Feedback Wanted On My Fuzz Face Experiment

[afrogoose]

Hey Everyone!

For a long time I have been curious about some of the folklore of the fuzz face, so I ran an experiment and wrote a blog about it..  Specifically, I tested different types of batteries and voltages to investigate their differences, if any.  I was hoping to get some feedback on it.  There are so many diystompboxes members that have such great experience and expertise, I was hoping to steal a bit of it!  If anyone has a few minutes a minutes to check it out, I'd love to hear what you think, good/bad/whatever.

Thanks!
Andrew

link to blog:
http://www.andrewmartinmusic.net/the-lab

[LucifersTrip]

the most obvious is the pedal power clip is the worst...very weak sounding and less fuzzy

[Thecomedian]

I suspect the reason some people think "almost dead" batteries are key, is when it comes to a unit that has slightly higher hFE and a lower battery voltage will bring the bias down into the "mojo" region. Its always a fun way to while away a night shifting DC voltage around on a spice simulated version of FF and looking at all the little graphies.

As an example, let's take a FF that shows 6.5v at the Q2 collector and 1.37v at Q1 collector. drop the voltage from 9 to 6, and Q1 is down to 1.31, not much difference, but Q2 is down to 3.7v, and the voltage waveforms of Q1 collector and Q2 collector are now overlapping where before they were separated. This overlap means that they are the same voltage or even going into "negative voltage" with respect to the required bias for the B-C junction (which is supposed to be 0.2-0.3v for Ge and 0.6-0.7v for Si). The fuzz in this instance will seem to be much more "alive", because the battery juice is causing the biasing to change and actually get the desired fuzz function out of the circuit.

Using a looper isn't going to get the same results as plugging your guitar straight into the Fuzz. The idea of eliminating slightly different or "off" strokes of the string in repeated tests is a good one, but the looper wont interact with the fuzz like straight from guitar to fuzz. This is probably why there was pretty much zero difference, no matter the battery changes. Logically, there should have been very noticeable differences for the changes in voltage of the batteries, however there weren't and I'd guess it's because the looper doesn't simulate a guitar's outputs, with it's impedance, it's low current output, and so on. I'd be willing to be the looper has a buffer output.

You may not have the or inclination, but ideally, you'd set a volume from guitar resistance to specific ohms using a DMM, do the same for the gain pot of the unit and the volume control of the unit (the output cap and the volume pot form a low pass filter, which is why bonamassa fuzz faces are considered "darker"),  and then you have yourself a huge battery of tests with all the permutations involved of the 3 pots that will affect tone in addition to the 3 batteries and the 2 different voltages per battery. You might have masked any tonal differences for battery charge or type by not running through those or by using the looper instead of guitar through fuzz.

http://www.geofex.com/article_folders/fuzzface/fftech.htm

The split collector load resistor of the second transistor acts like a volume pot permanently set to a low value. This is because the power supply is effectively at AC ground because of the low AC impedance of the battery. Incidentally, this is why the FF sounds different with different batteries and with the same battery as it gets run down - the impedance of the battery can change the effective value of the smaller resistor by an significant amount.

If R.G. or PRR get around, they might correct some of my intuitions.

the most obvious is the pedal power clip is the worst...very weak sounding and less fuzzy

?? I honestly didn't hear the difference between pedal power and the other bit.

[afrogoose]

Thanks for the feedback guys!

I agree that the pedal power 2 clips sound the most different.  Whether that is better or worse is subjective, I guess.

Thecomedian; I think I follow you on the effects of a lower voltage battery in a Fuzz Face, but I don't understand how any of those effects are changed when a guitar is 'playing' the fuzz vs a looper?

I'm also a bit confused about the guitar volume, fuzz gain and fuzz volume bit.  I am interested in determining the potential difference in battery types and voltage.  The effect on a fuzz face by turning down your guitar's volume knob, and adjusting the volume and gain knobs on the fuzz are pretty apparent.  Am I missing something?

Thanks again!!

[afrogoose]

bump for science

[Thecomedian]

apologies for not responding sooner. Been a bit busy 

http://www.petecornish.co.uk/case_against_true_bypass.html

Some pedals have an input impedance which is far from high in real terms; the input impedance of the vast majority of amps is 1 Megohm (one million ohms) and in my experience there are few effects pedals that have the same input impedance. A load on the guitar of less than 1 Megohm will reduce the volume and high frequency content of the pickup signal thus giving rise to complaints that "this pedal looses tone/volume" etc. Many effects I have tested have an input impedance of less than 100 Kilohms (ie: only one tenth of the amp input impedance) and cause serious signal losses in the effects chain.

http://www.prymaxevintage.com/hartman-electronics-germanium-crystal-valve-fuzz/

Recognizing that some of fuzz's greatest sonic beauty lies in its ability to interact with the guitar and amp around it, but that flexibility is tantamount, the Germanium Crystal Valve preserves the critical interactions between a passive instrument's wiring harness and the fuzz's input but can also be stacked mid signal chain after other pedals without compromising its tone.

http://www.geofex.com/article_folders/fuzzface/fffram.htm

It also has a very low input impedance, which means that it heavily loads anything trying to drive it. [e.g. a guitar] This will be an important point later.

