Fred Briggs - Unknown Fuzz

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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briggs
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Post by briggs »

A new fuzz design from myself. It's silicon transistor based but with a difference. I've been playing around with the old Vox Tonebender circuit for a while and this is what sprung from those experiments. Taking inspiration from the Fred Briggs Fuzz I made a few years ago that used "piggy-backed" silicon transistors to emulate lower gain germanium devices I used a couple of piggy backed high gain silicon trannys in the first stage with the hfe set to 25. This first stage pushes a NOS BC108 transistor in the second stage - it sounds great, there's no ear shredding like the usual silicon fuzz boxes just a nice fat low end and a warm mid section. The three controls are for 1; a bass cut, 2; a width control (which adjusts how "wide" and gainy the fuzz sounds) and the third is just a volume control. As you can see there is no "usual" gain control, that's because the only gain control you need is your guitar's volume knob, it'll do everything from mild overdrive right through to full on FuZzZzZzZz.

So, here's the schematic for you:
And here's some design notes:
*NOTE* - To further control the high end and upper mids I would recommend you add in a 2n2 cap in parallel with the 22K resistor and 100kB "Width" pot. It really calms down the harsh frequencies. I included the 2n2 cap on my final build!

*NOTE 2* - Piggy backed transistors are a little picky, you may have to pair up a few 2N5088 transistors before you find a couple that are happy together :-)
And the schematic and build pictures:
briggs_unknown_fuzz_schematic_vint.jpg
briggs_unknown_fuzz_2.JPG
briggs_unknown_fuzz_1.JPG
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juanro
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Post by juanro »

Nice, I like the "piggy-backed" transistors idea very much.
Any tips on how to adjust the 100k trimmer? (Ear-wise aside)

Regards,
Juanro
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Post by Duckman »

Another lovely pedal from the Briggs vault :applause:
juanro wrote:Any tips on how to adjust the 100k trimmer? (Ear-wise aside)
Bass Cut or Width? Seems a pure taste task :hmmm:

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briggs
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Post by briggs »

The 100k trimmer between the piggybacked transistors needs to be tweaked until Q1 gives a hfe reading of approx 25. The 10k trimmer on Q2 you need to adjust so that there is approx 4.5v on Q2's collector.

I'm really enjoying this circuit, with the right tweaking and transistors it sounds great and is pretty versatile...

It's worth taking into accounts the circuit notes though -
*NOTE* - To further control the high end and upper mids I would recommend you add in a 2n2 cap in parallel with the 22K resistor and 100kB "Width" pot. It really calms down the harsh frequencies. I included the 2n2 cap on my final build!

*NOTE 2* - Piggy backed transistors are a little picky, you may have to pair up a few 2N5088 transistors before you find a couple that are happy together
Duckman wrote:Another lovely pedal from the Briggs vault :applause:
Cheers, I'll have another one for you soon :horsey:
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Post by juanro »

briggs wrote:The 100k trimmer between the piggybacked transistors needs to be tweaked until Q1 gives a hfe reading of approx 25. The 10k trimmer on Q2 you need to adjust so that there is approx 4.5v on Q2's collector.
Yeah, the 10K biasing was clear.
So I think I'll make a "daughter mini board" with two three-pin sockets and the trimmer, and three legs to insert it in the "virtual-Q1" spot, so I can adjust it for 25hfe "off board" and also swap Q1 and Q1' if they don't work. I'm needing(*) a fuzz so I'll give it a try over the weekend.

Thanks,
Juanro

(*) Yes, "need". I always "need" pedals, never "want", hehe.
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briggs
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Post by briggs »

The little daughter board is a really good idea actually. It's a nice fuzz tone from this circuit, it can get gnarly but I wanted this to be a pedal I could use in a band situation without them kicking off as I drown them out with fuzz so it's voiced for the mid ranges and held back from being like a Tonebender MKII..
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Post by Mbas974 »

Fred another great design !
Just finished my sound test and.... it have to go into a box sooner !!!

Thanks a lot !!

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Post by Mbas974 »

I set Q1 hfe by hearing using my taste..
whether I want be more specific how to get the measure hfe=25 ?

I know hfe = current dran / current base
current is Voltage/resistance so, for obtaining the current I can measure voltage with a DMM on base and drain but I get mess with the resistance

any suggestion please.

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Post by briggs »

Hi Mbas, I just set the 100k trim by ear to what I liked best and then removed the transistors and used a DMM with a hfe measuring function to measure the gain of the piggybacked transistors. I'm glad you like the pedal, it's one of my favourite fuzzes :blackeye
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