4 Channel VCA/VC Mixer

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burdij
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4 Channel VCA/VC Mixer

Post by burdij » Wed May 18, 2016 10:04 pm

This 2MU mixer is heading to board fab this week. It contains 4 VCAs with separate outputs, selectable Log/Lin response, and a VC panner per channel. The panner outputs can be assigned to the left and/or right channels of an internal stereo mixer. The stereo outputs have master VC gains for each channel. Besides the assignment switches, there is a solo and mute button for each channel. Internal pre and post fader connections are provided to feed an external aux mixer.

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Verifying the pan law circuit:

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The FFT shows less than 1/3 of a percent harmonic distortion at 10kHz.

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Post by sduck » Wed May 18, 2016 10:17 pm

Very nice! When panning, does the volume stay constant over the whole range, or is there a dip in the middle like many of these circuits?
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Post by burdij » Wed May 18, 2016 10:30 pm

I am implementing the 3dB pan law. You can see this in the scope photo. The discontinuity occurs at 0 Volts and it represents .707 times the channel input level. When both channels are added in a mono mix, the output will then be 3dB higher than unity gain. The mono signal will actually be slightly louder when positioned in the center. This will serve to prevent that center panned signal from getting lost in a crowded mix image as it would if it were based on a 6dB law.
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Post by JohnLRice » Thu May 19, 2016 1:05 am

Looks really great, John! :tu:

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Post by kindredlost » Thu May 19, 2016 7:00 am

Potential game changer for 5U.

Do the internal auxiliary mixer connections work in some way with your GMS-725 Mixer/Processor module, or am I missing the point of the use for these connections?

Pretty tight panel layout. How small do your fingers have to be to operate the push buttons?

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Post by burdij » Thu May 19, 2016 1:40 pm

kindredlost wrote:Potential game changer for 5U.

Do the internal auxiliary mixer connections work in some way with your GMS-725 Mixer/Processor module, or am I missing the point of the use for these connections?

Pretty tight panel layout. How small do your fingers have to be to operate the push buttons?
That is an interesting idea but it would require a little adapter board to convert from ribbon cable type connector to the normalized jacks on the 725. What I had in mind is a panel with 8 level controls and a switch for each that would select between the pre and post signals from each channel and combine them into a mono output. Depending on how the ribbon cable from the amplifier is connected, you could use the auxiliary mixer to form 2 4 input aux mixes or combine two amplifier panels into an 8 channel aux mix.

I was trying to allow as much "air" around switches, knobs and jacks but there are a lot of functions combined on this panel. I am using the skinnier and taller knobs like the ones on the Moog Mother 32. These give a bit better grip. The switches are a little hard to envision from the photo so I have a detail here with a calibrated measuring tool. If you are literally "all thumbs" it might be tight but I think ordinary people will be fine.

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Post by JohnLRice » Thu May 19, 2016 2:09 pm

I know some people might not like this idea if they are running out of room and are in denial over the fact that another case is inevitable :hihi: but I think most people might prefer this module in a 3 MU panel so things could be space out a little more generously?

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Post by ba1 » Thu May 19, 2016 2:41 pm

This looks great! When and how much?

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Post by Stereotactixxx » Thu May 19, 2016 3:02 pm

JohnLRice wrote:I know some people might not like this idea if they are running out of room and are in denial over the fact that another case is inevitable :hihi: but I think most people might prefer this module in a 3 MU panel so things could be space out a little more generously?
I am definitely among those people. Fortunately though, I'm not looking for another mixer right now, so my opinion can be ignored. This module seems like a golden ticket for those craving density (despite opting for MU).

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Post by burdij » Fri May 20, 2016 12:21 pm

ba1 wrote:This looks great! When and how much?
The initial price of the module will be $429.00 although there might be some introductory level pricing and promotion.

There will be two companion modules, the aux mixer module and a master module, the GMS-980, capable of handling up to four VCA modules and that will have aux returns, a headphone amp, master gain control, metering and drivers for 600 Ohm balanced line output.

I think all the parts will be available in less than 60 days.
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Post by PeterDeVault » Fri May 20, 2016 4:06 pm

burdij wrote:There will be two companion modules, the aux mixer module and a master module, the GMS-980, capable of handling up to four VCA modules and that will have aux returns, a headphone amp, master gain control, metering and drivers for 600 Ohm balanced line output.

I think all the parts will be available in less than 60 days.
Oh, man. And to think this is being built in my backyard. :party:
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Post by Rex Coil 7 » Wed Jun 08, 2016 10:50 am

burdij wrote:I am implementing the 3dB pan law. You can see this in the scope photo. The discontinuity occurs at 0 Volts and it represents .707 times the channel input level. When both channels are added in a mono mix, the output will then be 3dB higher than unity gain. The mono signal will actually be slightly louder when positioned in the center. This will serve to prevent that center panned signal from getting lost in a crowded mix image as it would if it were based on a 6dB law.
FINALLY! FFS someone who finally understands this has gone and done it!