The interaction of the guitar will change due to the loading the FF puts on it. The looper is likely to have a high input impedance and low output impedance, in order to be able to accurately copy the guitar input and push it out to any amp or next pedal's input without losses.

It loses dynamics. In this sense, I mean dynamics of how the changes in impedances and resistances between fuzz and guitar can alter the signal. At certain points with a well biased fuzz, you can have the fuzz sound a particular overdriven yet crisp way with the guitar volume at max, and then lower the guitar volume and increase the fuzz gain to get that same sound, yet it will be very tonally different, slightly darker or more blunt, so to speak.

[afrogoose]

Thecomedian, thank you very much for aggregating all of those articles.  There was some good reading in there!  I'm sure it took some time to paste all of that in, and I appreciate it! 

Although I am not as knowledgeable with the technical aspects, I am certainly aware of the practical results of turning down your guitar's volume knob when ripping through a cranked Fuzz Face.  Rolling back the volume cleans things up, and I'm sure you are right that it is similar but maybe not exactly like turning the gain knob down on the Fuzz Face itself. 

My question though, is this:  Does using a looper somehow neutralize/negate the difference between different types of power sources i.e. an alkaline battery, a carbon zinc batter and and AC power adapter?  Further, does a looper neutralize/negate the effects or differences of a lower voltage power source vs a full 9 volt power source?

I know the answers are out there!  I'm sure someone on DIYstompboxes can help me out! 

Thanks in advance!   

[induction]

My question though, is this:  Does using a looper somehow neutralize/negate the difference between different types of power sources i.e. an alkaline battery, a carbon zinc batter and and AC power adapter?  Further, does a looper neutralize/negate the effects or differences of a lower voltage power source vs a full 9 volt power source?

Not so much 'neutralize/negate'. More like 'dominate'. That is, the fuzz face circuit really wants to be first in the chain, because it works better (IMHO) when it sees a signal with a high output impedance. The ditto looper has an output Z of about 1k, so running your signal through your looper may not be as bad as putting the fuzz face after a buffer* (have you tried this?), but could very well change the response of the circuit to a degree that outweighs the change you'll hear from different power sources. So while you may still hear differences between batteries in your experiment, you are not really hearing the 'real' result, and therefore any preference you determine from your experiment should not be assumed to apply to a realistic use of the pedal. It's kind of like comparing several brands of cheesecake, but dousing them all in soy sauce first.

You can get around this problem by putting a pickup simulator a la Jack Orman between the looper and the fuzz face. The pickup simulator does a good job in recreating the output impedance of a passive electric guitar and restoring the classic fuzz face response. (I use one to allow my wah to play nice with my fuzz face: wah -> buffer -> pickup sim -> fuzz face.) It's also good for re-amping recorded guitar tracks, which is essentially what you're doing. Whether an additional buffer in front of the pickup sim is necessary in your case, I couldn't say for sure. Might be worth some experimentation.

*For reference: a buffer's output Z is generally between 10 and a few hundred ohms, a typical guitar has an output Z between 5k and 20k.

Edit: Sorry, the output Z I quoted for the Ditto is actually for the Hardwire DL-8. I have no idea what the output Z of the Ditto is, but I'm guessing it's pretty low. I wouldn't be surprised if it was less than 100 ohms, but I would be surprised if it was more than 1k.

[psychedelicfish]

My question though, is this:  Does using a looper somehow neutralize/negate the difference between different types of power sources i.e. an alkaline battery, a carbon zinc batter and and AC power adapter?  Further, does a looper neutralize/negate the effects or differences of a lower voltage power source vs a full 9 volt power source?

It won't fully negate the effects of lower battery voltage, but it will reduce their audibility. When you change the battery voltage, the biasing (DC voltage on the base) of the transistor also changes. This changes the way the circuit behaves.

Guitar pickups "like" high impedances. Try plugging a guitar with ordinary (not active) pickups into the low impedance input of an amp (This is labelled "2" on fender amps or "low" on others, meaning low gain and input impedance), and you'll find that the sound you get is very lacking in high end, and has quite a compressed sound.

The FF circuit has, amongst other things, a very low input impedance. When you plug your guitar into it, you get the same (well, similar anyway) sound as you would plugging your guitar into the low impedance input of an amp. Because of this you get a more sustained, less harsh sound out of the FF.

