Quad VCA anyone?

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patchdub
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Post by patchdub » Mon Dec 27, 2010 3:25 am

put together the quad vca today. i went from 2 vcas to having 6! i'm starting to see why people are always saying you can never have enough vcas. lots of fun...

i made a temporary panel out of a piece of 8th inch plywood while i wait for blanks to come from bridechamber.

Image[/img]

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Post by mmm » Mon Dec 27, 2010 10:19 am

Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. :banana:

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patchdub
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Post by patchdub » Mon Dec 27, 2010 2:23 pm

mmm wrote:Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. :banana:

really really fun! this is opening up a whole world of tweaking.

i did however miss read your wiring diagram and my pots are all backwards. oh well, i'll fix that booboo when i get my panel.

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patchdub
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Post by patchdub » Thu Dec 30, 2010 12:14 am

mmm wrote:Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. :banana:
seriously fun stuff. i've spent hours just running vcos into the quad with an eg or a lfo and overdriving different channels. sounds really good.

contemplating another...

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Post by mmm » Thu Dec 30, 2010 12:25 am

patchdub wrote:
mmm wrote:Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. :banana:
seriously fun stuff. i've spent hours just running vcos into the quad with an eg or a lfo and overdriving different channels. sounds really good.

contemplating another...
You are now officially playing around in no mans land. I've never tried real-time gain changes on those.
:bananaguitar:

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patchdub
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Post by patchdub » Thu Dec 30, 2010 12:39 am

it is pretty awesome sounding. haven't felt the need to break out a filter in awhile. all the adjustment options color the tone so nicely! :party:


now how is that fiy sequencer coming along? :hyper:

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Post by mmm » Thu Dec 30, 2010 12:58 am

patchdub wrote:it is pretty awesome sounding. haven't felt the need to break out a filter in awhile. all the adjustment options color the tone so nicely! :party:
Cool. :headbang:

now how is that fiy sequencer coming along? :hyper:
Where's the LMFAO emoticon??????????????????

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emdot_ambient
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Post by emdot_ambient » Wed May 04, 2011 9:04 pm

So my quad VCA PCB came in today...beauty!

...then I have to look here and read about front panel trimmers... :eek:

I'll look at it 'cause that sounds too tempting to pass up!

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patchdub
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Post by patchdub » Wed May 04, 2011 9:07 pm

emdot_ambient wrote:So my quad VCA PCB came in today...beauty!

...then I have to look here and read about front panel trimmers... :eek:

I'll look at it 'cause that sounds too tempting to pass up!
highly recommend it!

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Post by mmm » Wed May 04, 2011 10:44 pm

emdot_ambient wrote:So my quad VCA PCB came in today...beauty!

...then I have to look here and read about front panel trimmers... :eek:

I'll look at it 'cause that sounds too tempting to pass up!
Sorry it took so long :mrgreen:

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Post by mmm » Wed May 04, 2011 10:50 pm

emdot_ambient wrote:So my quad VCA PCB came in today...beauty!

...then I have to look here and read about front panel trimmers... :eek:

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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emdot_ambient
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Post by emdot_ambient » Thu May 05, 2011 9:10 am

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. :twisted:

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Post by mmm » Thu May 05, 2011 11:07 am

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!
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. :twisted:
Wow. That's ambitious :tu:

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rdonker
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Post by rdonker » Sat Dec 17, 2011 3:29 am

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.
-RPD

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Post by ubiquiphilia » Wed Sep 17, 2014 9:52 pm

I'm wondering if I might ask here where or whether there is a thread with bom/pot values/build notes around this forum or elsewhere?

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Post by mmm » Sat Oct 18, 2014 3:46 pm

ubiquiphilia wrote:I'm wondering if I might ask here where or whether there is a thread with bom/pot values/build notes around this forum or elsewhere?
Sorry for the delay. I was on vacation for once :sadbanana:

I sell my FIY PCBs as built and tested boards. Then, let the customers create their own panels, find their favorite panel components and cosmetics.

The existing completion page is found on my DIY WIKI:

http://www.mattsonminimodular.com/wiki/ ... fier_Board

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