Fuzz Face Volume Pot/Guitar Volume Pot Interaction

[RRJackson]

Let me start out with an apology for being a little slow understanding some of this stuff from time to time. I'm sure I'm about to ask something that a simple grasp of basic principles of electronics would have already told me. That said...

I built a few Fuzz Face pedals and found that when they were on my bench I really hated the sound of the Volume control at anything other than all the way on. Now, part of this may be because the little Champ clone I use at my workbench points right at my face, so I may be hearing things that most people wouldn't notice, but it really sounded bad to me. A little noisy, but also very...I dunno almost artificial or something, which may be the filter created by the resistance of the pot and in the input cap. Anyway, I figured I'd try to drop the corner frequency of that, so I started using 1 meg pots and now I don't mind turning down the Volume control. I also use a 22K resistor on the input because it seems to help the circuit play nice with humbuckers.

OK, that preamble was all to explain how I have my Fuzz Face clones configured. The issue I'm having is with the Volume pot on my guitar controlling the level of distortion from the Fuzz Face. Really, the main reason I like the Fuzz Face circuit is because I can control it with the Volume pot on my guitar. However, some of the clones I've built allow a very smooth reduction in distortion throughout the range of the guitar's Volume pot and some of them have a very narrow range of adjustment that's pretty much all right at the very end of their throw. This almost seems random, but there's obviously something going on that would be repeatable if I wasn't missing some important something.

Anyway, I really appreciate any insight that any of you could bring to the situation. I've been wiring up guitars for decades, but I'm fairly new to building effects and I'm constantly wishing I knew a little more about what I'm doing.

-Rob

[peterg]

Welcome to the forum! Are you using the same guitar with every Fuzz Face? If you are using different guitars they may have different volume pots. An audio pot will give you a smooth reduction and a linear pot will cause the bunching you describe.  You could always build your Fuzz Faces with a 100K audio pot at the input to control the gain.

[LightSoundGeometry]

Hello, this is why you have to layout the circuit ahead of time on the breadboard and experiment with the active pieces before you make the permanent move to the pedals. This way you can work out all the bugs and get that tone you are looking for. There was another thread on here that touched on the subject of transistor timbre as something that cannot be calculated on a data sheet, but only by trying them out in a test run.

[RRJackson]

Welcome to the forum! Are you using the same guitar with every Fuzz Face? If you are using different guitars they may have different volume pots. An audio pot will give you a smooth reduction and a linear pot will cause the bunching you describe.  You could always build your Fuzz Faces with a 100K audio pot at the input to control the gain.

I have a Junior with a 500K linear pot and a single humbucker that I use to test it with a humbucker and an old Yamaha SSC500 with three single coils and a 250K audio pot that I use for single coils. Yeah, come to think of it the Yamaha usually seems to work a lot better, but I always attributed that to the single coils. Huh. Thanks!

[RRJackson]

Hello, this is why you have to layout the circuit ahead of time on the breadboard and experiment with the active pieces before you make the permanent move to the pedals. This way you can work out all the bugs and get that tone you are looking for. There was another thread on here that touched on the subject of transistor timbre as something that cannot be calculated on a data sheet, but only by trying them out in a test run.

I actually use this aesthetically-less-than-appealing testbed to try out different component values and (mostly) to match transistors. I built it with sockets because instrument measurements are wonderful, but I like to make sure my ears get involved.



-Rob

[LightSoundGeometry]

I only have one guitar, so its easier for me to tweek things to my liking because I am only worried about the one rig/set up.  I misread your  post, i thought you were boxing up the fuzzes and then finding out they werent playing along with your guitar and amp.

you have more electronics skills than you admitting to lol , especially if your junk test box is in an NOS turret style form; me thinks you know a lot more than you letting on 

[RRJackson]

Oh, I've been soldering on guitars for decades, but with no real electronics training or experience. Most of what I know how to do is more from trial and error than any kind of thinky-thinky stuff I should have learned formally. So when I run up against something I don't understand my immediate assumption is that it's probably a problem I wouldn't be having if I'd spent more time on the Engineering side of the campus and less on the Performing Arts side when I was younger. 

That testbed is funny. I got the aluminum sheet I used to make the, "enclosure" to make some control panels and it was just too thick for my brake to bend accurately. So when I want to put together a testbed I drill some holes, make a couple of crude bends and call it a day. That board was cut off an old amp board from a homebrewed JTM45 build that I swapped out for something different after a few months. I kinda recycle everything.