Bipolar Junction Transistors (BJTs) work by a current on the base controlling how much current flows from the collector to the emmiter (or vice versa, depending on BJT types). Valves/tubes and Field Effect Transistors (FETs) are transconductance devices, so a voltage on the grid/gate (the "equivalent" of the base) controls how much current flows through the device. Because the current controls a BJT, anything driving it (a guitar, for instance) "sees" a low impedance. When you change the biasing, the input impedance also changes, so when feeding the FF directly from your guitar, the sound will change.

The looper, unlike your guitar, can (is designed to) drive low impedances, so it's sound won't change when fed into the FF. If you were to feed the output of the looper through one of the circuits in Thecomedian's post, you could get the output of the looper to load down and get a reasonably similar sound to your guitar driving the fuzz face.

induction got his reply in before me, but I spent so long typing that that I'll post it anyway

[kingswayguitar]

sorry
i don't hear any difference in batteries
very subtle difference in the way they were played though (not in an offensive way, just natural)

[psychedelicfish]

very subtle difference in the way they were played though (not in an offensive way, just natural)

Only the first sample was actually played; it was recorded on a looper and replayed on the subsequent samples. That's what most of the conversation has been about so far.

i don't hear any difference in batteries

I can definitely hear a difference between the batteries and the pedal power 2, but I agree with you on there not being an audible difference between battery types. Surely the internal resistance (and therefore sag) would vary between battery types? I can't hear anything. Then again, it might be similar to the the way I feel about valve amps. I can't hear any major differences between solid state and valve amps (except for distortion, but any good solid state circuit can get that right), but when I play through a valve amp, it just feels more "alive". The battery types might be similar, in that any difference can't be heard, but the guitarist can certainly "feel" the difference.

[Gus]

People are still not understanding the FF type circuit the guitar/bass is part of the circuit and the input is an imperfect summing node

There is a feedback resistor from Q2 E to Q1 B this forms a circuit like an inverting opamp however it does not have the gain of an opamp.

With an opamp the input node voltage does not "move" the current changes in the feedback path to keep the node from "moving"

Don't just post what you read on the web think about what is happening.

A FF first stage is like an inverting opamp HOWEVER the open loop gain is limited and depends on where Q1 is biased and the signal level changes things, so the first stage can be viewed as an imperfect inverting circuit due to the limited open loop gain of Q1

Look up an inverting opamp circuit with the typical two resistor example, change the input resistor to the guitar/bass RLC network.  Now look at a FF schematic The gain(guitar/bass volume control changes with the RLC of the guitar) and EQ is caused by the limited gain of Q1 along with the feedback resistor value /the input(the guitar/bass)

I post sim screen shots with guitar/bass cable sims as the input to the circuit

[afrogoose]

induction/psychedelicfish:  Thank you for breaking down the Fuzz Face in language I can understand!  If I'm understanding your guitar amp analogy correctly, than it seems that this high vs low impedance effect is evident in the clips.  I'm hearing the clip without the looper to be a bit darker than the clips that use the looper.  Am I correct that this is the expected effect of using the looper?

Also, thanks for that link to the Jack Orman pickup simulator. (Thank you Jack Orman!!)  That thing looks completely badass and I've already ordered the parts to make one.  I'm going to build one in a pedal and re-record the experiment with looper --> pickup simulator --> fuzz face.  I'm very excited to get a little bit closer to the truth behind these "fuzz face folktales".

Gus:  Thanks for hopping in and further clarifying the fuzz face circuit.  I hope that it is helpful for others, because although I concentrated extra hard while reading your post, I am apparently too stupid to understand it.  However, I can recognize that it is extremely expert information, and I am honored by it in this thread!

[psychedelicfish]

although I concentrated extra hard while reading your post, I am apparently too stupid to understand it.

I think "inexperienced" is the word you're looking for.

[kingswayguitar]

very subtle difference in the way they were played though (not in an offensive way, just natural)

Only the first sample was actually played; it was recorded on a looper and replayed on the subsequent samples. That's what most of the conversation has been about so far.

i don't hear any difference in batteries

I can definitely hear a difference between the batteries and the pedal power 2, but I agree with you on there not being an audible difference between battery types. Surely the internal resistance (and therefore sag) would vary between battery types? I can't hear anything. Then again, it might be similar to the the way I feel about valve amps. I can't hear any major differences between solid state and valve amps (except for distortion, but any good solid state circuit can get that right), but when I play through a valve amp, it just feels more "alive". The battery types might be similar, in that any difference can't be heard, but the guitarist can certainly "feel" the difference.

well that confirms my poor hearing


i completely agree about the "feel" of a pedal

[induction]

I'm hearing the clip without the looper to be a bit darker than the clips that use the looper.  Am I correct that this is the expected effect of using the looper?

