2 effects, 1 enclosure

[archerarcher]

Hi all, I'm attempting to build a positive voltage fuzz face clone and an mxr envelope filter clone and house them in one enclosure. I want a switch for each effect and would like to be able to use them separately or together, and I was also hoping to wire a blend knob between the two for mixing.
Is this possible? From what I've read so far, I should be able to wire the output from one circuit to the input on the other, but I don't know about the wiring for the blend knob in that case, and I don't know how I would go about wiring the power for both circuits.

Any help is much appreciated.

[R.G.]

If your blending and mixing is done after any DC from the insides of the effects are blocked by capacitors, it'll be fine.

This is true even if both run positive ground or negative ground, too.

Be sure to think through the power issues with a positive ground circuit and a negative ground circuit in the same box though. That calls for one ground (the only one, which references the signal) and two power supplies: +9V and -9V.

[archerarcher]

I must've worded that wrong. I'm looking for specifically:
1) How and where I would wire a blend knob for the two circuits and also what type of pot should I use?
And

2) How would I go about wiring the 9v terminals on each circuit to one 9v dc jack, assuming both circuits are positive ground?

[MikeH]

I must've worded that wrong. I'm looking for specifically:
1) How and where I would wire a blend knob for the two circuits and also what type of pot should I use?
And

2) How would I go about wiring the 9v terminals on each circuit to one 9v dc jack, assuming both circuits are positive ground?

To achieve blending, the circuits would typically be run in parallel, as opposed to series, in which you would wire the ouput of one into the other.  There are a few builds that do this, some more complex than others.  My personal favorite is the splitter/blend project at runoffgroove.com.

And if the circuits are all the same polarity, just connect all of the 9v leads to the same place on the DC jack.

[earthtonesaudio]

1.  Your requirements are a bit more complicated than they may first appear.  Wiring two effects in series is trivial, just wire them as if they're two separate effects that just happen to be located inside the same enclosure.  Wiring two effects so that you can "blend" them together implies you are using them in parallel.  The standard approach to parallel processing is to first split the incoming signal, run each of the branches through an effect, then mix back to a single signal (the "mix" being your blend control).  Series connection is incompatible with parallel connection! 

For some circuits you can just hard-wire the two inputs in parallel but the Fuzz Face has a low input impedance.  This means if you simply wire both inputs in parallel the Fuzz Face will hog all the current and the MXR will get a much weaker signal. 
A buffered splitter is the obvious solution but that creates a Fuzz Face-specific problem, because driving a Fuzz Face with a low impedance will increase the gain and treble dramatically.  This may not be an issue for you but if it is you can add some series impedance between the buffer and the Fuzz Face to drop the gain and treble back to it's approximate starting point.

All of this implies the switching will be more complicated than a pair of bypass switches, because you are asking for the following combinations:
1. no effects engaged (bypass)
2. Fuzz only
3. MXR only
4. Fuzz and MXR (series)
5. Fuzz and MXR (parallel)

If you wanted to select from these choices with a rotary switch that would be doable, but I suspect you want some or all of these to be footswitch-accessible.  Here is where it can get complicated, and where your preferences will dictate everything.

-One of the simplest scenarios is to have a master bypass switch as a foot control, and select the other options with rotary or toggle switches.
-For series operation only, you can use one footswitch per effect.
-For parallel operation only, you can still use one footswitch per effect, but achieving "true" bypass is difficult; buffered bypass would be the way to go.
-For series/parallel/one/none all controlled with footswitches I think you must include some logic circuitry and electronically controlled switches.  One switch for each effect and a third switch for series/parallel selection is the simplest way I think, but you could do something more fancy by making it so both switches pressed simultaneously toggles the third parameter, or holding a switch for a long time, etc.

2.  The easiest way to deal with the power is to build an NPN Fuzz Face which would normally be powered by +9V and 0V (ground).  Then power for both circuits is exactly the same and you can simply run power/ground wires to each effect from a single jack.

[archerarcher]

Awesome! Now I feel like I'm getting somewhere.
So if I run them in parallel, I'd be able to get just one effect or the other anyway by using the blend, correct?
Could you point me in the right direction for the buffer?

[archerarcher]

Also, if I run them in parallel I wouldn't need a footswitch for each effect, would I? Because when you switch it on, both effects are going to be turned on.

[earthtonesaudio]

Here is a simple splitter/mixer circuit.  First note that I did not include any DC-blocking capacitors on the splitter's outputs.  I am assuming that your Fuzz Face and MXR Envelope Filter circuits both have those already.  Note also there are three options shown for connecting to the fuzz: straight wire, resistor only, or inductor-resistor/potentiometer.  Choose one.  See also this explanation on guitar pickup simulation for why I included the inductor option.
The output is a simple passive mixer followed by a buffer.  You can use a dual op-amp package.  Values shown may not be optimal, particularly the 1M mixer pot.  I was assuming you will keep the volume control from the Fuzz Face, which will help with mixing because the fuzz will probably sound louder than the filter at most settings.  You can alter the value of the mixer pot and/or the biasing resistor on the op-amp buffer that follows it to get the optimal "feel" to the mixing in terms of rotation versus relative mix of each effect.




A very simple way to bypass all of this is to treat "input" and "output" as in/out of a single effect and bypass that using your favorite switching scheme.

[archerarcher]

Wow, thank you so much! I really didn't expect this much useful information so quickly. I'm going to get cracking on this ASAP.

[DavenPaget]

Here is a simple splitter/mixer circuit.  First note that I did not include any DC-blocking capacitors on the splitter's outputs.  I am assuming that your Fuzz Face and MXR Envelope Filter circuits both have those already.  Note also there are three options shown for connecting to the fuzz: straight wire, resistor only, or inductor-resistor/potentiometer.  Choose one.  See also this explanation on guitar pickup simulation for why I included the inductor option.
The output is a simple passive mixer followed by a buffer.  You can use a dual op-amp package.  Values shown may not be optimal, particularly the 1M mixer pot.  I was assuming you will keep the volume control from the Fuzz Face, which will help with mixing because the fuzz will probably sound louder than the filter at most settings.  You can alter the value of the mixer pot and/or the biasing resistor on the op-amp buffer that follows it to get the optimal "feel" to the mixing in terms of rotation versus relative mix of each effect.




A very simple way to bypass all of this is to treat "input" and "output" as in/out of a single effect and bypass that using your favorite switching scheme.

Isn't 1H MASSIVE ?

[earthtonesaudio]

Isn't 1H MASSIVE ?

Absolutely huge!  However, many single coils are in the 2H range, and humbuckers might have more than 10H.  The idea is to simulate that inductance.  The Muzique.com page recommends an easy-to-find transformer for this part, using only the primary winding.

The inductance value is not critical, it's just to get you closer to the "guitar impedance" ballpark.  Some people may think the straight wire sounds find, others may be satisfied with the resistor only.  It's a trade-off between authenticity and the amount of effort/cost you're willing to spend.