICE0=0.23m

I also have two others I bought at the same time with these values:

Extra 1:
hFE=510
Ie=3.1mA
Ube=150mV
ICE0=0.18m

Extra 2:
hFE=597
Ie=3.5mA
Ube=151mV
ICE0=0.44m

Any advice and settings, parts, etc. I can change to get the signal to clean up at low guitar volume would be greatly appreciated!

 

[SillyOctpuss]

Your transistors are pretty leaky. I'd be trying to find some lower leakage examples to start with.

What voltages do you get now on the EBC of each transistor as it is now?

 

[keevohn]

By coincidence, I just finished a Tactical Fuzz tonight. I'm getting great cleanup from the volume pot, just like the Tacit Blue demos on YouTube. Gain for Q1 is in the high 80's, while Q2 is around 120. Both are low leakage and biased easily to 4.5V.

If you haven't, take a look at the RG Keen article on the Fuzz Face: http://www.geofex.com/article_folders/fuzzface/fffram.htm

You might want to build the transistor tester from that site, just to confirm your TC-1 measurements.

Finally, if you're having trouble finding NPN transistors in the right gain range, take a look at the link in this thread: https://forum.pedalpcb.com/threads/us-source-for-germanium.22192/

I bought 4 used transistors and they've all tested fine. I'll try them all in the Tactical Fuzz this weekend and report back.

Good luck! It's a great sounding pedal.

 

[apierz]

Your transistors are pretty leaky. I'd be trying to find some lower leakage examples to start with.

What voltages do you get now on the EBC of each transistor as it is now?

With the trimpot fully clockwise and the pots at noon:

Q1:
E: -3.63
B: -4.55
C: -3.43

Q2:
E: -3.51
B:-3.43
C: -3.50

 

[darwin999]

Those are very high gain transistors compared to what is recommended in the build doc:



But I would first re-check your transistors' gains either with a DCA75 or via the RG Keen article noted above, I'm not sure whether the TC1 provides accurate gain values in the presence of leakage. (There surely are thread here on that issue of TC1 accuracy.)

 

[apierz]

Those are very high gain transistors compared to what is recommended in the build doc:

View attachment 90855

But I would first re-check your transistors' gains either with a DCA75 or via the RG Keen article noted above, I'm not sure whether the TC1 provides accurate gain values in the presence of leakage. (There surely are thread here on that issue of TC1 accuracy.)

Yeah, I bought four hoping at least two would be close but none of them ended up being suitable. I’ve ordered a set of new transistors that’ve been pre-measured to have good values for fuzz face style pedals. I will swap those in when they arrive and report back.