Audio - VCO only working when powering down...

Thread Starter

brodiewedding

Joined Sep 28, 2019
3
Hi, I'm new here so please let me know if this is in the wrong place to post this or if I should be doing anything differently. (also, hi!)

So I'm building a modular synth system using the Frequency Central Power Supply. I've recently built this VCO on a breadboard, and it functions perfectly:
https://www.allaboutcircuits.com/projects/diy-synth-series-vco/
I've then built it on proto board and here's the weird part. It doesn't work when the power is on, but when I switch the power supply off, it works while the power supply is powering down. I've hooked up a multimeter and it looks like it starts functions as the voltage drops to below 11.5v or something, but it's difficult to tell exactly. The circuit uses 3 x LM358s, which should work just fine at 12v, and the only modifications I made the circuit in the link is removing the exponential converter.

The power supply functions great and is putting out +12v, -12v and ground, I've run the bread board version of the circuit with the exact same power source, I've checked that the proto board is exactly the same as the breadboard, and that there are no shorts, and swapped out the ICs just in case)

This is pretty confusing for me, so please let me know if you need any more information to help, I really appreciate it! :)
 

Thread Starter

brodiewedding

Joined Sep 28, 2019
3
Did you match the transistors?
Thanks for replying Wolframore :) I didn't build the exponential converter, just the VCO, so don't need to match or thermally connect the transistors. I just built the summing circuit that the CV plugs into and added a pot to adjust CV input. It works on my breadboard but this seems like the only issue when I've moved it onto the PC...
 

Wolframore

Joined Jan 21, 2019
2,317
If it worked on breadboard, it must be a bad connection somewhere. There are a lot of parts, if you have an oscilloscope perhaps you can follow the signal. You can always probe the voltage around. I always start with the transistor. perhaps you can post a picture of your work.
 

Thread Starter

brodiewedding

Joined Sep 28, 2019
3
If it worked on breadboard, it must be a bad connection somewhere. There are a lot of parts, if you have an oscilloscope perhaps you can follow the signal. You can always probe the voltage around. I always start with the transistor. perhaps you can post a picture of your work.
Thanks a lot, I'll go back and check everything too. Do you think a bad connection could be causing the weird power issue, where it only works as the voltage starts dropping (upon powering down)?

I've connected all the grounds and + and - voltages together, do you think there could be an issue with them needing to be connected closer to the IC or something (I read that audio amplifiers need to have ground and voltage wiring specifically to avoid noise)? I didn't think so but worth asking.
 
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