Germanium Fuzz Face (AC128)

[NickKUK]

So my next adventure will be a simple germanium fuzz face, I love the tone of the red dunlop fuzzface but rather than pay £160 for the official version, I'll DIY it. I've got a potential source for some AC128s so this is an order parts build but a 'keep it as cheap as possible' including some component reuse/salvage on some strip board. The order in means it won't qualify for the competition but this one is for some honking Hendrix tones so it will slowly evolve.

I'm just waiting to hear back what hfe they have available. One of the key points is a low hfe ~120 on the first PNP and then a higher on the second. I'll order four and see what fun we can have with adding some mods - potentially a opamp buffer/driver - however it depends on how the FF interacts with the impedance of the amp. A second mod may 'supercharge' the fuzz. Lots of options can fit into a mini pedal these days.

 

[NickKUK]

I may have had an oops moment due to an unexpected tax refund..


Given the CV7003 are £54 each at the moment (not including eBay fake/busted roulette) and basically unobtainable military version of the OC44 and that's about the last pedal I can find not for stupid money..

I'm still interested in building a fuzz face but the AC128s are only £5 each, I can then make a switchable FF by stacking the boards in the mini enclosure.

 

[hamerfan]

To my experience hfe 120 is quite high for a Germanium. I could be wrong, i have about 20 russians from 17 to 94. My point is to use a 120 for the second PNP. BTW the hfe 17 is now in a Dragons Breath.
The NPN are more expensive and not as easy to obtain, but you could use a PPCB TwinFace board with NPN and PNP to have two different Faces.

 

[NickKUK]

To my experience hfe 120 is quite high for a Germanium. I could be wrong, i have about 20 russians from 17 to 94. My point is to use a 120 for the second PNP. BTW the hfe 17 is now in a Dragons Breath.
Since the NPN are cheaper and easier to obtain, you could use a PPCB TwinFace board to have two different Faces.

I'd be tempted to make a multi pedal with a number of fuzz circuits in it - 2x pnp and 3x npn then have a 5 way rotary selector switch on the front. The support components can be SMT leaving THT for the transistors themselves and allowing more to be packed in to target a small pedal board foot print.

I have to say I'm less knowledgable about solid state BTJ than I am mosfets, regulators and tubes, so this will be more of a learning experience.

 

[hamerfan]

To my limited experience the pot settings on the FF circuit were more important than different trannies. I swapped different tranny combos around until i found the one. My friend liked the Fuzz pot on fixed point of 80% and opted for input pot instead. This works like the smoothing out with the guitar volume.

 

[NickKUK]

To my limited experience the pot settings on the FF circuit were more important than different trannies. I swapped different tranny combos around until i found the one. My friend liked the Fuzz pot on fixed point of 80% and opted for input pot instead. This works like the smoothing out with the guitar volume.

I was considering a couple of 'additions' with an input buffer and driver with switchable bypass for each, and some power supply options. The idea being I can slowly collate a number of options without having to build yet another pedal.

 

[NickKUK]

I have four Mullard metal can AC128s coming. I almost added two AC125 NKT275s (non dotted) to the order.. but let's start simple. I've asked for two pairs - one lower gain and one higher gain, both pairs about 20-40 apart. It would then give more OD and a harder fuzz.

For silicon I'm tempted to add the BC108C for starters, but I'll probably order that at the time I get some more components in.

 

[hamerfan]

No input buffers. A FF needs a passive guitar impedance to work as intendend or a debuffer circuit with an input transformer, if you want to use it upstream in your signal chain. Old school circuit, y’know.

 

[PedalBuilder]

For silicon I'm tempted to add the BC108C for starters, but I'll probably order that at the time I get some more components in.

My experience with silicon fuzz faces (and silicon fuzzes in general) is that part numbers don’t really matter except insofar as they are proxies for hFE and noise. Modern silicon transistors like BC549x have noticeably lower levels of noise but otherwise behave identically to their older counterparts. As an added bonus, they’re also cheaper and much easier to source.

 

[NickKUK]

My experience with silicon fuzz faces (and silicon fuzzes in general) is that part numbers don’t really matter except insofar as they are proxies for hFE and noise. Modern silicon transistors like BC549x have noticeably lower levels of noise but otherwise behave identically to their older counterparts. As an added bonus, they’re also cheaper and much easier to source.

I agree, I don't think the transistor has really progressed much in terms of the curve and as you've said the substrates and junctions have improved dropping the noise.

The speed of transistors above a certain point result in little return in the audio range - the BC549 is 300Mhz, its capacitances are small to allow that and finally curves are more and more linear leaving just the cutoff and saturation points along with the limits and SOA that really offer differentiation, given the guitar signal and pedal voltages, that leaves fewer and fewer transistors that basically become identical over time.

Add the move to digital, with opamps being increasingly used prior to digitisation, and then following that, often it's digital output is then just filtered and drive (again opamps). The humble transistor is left out, whilst everyone occurs on the IC substrate, with it's less than linear output as a component.

Naturally a way to reduce the slew rate is to add snubbers that soften the corners of the wave forms, giving an older sound. You can reduce leakage by using current mirrors for legacy transistors and then using techniques to stabilise ltegacy BJTs to prevent thermal run away.