Synth-DIY Yahoo! Groups Archives

AM Mod?

2011-07-22 by 7yash

I was looking at the schematics and trying to understand the FM-800 mod. So I gather that the Osc 1 is routed to P 19 - VCF Cutoff Lin In for FM.

This got me thinking that we could use another pin for amplitude modulation using DCO2, e.g.:

IC 5 - P 7 routed to either:

1. NJM2609 P 9 - VCA Level CV Lin In (risk of feedback here?)
2. NJM2609 P 2 - Mixer Signal 1 Level CV In

2 seems much more fun to me as then, DCO2 could Amp Mod DCO1, which itself routes to the FM Mod.

Is there any additional parts needed than resistors and a suitable potentiometer here?

This would make for some electric piano sounds or more types of sound effects as in those examples:

http://www.propellerheads.se/substance/discovering-reason/index.cfm?fuseaction=get_article&article=part20

Your thoughts?

Re: [korgpolyex] AM Mod?

2011-07-22 by billmeirelles@uol.com.br

There is no risk of feedback, CV means control voltage, it has nothing to do with audio.
Your ideas seams to work, you should give it a try, no extra parts needed but take
it easy with solder iron, if you warm up the chip too much you can render it unusable.

Em 22/07/2011 17:18, 7yash < josh.nursing@... > escreveu:

I was looking at the schematics and trying to understand the FM-800 mod. So I gather that the Osc 1 is routed to P 19 - VCF Cutoff Lin In for FM.

This got me thinking that we could use another pin for amplitude modulation using DCO2, e.g.:

IC 5 - P 7 routed to either:

1. NJM2609 P 9 - VCA Level CV Lin In (risk of feedback here?)
2. NJM2609 P 2 - Mixer Signal 1 Level CV In

2 seems much more fun to me as then, DCO2 could Amp Mod DCO1, which itself routes to the FM Mod.

Is there any additional parts needed than resistors and a suitable potentiometer here?

This would make for some electric piano sounds or more types of sound effects as in those examples:

http://www.propellerheads.se/substance/discovering-reason/index.cfm?fuseaction=get_article& article=part20

Your thoughts?

Re: AM Mod?

2011-07-22 by 7yash

Awesome, thanks Bill, I will try this and report on my experiments.

Ideally, I get the External Audio mixed in with DCO2, then use DCO2 as AM source to modulate DCO1's CV In, and all this can be used in combination with the Moog slayer mod as well as the FM-800 mod where DCO1 modulates the VCF Cutoff CV In.

Fun times ahead!

Re: AM Mod?

2011-07-22 by 7yash

Here's a preliminary update on the AM mods!

1. Connected IC 5 - P 7 (upper pin R76 too on second try) to NJM2609 P 2 - Mixer Signal 1 Level CV In. [DCO2 AM DCO1]

Result: It works! It also works in conjunction with the FM Mod and of course the Moog Slayer Mod, of course. There's a nice beating effect.

Question: should I connect to the further pin of R20 before coming into the NJM P 2?

Also tried:
2. IC 5 - P 7 (upper pin R76) to NJM 2609 P 4 Res CV In
Result: It works! Nice internal modulation of the synth's resonance with DCO2's shape.

3. IC 5 - P 7 (upper pin R76) to NJM 2609 P 9 VCA CV In
Result: It works! The result is a bit trashy/distorted, but maybe can be better with a pot.

4. IC 4 - P7 to NJM2609 P 3 - Mixer Signal 2 Level CV In [DCO1 AM DCO2] -works, of course, which means both 1 and 4 could potentially be used for Cross-Modulation.

I uploaded a new file describing this:
http://f1.grp.yahoofs.com/v1/4PIpTgG_-ttyX_XHKF6tSHeVG2CM9UgjjaQHu5Or7CSefcF2BsELkDt3zCP3SlMbLzbol3WCPVAGHc7Z4XUM-EBPqDGTniQ/4%29%20Modifications/AM%20Mod%20%26%20AM%20Cross-Mod%20Proposed/AM%20Mod.jpg

Re: AM Mod?

2011-07-24 by 7yash

Additional info on the DCO2 - DCO1 AM Mod: I connected a 4.7K potentiometer as in the diagram in the Files section.

Clangorous tones, gets the same multi-notes distortion was the FM-800 mod.

I didn't use any resistor on the middle pin of the potentiometer and found that I had little range, or more precisely, that the AM mod only kicks in near the end of the potentiometer turn. Is that because of the lack of resistor?

I found that the effect on the Resistance CV In was much more musical, so I might wire this one instead.

Re: [korgpolyex] Re: AM Mod?

2011-07-24 by billmeirelles@uol.com.br

For this type of connection you should use a 50k pot, 4.7k has too little resistance
to separate the positive signal from ground efficiently, a small resistor at the output
of the pot could help, try 1k, maybe 470Ω, funny the other day I was thinking about
trying this for the FM800 mod as it affects the filter in such a strange way.

Em 24/07/2011 18:21, 7yash < josh.nursing@... > escreveu:

Additional info on the DCO2 - DCO1 AM Mod: I connected a 4.7K potentiometer as in the diagram in the Files section.

Clangorous tones, gets the same multi-notes distortion was the FM-800 mod.

I didn't use any resistor on the middle pin of the potentiometer and found that I had little range, or more precisely, that the AM mod only kicks in near the end of the potentiometer turn. Is that because of the lack of resistor?

I found that the effect on the Resistance CV In was much more musical, so I might wire this one instead.

Re: [korgpolyex] Re: AM Mod?

2011-07-24 by billmeirelles@uol.com.br

Oh, and probably you are using a LOG pot, try a LIN one, this could
explain why you only get an audible response at the end of the pot.

Em 24/07/2011 18:21, 7yash < josh.nursing@... > escreveu:

Additional info on the DCO2 - DCO1 AM Mod: I connected a 4.7K potentiometer as in the diagram in the Files section.

Clangorous tones, gets the same multi-notes distortion was the FM-800 mod.

I didn't use any resistor on the middle pin of the potentiometer and found that I had little range, or more precisely, that the AM mod only kicks in near the end of the potentiometer turn. Is that because of the lack of resistor?

I found that the effect on the Resistance CV In was much more musical, so I might wire this one instead.

Re: AM Mod?

2011-07-24 by 7yash

Thanks Bill, I will try the resistor. Yes, I think I am also using a Log Pot because although I wanted Lin ones, they were out of them.

The NJM2609 also has CV Log Ins, I might try that too.

I will probably get to do a few mods tonight and will report back on the results of these explorations.