New DIY Pedals

What a busy vacation.  I spent a good part of it finishing some pedals I've been experimenting with over the last few months.  All three of these are simple designs by the DIY guru, Tim Escobedo.  I remember coming across his page years ago and always wanted to give all of his circuits a try.  However his Geocities page was taken down a while ago.  Someone was nice enough to re-post his work here: http://www.jiggawoo.eclipse.co.uk/guitarhq/Circuitsnippets/snippets.html  I've bread boarded quite a few of his circuits, but choose these three for the time being.  Lets take a look at some demos I made of each one, and the small mods I added to each one.

Push Me Pull You

I'm starting to have a large octave fuzz collection these days.  I didn't need another octave fuzz, but what drew me to this one was how clean it could get.  I decided to mod the Q3 transistor by cutting the collector or emitter in order to kill the octave effect, making the pedal a stand alone fuzz with the stomp of a switch.
  

Original Schematic

 In addition to omitting the Q3 transistor, I added a 3PDT switch where the Q3 would normally go and added a 2n5087 silicon PNP transistor and a AC125 germanium PNP transistor so I could switch between the two.

There seems to be a debate over which matches of transistors works the best for a strong octave effect.  I found the following to work fairly well: Q1 2n5088 Q2 2n2222 Q3 (switchable 2n5087 / Ac125)  I also changed out the 500K resistors for 470K resistors.  I think it help the octave a little. 

Modified Schematic

Octave Fuzz (Tim Escobedo's Push Me Pull You)

Harmonic Jerkulator

This one is not subtle nor pretty in anyway.  What drew me to this one was the tone of Steve Albini.  His Big Black albums have the craziest tones, almost metallic and harsh.  His rig is hard to reproduce, especially considering his main dirt box is the extremely rare Harmonic Percolator.  There is even much debate about reproducing the original.  The values are questionable.  I think Tim did a pretty good job with this one.  We can get in the ballpark for that tone, but some more tinkering might be in store.

Lets look at the original schematic:

Original

This is the bare circuit.  Supposedly the original had a something resembling a pair of clipping diodes with a 1K resistor one the last diode at the end of the signal right before the volume pot.  I added a switch to include or take out these diodes in my pedal.  The diodes seem to add a type of compression or "grind" to the sound.  However, at high gain settings, it adds noise and feedback.  The 22uF cap can be increased in value to reduce the noise, however I didn't experiment more with that enough.  I used a pair of 1N4001 diodes, but I'm sure there are better options.

Modified circuit

I also added a switch to change the NPN transistor between a MPSA18 and a 2n3904.  There is a slight difference between the two.  Not much, but the MPSA18 has less feedback overall. 

The last mod I did was to change the 1K resistor from the gain pot to a 10K.  The drop off of gain was a little less.  The 1K basically made the gain go away completely, the 10K made it more useful. 







Harmonic Percolator variant (Tim Escobedo's Harmonic Jerkulator)

Some Big Black graphics I hope to add to the pedal

Utility Boost

This is one of the easiest boosts to build.  Lots of volume on this one.  The variation really seems to rely on the type of transistor or jfet used.  So I added a switch to give me both a jfet and transistor.  The J201 is super clean.  It only starts to slightly hair up at max.  The 2n3904 transistor has much more gain and fuzz to it.  However there is a sweet spot on it and anything above that is not so musical or pleasant.  I think i might switch out the transistor.  Maybe I can get a hold of a NPN germanium soon.  Here's the original schematic.

Boost Pedal Clean/Dirty (Tim Escobedo's Utility Boost)