Tuesday, 22 January 2013

Fallstaff OD

Fallstaff OD, or "Fat Mastered" from Jon Patton. It's a modern take on Rangemaster with a few quite cool features. I replaced 8K2 resistor from Q2 base to ground with a 20K trimmer for easier biasing.
From Jon: The Fallstaff overdrive (or "Fat Mastered boost") is a variation on the Rangemaster, but with a buffered input stage and a color knob to fatten the sound in a way that offers a nice change from the usual input cap mods. It can be tweaked to sound a lot like a traditional rangemaster, as a full range boost with sparkly top end, or as a dark mids boost. The extra input stage makes the pedal behave the same whether it's before or after another pedal. It provides a 20db of boost or more depending on the gain of the transistors you use. Unity volume on my prototype was about 10:00.

For Q2, values as low as 35hfe were acceptable with proper biasing, but gain ranges around 50-60 are ideal for the values shown. I got decent results with values as high as 120hfe. NPN Si transistors in that range will work, too. R5 and R6 bias Q2, like a rangemaster, to ~7v on the collector. Use sockets or trim pots or breadboard before building if your transistors aren't pretested! Q1 can also be a JFET. I used 2N2925 instead because it sounded really good and I didn't have to twist the leads to get it in the sockets in my layout.





5 comments:

  1. Hey, sorry about this, but I made a mistake in the schem a long time ago, and kept copying it over until recently. That 1M resistor should be 22K. (At some point I had a default value of 1M and missed it until I was building the BOM.) Here's a link to the build doc with the current schematic for reference: https://docs.google.com/document/d/1033QEzKtTQJ0B3pTqJyp3mo-y4V7ErbM35hi3phTJLI/edit

    The trim is a good idea. I probably should have used one on my PCB, but I was (maybe overly) concerned about noise.

    Sorry for any inconvenience this might have caused anyone. The 1M won't break the pedal, but it will keep the diodes from doing anything. :)

    -Jon

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    1. Thanks Jon! I'll fix the value on the layout.
      +m

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  2. Made this and boxed it - nice thanks.

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    1. Nice one David, you've been on fire!

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