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I am currently working on and breadboarding 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.
I am sorry that I do not have anything to add to this other than I can certainly appreciate the early Mark Farner tone.
I agree the early Mark Farner tone is somewhat unique. The guitar used, a Musicraft Messenger was a fairly big part of the early GFR sound/tone. Hollow body with single coil pickups and an aluminum neck. The guitar itself sounds really good clean with low gain, but kick in the onboard fuzz and it’s a signature sound.
That Playboy show really gives good clear insight into that tone.
and this… in case anyone else is wonder wtf we are all going on about?
Why can’t we get these aging musicians to understand the potential keys to their tone which was ultimately the keys to their success. Grand Funk is not the only example but it is quite audible.
I realize as they get older they want more refined gear and more refined tones. Along the way they sometimes lose something. I can name a dozen bands easily that fits.
Maybe I should create a Mark Farner NostalgiTone, though I’m not sure how much it would be appreciated.
I would be up for a Grand Funk NostalgiTone. And you posted my absolute favorite GFR live performance.
I thought I would revisit the circuit a little as some new information was provided to me by friends.
I spent last weekend at the Penn State Arts Festival (Central PA Festival of the Arts) where I have been meeting up with my college friends nearly every summer for many years. Out of the 4 guys, I am the only one who is not an electrical engineer. Speaking about this circuit with one of my engineer friends, he told me “well you know that inductors can act somewhat as both a resistor and a capacitor and is frequency dependent.” Intrigued, I read up some more about Inductors (emitter leg of Q1 of the circuit) and it is true.
For DC current, the “resistance” of the Inductor is pretty much nil. However with AC, as in a sine wave guitar signal, the resistance to current flow is technically Impedance (or Reactance with an inductor). That is, DC current will pass straight through an Inductor which basically acts a straight wire.
However, the magnetic field generated by AC current flowing through an Inductor will induce a resistance to current flow. The effective Impedance (think resistance) of an Inductor is dependent on the frequency with increases in frequency causing an increase in the Impedance/Resistance. Also, the larger the Inductor, the more resistance there is to higher frequency current flow. Therefore higher frequencies don’t flow as well through the Inductor and the larger the Inductor is, the greater higher frequency current flow is impeded. This explains why when I put larger value Inductors on the emitter leg of Q1, there appeared to be greater lower frequency content in the output signal. The higher frequencies were basically being filtered out.
For example, the “resistance” of a 100uH Inductor for a typical lower guitar signal frequency of 82Hz is 0.05 Ohms, and 3.1 Ohms for a higher 5 KHz guitar signal frequency. Therefore: Higher Frequency = Higher Resistance and less high frequency content.
Also the Magnetic Field of the Inductor stores electrical energy as does a capacitor, just in a different fashion. When the current to the inductor is turned off, the magnetic field of the Inductor continues to cause current flow through the Inductor as it gradually dies down (gradually collapses) until it is completely collapsed to the point that there is no more induction of current. This is somewhat similar to a discharging capacitor causing a continuation of current flow for a certain period of time. Inductors store electrical energy in a magnetic field and a capacitor stores electrical energy in the form of a charge.
Follow-up.
I’m done trying all kinds of different component swaps on this circuit. I used the neck single coil pickup of my very expensive Squier 51 guitar (cost a whopping $99 new in 2007) to simulate the neck pickup of Farner’s Messenger guitar since I don’t own a thinline hollowbody with single coil DeArmond pickups. I get pretty close to the sound of the GFR live in 1969 sound (Inside Looking Out and Paranoid) when playing along with the video.
I finally settled on pretty much doing the stock circuit, but using higher gain transistors. Others have used BC108/109 transistors, which can be around 400-600 Hfe. I am using 2N5088’s that have Hfe’s around 575. This gives quite a bid of distortion and one can get some of the octave up distortion heard on the Inside Looking Out solo, but it is not as prominent as in the recording unfortunately.
For the emitter leg of Q1, I tried going straight to ground (most distortion), a Ge diode some have tried (cleans up some of the fuzziness), and various Inductors ranging from 10uH to 1mH. The Inductor value doesn’t seem to matter much.
I’m leaving off the 470k resistor to ground at the output since it didn’t do a whole lot. I am not going to use a Gain pot at the input because the guitar volume pot works fine here. I am planning to use a 100nF Input cap switchable with a tone control (blendable cap network as in the schematic). I also tried a 47nF Input cap but it didn’t make much of a difference.
At the output, I will use a A500K Volume pot that can be switched to a direct out path as in the schematic.
Interestingly, I compared the fuzz to the Grand Fuzz Railroad pedal I built a few years ago, which is based on a Heathkit TA-28 Fuzzstortion circuit that I modified. The Messenger fuzz I breadboarded and the Grand Fuzz pedal I built sound very similar, but the Grand Fuzz has less to maybe zero octave effect high on the neck (primarily above 17 frets) compared to the Messenger. There is some octave like effects from the Grand Fuzz when I changed the PNP Si Q2 to a PNP Ge Q2 that has around a 275 Hfe gain and low leakage, but there is less overall output from the pedal. One of these days I will get around to building this on veroboard.
Final diagram below:
The 1n cap before the vol pot is creating a high pass filter with the selected resistance in the vol pot. This value may be too high to pass your low freq content. Try increasing the cap value.
I am almost ready to return to action on GPCB. The construction of my new shop is nearing completion. I can still be reached at wilkie1@comcast.net. Nice work on this circuit!
Thanks Wilkie!
Stupid me! I should have recognized that the output of the circuit of a capacitor paired with a variable resistor is a Low Pass Filter. With the full 500K of the pot, and a 1n cap, the 3db cutoff frequency is 318 Hz. This is above the lowest frequency of 82 Hz typical for a standard guitar. Raising the cap value to 10n gives a cutoff frequency of 31.8 Hz, below the lower guitar frequency of 82 Hz.
Found I mis-typed. That is a High Pass Filter configuration. I’m probably going to use a 47nF output cap. A modified Messenger Fuzz schematic I found shows the person who tinkered with the circuit added a 47nF output cap with a volume control. I should have figured out what he did. The 1nF cap actually makes the fuzz too fizzy, so I suspect the output cap from the original circuit board is likely higher than a 1nF, which was a guess from those trying to reconstruct the circuit. It likely is 10nF or higher.
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