Hi all,
I’m building some effects modules and I’m planning to mod them with a bypass switch with a twist. I’m going to bypass them using a relay and a switch in an “OR” configuration, so that if either a trigger signal on the “bypass” jack is present, or if the “bypass” switch is engaged, the effect will engage. I’d like to experiment with having my sequencer toggle effects on and off, and this seems like a great way to do it. Here are the relays I’m using:
Product page:
Data Sheet:
The place where I could use some assistance is the “OR” logic for the relay. I’m concerned that shorting 5 volt from the switch directly to the trigger source could damage one or both of them. Is there some method I can use to protect them, such as diodes? What sort of diodes would do the trick? I’m a bit ignorant on this. I’ve prepared the following sketch to make my idea more clear:
I’m also wondering if there would be any benefit to method 1 vs method 2. Method 2 would allow me to switch a stereo signal with one relay, but I don’t know if I would get a loss of tone by having the input constantly connected to the effect send, regardless of whether the effect is engaged.
Any input y’all can offer is greatly appreciated. Thank you so much as always!
-Wes
The following is my various musings on hw to get it into a verified, useable state.
It works mostly as intended, and the trigger inputs allow me to toggle the bypass state from my sequencer or DAW, through my midi to CV converter, which is rad. I’ve noticed, however, that certain uses of this module cause some of my oscillators to go flat, which leads me to believe that the module is using an impractical amount of current. I’m not sure if I simply need to add resistors before the 5V input on the relays, or if it just takes an impractical amount of current to switch these things. Can’t make heads or tails of the datasheet on that:
There are two power supply units in my rack. The first has all my oscillators, and my midi to CV converter. The second, powers all the relay bypass modules (and other stuff). I noticed that the oscillators DON’T go flat when I use the manual switch, but they DO go flat when I use the trigger input to flip the relay. My theory is that power supply #1 is already close to its max current, and toggling the relay from power supply #1 via the midi to CV converter puts it over the top. Whereas when I use the manual switch, that current is coming from power supply #2 instead, and nothing bad happens (presumably because no power hungry digital modules are plugged into it).
I’m still head scratching over what to do about this - I suppose one of the following:
Figure out a way to make the module use less current. Maybe I’m just using these things all wrong.
Incorporate a transistor, such that the trigger input just opens the gate on the transistor and the transistor pulls the necessary current from power supply #2 instead of trying to pull it through the midi to CV converter.
Maybe the elecro-mechanical relays are totally overkill for re-routing CV signals and I should just be using transistors for the entire path.
I’m not sure, but I am loving being able to automatically re-route oscillators through different filters and effects just by flipping through different pre-sets I’ve set up. I’d love to be able to get these modules set up in a more legit fashion - hopefully I’ll get there soon. If anyone has thought/suggestions/advice, I’m wide open. When I get this completed to my satisfaction, I will share my results.
Generally speaking you don’t want to draw anything more than minimal current from a CV source. Without trying to puzzle out your circuit, I’d say from your description it sounds like you’re trying to use a CV as a current source, and that’s to be avoided. One good way not to do that is, yes, use the CV to switch a transistor which is connected to a power rail.
Options 1 and 3 might be even better, I don’t know, but if you have nothing better, then option 2 sounds like a good way to go.
I’ve been doing a bit of a deep dive on this subject and it turns out there are a lot more design considerations than I anticipated. I finally constructed a module that seems more or less correct, but it started causing my other modules to act funny (and scared the pants off me), probably because I was using way too much current. Other switching methods are looking like quite a pain. The solution I’ve landed on for now? Buy an 8 channel pre-made relay board, power it with a separate wall wart power supply tucked into my case, and hope for the best.