Yes. A source with low output impedance will generally make the fuzz face sound more shrill and will be less responsive to dynamics.

[Gus]

[
You can get around this problem by putting a pickup simulator a la Jack Orman between the looper and the fuzz face. The pickup simulator does a good job in recreating the output impedance of a passive electric guitar and restoring the classic fuzz face response. (I use one to allow my wah to play nice with my fuzz face: wah -> buffer -> pickup sim -> fuzz face.) It's also good for re-amping recorded guitar tracks, which is essentially what you're doing. Whether an additional buffer in front of the pickup sim is necessary in your case, I couldn't say for sure. Might be worth some experimentation.

*For reference: a buffer's output Z is generally between 10 and a few hundred ohms, a typical guitar has an output Z between 5k and 20k.

Edit: Sorry, the output Z I quoted for the Ditto is actually for the Hardwire DL-8. I have no idea what the output Z of the Ditto is, but I'm guessing it's pretty low. I wouldn't be surprised if it was less than 100 ohms, but I would be surprised if it was more than 1k.

The pickup sim in not exactly like a guitar it does not have the tone change with the guitar volume control.  You can also use something like a 10K resistor.

The guitar/bass and cable are part of the feedback EQ of a FF like circuit take the 100K or 47K or whatever the feedback resistor is divided by guitar/bass model and cable, you also need to know the Q1 openloop gain

[induction]

The pickup sim in not exactly like a guitar it does not have the tone change with the guitar volume control.  You can also use something like a 10K resistor.

The guitar/bass and cable are part of the feedback EQ of a FF like circuit take the 100K or 47K or whatever the feedback resistor is divided by guitar/bass model and cable, you also need to know the Q1 openloop gain

True, the pickup sim is not a perfect solution, but it will definitely help in this experiment. It doesn't respond the same to adjustments of the volume knob on the guitar, but it does respond pretty well to adjustments of the volume knob on the pickup sim itself. <tangent>By the way, the fuzz face is the only circuit I've come across that benefits from treble bleed caps in the guitar volume control. I've converted all of my guitars except one to 50's les paul wiring because I usually can't stand the way treble bleed caps thin out the sound at lower volume knob settings. I've kept the treble bleed cap in one strat simply because the fuzz face likes it so much. Rolling off the volume gives a bright, cleaned-up but still very aggressive sound from a bridge single coil, and a beautiful, clear tone with a fat, round bottom from a neck single coil.  I haven't been able to get these sounds any other way.</tangent> Obviously, a volume knob on the floor is not as convenient as a volume knob two inches from the strings (unless you fit it into a rocker pedal), but that objection doesn't apply when the signal is coming from a looper instead of a live guitar.

Remember, the goal here is to help the op isolate the sonic effect (if any) of different battery types by minimizing the by-products of the test itself. In my opinion, the pickup sim does that very well. A deep and thorough mathematical understanding of the fuzz face circuit certainly wouldn't hurt, but is not strictly necessary to anyone who wants to perform such a test (as long as they recognize a few basics, such as the importance of the output impedance of the signal source, and the fact that his experiment is only an approximation of live use of the circuit since 'feel' considerations are not captured by the test). This is convenient since the op doesn't have that mathematical understanding (yet), but still wants to perform the test. He heard a story about batteries and fuzz faces, and instead of swallowing it whole, he decided to check for himself. I think this should be encouraged. My own understanding of the circuit is spotty at best, but I have done extensive empirical testing with it, and I feel there is much to gain from these kinds of experiments.

Whether a 10K resistor will perform as well as the pickup sim is something you'll have to test for yourself. In my experience, the resistor works well for subduing the wah/fuzzface catfight, but doesn't do the volume pot cleanup trick quite as well as the pickup sim. My experiments were performed several months ago, at a volume that wouldn't get me arrested, under not-so-controlled methodologies, so YMMV.

[afrogoose]

Ok, so I ordered the parts, and built Jack Orman's pickup simulator into a pedal.  It's pretty cool!  I'm getting ready to run the experiment again, but I'm wondering if anyone has any good ideas for discharging 9 volt batteries?  As of now I've been holding various metal things (car keys, screwdrivers, etc) across both terminals and then remeasuring.  However, I'm not sure this is really safe and it's pretty slow going.

Thanks!
A

[afrogoose]

Hey Everyone!

Thanks again to everyone for contributing to this thread!  I re-ran the experiment with the Guitar Pickup Simulator and updated my blog with the new results.  I also ran the same experiment on a Tube Screamer.  For clarity's sake, I've opened up a new thread with links to the new blog/experiment.

http://www.diystompboxes.com/smfforum/index.php?topic=105178.0

A