PSI FUZZ IS BORN!
ÌÕMake a Muffin BetterÌÒ, Frank Zappa
We set out to takeÌ_a classic design with lots of history Ì_and make it obviously something new. Ì_We took the op-amp version of old PI and inverted one of the stages, brought out the midrange, tightened the bass, and most importantly, added a Germanium transistor output! Ì_Yes, this is a opamp-transistor hybrid. Ì_Don̥t be miffed by op-amps in your pie folks, the germanium touch at the end makes everyone smile around the shop here.
We wanted to celebrate our 12th pedal of the year by offering it in two forms. Ì_Two choices, 1) Custom Art in a late 1960̥s style or 2) Greek Gold Deco. Ì_The first is handÌ_drawn by Erin Lofties. Ì_Her stunning artwork looks out of the 60̥s and was completed this week specifically for this pedal. Ì_ThenÌ_then Gold Brick Greek God model. Ì_Stripped down, simple and clean.
Audio and Video Clips soon ̐ Shipping After Christmas is more than likely unless you were part of the first 50.
ÌäThis is how the first phase of our design went: (from Bob̥s Blog)
How do you make a designÌ_different? Ì_Put your own spin on it? Ì_You can make it distort differently, you can make the tone different, add some features, Ì_you might even be able to put a little lipstick on it. Ì_At the first audio/video repair shop I worked at in 1989, I remembered seeing clipping or limiting diodes, LEDs in fact, Ì_in certain types of gear where there were A/D converters. Ì_I noticed as I was working on the equipment that the LEDs were lighting up on the inside of the unit when the program material was high enough. Ì_No one could see them except the service tech. Ì_How cool would that be if everyone could see them on their distortion pedals?! Ì_So I̥m pretty sure I was the first to make it a standard feature on a guitar effects pedal by putting the clipping LEDs on the outside of the pedal when I built the DS-1 Seeing Eye mod and later the Ultra mod. Ì_It̥s done pretty regularly now on my pedals including the latest Red Dirt Pro and Stahlhammer. Ì_They might not light up very brightly, but that doesn̥t matter, they are still doing their job. Ì_And so, I wanted to dive into the old Muff and make it mine. Ì_Rearrange things, add some bling, make it Psi Fuzz!
It seemed like I could have fun doing an all germanium one, but that was done already. Ì_It seemslike there isn̥t gross overpopulation ofÌ_op-amp versions of the old gal. Ì_But what to do to make it mine, at least in some way? Ì_Well we can add to the circuit. Ì_Again, I was thinking germanium transistors since they always have a fun sound. Ì_So let̥s add a common emitter amplifier to the end. Ì_That would put a germanium spin on the overall sound. Ì_But we have phase inversion then. Ì_Input and output are in phase on the vintage pedals and I wanted to maintain that. Ì_Great! Ì_I get to play with the stages! Ì_The first thing I wanted to alter was the 2nd ÌÕgain-stageÌÒ and filter. Ì_That̥s a Sallen-Key filter and you can only make it using a non-inverting style op-amps. Ì_I got to play around with values and changed things up a bit. Ì_I wanted to know how it felt to swing that 1KHz 2nd order filter around. Ì_So I made it go up and down. Ì_In and out came the harmonicsÌäand the noise. Ì_Very cool. Ì_I can set that filter to where I want it. Ì_I want it to have a bit of fire and life and not feel too cramped in the high end. Ì_I̥ll use a lower noise, mildly more expensive IC to combat noise instead of kill the guitar tone. Ì_Okay, still have to invert the phase somewhere! Ì_Yup, the first stage is where it gets it. Ì_I changed a few things around to make it a non-inverting op amp and it works well. Ì_Ì_I̥m still playing with those values but I dig it. Ì_Right now the low pass filter for the first stage is about 10Hz if I remember correctly and that̥s okay with the girls I date. Ì_Phase is correct (with the soon to be added germanium gain stage) and I̥ve changed the design so far, even if trivially.
The Big Wazoo
So I changed the 6 silicon diodes in the feedback of the third stage to 2 LEDs and yes, one of them will poke through the hole in the top. The ÌÕKeeley ModÌÒ has been done to it, including blue as Neptune Psi Fuzz Blue LED. Ì_(Yes, another first from Keeley Electronics.) Ì_And finally, the pre-climax to this story, our phase is in crisis, the hero takes action, the germanium amplifier stage! Ì_Ahhh, fitting like a glove between the Voice control and the Voltage control is a common emitter amplifier using a AC187. Ì_I am pretty happy with the biasing of it. Ì_The collector sits around 4.5V and we get a gain of 10dBÌ_out of it. Ì_Oh wait! Ì_We don̥t want this thing not putting out when it gets hot! Ì_That would be as wrong as a double negative! Ì_You know, when it̥s a 113 degrees in the shade and some Rock God is on stage in Texas, Ì_just working it for all it̥s worth, he don̥t want things to blow ya know. Ì_Craighton and I get the heat gun out and sure enough, Mr. Semi-Conductor from the 60̥s sags and wimps out in the heat. Ì_Just like your poor old fuzz face. Ì_When the mercury hit 115 the lights went out. Ì_Okay, off to the parts room. Ì_Out comes a real germanium diode. Ì_Not the Shenzhen ChinaÌ_SchottkyÌ_ones, but some good strong American ones. Ì_Ones that behave the same as the transistor when it gets hot. Ì_We used the germanium diode in a reverse polarity fashion across the base-emitter junction of the transistor to offset the temperature coefficient problem. Ì_Turned on the heat gun, just let it blowÌäit got hot..really hotÌäwell over 140 degreesÌäand it never stopped pumping out the love.
Come As You Are
Our version has a single integrated circuit package, a quad op-amp, and a single transistor. Ì_Trim and Slick! Ì_I love it! Ì_Sounds terrific! Ì_We still need to fine tune this design a bit more but, there you have it; Ì_The Psi Fuzz by Keeley Electronics. Ì_Coming soon to a pedal board near you!
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