Mute Mutations (Experimenting w/ LFO Driven Mute Circuits)

[Ohioisonfire]

Hello Again,

I have been working on an automatic mute/stutter/square wave tremolo circuit for some time. In summary, an LFO driving something that would mute the signal on and off constantly.

Originally I intended to use relays. I breadboarded this and was overall quite happy with the result. I decided to move on from this for a number of reasons, but the two biggest factors were relay lifespan and current consumption.

The next circuit tested was opto-fet/opto-coupler/whatever you call them devices (TLP222 or similar). These seemed attractive as they are very easy to drive and solve my two biggest complaints with the relay. However, I could not get the clicking/popping quiet enough with the circuits I tested. I suspect this is the result of these devices rapidly turning the audio on and off without any consideration for zero crossing or similar. I also have obsolescence concerns with these parts. Would be happy to dive deeper into these if someone thinks the clicking/popping can be tweaked out.

I am now looking into JFET mute circuits since I can control the on/off speed, thankfully there are a lot of resources available on designing these circuits, unfortunately most of it is geared towards dual rail supplies. Something I would like to understand better:

• I understand for a series JFET mute, the gate voltage needs to be bigger than Vgsoff + signal Voltage. This gives a sort of "headroom" as to how much signal can be applied and the mute still function properly. Does this also apply to a shunt mute?

Based on what I've learned so far, this is the circuit I have come up with. I chose a P-Channel JFET so that I can negate the need for a negative voltage by referencing the source and drain to ground and the gate to V+. Would love to use something like a J111 for its lower on resistance, but do not have enough supply voltage. Please ignore the incorrect schematic symbol for the JFET. I plan to experiment with two JFET mutes in series for better "offness" and/or a series/shunt mode hybrid circuit.

[amptramp]

Some time ago, I designed a signal switching circuit that could accomplish noiseless switching with 4066 CMOS by determining when the two signals were equal and switching at that point in time to ensure there was a minimum of switching pop.  Look at the last picture in this thread:

https://www.diystompboxes.com/smfforum/index.php?topic=120006.msg1122294#msg1122294

This could be simplified for your needs because one of the inputs is zero signal.

[Ohioisonfire]

Some time ago, I designed a signal switching circuit that could accomplish noiseless switching with 4066 CMOS by determining when the two signals were equal and switching at that point in time to ensure there was a minimum of switching pop.  Look at the last picture in this thread:

https://www.diystompboxes.com/smfforum/index.php?topic=120006.msg1122294#msg1122294

This could be simplified for your needs because one of the inputs is zero signal.

Thanks for sharing this! Still studying these circuits and devices trying to understand how they work. I would assume for this application, instead of switching when the two voltages are equal, I would want to switch when the signal is crossing zero? Trying to wrap my head around how that would work with the timing of the LFO as well..