Debugging VCO Pitch unstability continued

With PW set to zero

This mostly removes the noise. Not completely, but quite a lot better

With triangle DCO

The frequency seems to vary with the triangle wave as well
 

But when increasing the resolution and VCO frequency, we see that it is not a complete triangle, it seems to drop abruptly at the top of each DCO cycle.

Square wave is rounded

 

An observation - the frequency square wave is rounded, almost like it is low pass filtered.

Removing waveform mixer VCA

The square wave has its VCA on the waveshaper board so it is still visible  

Setting DCO to triangle, waveform mixer VCA is still removed

The triangle wave now never reaches the waveform mixer, but the square wave still breaks through. The frequency variations are almost exactly the same as what we saw when the triangle wave WAS connected, see "with triangle DCO, high resolution" above. Perhaps the triangle does in fact NOT affect the CVO.

Setting DCO to square, PW to 0. Waveform mixer VCA is still removed

 

There is still a small variation, but it is less than we saw before. However, there IS a slight up and down squarish effect here. Could it be coming from the input to the sub oscillator flip flop?

Also, there are significant spikes at the period marks. It could be that a PW of 0 is not quite turned off OR it could be from the sub oscillator circuit.

Moving waveshaper off board with jumper cables

The noise is the same as previously, distance doesn't matter

 Single DCO set to triangle

Square still breaks through

Pulse output from waveshaper board disconnected 

This is very interesting, almost not understandable. The pulse output is disconnected so the pulse wave does not reach the mainboard. But still we see the frequency noise! We also see the clicks on DCO period start.

Disconnecting the DCO input

Disconnecting the DCO from the waveshaper makes everyhing go away. Not surprising but a nice check. 

Recap

So, what we see this time is that 

- The noise is most likely only caused by the pulse wave (?), or at least not as much by triangle etc.
- The noise is present even when the pulse wave is disconnected from the mainboard
- There are heavy spikes at the start of each cycle

Theories

- The noise may originate from two sources: The saw-to-clock-pulse converter around  IC6 (LM311), and the pulse wave generator around IC1
- The noise does not travel (exclusively at least) through the pulse pin. 

Next up

- Disconnecting other waveform pins
- Disconnecting sub oscillator pins
- Disconnecting trimmer pots, replace with resistors
- Stopping the sub oscillator, with and without pw at 0
- Halving the DCO input to completely stop PW output
- Moving GND pin for the waveshaper to not return to the mainboard
- Check if flipflop stops
- Reconnect everything and move GND only.
- Move VCO offboard and do stuff suggested in the previous post.