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CS-50 cv/gate inputs for Midi control
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author CS-50 cv/gate inputs for Midi control
j.dilisio
Greetings!
I'm trying to figure out how to control my CS-50 with midi.
I have a PAIA midi to cv converter which is capable of 4 note poly mode so all I should need are CV and Gate inputs.

For the CV input I've been trying the VB1-4 connections on the R7 board (connects to V input on voiceboards) which works but gives me less than an octave in range.

For the Gate input I'm feeding an inverted gate to the TR connections from the KAS boards which seems to work fine.

I'm hoping someone here can shed some light on how to properly add CV inputs for a full range.

Here are the connection points on the boards..
Picture file
Picture file

And a link to the service manual..
http://www.cem3374.com/docs/Manuals/Yamaha/CS-50_SM.PDF

All thoughts and ideas are welcome.
Thanks!
J
j.dilisio
I'm making some progress here.
Instead of the V connections on the voice boards I tried the K connections and had much better results.
You can connect to both sets of points on the Sample and Hold board..


This works great using sequencers and inverted gates but I started having trouble when trying the PAIA cv converter.
It seems the CS synths use exponential V/Hz whereas the PAIA converter uses V/octave.
They used to make a V/Hz optional board but it's out of production.
CV_Wonder
That's exciting you found those points! Does it now give you a greater octave range when using a sequencer?

I don't know how to help in the V/hz area. I only have a eurorack converter for my CS-15. [/quote]
oldcrow
Inserting the pitch CVs ahead of the SH board is correct. To make a V/Hz MIDICV device you use a dual DAC with external vref pins such as the MCP4922 and use one DAC to set the range of the other. you need to convert gates to the proper range as well. --Crow

j.dilisio wrote:
I'm making some progress here.
Instead of the V connections on the voice boards I tried the K connections and had much better results.
You can connect to both sets of points on the Sample and Hold board..


This works great using sequencers and inverted gates but I started having trouble when trying the PAIA cv converter.
It seems the CS synths use exponential V/Hz whereas the PAIA converter uses V/octave.
They used to make a V/Hz optional board but it's out of production.
nvining
I seem to recall that the gate levels are something wacky, too: 8.5V is on, -6.5V is off. You'll probably want to check the CS service manual which has details of the S&H circuit operation.
oldcrow
I made a MIDI/key assigner replacement for my CS-15 a while back. I can probably do something similar for the CS-50/60/80. Not a full key assigner (though I could do that, I just don't have time at the moment), but something that could take MIDI and generate CVs and gates. I'll tinker with it when I have time. It would be a replacement SH board with extra parts added.

Crow
/**/
j.dilisio
Yes, those points give you about five octaves to work with using a step sequencer.
The gate levels are definitely wacky. Inverting the gates from my Klee sequencer and then attenuating them to a very specific range seems to work.
I've been trying to figure out how to use the PAIA gates with no luck so far.

Crow, your replacement SH board sounds amazing! It seems like there is a lack of documented mods online for these instruments despite there being no lack of interest.
I'm sure a lot of folks would appreciate your efforts!

There's just enough room on the back panel for 8 jacks..
j.dilisio
I just found schematics for the PAIA V/Hz conversion board that's out of production..
https://www.paia.com/talk/viewtopic.php?f=4&t=35
It looks like it would be pretty easy to lay out on veroboard or something.
kvitekp
You may want to have a look at this embeddable Midi2CV converter -- it does 4 x CV (12 bit DAC) and 4 x Gate (variable level and polarity).

The published firmware does not have 4 x Poly mode, however i have a custom firmware variant that does it.

/Peter
cranleigh
oldcrow wrote:
I made a MIDI/key assigner replacement for my CS-15 a while back. I can probably do something similar for the CS-50/60/80. Not a full key assigner (though I could do that, I just don't have time at the moment), but something that could take MIDI and generate CVs and gates. I'll tinker with it when I have time. It would be a replacement SH board with extra parts added.

