Fuzz Bender: GBOF x 2, TwEQ

[Anonymous]

This was a fun project to complete.  I wanted to take a deeper dive into the circuitry of pedals, and what better place to start than the Tone Bender and Fuzz Face.  So much is out there about how these pedals work and different mods you can apply to make them your own. Barry’s GBOF boards were a great platform to start this adventure.

I ended up socketing just about every capacitor, resistor, diode, and transistor on these boards.  The build began by using the Neckbeard resistor and capacitor values as a base and then choosing my transistors.  After testing a few dozen NPN GE transistors of various types I ended up going with 2N1304 in Q1 and Q2 with a AC130 in Q3, hFEs 65, 85, and 140 respectively.

Once that was done, it was time to go back and play with resistors and capacitors.  After hours of swapping, testing, and tweaking, most of my components were similar to those in the Mayer/Hendrix FF mod, with the exception of the coupling capacitor before Q2.

After that, I added the TwEQ with a trim pot for the volume and an external bias pot.

The end result is sublime.  The fuzz only gives you that amazing fat 60’s Ge fuzz sound that made the pedal so popular.  Hit the switch for the tonebender and you add that extra transistor for some increased gain.  The external bias helps to dial in the fuzz, and the TwEQ gives you so much flexibility in setting just the right tone.

Pics for everyone.  Also, I added my FF/TB build doc as a reference for anyone interested in my values. 

 

[Big O]

That looks really nice.  I have been thinking of building a neckbeard with AC127 Transistors (NPN) I have, probably a year or two in the future as I have several planned projects in the future.  I have an actual Keeley Fuzzbender and it is a great pedal.

Currently I am working on a Vox Tonebender based off the PUFF.  I have breadboarded it and construction will start tomorrow.  I got delayed by babysitting our 8 mo. old grandchild for 10 days and who happened to be sick with daycare kiddy crud.  My wife and then inherited it from her and have been sick nearly two weeks.  Then a couple of days ago we had to contend with Ian, being hit with the northern eyewall having 120+ mph winds.  Fortunately we lost only a couple of screen panels from our pool cage and a couple of roof tiles.  The worst part was being without internet for 2.5 days both from Comcast and Verizon, who apparently share the same infrastructure as we found out.

I dialed in the “correct” or optimal collector voltages on Q1 and Q2 by using trimpots.  I will keep a trimpot for the 85 HFE Q1 to adjust as I see fit and the Q2 bias will be an external bias.  Breadboarded it sounds pretty good and different than a FF.  Probably because the input cap is 220n instead of the FF 2.2u input cap.

I still have a Ge Hornby Skewes treble booster to make (breadboarded as well), a PURP, Colortone OD, Llama, Harmonic Percolator, TB MK3, Bosstone Fuzz and Fuzzrite (actual simple circuit – not the American fuzz version).  It sounds pretty nasty when breadboarding it and using matched 170 HFE 2n3904 transistors.

 

[Anonymous]

Good luck on the Tonebender build.  I’m sure it will be awesome!

My original plan was to use some AC127s, so I bought a few from a reputable online vendor and every one of them had leakage problems.  I then bought a few more, as well as some other kinds of Ge NPN transistors from the same place, and had the same issues.  I ended up with a dozen transistors, only three that had leakages less than 300uA, and only one of those with a usable gain.

I had previously built a PUFF with Barry’s hand-selected Bonamassa transistors, which was super nice and convenient.  So I found someone who could guarantee low leakage transistors with a narrow window of hFEs and bought from them. Costs a little more, but well worth it.

This pedal was very much inspired by the Keeley Fuzzbender.  I thought about using trimpots for the Q1 and Q2 bias, but instead socketed, swapped, and tested the voltage divider resistors and ended up where I wanted.  In all honestly, swapping most of the parts didn’t really change the sound that much (i.e. R3 was tested with 33k, 39k, and 47k values).  As you mentioned though, I did find that changing the input capacitor on the fuzz did make a difference.

 

[Big O]

I recently purchased some AC127’s from Small Bear and all had leakage <300 according to my DCA55.

Using a trimpot for the Q1 bias on the Vox TB build, a value of 14.6K was found to set the Q1 collector voltage to -0.7V.  Replacing the trimmer with a 15K resistor provided a Q1 collector voltage to -0.68V, so I suppose a 15K resistor instead of the trimpot might suffice.  The Vox TB schematic uses a 10K resistor on the collector side of Q1, which provided a Q1 collector voltage of -0.8V, and I suppose this would be OK.  But I am thinking about leaving the trimmer on the collector side of Q1 so I can first adjust the Q1 collector voltage to the ideal -0.7V and then adjust by ear after that.

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