This same design application (3db protocol) has been in my "Git round Tuit" binder for years. I've found it simpler to wait for someone else to actually create stuff, then I can complain about having designed it first, rather than actually going through the painstaking steps to actually create the tangible product! (To be clear, this is self mockery).

Great job, excellent application, and a YUGE big ol' hug for taking the time and brain-drain to actually gititdun. Pan modules have sorely sucked for far too long. You've not only addressed the suckage, but taken the idea to it's fullest throated expression.

Thank DOG for long midwestern winters that force talented designers inside, where all they can do is refine refine refine until the Sun comes out and they have access to their shops again. By the time the mill and lathe are fired back up, the design is honed and ready.

Or, at least it's fun to think it goes that way .... :)

5U/MU is the next frontier of density. My money says it won't be long before 3.5mm MU modules are seen. At least for certain functions (mod matrix "on module" type of things). It's an outright necessity. The MU world needs things such as the MATHS, the Doepfer Matrix Mixer, more featured EGs, and of course this wonderous wonder that has been presented to us here in this thread.

This module would REALLY help my little system, no doubt. Savin' up them vacuum cleaner nickels.

:tu:
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Post by EPTC » Wed Jun 08, 2016 11:48 am

burdij wrote:There will be two companion modules, the aux mixer module and a master module, the GMS-980, capable of handling up to four VCA modules and that will have aux returns, a headphone amp, master gain control, metering and drivers for 600 Ohm balanced line output.
Oh man! Photos, please. Would love to see the entire system.

THANK YOU FOR MAKING THIS.

When you have voltage going through the pan, does the left/right knob still work, or is it defeated? Those solitary L/R buttons look like really awesome fun.

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Post by burdij » Thu Jun 09, 2016 10:55 am

Rex Coil 7 and EPTC, thank you for your comments. Yes, it was a very productive winter. There is more to come. 8-)
EPTC wrote: When you have voltage going through the pan, does the left/right knob still work, or is it defeated? Those solitary L/R buttons look like really awesome fun.
The circuit is completely DC coupled so it will work with both audio and control signals. Panning, the mute function, and the output VCAs will work for both control and audio. If a channel is assigned to only one bus, the panning function is disabled so two independent mixes of two inputs could also be made. The input VCAs are equipped with linear/exponential switches so that they can be set to best accommodate the type of signals being used.

Testing out some new knob colors:

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Post by EPTC » Thu Jun 09, 2016 9:03 pm

burdij wrote:
Testing out some new knob colors:

Image
Wow, I know that a few might prefer a traditional black, but I love those! They add such an interesting character to the layout.

This module is exciting. I've been looking at other variations lately, like the Intellijel Planar (which looks aesthetically weak compared to this) or the Ekdahl Quad Massager (which feels cumbersome but is close in features) - I'm not too interested in the joystick for either; it's the CV panning.

- Do you know if the planned depth for this would fit in a Dotcom Box 2? This would be great on a desktop with other mixing equipment.
- Also, pardon my ignorance, but I see a master output that's two channels, but for a stereo module I'm a little confused about the individual single-jack output for each individual channel. Are those mono sockets or TRS/stereo?

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Post by burdij » Fri Jun 10, 2016 1:12 pm

This will be the "white tie" version, I suppose.

Each VCA has an output on the panel that is before the panning function, like a direct output on a mixer.

The depth behind the panel including the power connector is 2.20 inches (56mm0 so it should fit in a Box 2 which has 2.375 inch clearance. It may be a little tight if the expansion connector is used, though, as that is a ribbon cable type IDC header.
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Post by EPTC » Fri Jun 10, 2016 1:40 pm

burdij wrote: Each VCA has an output on the panel that is before the panning function, like a direct output on a mixer.
Nice! Ah, right - That makes perfect sense. Thanks for the detailed reply!

(Laughed at white tie joke, too - And I'd likely go for that option)

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Post by VinceL » Fri Jun 10, 2016 4:00 pm

JohnLRice wrote:I know some people might not like this idea if they are running out of room and are in denial over the fact that another case is inevitable :hihi: but I think most people might prefer this module in a 3 MU panel so things could be space out a little more generously?
I definitely agree with John.

It seems that there are several MU manufacturers out there trying to cram as much functionality as possible into their modules. This results in having to use smaller knobs and tighter spacing of the knobs, jacks, switches, and buttons. :bang:

We are using MU/5U systems here people! :pan: They are big and spacious.