I only have one guitar, so its easier for me to tweek things to my liking because I am only worried about the one rig/set up.  I misread your  post, i thought you were boxing up the fuzzes and then finding out they werent playing along with your guitar and amp.

you have more electronics skills than you admitting to lol , especially if your junk test box is in an NOS turret style form; me thinks you know a lot more than you letting on 

[smallbearelec]

I actually use this aesthetically-less-than-appealing testbed to try out different component values

The test-bed idea is good. Suggestion: Replace the turret board with a small breadboard strip, and you will have more room for components. The guy who runs KillerTone http://www.killertone.com/ created a product on this idea.

This one http://diy.smallbearelec.com/HowTos/IdeaBoxAndBoard/IdeaBox.htm was my contribution.

Welcome to the Forum, and Happy Construction!

[RRJackson]

Oh, that is really clever. Nicely done! I'm gonna have to try that.

-Rob

This one http://diy.smallbearelec.com/HowTos/IdeaBoxAndBoard/IdeaBox.htm was my contribution.

Welcome to the Forum, and Happy Construction!

[RRJackson]

BTW, I've done these "ugly" testbeds for a few different circuits. Here's the one I did for a Buzzaround a while back.

-Rob

[tubegeek]

...my immediate assumption is that it's probably a problem I wouldn't be having if I'd spent more time on the Engineering side of the campus and less on the Performing Arts side when I was younger. 

Well, at least you got laid that way, though.

[Gus]

LT Spice and other programs can help you understand the interactions
Three screenshots from LT Spice of a fuzz
guitar part of the sim is a single coil with tone at max treble and 390 pf cable cap. The guitar volume is changed from min(bottom green) to max
first graph is with R14 120 ohms, second is with the 120 R14 shorted

[anotherjim]

The issue with the Junior might be how the vol pot is wired - and I've never liked linear pots on guitars either - but is the pot wired wiper to pickup or wiper to jack tip? The latter would preserve highs as you turn down, while the former will dull as you turn down - which might work better for you -  or not

[RRJackson]

The issue with the Junior might be how the vol pot is wired - and I've never liked linear pots on guitars either - but is the pot wired wiper to pickup or wiper to jack tip? The latter would preserve highs as you turn down, while the former will dull as you turn down - which might work better for you -  or not

Wiper to jack tip. I don't think I've ever wired a guitar with the wiper to the pickup. I guess I just never saw it done like that.

-Rob

[Cozybuilder]

Rob-
Heres a useful site for different guitar wiring schemes:

http://www.guitarelectronics.com/product/WD1H11_05/Guitar-Wiring-Diagram-1-Humbucker1-Volume1-ToneSeries-Parallel.html

[RRJackson]

I'm not sure I follow you here. Are you showing me how a change in output impedance can influence can change the arc of response? I'm sorry if I'm being really obtuse here.

LT Spice and other programs can help you understand the interactions
Three screenshots from LT Spice of a fuzz
guitar part of the sim is a single coil with tone at max treble and 390 pf cable cap. The guitar volume is changed from min(bottom green) to max
first graph is with R14 120 ohms, second is with the 120 R14 shorted

[RRJackson]

Rob-
Heres a useful site for different guitar wiring schemes:

http://www.guitarelectronics.com/product/WD1H11_05/Guitar-Wiring-Diagram-1-Humbucker1-Volume1-ToneSeries-Parallel.html

I actually paid them to do the layout for this bass model that I never ended up introducing into the lineup. I was kinda hoping they'd have a trick up their sleeve to keep there from being a volume drop with both pots rolled all the way on, but I guess there really ain't no such thing as a free lunch. BTW, the top pot is the P volume and the bottom pot is the pair of Js.

[Gus]

I was trying to show two things both graphs show the sweep the guitar volume with the FF like circuit gain fixed

One how the guitar volume interacts with the input of the FF like circuit
Two how things change with the setting of the gain of FF like circuits even 120 ohms can make a difference.

[RRJackson]

Kind of scary how easily I miss the point. Point taken. Thank you.

-Rob

I was trying to show two things both graphs show the sweep the guitar volume with the FF like circuit gain fixed

One how the guitar volume interacts with the input of the FF like circuit
Two how things change with the setting of the gain of FF like circuits even 120 ohms can make a difference.