I am currently working on and breadboarding a Messinger Guitar Fuzz, the onboard (built in) unit that is/was a part of Mark Farner’s (Grand Funk RR) guitar in the early days of GFR. This circuit provides a pretty aggressive, raunchy fuzz/distortion when paired with the single coil pickups in the hollowbody Messinger Guitar. Such a fuzz was available one time through Basic Audio, but none are found even on Reverb today. The Basic Audio version has Gain, Tone and Volume controls.
I did as thorough as research as I could do through the internet and a basic schematic was constructed by many contributors based upon photos of the fuzz circuit itself. Using the photos I found, I have confirmed all the resistor values, although I am not totally sure of the cap values, although they look valid. Transistor Hfe’s are unknown, but some have suggested around 300 Hfe or slightly greater, which would make sense since the common Si transistors when this fuzz was designed were BC108’s and BC109’s, which had an Hfe around 300-400 at the time.
One of the circuit boards has an additional 470K resistor on it, not seen on the other photo of the two I have, so there may be at least 2 variations of the fuzz. The 470K resistor appears to be on the output end and perhaps it was designed to run in parallel to a volume pot. A 500k volume pot in parallel to the 470K resistor would act as a 250K pot, typical value for a single coil pickup guitar, I believe.
There is also a “mystery” part, which most believe is an inductor off the emitter leg of Q1, which can act as a frequency dependent resistor and therefore was probably used in lieu of a standard emitter resistor. Below is the basic schematic.
I modified the schematic to add a gain control pot at the input. I have seen a 500k pot on some of the schematics in this position, but I changed it to the default 250K pot value typically used in single coil guitars and it seems to work fine. I also decided to add a switchable input capacitor blend pot as a tone control, which can be switched out to the standard 100n input cap.
I did think about a switchable inductor off the emitter leg of Q1 from the 100uH I have seen on some schematics to a 1mH inductor, which adds a little more low end. The value of the inductor is pretty much anyone’s guess as I believe the inductor value has not been established as fact.
Finally, I added a volume control at the output. Some people who have tried this circuit added a 100k pot at the output, but I discovered using this value cut out a fair amount of the low end content of the signal. Using a higher value pot kept in some more of the low frequency content – 250k added more low end and 500k was not that much different than bypassing the volume pot. I am not certain that this onboard fuzz was added before or after the volume pot since I don’t have an original Messinger Guitar to inspect. The photos of the circuit board don’t show where the input and output of the fuzz connect to, so I decided to put controls at both the input (serves as a gain control) and at the output (volume control). Maybe the guitar pots are even bypassed when the effect is switched on, who knows.
My question to the experts on this board – why does using a pot at the output take away some of the lower frequency content? I can’t figure this out.
Below is my final schematic as of right now. Any suggestions or insights are welcome.
Login
Register
FAQ
Search
