samgraysound
Well-known member
Hi All,
I just did some work on a Poly 61 adding filter and envelope controls and thought people might want to see the project.
I followed the mod outlined here
Which calls for tapping a +5v source, creating a -5 voltage source, and then using a pot to send a cv derived from them to sum with the output of DAC that normally controls the parameter. I liked this better then the standard approach of placing a voltage divider between the DAC and the parameter because it allows the stored patches to work normally when the pot is in the center position, and also allows you to vary the control up or down from the the stored parameter position.
I was doing the work for a client, they originally asked for cutoff, resonance, and full ADSR, but eventually scaled the project back to just cutoff and Release with the intention to come back and get the rest of the controls installed when they had further funds. So I implemented those controls with room to add the others at a later date.
I built the Op amp circuit on stripboard.
I used these pots mounted on perfboard, and connected them up with solid core wire.
I mounted the perfboard on the lefthand plastic piece where the joystick was mounted. I had to dremel out a lot of the plastic ridge in there so it would mount flush.
Problems I encountered:
I just did some work on a Poly 61 adding filter and envelope controls and thought people might want to see the project.
I followed the mod outlined here
Which calls for tapping a +5v source, creating a -5 voltage source, and then using a pot to send a cv derived from them to sum with the output of DAC that normally controls the parameter. I liked this better then the standard approach of placing a voltage divider between the DAC and the parameter because it allows the stored patches to work normally when the pot is in the center position, and also allows you to vary the control up or down from the the stored parameter position.
I was doing the work for a client, they originally asked for cutoff, resonance, and full ADSR, but eventually scaled the project back to just cutoff and Release with the intention to come back and get the rest of the controls installed when they had further funds. So I implemented those controls with room to add the others at a later date.
I built the Op amp circuit on stripboard.
I used these pots mounted on perfboard, and connected them up with solid core wire.
I mounted the perfboard on the lefthand plastic piece where the joystick was mounted. I had to dremel out a lot of the plastic ridge in there so it would mount flush.
Problems I encountered:
- knurling on the pots was not what I expected and got wrong knobs, need to look for proper ones
- on some parameters (noticed on attack) the range is too wide and extreme pot positions will cutoff all sound. could play with adjusting the value of the coupling resistor to see if that helps.
- need to figure out a tidier way of laying out drilling. right now I mark and drill and it is a little sloppy
- would probably use strip board for the pots as well in the future.