Crow
/**/


OOOH yes! Very interested in this for my CS60. One thing I have always wanted to be able to do is play it via midi and double up the oscillators to make it a 2-osc-per-note 4 voice poly. Might this be possible with your assigner?
nvining
Back when my CS60 had a dead YM26700 DAC, I considered designing a replacement board that would replace the keyboard assignment circuit boards (I don't have the names - KAS and KBC I think?) It started looking like a particularly hairy project, though; the software side of it is easy enough, but there's a lot of nasty hardware issues, ranging from the aforementioned wacky gate levels to trying to figure out the portamento and glissando clock to trying to make something that would, optionally, interface and/or replace the polyphonic aftertouch board. You need a lot of circuitry to get all the levels right and it's just a little bit out of my engineering capacity.

I then, fortunately, was able to find a DAC and consequently sold the CS60. Whew!

I'm not averse to doing the programming for such a device if somebody wants to design or assist with the electronics; I live in constant mortal terror of my CS80 dying one day when I turn it on, and suddenly discovering all my keys don't work. The YM26600 and YM26700 are now basically unobtanium. (That said, I would also need to track down a CS50 to experiment on, because I'm not doing that on the CS80 until I have a working prototype on a smaller synthesizer.)
oldcrow
I made one CS80 KAS replacement about 10 years ago. It used two PIC MCUs, though today I'd use one STM32 part. The trick to doing the bipolar gates is to use RS232 driver chips, such as the old but still useful MC1488. Logic input, bipolar output, just wire the supply pins to the +8.5v and -6.5v. You can convert the other way too, use an MC1489A receiver chip to turn the bipolar signal into a 5v logic one.

The 'stopgap' MIDI interface that would replace the SH board in this case would switch out the local keyboard in favor of the MIDICV. You would select either local keyboard or MIDI mode. In general it is rare someone uses both the local keyboard and MIDI IN, so this is not a huge issue.

Crow
/**/

nvining wrote:
Back when my CS60 had a dead YM26700 DAC, I considered designing a replacement board that would replace the keyboard assignment circuit boards (I don't have the names - KAS and KBC I think?) It started looking like a particularly hairy project, though; the software side of it is easy enough, but there's a lot of nasty hardware issues, ranging from the aforementioned wacky gate levels to trying to figure out the portamento and glissando clock to trying to make something that would, optionally, interface and/or replace the polyphonic aftertouch board. You need a lot of circuitry to get all the levels right and it's just a little bit out of my engineering capacity.

I then, fortunately, was able to find a DAC and consequently sold the CS60. Whew!

I'm not averse to doing the programming for such a device if somebody wants to design or assist with the electronics; I live in constant mortal terror of my CS80 dying one day when I turn it on, and suddenly discovering all my keys don't work. The YM26600 and YM26700 are now basically unobtanium. (That said, I would also need to track down a CS50 to experiment on, because I'm not doing that on the CS80 until I have a working prototype on a smaller synthesizer.)
nvining
What a neat part! Okay, let me find a CS50 and see if I can breadboard a little something.
j.dilisio
I just got the gates working from the PAIA midi/cv converter.
They just needed an op amp inverter with a 5k resistor on the output.

Peter, I've been eyeing up your midi boards.
Am I correct in understanding you need a midi controller with a pitch wheel in order to program the cv scale or is that something that can be done with software?

Here's the gate converter board..
kvitekp
j.dilisio wrote:
Peter, I've been eyeing up your midi boards.
Am I correct in understanding you need a midi controller with a pitch wheel in order to program the cv scale or is that something that can be done with software?

It could be done via sysex. Updating this sysex manually in MidiOx editor is a bit tedious but totally doable.

/Peter
midnightmarauder
Hi j.dilisio,

How did the project turn out? Did you get a decent CV octave scale from the midi cv converter? And the gate voltage converter is working fine?


j.dilisio wrote:
I just got the gates working from the PAIA midi/cv converter.
They just needed an op amp inverter with a 5k resistor on the output.

Peter, I've been eyeing up your midi boards.
Am I correct in understanding you need a midi controller with a pitch wheel in order to program the cv scale or is that something that can be done with software?

Here's the gate converter board..
j.dilisio
I never did finish this project.
If anyone has had more luck with it please share.
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