Adding sidechain/key input to noise gate

[fractal33]

Just wondering how big of a task it would be to mod an existing somewhat simple noise gate, like the muffler for example, to accept a sidechain input to trigger the gating. Im looking at incorporating something like this into a double pedal with a distortion (pomethium) so the gate would be triggered by the guitar input signal, but it would shut after the output of the distortion pedal. At the moment I’m doing this with digital effects and love the ability to silence a screaming high-gain tone by just muting the strings of my guitar.

The muzzle seems to be an obvious choice, but it seems like it might be a bit overkill for this application, not to mention obtaining some of the components seems to be fairly challenging.

Would love to hear some thoughts on the matter, hours of googling and searching hasn’t lead me to much as far as this particular question goes. Im spending a lot of time trying to study and understand how these pedal circuits work, but alas I’m still very much a beginner. Thanks!

*edit*
After doing some more research I'm getting a better understanding of how these noise gates work and I'm starting to realize it isn't that easy. Simple noise gates function very differently from my understanding by just attenuating the input signal under a certain threshold while a more complex key input gate requires more sophisticated logic to attenuate a separate signal relative to the key input signal's attenuation. Guess I better figure out how to get the components for the Muzzle!

 

[bowanderror]

It kinda depends on how the circuit is set up and what gain-reduction element it's using.

You'll obviously have to disconnect the input signal from the sidechain, but also add a buffer to interface your key input. If there is a lot of gain, phase shift, or filtering before the sidechain splits off, then you'll have to add additional circuitry to bring your key input up to that level.

The Muzzle input is just a simple buffer, from which the sidechain splits off immediately after. This is a pretty ideal simple circuit for a key input, but you'll have to post a schematic for whichever noise gate you have.

 

[fractal33]

It kinda depends on how the circuit is set up and what gain-reduction element it's using.

You'll obviously have to disconnect the input signal from the sidechain, but also add a buffer to interface your key input. If there is a lot of gain, phase shift, or filtering before the sidechain splits off, then you'll have to add additional circuitry to bring your key input up to that level.

The Muzzle input is just a simple buffer, from which the sidechain splits off immediately after. This is a pretty ideal simple circuit for a key input, but you'll have to post a schematic for whichever noise gate you have.

Yeah I was thinking I would split the input and send one buffered clean signal to the key input of the noise gate and the other to the distortion input, then connect the distortion output to the noise gate input. I don't have a specific one in mind but I was thinking maybe trying to do this with the Muffler, however I'm not seeing how this would be possible unless I'm misunderstanding how the gate works(which is highly likely).
I've attached the muffler schematic below.

 

[bowanderror]

I'm thinking that Q3 is being used as a voltage-controlled resistor, but I haven't seen one set up like this before. Usually the JFET would be set up with the drain connected to the through signal path & the source routed eventually to ground. The gate is typically the control signal, but it seems to be both the control signal & the VC resistor output on this. Maybe someone else can chime in to correct me if I'm wrong.

Your best bet might be duplicating the Muffler input section ("IN" through Q1) and where it splits off to the sidechain (C2) & R13, replace C2 with the input cap of your distortion. Then the actual muffler circuit will be the same, except the input to C2 will be from the emitter of the duplicated input section rather than the emitter of the actual Muffler. You could do the same with a simple opamp buffer instead if you prefer.

I'd be interested to see how this sounds, as your gated signal is quite different from the sidechain input. My experience with JFET compressors is that that a control signal vastly different from the source is prone to distortion, which is why you'll often inject some of your output signal in to it. The attack & release times on this are likely MUCH slower though, so that may mean that's not an issue.

 

[Robert]

It's been a while since I looked at this schematic, it had me scratching my head for a minute.
The drawing could definitely be improved, it's a little confusing at first glance.

It's not immediately obvious but the through signal goes through C8 to the non-inverting input of IC1.2, notice VREF_A isn't decoupled so it's not a typical virtual ground.

Q3 shunts the signal to VREF_B (which is decoupled) when the gate clamps.

Technically you should be able to duplicate the input stage for your Key input, break the connection to the left end of C2 and connect the Key signal there. Something like this:



Or, alternatively you can wait a few weeks for the THAT4301 modules to arrive and build a Muzzle.... (Probably the better option)

THAT4301 RetroFit Module - PedalPCB.com

Dynamics Processor

www.pedalpcb.com

 

[fractal33]

@bowanderror and @PedalPCB Thanks a lot I really appreciate both of you taking the time to help me figure this out. It is still a little over my head, but I definitely have a better understanding of it now and makes me feel a little better knowing PedalPCB was confused by it too. I didn't realize those were coming soon so after all of I might just have to wait for the modules to arrive... I'm assuming more through-hole Muzzle PCBs will be available then too?

 

[Robert]

Yep, both are on order.

 

[bowanderror]

It's been a while since I looked at this schematic, it had me scratching my head for a minute.
The drawing could definitely be improved, it's a little confusing at first glance.

It's not immediately obvious but the through signal goes through C8 to the non-inverting input of IC1.2, notice VREF_A isn't decoupled so it's not a typical virtual ground.

Q3 shunts the signal to VREF_B (which is decoupled) when the gate clamps.

Technically you should be able to duplicate the input stage for your Key input, break the connection to the left end of C2 and connect the Key signal there. Something like this:
View attachment 16330


Or, alternatively you can wait a few weeks for the THAT4301 modules to arrive and build a Muzzle.... (Probably the better option)

THAT4301 RetroFit Module - PedalPCB.com

Dynamics Processor

www.pedalpcb.com

Ahh, that's easier to read & looks more like the JFET as variable resistor circuits I'm used to. It even has a bit of feedback injection into the gate for lower distortion, which could definitely be an issue if the sidechain signal is vastly different from the wet path.

I agree it's probably best to wait for the Muzzle if you're not up for some breadboard iterating.

 

[manfesto]

It's been a while since I looked at this schematic, it had me scratching my head for a minute.
The drawing could definitely be improved, it's a little confusing at first glance.

It's not immediately obvious but the through signal goes through C8 to the non-inverting input of IC1.2, notice VREF_A isn't decoupled so it's not a typical virtual ground.

Q3 shunts the signal to VREF_B (which is decoupled) when the gate clamps.

Technically you should be able to duplicate the input stage for your Key input, break the connection to the left end of C2 and connect the Key signal there. Something like this:
View attachment 16330


Or, alternatively you can wait a few weeks for the THAT4301 modules to arrive and build a Muzzle.... (Probably the better option)

THAT4301 RetroFit Module - PedalPCB.com

Dynamics Processor

www.pedalpcb.com

Just checking, is the module all-in-one, or is it an adapter board and we’ll need to source the 4305 and other parts separately?