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kx
Joined: Dec 05, 2009 Posts: 17 Location: New Zealand
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Posted: Mon Oct 15, 2012 10:11 pm Post subject:
Fake ground to analog modular? |
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Hi All, I hope circuit bending is the right place for this, but here goes...
I'm doing some CV control of a Roland System 700 at my University with Max/msp using the DC output of a MOTU 828 MKII, but I'm having a hard time triggering the envelopes. I tried a number of ways to amplify the CV inside the modular, but I guess it's just not high enough.
To save on building a special CV amplifier box, I was thinking of making an adapter cable which would take the -ve voltage from one output of the MOTU and wire it as a fake ground to the Modular, effectively doubling the height of the trigger signals.
It seems a bit risky though, fake grounds conflicting with real grounds and all... so I thought I'd ask you guys first whether this kind of thing works, or is a big nono.
Any advice would be appreciated.
Thanks |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Tue Oct 16, 2012 6:57 am Post subject:
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Better don't do that, you'll short the -ve to ground then ... which may cause the MOTU to not ever work again. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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kx
Joined: Dec 05, 2009 Posts: 17 Location: New Zealand
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Posted: Tue Oct 16, 2012 8:58 am Post subject:
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ah, ok I was afraid of that. Thanks for your reply! I guess I'll have to go with making the CV amplifier then.
cheers |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Tue Oct 16, 2012 9:13 am Post subject:
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You could use a simple one transistor buffer for that. Like the "Common Emitter Amplifier Circuit" at http://hades.mech.northwestern.edu/forums.html/Diodes_and_Transistors .
This one inverts though, so this assumes you can invert the polarity of triggers in the PC software.
Where it says 10V just use the +Vcc from the modular. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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kx
Joined: Dec 05, 2009 Posts: 17 Location: New Zealand
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Posted: Wed Oct 17, 2012 2:25 am Post subject:
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Thanks a lot for referring that circuit.
Inverting the triggers would be no problem (using max/msp), but getting the modular's VCC may be tricky, since it's the University's System-700 which I am not able to open up. Or do you mean, trying to get a high voltage out of one of the modular's CV generators for that?
Also, please forgive me ignorance, but I see a Vin which I suppose the trigger signal from the PC goes in, and a V+ from the modular, but where would I connect the output to trigger the envelope?
Also, do you have a suggestion of which model # of transistor would fit this purpose the best?
Thanks again |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Wed Oct 17, 2012 4:50 am Post subject:
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kx wrote: | Thanks a lot for referring that circuit.
Inverting the triggers would be no problem (using max/msp), but getting the modular's VCC may be tricky, since it's the University's System-700 which I am not able to open up. Or do you mean, trying to get a high voltage out of one of the modular's CV generators for that? |
Modular Vcc would be ideal but using a high CV output probably works too.
(depending on how high it is,. and what voltage the trigger needs)
Quote: | Also, please forgive me ignorance, but I see a Vin which I suppose the trigger signal from the PC goes in, and a V+ from the modular, but where would I connect the output to trigger the envelope? |
The collector of the transistor (connected to the 1K resistor) would be the output for your trigger. You can increase that resistor btw, somewhere in the range of 10K-100K should work fine and lowers the current draw.
Quote: | Also, do you have a suggestion of which model # of transistor would fit this purpose the best? |
since you're not working at extreme speeds/currents/voltages any general purpose transistor will do.
I grew up with BC547 myself, but you could also use a 2n3904 or similar. just as long as it's an NPN. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
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kx
Joined: Dec 05, 2009 Posts: 17 Location: New Zealand
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Posted: Thu Oct 18, 2012 9:42 pm Post subject:
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Thanks a lot for your info, I'll try this at my next chance.
So, just to make sure I'm 100% clear, where it's marked 10v on the diagram is the 'high' voltage from the modular. On the other side of that resistor, the collector, is the trigger output, and I have the PC connected through a 10k to the base.
It might be a wee while till I can try it out (I'm going away for a few weeks) but I'll be sure to let you know how it goes.
Cheers |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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kx
Joined: Dec 05, 2009 Posts: 17 Location: New Zealand
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Posted: Mon Nov 26, 2012 5:08 am Post subject:
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Hi All,
Just wanted to say that I tried the transistor circuit today on the System 700 and it worked perfectly.
Thanks a lot Phobos and Blue Hell for your tips! |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Mon Nov 26, 2012 9:05 am Post subject:
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_________________ Jan
also .. could someone please turn down the thermostat a bit.
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