Oscillator not shaping signal

dylar · Joined: Apr 25, 2011 Posts: 55 Location: iowa

Hi electro-gurus!

I built a synth from MFOS modules and am having a problem with one of the oscillators. This is a fully modular synth built from individual modules (not a SoundLab).

One of my oscillators does not shape the signal at all. The square, tri, ramp, and sine all make the EXACT same sound. It's not a problem with the patch or the amp/speakers--my other oscillator works fine. I am relatively new to electronics and my knowledge is quite limited. Does anyone have any ideas about why this would happen?

dylar · Joined: Apr 25, 2011 Posts: 55 Location: iowa

Update: The square wave actually works and the PWM applies properly.

The other three signals all sound the same (sort of ramp-y). My guess is that the signals are not being shaped in the TL074. I replaced the TL074 with a new TL074 but nothing changed. P.S. I do not have an oscilloscope, so my troubleshooting abilities are limited.

alieneYe · Joined: Jul 25, 2008 Posts: 38 Location: Phoenix, Az

so the Pulse wave and Ramp wave are operating correctly but the sine and triangle are not?

do the shaping trimmers change the sound when adjusting them? might start there.

might double check the polarity of your diodes in that part of the circuit, as well as your resistor and cap values.

it can be a bit hard troubleshooting without a scope but not impossible.

this is off the top of my head looking at the schematic. not in front of my modules currently.
hope this helps
t

dylar · Joined: Apr 25, 2011 Posts: 55 Location: iowa

Thanks for your response! The shaping trimmers do not change the sound at all on the ramp, tri, or sine. Diode polarity is all correct.

I think it would help if anyone familiar with the circuit could explain why this might happen. I am confused as to how the signal can pass through all this stuff and get to the output without being affected by the components. The only thing I can see that all three bad signals pass through is the TL074, but like I said, I replaced the IC and nothing changed. Is there something else that could be responsible for "shutting off" the shaping? It seems like the signal must be passing through the trimmers if it's getting to the output, but the trimmers don't do anything. How is this possible? It's as if there is a short from the raw ramp to the out. Would this happen if no power was getting to the TL074?

dylar · Joined: Apr 25, 2011 Posts: 55 Location: iowa

Fixed! It was a cold solder on the TL074