Simple Muff Fuzz woes...

[clipman3]

The simple ones are always harder for me for some reason... 
I recently built a muff fuzz from this schem: http://fuzzcentral.ssguitar.com/schematics/mufffuzztransschem.gif
Super simple circuit. Really similar to a fuzz face, but with clipping diodes and a set gain. I decided to add a 100k trimpot right before the input cap so I could vary the gain in a natural sounding way, as if the guitar was being rolled off. Easy mod. I didn't have any 100k pots on hand for the volume, so I just used a 500k and thought nothing of it. My main goal of this pedal was to make a nifty lead boost/low gain pedal to compliment my main dirt pedal, but now I'm stuck with this thing being SUPER bright. I've been changing out the output caps all day to try to tame the ear-piercing high end to no avail (went up to ~5uf), Ideas??

[pappasmurfsharem]

You can try a low pass filter prior to the volume.

A 1.2k resistor in series then a .01 uF to ground. That puts a corner frequency. At 13000hz

You can try various values but I did something similar on a BSIAB build with a 3 knob tone stack.

[pappasmurfsharem]

Use the RC filter calculator here to find the values you want at the frequency you want
http://www.muzique.com/schem/filter.htm


Phone won't let me edit the previous post

[clipman3]

You can try a low pass filter prior to the volume.

A 1.2k resistor in series then a .01 uF to ground. That puts a corner frequency. At 13000hz

You can try various values but I did something similar on a BSIAB build with a 3 knob tone stack.

Thanks bud, I'll give that a go tomorrow. I have used the RF calculator before, but I'm not great at honing in on what frequency I want.

[pappasmurfsharem]

You can try a low pass filter prior to the volume.

A 1.2k resistor in series then a .01 uF to ground. That puts a corner frequency. At 13000hz

You can try various values but I did something similar on a BSIAB build with a 3 knob tone stack.

Thanks bud, I'll give that a go tomorrow. I have used the RF calculator before, but I'm not great at honing in on what frequency I want.

I'm not either... that number is just a guesstimate but remember you can't hear over 20k usually.  At 13 it will roll off considerably above 13k and a bit below as well. 13 just being the corner

[pappasmurfsharem]

I need to adjust my BSIAB build a bit. I did a roll off around 11k and it's slightly blanket over a speaker sounding I used a 2k and a 6n8. So im going throw a 1k in and a 1k trim so I can dial it in better

[LucifersTrip]

I'm slightly confused...Are you saying the 500K volume pot caused the brightness?

[clipman3]

I'm slightly confused...Are you saying the 500K volume pot caused the brightness?

I'm just saying that the thing is super bright when I give it a boost, and I can't seem to tame the highs

[LucifersTrip]

Did you check to make sure you have correct voltages, the diodes are in correctly and you didn't accidentally throw in a .001 output cap?

That thing is really not bright (thus, the name Muff) if built properly.

[clipman3]

Did you check to make sure you have correct voltages, the diodes are in correctly and you didn't accidentally throw in a .001 output cap?

That thing is really not bright (thus, the name Muff) if built properly.

I didn't check the voltages, but they're wired up correctly and it's pretty loud. It's not very bright on it's own, but is bright when I put something else behind it to boost it. I'm just using silicon diodes, and have taken the output cap up to 4.7uF. Didn't wanna change the input cap, because I wanted to keep it's distortion characteristics. Directly from in from the guitar, its REALLY dark, but it's placed after a buffer in the chain right now

[LucifersTrip]

That's a tough one...let's say you figure out some way so it works well with the boost your currently using. Will it also sound good if you use a different boost in the future?

[clipman3]

That's a tough one...let's say you figure out some way so it works well with the boost your currently using. Will it also sound good if you use a different boost in the future?

Probably... The overdrive alone isn't a particularly bright one in and of itself. It's a Boss OS-2 I modded to be a bit more upfront in the Overdrive section. I'm thinking about having a switch so I can have a bright and dark output should I ever need it to brighten up a bit, or maybe a BMP tone control? I've never messed with the BMP tone control before so I don't know how well it responds in related circuits, but I have heard it's phenomenal. I know it is in the original pedal.

[wilrecar77]

In a pedal like a fuzz face, which the muff fuzz essentially is, the low impedance of the input rolls off highs of the guitar in an interactive way with the guitar. Putting almost any pedal before it, even if it is not a buffer, will act at least somewhat as a buffer. If it is the low impedance being buffered causing the brightness, you could put a low pass filter at the beginning of the pedal to roll off the highs going into it, but it may still act funny when used alone vs used with other pedals.

[clipman3]

In a pedal like a fuzz face, which the muff fuzz essentially is, the low impedance of the input rolls off highs of the guitar in an interactive way with the guitar. Putting almost any pedal before it, even if it is not a buffer, will act at least somewhat as a buffer. If it is the low impedance being buffered causing the brightness, you could put a low pass filter at the beginning of the pedal to roll off the highs going into it, but it may still act funny when used alone vs used with other pedals.

That is exactly what I was thinking the problem was, but I didn't think to roll of anything before the gain stages for fear of affecting the fuzziness. Thats a great idea, though, and seems like it'll fix it. That would also explain why changing the output caps wasn't doing much, and why it gets brighter and brighter with more boost. Thanks man  It's a great little pedal.

