I’ve been adapting one of the YuSynth/Eddy Bergman designs for a simple hardy VCA and I seem to have hit a wall and I cannot figure out why.
Basically I have built one of the designs from Eddy’s site in the past and I use it quite often, but I wanted to use a TL074 instead of a TL072 and have a dual all in one with indicator lamps so I can see when it’s being triggered (more flashing lights = better right?).
I’ve used basically the same schematic design but adapted it to my own stripboard setup, and after I’ve tested this I’ll whip it into a PCB for anyone who’d like it.
My problem however is that it doesn’t appear to behave the same way as the original, and although I’ve spent all day carefully running over it with far too many coffees I cannot figure it out. I know that Eddy’s design inverts the output by running through another op-amp, but I don’t think that should have anything to do with what I’m doing here?
What happens is that at the point of fading in the input signal to the output, it “pops”. If I use the initial level trimmers to bring it just to the edge, it’s like it’s jumping up a cliff, kind of popping as it passes the threshold, almost like a dry joint might sound.
On my oscilloscope I can see that the waveform is being distorted, and instead of a square wave but at a lower level, I can see it’s jumping in at a certain level, and kind of angling the intial upward edge of the square wave. It’s quite a distortion and sounds bad.
If it were just one side I’d suspect a dud connection or faulty TL074, but I’ve checked all of this over and switched the IC also, both sides act the same way.
Here’s the schematic:
Here’s my stripboard layout:
I’ve also removed the LEDs in case they were somehow interfering with things, but no luck
Any pointers for my tired brain would be great