I have a microprocessor based project (product hopefully) which will help the musician that prefers individual pedals to multi-effects pedals, to have some of the benefits of the latter, and I am strongly considering routing the audio around using either VACTROLS, or their cheaper LCR0203 cousins. These are all opto couplers and are generally great for routing audio because of their fast but less than instantaneous response, and the fact that they are completely linear.
So anyway, on a typical musicians pedal board. many of the pedals have built in SPDT switches, or electronic versions of same and they usually work like this: The input typically comes from an electric guitar or another pedal.The former is usually a very high impedance source (a pickup), and the latter is usually lower impedance. So these pedals usually have an input buffer amplifier. which routs the input to the effect electronics. The SPDT switch normally switches the output between the output of the effect electronics, or the input. The the effect electronics is always active, and is switched in or out of the circuit.
So I want to do some similar routing with the VACTROLS. In my proposed scheme, there will be an input OP Amp and an output OP amp, for the guitar input and final output to an amplifier. In between, all the effects pedals are set up so they are permanently on. Then, at each point where there is a pedal, I will have a VACTROL to break the circuit at that point. The point in the chain before the VACTROL will also be paralleled to the input of that pedal. Finally, a second VACTROL will take the output of the pedal and rout it to the point in the chain AFTER the first VACTROL. As long as the controlling electronics ensure that only one of the two VACTROLS are on at a given time, I will have accomplished what that pedal's stomp-switch would have done.
So here is where I have a question. If I used a third vactrol at the INPUT of each pedal, I will be doubly isolating that effect from the chain, since both the input AND output could be taken out of circuit. But I'm thinking that as long as I have a good OP-Amp at the beginning and end of the chain, the added signal loads of keeping all these pedal inputs connected should be minimal. And, I'm thinking that for some effects like a compressor, the effect probably function better if their inputs were continually receiving the the audio signal. Now I'll admit that the bottom line inspiration for not having a third VACTROL is that even using cheaper versions, they are expensive. And since I do not want to sacrifice ideal operation or quality for a small added cost, I'd like to see if others have done similar things with Opto-Isolators, and what their results have been.
So anyway, on a typical musicians pedal board. many of the pedals have built in SPDT switches, or electronic versions of same and they usually work like this: The input typically comes from an electric guitar or another pedal.The former is usually a very high impedance source (a pickup), and the latter is usually lower impedance. So these pedals usually have an input buffer amplifier. which routs the input to the effect electronics. The SPDT switch normally switches the output between the output of the effect electronics, or the input. The the effect electronics is always active, and is switched in or out of the circuit.
So I want to do some similar routing with the VACTROLS. In my proposed scheme, there will be an input OP Amp and an output OP amp, for the guitar input and final output to an amplifier. In between, all the effects pedals are set up so they are permanently on. Then, at each point where there is a pedal, I will have a VACTROL to break the circuit at that point. The point in the chain before the VACTROL will also be paralleled to the input of that pedal. Finally, a second VACTROL will take the output of the pedal and rout it to the point in the chain AFTER the first VACTROL. As long as the controlling electronics ensure that only one of the two VACTROLS are on at a given time, I will have accomplished what that pedal's stomp-switch would have done.
So here is where I have a question. If I used a third vactrol at the INPUT of each pedal, I will be doubly isolating that effect from the chain, since both the input AND output could be taken out of circuit. But I'm thinking that as long as I have a good OP-Amp at the beginning and end of the chain, the added signal loads of keeping all these pedal inputs connected should be minimal. And, I'm thinking that for some effects like a compressor, the effect probably function better if their inputs were continually receiving the the audio signal. Now I'll admit that the bottom line inspiration for not having a third VACTROL is that even using cheaper versions, they are expensive. And since I do not want to sacrifice ideal operation or quality for a small added cost, I'd like to see if others have done similar things with Opto-Isolators, and what their results have been.
Last edited: