Prophet 600 Noise Source Modification
So, I modified my Prophet 600 to have a noise source, with a level parameter that is storable with a patch. I was inspired by a Japanese Prophet 600 mod I saw online a while back. He documented what he did very well.
http://prophet-600.blogspot.com/2014/09/prophet-600-adding-noise-waveform.html
The goals were as follows:
1) Modify the GliGli FW to add a noise source using what was the external filter CV input
2) rewire the external filter CV so I still have an external filter CV and it no longer goes thru U458 (CEM 3360)
3) build a hardware noise source run it through U458 which is under software control, accessible using "To tape" and pressing 0 twice ("To tape 0 twice" is/was a duplicate arpeggio speed control.)
So here is where I'm at:
1) The code is done and works. I can save and recall the Noise parameter and the code controls U458 to make the noise level settable by the front panel. The code I modified so far seems stable.
2) I cut a trace leading from pins 1 and 2 of U467 to the Filter CV inputs of the six CEM3372s. I ran a wire from U467 pin 1 to a 100K ohm resistor (6 in total), going to the A input on every CEM 3372.
3) I installed the hardware noise source and lifted R4219, feeding the noise source to R4219 and jumped the CV in jack to the Filter CV inputs of the six CEM3372s.
P600_ノイズ追加本体改造ExtFilterCV_NoiseMod.jpg
The goals were as follows:
1) Modify the GliGli FW to add a noise source using what was the external filter CV input
2) rewire the external filter CV so I still have an external filter CV and it no longer goes thru U458 (CEM 3360)
3) build a hardware noise source run it through U458 which is under software control, accessible using "To tape" and pressing 0 twice ("To tape 0 twice" is/was a duplicate arpeggio speed control.)
So here is where I'm at:
1) The code is done and works. I can save and recall the Noise parameter and the code controls U458 to make the noise level settable by the front panel. The code I modified so far seems stable.
2) I cut a trace leading from pins 1 and 2 of U467 to the Filter CV inputs of the six CEM3372s. I ran a wire from U467 pin 1 to a 100K ohm resistor (6 in total), going to the A input on every CEM 3372.
3) I installed the hardware noise source and lifted R4219, feeding the noise source to R4219 and jumped the CV in jack to the Filter CV inputs of the six CEM3372s.
P600_ノイズ追加本体改造ExtFilterCV_NoiseMod.jpg
Of note, when I flashed the FW, I had unrelated tuning problems (I checked by going back to the official 2.1 release 3 that was previously working for me). I ended up having to retune by letting it warm up for like 30 min and adjusting the scaling trimmers for all 6 voices (A and B) so they matched each other (using the voice defeat one voice at a time) then hitting Tune. It seems to be the only thing that worked for me. I tried hitting the tune button a few times before adjusting the scaling and the voices were horribly out of tune with each other)
I am hoping to put up a video and some photos of the Mod within a few weeks.
Here is my updated .SYX file for a gligli modified P600. My code (version 2.20) is based on version 2.10 RC3.
For the noise source, I used the circuit form the TR909. I found some PCBs from Michigan Synth Works that made the job easy. Of note, the shift registers were a pain to find.
The noise source PCB installed in my Prophet 600. The scope shows the noise at about 6V p-p.
Hello, I was looking at this and then wondering if it would be possible to switch/fade between a white noise and pink noise source, I'm assuming the CV goes from 0-2V for the external input control. If I put this through some opamps I can make it fade from 2V-0V and 0V-2V on two different outputs, 0V for both outputs being half way on the original CV, feed these into the orginal and a copy of the 3360 circuit each one being fed from a pink and a white noise source. Mix the outputs of the 3360's together and you have a dual noise source, I have an Electric Druid Noise2 chip for the source, it generates 0-5V pink and white noise.
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