[Mark Hammer]

The Muff Fuzz is basically a silicon Fuzz Face with fixed gain and clipping diodes to "help out".  Putting a variable resistance and a 10-22uf cap between the Q2 emitter and ground will let you vary the gain of the circuit, as in the Fuzz Face, and get a much broader palette of sounds, as illustrated here: http://www.youtube.com/watch?v=npxq2DSAyuk

There are a few ways to do it, depending on how much gain you want.  For example, one way might be to run a 680R fixed resistor and 2k pot from emitter to ground, and run the cap from the pot wiper to ground.  If the fixed resistor is connected between the pot and emitter, then max gain is greater than stock, but not over the top.  If the pot is situated between the emitter and fixed resistor, gain can get very hot.  Both work, choice depends on taste.  If the pot is the one tied to ground, then moving the wiper all the way to the ground side yields the stock Muff Fuzz sound.  Andas the video illustrates, it still cleans up in response to guitar volume changes.

Alternatively, you can leave the 2k7 in place and run a 5k pot and 22uf cap in parallel with the 2k7.  When the path between emitter and cap gets below 2k7, you start to add more gain.  Greater than 2k7 and you're back to stock, more or less.

Yet one more way is to leave the 2k7 in place, as above, and connect the wiper of a 10k linear pot to the emitter.  One outside lug of the pot does to ground through a 22uf cap, and the other goes to ground through a 1uf cap.  In the one direction from midpoint it adds gain across the spectrum, and in the other direction it adds gain just for highs, becoming a kind of treble booster.  

If this sort of thing appeals to you but you'd like it simplified, use a SPDT on-off-on toggle to connect a fixed resistor and selected cap to ground...or not.  Middle position is stock 2k7 and no cap.  Outside positions are the boost parameters of your choosing.  So, perhaps  1k and 22uf on the one side (more full bandwidth growl, but not over the top), and 100R + 1uf on the other (more top end bite).

I stuck an SWTC-type treble cut between the diodes and volume pot on the one illustrated in the video.  As you can hear, it helps to rein in the fizz nicely.

Finally, note that the diodes are a nice addition but not a requirement.  Fuzz Face circuits have been happily churning out distortion for several generations now in the absence of clipping diodes.

[clipman3]

The Muff Fuzz is basically a silicon Fuzz Face with fixed gain and clipping diodes to "help out".  Putting a variable resistance and a 10-22uf cap between the Q2 emitter and ground will let you vary the gain of the circuit, as in the Fuzz Face, and get a much broader palette of sounds, as illustrated here: http://www.youtube.com/watch?v=npxq2DSAyu

Thanks for the extensive response! That gives me a lot more options on what I can do... I'll probably start by adding another input cap that is much larger before the first one in the schematic, and then move to this. I like the idea of changing the distortions characteristics with a switch.
It's funny, cuz I swore I'd never build a fuzz face because I hated how they sound, but here I am messing with one and loving it lol

[Mark Hammer]

One thing I find really interesting is the way that ZVex uses a variable resistance between the emitter of Q2 and the base of Q1 in the Mammoth (itself a Fuzz Face tweaked for bass use).  You can see it illustrated here in the madbean Sabretooth: madbeanpedals.com/projects/Sabertooth/docs/Sabertooth_ver.4.pdf‎

That feedback resistance interacts with the gain control in the Mammoth in interesting ways.  There is every reason to expect that it could also do so in the Muff Fuzz.

Again, it does not have to be a pot but can be 3-position toggle.  Let's say the stock 100k resistor between Q1-base and Q2-emitter is now a 100k resistor and 330k resistor in series (the order doesn't matter).  The common of the toggle is tied to their junction.  One outside lug of the toggle simply bridges the 330k resistor with straight wire so that you end up with 100k.  The other outside lug bridges the 330k with some parallel resistance to achieve something more than just 100k in total, but less than 430k (100k+330k).  So, you get stock, plus two other settings.

You might not find it useful in a stock Muff Fuzz, but once you add the variable gain, I'm sure you will.

[Gus]

One thing I find really interesting is the way that ZVex uses a variable resistance between the emitter of Q2 and the base of Q1 in the Mammoth (itself a Fuzz Face tweaked for bass use).  You can see it illustrated here in the madbean Sabretooth: madbeanpedals.com/projects/Sabertooth/docs/Sabertooth_ver.4.pdf‎

That feedback resistance interacts with the gain control in the Mammoth in interesting ways.  There is every reason to expect that it could also do so in the Muff Fuzz.

Again, it does not have to be a pot but can be 3-position toggle.  Let's say the stock 100k resistor between Q1-base and Q2-emitter is now a 100k resistor and 330k resistor in series (the order doesn't matter).  The common of the toggle is tied to their junction.  One outside lug of the toggle simply bridges the 330k resistor with straight wire so that you end up with 100k.  The other outside lug bridges the 330k with some parallel resistance to achieve something more than just 100k in total, but less than 430k (100k+330k).  So, you get stock, plus two other settings.

You might not find it useful in a stock Muff Fuzz, but once you add the variable gain, I'm sure you will.

Mark the feedback resistor does two things it adjusts the closed gain of Q1 somewhat AND when it is at the higher resistance value it "starves" Q1 current going to the base and upsets the bias of the complete circuit

For others think of the fuzz face circuit as an imperfect inverting opamp.  If Q1 had the gain of an opamp the input would be a summing node of about 0 ohms.  Substitute the input resistor with the guitar/bass RLC and the cable and note the reduced openloop gain of Q1 compared to a opamp

If you look at screenshots of sims I post I often include a simple model of a guitar or bass

Clipping diode clause "edges" and can add to brightness