Errata

This is a collection of known PCB fuckups.

56 ch sample-and-hold card v1.0

- Rear rows of the output connectors are not connected to CV output so no CVs will arrive at the mainboard.

Fixed in version v1.1

 

Mainboard v1.1.1

- IC2, selector switch for Waveform/PCM Wave: The control and output pins are mixed up. For testing, a workaround is a manual jumper and no DG413 switch, since PCM Wave is a future ad-on anyway. Can also be solved by creating a custom card with an SMD DG413 on it, with the pins routed correctly

Fixed in v1.1.3

 

- Waveshaper sub oscillator waveform selectors: Waveforms for sub-1 and sub-2 have been reversed, so when sub-1 is square, sub-2 is saw and vice versa. Can be fixed on an updated waveshaper card or the same way as the IC2, by doing a custom DG413.

Fixed in v1.1.3

 

 - The VCO temp sensor is not connected to +3v3 and does not work. There is no 3v3 nearby so best fix would be to add a voltage regulator locally.

Fixed in v1.1.3

 

VCO v2.0

- The saw output from the saw never reaches above 4V, it flatlines halfway through. This is caused by the 1k/1k resistor voltage divider in front of the comparator used to create the square wave. Also, the 1k/1k divider reduces the 0-8V saw to 0-4V, it should have been 0-5V. 

This seems to be fixed by replacing the divider with 100k/168k.
PS: Need to check that this fix does not affect the pitch of the VCO! Isn't this exactly why we have a cusstom pulse wave generator connected? But - there is no reason for the pitch to change because the voltage drop SHOULD be constant.

Distortion, multi FX v1.1

When doing the multi-FX board I used the wrong version of the distortion circuit, so this one has no output gain. Thus, the output is way too low.

There are no spare op amps on the board, but there IS one spare OTA. Perhaps I can reconfigure that one as gain. It would probably be a good idea to add a trim pot to make gain adjustable.

Juno filter

- Not sure this is an error yet, but the output directly from the circuit seems to be +/-500mV from a +/-5V input. It should be +/-1V I think. I misread the schematics, I put an external 230k resistor on the input when the juno board already has one, meaning the input was attenuated by 50%

Filter linear FM

Filter linear FM can never go below 0. It means that it will not oscillate around the set cutoff frequency, instead it will go from the cutoff frequency and up. Not sure if it is an issue or if linear filter FM is usable anyway, I may just remove it entirely.

BUT: VCO lin FM is AC coupled, so the DC component is filtered out. By adding a cap in front of the linear input (or on the filter board) I may not have to do centering/bipolarity. I would have to keep the CV at a normal level of 2.5 volts though. 

TODO: Test both VCO FM and Filter FM without centering but with cap.

Sine phase at output mixer

Sine 1 and 2 direct are not in phase with the output from the SVF and LPFs (it is inverted).

Bus mixer - SVF chain is inverted

This means that we need to invert the SVF output to prevent it from cancelling the LPF signal. If one was to use both SVF and LPF outputs directly to the voice mixer, AND chain the SVF to the LPF as well, SVF and LPF at the bus mixer would cancel out. Definitely a corner case but if it can be fixed, it should.

Bus mixer - gain error in output B

Because of the chaining input, sum B gain is doubled (even when chain switch is open it seems) due to R69 and R50 forming a voltage divider.

A possible fix for both bus mixer problems is to add a two channel op amp. Invert both SVF_CHAIN and SUM_B, then IC2C can be a normal inverting summer.

IC2B can probably be left as is.

Waveshaper

The waveshaper sings! Some caps oscillate and make and audible sound. It can hopefully be fixed by replacing the 100nF caps on the flip flops with C0G.

Fixed in v2.3

 

The LM311 comparator circuit on the sub oscillator creates noise on the ground plane, which is picked up by the VCO, making it wobble. The fix is to redo the comparator using an op amp and reduce the CMOS power to +5V.  

Fixed in v2.3

 

Oscillator bleed-through: When the envelope is fully closed and all VCAs at 0, you can still hear a faint sound. It measures around 2mV on the headphone output. After removing the Waveshaper, routing the DCO saw to the triangle input of the waveform mixer, the bleed through disappears. Retest once a new waveshaper without LM311 is present.