So now we’re up to version 1.4!
In an attempt to simplify the circuit I decided to try the circuit again without this first JFET buffer
All I did was take out everything from R1 to C2 (inclusive), and bridge the input and the non-inverting input of that first TL072 (including R4) with C1. C1 is 22n, R4 is 1M, together they form a high pass filter with a cut off at 7.23Hz.
Here’s a quick vid with the results.
After I took out the JFET buffer I found a couple of interesting things occurred. Firstly the noise I was getting from the breadboard decreased, though this could be for a couple of reasons. Noise during breadboarding is pretty common, and can be caused by a few different things. I’ll be doing some more articles about breadboarding soon, so I’ll leave some of the specifics until then. The reduction in noise could also be because I tidied up the breadboard layout. I removed a lot of the jumpers and replaced them with the straight connectors. Stray wires, especially jumpers that loop around the circuit can add a load of noise. I also swapped the TL072 for a NE5532, they have the same pinout, and the 5532 are touted as low noise op amps. When I get the PCBs back for the prototype, I’m going to try swapping between the two for a proper AB test.
As you can probably see in the amended schematic above I also decided to take out the LEDs. For some reason I can’t explain, without that first buffer they didn’t affect the sound as much. I wasn’t married to the idea, so this wasn’t a great loss. It seemed like a good idea to not complicate things.
I was a little against the clock trying to get this prototype (and a couple of others) ready so I didn’t miss the PCB fab house deadline for Chinese New Year like I did last year. So I decided to keep it simple, there were some nonessential findings that I didn’t address this time round.
Having said all that, I was pretty happy with how sausage fingers had shaped up, and I thought I might just have enough time to go back and try something I’d planned on leaving… a synth mod! Check in next time for some fun stuff.