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Muff's Modules & More
cats and modular synths, but mostly cats
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Quad VCA anyone? |
mmm
yummm!
Joined: 27 Oct 2008
Last Visit: 18 Jun 2013
Posts: 726
Location: Western Washington
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 Posted: Wed May 04, 2011 10:50 pm Post subject: |
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| emdot_ambient wrote: | So my quad VCA PCB came in today...beauty!
...then I have to look here and read about front panel trimmers... 
I'll look at it 'cause that sounds too tempting to pass up! |
Oh, yeah. A 5V CV will output unity gain with the channel attenuator up all of the way.
Without a CV input, I set the gain to around 2X output at on.
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George
http://www.mattsonminimodular.com |
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emdot_ambient
Super Deluxe Wiggler
Joined: 15 Oct 2009
Last Visit: 19 Jun 2013
Posts: 2446
Location: Frederick, Maryland USA
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| Posted: Thu May 05, 2011 9:10 am Post subject: |
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Actually I'm not quite following how this works. Is the Channel Level actually an attenuator or does it put a DC offset current into the VCA, opening up the VCA manually?
I did a quick 2U wide (MOTM panel size but not using MOTM's grid or knob or pot sizes) based on a design for the Dual 258j VCO I'm working on and found that I could actually fit 4 16mm pots horizontally, and then 4 rows of those vertically with plenty of finger room (I've found that tight horizontal placing is fine with the 0.5" knobs I use, as long as there's enough vertical height to allow for my fat fingers)...plus just barely enough room for a master gain knob.
Thus, I could do one row of Channel Level, one row of Channel Gain, one row of CV Amount...and one row of attenuverters going into a CGS DC Mixer. 15 jacks (3 copies of the Mixer Out).
Pretty epic. 
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"None of your five bar gate jumps and over sort of stuff." |
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mmm
yummm!
Joined: 27 Oct 2008
Last Visit: 18 Jun 2013
Posts: 726
Location: Western Washington
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| Posted: Thu May 05, 2011 11:07 am Post subject: |
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| emdot_ambient wrote: | | Actually I'm not quite following how this works. Is the Channel Level actually an attenuator or does it put a DC offset current into the VCA, opening up the VCA manually? |
The channel levels are just 100K attenuators connected to the signal input jacks. Full up allows the signal to the VCA input at full input level and full off grounds the channel input.
But, the channel trimmers are active, applying 0 to -DC offsets to another VCA and then inverted to the main VCA CV.
The "no CV input" trimmer sitting on the other side of the board by itself applies a 0 to +V CV through the switched CV input jacks so that the VCA gain is always up in case you choose to use the channel as a Channel level attenuator or, a preamp.
The CV inputs are cascaded from channel 1 through channel 4 so, any CV applied to a lower number channel will control all subsequent channels until you break the cascade with another CV input. Sort of an on-board user controlled CV mult.
I apply a 5V CV input into the channel 1 CV and apply a triangle wave of known amplitude to each channel. Then, set each channel trimmer for a matching output. Then, I pull the channel 1 CV input and set the internal gain trimmer to provide a 2X gain.
That way, each channel can be used as an independent 2x gain preamp when no CV is applied to a channel and used as a unity-gain VCA with a 0-5V CV input. You can mix and match which they will be based on following the cascade so, use the higher numbered channels for CV control first and that leaves the lower number channels without the CV inputs as preamps.
Phew!
| Quote: | I did a quick 2U wide (MOTM panel size but not using MOTM's grid or knob or pot sizes) based on a design for the Dual 258j VCO I'm working on and found that I could actually fit 4 16mm pots horizontally, and then 4 rows of those vertically with plenty of finger room (I've found that tight horizontal placing is fine with the 0.5" knobs I use, as long as there's enough vertical height to allow for my fat fingers)...plus just barely enough room for a master gain knob.
Thus, I could do one row of Channel Level, one row of Channel Gain, one row of CV Amount...and one row of attenuverters going into a CGS DC Mixer. 15 jacks (3 copies of the Mixer Out).
Pretty epic. |
Wow. That's ambitious 
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George
http://www.mattsonminimodular.com |
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rdonker
100 posts then buy/sell only
Joined: 08 Dec 2011
Last Visit: 24 Sep 2012
Posts: 113
Location: Vashon, WA
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| Posted: Sat Dec 17, 2011 3:29 am Post subject: |
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I agree with the vc mixer idea. I still perform in quad and I use the Serge qpf, that aside I believe a vc mixer is a excellent approach and might be more flexable.
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-RPD |
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