NPN Fuzz Face/Big Muff hybrid

[floribe123]

Hey there, I'm trying to build a pedal that combines a NPN Fuzz Face circuit with a Big Muff. This is my first attempt at making a pedal and despite having had a couple of electronics classes I'm still very new to it.
I would like to know two things:

1) On the Fuzz Face portion of the circuit, can I just switch the 9V battery connection for a VCC like the Big Muff portion? If not, what do I need to do in order to substitute it for a VCC connection?

2) A teacher told me that the Blend and Volume knobs' values are a bit high. What would the ideal values for those knobs be?

Thanks in advance for your help!

[duck_arse]

welcome to the forum, floribe123.

your circuit, I think, shows the battery near the fuzzface section with positive ground. this is wrong for the npn version, it should be negative ground, and can use the same Vcc as the big muff section. you may want/need isolate the two sections with a supply R/C filter to prevent interactions and feedbacks.

your diagram shows the mix pot connected wrong. it should have one end to each output, and no ground connection. no bypass switching?

also, the fuzzface input impedance will load the input signal some, and may proove deleterious to the workings of the big muff, sucking toan. you will need others, more versed, to advise here.

[PRR]

................A teacher told me that .....

Teachers may be good for making you think. They are far from infallible. They may know less than they put on their application. Or this is not their best subject. Most are very over-worked and under-paid, so you may not have their full attention.

Your "Blend" and "Volume" do the same thing: reduce the level of the *combined* sound. As Duck says, the "Blend" could be wired different. (and battery too.)

And yes, the input of a FF is a heavy load on the guitar which will change the signal seen by a parallel path. (And a buffer is not the fix because the FF's loading on wound pickup and pot is part of its "tone".)

Without really thinking, I'd suspect the 4-transistor path has MUCH more gain than the 2-transistor path. Slightly equalized by the "blendless" plan showing 330r on one side and 15k on the other side, making loss of 45 on the Muff side.

However, battery polarity fixed, I do not see anything which will SMOKE. And stuff like this, it is far easier to build it and see, than to analyze it in advance. On breadboard or a good layout and a hot solder iron, you can quickly try different connections of the mix and output network, even quicker than I can mouse parts in SPICE (which won't tell us how it "sounds").

[antonis]

your diagram shows the mix pot connected wrong. it should have one end to each output, and no ground connection.

What he said..

[iainpunk]

welcome to the forum!

i was wondering what the rationale is behind putting the FF and BMP in parallel?

cheers, Iain

[Mark Hammer]

Also, welcome.

A couple of things to consider:

• How different or similar are the output levels of the Muff and FuzzFace sides?  You are relying on the "Balance" pot to take care of any differences, but if, for example, you wanted to blend a higher-gain setting on one with a lower-gain setting on the other, could that be achievable in an audible manner?  Maybe the high-gain setting of the one side would be SO much louder than the low-gain setting of the other that you wouldn't be able to hear any of the low-gain sound no matter where you set the Balance control.
• What is your objective in being able to have both of these in one blendable pedal?  It's a lot of work and potential heartache for something motivated by "That would be cool".  Having a practical and well-defined goal will let you have some insight into what sorts of adjustment/modifications to the circuit might make it more usable and better-behaved.  For example, the Muff can be made wooly/dull-sounding with its tone control, but the FuzzFace comes without ANY tonal modification at all.  Will that restrict what you can do with this combination?
• Since both of these impose lots of gain, layout will be important to avoid any unwanted oscillation and noise.
• I'm not sure how much having both circuits' inputs sharing the same input feed will load them down in an undesirable way, producing something less than what each alone might do.

[floribe123]

Thank you all for your responses!

i was wondering what the rationale is behind putting the FF and BMP in parallel?

I just wanted to do something that was a little more than a Big Muff and since I've always been curious about using a Fuzz Face I figured I could try to do both in a single pedal.

How different or similar are the output levels of the Muff and FuzzFace sides?  You are relying on the "Balance" pot to take care of any differences, but if, for example, you wanted to blend a higher-gain setting on one with a lower-gain setting on the other, could that be achievable in an audible manner?  Maybe the high-gain setting of the one side would be SO much louder than the low-gain setting of the other that you wouldn't be able to hear any of the low-gain sound no matter where you set the Balance control.[/li]
[/list]

How would I avoid that? Would an individual volume knob for each section of the pedal solve that issue?

Here's how the schematic is, after making the changes people suggested

[antonis]

How would I avoid that?

A brute way is to also make Big Muff output stage of variabale gain by replacing R25 (3k3) with a 1k pot in series with 2k2 resistor and AC short pot's wiper via a 22μF cap..
(just like FUZZ1 pot..)

[Mark Hammer]

Let's consider your revised schematic with the 100k blend pot.  Imagine the 500k volume pot set to max, and the blend pot set all the way to one side.  Doesn't matter which.

One of the circuits will see 100k in series with its output, and 500k to ground, dropping its amplitude to a bit over 80% of maximum.  The other will "see" zero ohms in series, and 500k to ground.  Will this provide the sort of blend/mix/balance you were imagining?  I suspect not.  And as I noted earlier, at this point you don't know how loud each circuit is, relative to the other.

It will be a bit of a nuisance to adjust, but if you stick the respective volume pots on each of the circuits, and run a series resistor from their volume pot wipers to the output, for passive mixing, I think you'll get what you're trying to achieve.

We still haven't addressed the issue of whether passively coupling the two inputs to the same input jack will cause issues.

[ThermionicScott]

I figured I could try to do both in a single pedal.

Every so often, a comment makes me realize how what I consider to be conventional thinking has become dated.

Combination pedals are all the rage these days, and why not?  It's convenient to have more voices in a single pedal and you can mix or feed them into each other for even more variety.  If starting from scratch, why wouldn't one build a couple effects into one box?   

But I think in this case it's going to be hard to use both effects at once, for the reason Mark and Paul have already stated -- a Fuzz Face is what it is because it loads your guitar pickup in a way that modern buffered effects don't.  It seems likely that the presence of the Fuzz Face circuit will affect how the Big Muff output sounds.  But who knows, maybe you could breadboard the whole thing as proposed to find out?

If that doesn't work, there are lots of modern fuzz circuits (with buffered inputs) that could be grafted into this project instead...

[Mark Hammer]

I made some soup the other day that called for a couple egg yolks to be blended with it.  Naturally, the yolks had to be integrated with the broth in a certain way to avoid them getting instantly cooked and turning into yellow chunks in the soup.

I don't wish to rain on floribe's parade.  There is no reason why these two circuits could NOT be combined into one blendable pedal.  HOWEVER, like the soup, precautions need to be taken to compensate for, and avoid, all the sonic problems mentioned so far. 

[floribe123]

It will be a bit of a nuisance to adjust, but if you stick the respective volume pots on each of the circuits, and run a series resistor from their volume pot wipers to the output, for passive mixing, I think you'll get what you're trying to achieve.

Thank you so much for your input, Mark.

Let me see if I understood: You're suggesting I add both pedals' respective Volume pots and then add a different resistor in front of each of them in order for them to be more balanced before the Blend pot?

[Mark Hammer]

Not exactly.

Their individual volume controls WILL be your "blend", with the added resistor mixing the two outputs together.  That's why I say it may be a bit of a nuisance to adjust.  Getting the balance and level you want may require you to play with the individual volume pots until you get the blend AND level you want.