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Hi there, welcome to my blog - La Revolution Deux. It's an odd name - but I like it! Here you will find all the info on my various DIY Guitar effects builds, amplifiers and guitars. Everything from a humble Ibanez tubescreamer to the holiest KLON Overdrive.

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Wednesday, 20 June 2012

Fred Briggs - Pharmacy Fuzz


Here's something I've never seen before in a Fuzz Face type circuit; adjustable gain darlington pair transistors made up of individual germanium and silicon transistors. The first transistor of each pair is a germanium device of around 50hfe (low leakage!) and the second is a silicon device of around 250hfe. The adjustable nature of the transistors makes the Pharmacy Fuzz capable of a huge array of both vintage and modern fuzz tones - you can tweak and play with the circuit for hours and still find new possibilities.

When I build this up I'll be using a 100k trim for the gain control on the first transistor set and a 100k pot for the control on the second transistor set as this secondary pair is where most of the clipping magic happens (or indeed just use a single low/medium gain transistor instead of the first pair for simplicity). Also note the "Aggression" and "Bass Cut" controls. The "Aggression" control works as a circuit wide "overall gain" control and allows the circuit to go from mellow to full on rock out. The "Bass Cut" is just an implementation of the now pretty standard Fuzz Face tone blend control and governs the amount of low end signal that the circuit will gobble up at it's front and and fuzz out at it's end.

The 10k trim is there for bias - use this to set the voltage on the collector of the second transistor set to around half the supply voltage, or to wherever you think it sounds best!

You'll also note a few other little inclusions in the design - the 2 x Ferrite Bead inductors in series with the input of the circuit and the Suppression Choke in the power supply (whose overall resistance should be in the 50-100 ohm) region. These components together help to reduce noise and radio interference in the circuit. If you don't have them replace the suppression choke with a 100 ohm resistor and just omit the ferrite beads.

1 comment:

  1. Hi , me with another tricky cuestion ; What BRAND OF FUZZ was used in erick claptons "layla",there are about four guitars but at the very moment theres a very tinny sounding guitar;thats the one that i want to know,also is the same sound heard on "l.a. woman" by the doors.thanks

    ReplyDelete

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