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Quad VCA anyone? |
mmm
yummm!
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 Posted: Sat Jul 03, 2010 3:51 pm Post subject: |
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OK, I think I posted it clearly.
Let me know if I confused everybody.
G
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patchdub
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| Posted: Mon Nov 15, 2010 2:24 am Post subject: |
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hi. does the vc mixer still exist in the quad vca board? meaning, would it be possible to still have the the summed out and inverted out along with the individual outs of the quad vca?
as soon as i collect enough green tickets i am ordering the quad vca and the quad ad/asr!
must get food and firewood first though. trying to keep my priorities straight.
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BananaPlug
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| Posted: Mon Nov 15, 2010 8:00 am Post subject: |
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| patchdub wrote: | | hi. does the vc mixer still exist in the quad vca board? meaning, would it be possible to still have the the summed out and inverted out along with the individual outs of the quad vca? |
No but you can accomplish that easily with a small add-on as done here very neatly by negativspace. |
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mmm
yummm!
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Location: Western Washington
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| Posted: Mon Nov 15, 2010 10:12 am Post subject: |
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| patchdub wrote: | hi. does the vc mixer still exist in the quad vca board? meaning, would it be possible to still have the the summed out and inverted out along with the individual outs of the quad vca?
as soon as i collect enough green tickets i am ordering the quad vca and the quad ad/asr!
must get food and firewood first though. trying to keep my priorities straight. |
Food and firewood.  Thanks for the reminder. 
The Quad VCA is essentially the same circuit as the VC Mixer.
It's easy to sum the outputs of the IC's and run a normal and inverted buffer amp for the outputs.
The problem was, to get individual outputs, I had to split the common output between the amp outputs and run them into individual output buffers.
So, I had to add two more op amps to turn the VC mixer to a quad VCA.
Any summation and inversions would have to follow the channel buffers.
Best to do it the way negativspace did as BananaPlug suggested.
G
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patchdub
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patchdub
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mmm
yummm!
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Location: Western Washington
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| Posted: Fri Dec 10, 2010 12:11 pm Post subject: |
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| patchdub wrote: | is it possible to get the pcb without the on board gain trim pots so that i can then put them on the panel?
i'm trying to figure out if i can put the vca and the quad vca on a 2u motm style panel. |
Sure. But, I'll have no way to test it. I certainly won't be able to calibrate it. 
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patchdub
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mmm
yummm!
Joined: 27 Oct 2008
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Location: Western Washington
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| Posted: Sat Dec 11, 2010 12:18 pm Post subject: |
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| patchdub wrote: | | mmm wrote: | | Sure. But, I'll have no way to test it. I certainly won't be able to calibrate it. |
oh. bad idea then? i thought perhaps there might be a benefit to have the gain on the front panel. |
Not a bad idea at all. The trim pots adjust the gain per channel from crap to "slam the rails". There is also a trim pot for adjusting the internal voltage that gets normalled and cascaded to the CV control input jacks that sets the overall max gain for when there is no CV control input patched into the jacks.
You can set them globally to be a set gain with no CV input to be either a unity gain attenuator or a x gain preamp with no CV and set the channels to be a unity gain VCA or, each channel can have it's own unique gain setting.
I just set everything to unity gain across the board because that's what people are instinctively expecting. But, yeah, determining your own gain specs for your needs is OK.
I have mine set up to be 2X gain for individual CV or audio preamps with no CV patched in and, unity gain VCA's responding to 1:1 input to output ratio with a 5V CV patched in. That way, I have a quad VCA or four preamps in case some of my signals need a boost. If I need a couple of preamps AN a couple of VCA's, I used the patched CV on the higher channels numbers for my VCA channels and leave the lower channels numbers attached to the internal voltage in the cascade for the preamps.
Without the trim pots on the board, I can't verify that the board is operational before I send it.
But, nothing says you cant unsolder them and remote them to the front panel if you wish.
I could just "tack" them in enough to make connection and verify operation and not be a SOB to remove....
So, if you replace the 5 trim pots with panel pots remoted to the main user panel, it gives you real-time control of the gain structures.
Since these will amplify big time, you can use two channels, one to slam the rails (thus clipping at the power rails) Thus, distorting the hell out of the original signal and send that to another channel to attenuate the power-rail slammed distorted signal back down to the +/- 5V that should be.
By using the levels properly and being creative with the CV configurations, the module can become a voltage controlled distortion.
OK, My brain has rambled enough.
Keep in mind, I'll be closing the cart just before Xmas and not accepting any new orders until I re-configure my cost structure. Then, I'll re-open the cart in January with the new prices 
But, only one person has used the newcust5 5% discount coupon that is awarded by registering on my cart.
Everybody except one person has the opportunity to grab whatever they've been musing over and grab 5% off before I close the cart for the holidays.
G
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patchdub
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patchdub
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| Posted: Mon Dec 27, 2010 3:25 am Post subject: |
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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.
 [/img]
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mmm
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| Posted: Mon Dec 27, 2010 10:19 am Post subject: |
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Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. 
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patchdub
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| Posted: Mon Dec 27, 2010 2:23 pm Post subject: |
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| mmm wrote: | | Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. |
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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| Posted: Thu Dec 30, 2010 12:14 am Post subject: |
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| mmm wrote: | | Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. |
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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mmm
yummm!
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| Posted: Thu Dec 30, 2010 12:25 am Post subject: |
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| patchdub wrote: | | mmm wrote: | | Having those global and individual channel gain settings on the panel should add some additional "tweaking" fun. |
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.
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patchdub
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mmm
yummm!
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| Posted: Thu Dec 30, 2010 12:58 am Post subject: |
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| 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!  |
Cool. 
| Quote: | now how is that fiy sequencer coming along?  |
Where's the LMFAO emoticon??????????????????
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emdot_ambient
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| Posted: Wed May 04, 2011 9:04 pm Post subject: |
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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!
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patchdub
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mmm
yummm!
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| Posted: Wed May 04, 2011 10:44 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! |
Sorry it took so long 
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