If you want your controls and jacks jammed together, go buy a Euro system. :youkids:
VinceL

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Post by Mark11Audio » Fri Jun 10, 2016 4:24 pm

JohnLRice wrote:I know some people might not like this idea if they are running out of room and are in denial over the fact that another case is inevitable :hihi: but I think most people might prefer this module in a 3 MU panel so things could be space out a little more generously?
This comment from the guy who just bought 3 MOAR cases !!! LOL
:yay: :yay: :yay: :yay: :yay: :yay: :yay: :yay: :yay: :yay: :yay:

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Post by sunsinger » Fri Jun 10, 2016 9:02 pm

I've been wanting to buy from Grove for some tome, but all I've ever seen from them is nice pictures. Still waiting to hear if these "ideas" are ever produced and someone actually has one.

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Post by PeterDeVault » Sat Jun 18, 2016 10:25 am

sunsinger wrote:I've been wanting to buy from Grove for some tome, but all I've ever seen from them is nice pictures. Still waiting to hear if these "ideas" are ever produced and someone actually has one.
I have two of his polyresonator modules, and believe me, they are very real. :hyper:
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Post by burdij » Sat Jun 18, 2016 2:31 pm

VinceL wrote: It seems that there are several MU manufacturers out there trying to cram as much functionality as possible into their modules. This results in having to use smaller knobs and tighter spacing of the knobs, jacks, switches, and buttons. :bang:

We are using MU/5U systems here people! :pan: They are big and spacious.

If you want your controls and jacks jammed together, go buy a Euro system.
When I got close to filling up my fourth 22 MU case, I began to realize the scope of the packaging problem with MU systems. In order to have more I had two basic options, another stack of cabinets (and 8 and 10 foot patch cables) or modules with more functions per module. So that's why I started to make modules with more functions. Besides that, to add each additional MU of module, I would have to pay about $25 per module for cabinets, power harnesses, power supplies and other non-module hardware.

I have analyzed, with a quick back of the envelope calculation, the density of some of the current panels that exist and some of the new ones in the works to see how they compare with existing modules. The metric is functions per square inch where a function is a knob, a jack, an indicator, etc. To give a comparison with Eurorack, the function per square inch density of a Tiptop audio Z3000 oscillator is 1.25 fpsi.

Moon 569 6MU Sequencer - 1.26
GMS715 2MU Quad VCA Mixer - 1.08
GMS714 1MU Quad VCA - 1.05
GMS302 2MU Dual VCO/VCA - 1.02
GMS1340 2MU Polywav Player - 1.00
GMS724 1MU Multiples - 0.84
GMS782 2MU LFO/VCA - 0.70
GMS712 1MU Dual VCA - 0.63
Q119 8MU Sequencer - 0.52
Q106 2MU VCO - 0.46
Q109 1MU ADSR - 0.42

So about twice the number of functions per square inch as a typical DOTCOM module but not the most dense currently available, at least not yet.
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Post by Rex Coil 7 » Sat Jun 18, 2016 6:01 pm

burdij wrote:
VinceL wrote: It seems that there are several MU manufacturers out there trying to cram as much functionality as possible into their modules. This results in having to use smaller knobs and tighter spacing of the knobs, jacks, switches, and buttons. :bang:

We are using MU/5U systems here people! :pan: They are big and spacious.

If you want your controls and jacks jammed together, go buy a Euro system.
When I got close to filling up my fourth 22 MU case, I began to realize the scope of the packaging problem with MU systems. In order to have more I had two basic options, another stack of cabinets (and 8 and 10 foot patch cables) or modules with more functions per module. So that's why I started to make modules with more functions. Besides that, to add each additional MU of module, I would have to pay about $25 per module for cabinets, power harnesses, power supplies and other non-module hardware.

I have analyzed, with a quick back of the envelope calculation, the density of some of the current panels that exist and some of the new ones in the works to see how they compare with existing modules. The metric is functions per square inch where a function is a knob, a jack, an indicator, etc. To give a comparison with Eurorack, the function per square inch density of a Tiptop audio Z3000 oscillator is 1.25 fpsi.

Moon 569 6MU Sequencer - 1.26
GMS715 2MU Quad VCA Mixer - 1.08
GMS714 1MU Quad VCA - 1.05
GMS302 2MU Dual VCO/VCA - 1.02
GMS1340 2MU Polywav Player - 1.00
GMS724 1MU Multiples - 0.84
GMS782 2MU LFO/VCA - 0.70
GMS712 1MU Dual VCA - 0.63
Q119 8MU Sequencer - 0.52
Q106 2MU VCO - 0.46
Q109 1MU ADSR - 0.42

So about twice the number of functions per square inch as a typical DOTCOM module but not the most dense currently available, at least not yet.
T'is this set of notions precisely, that have made me take on using 3.5mm protocols within the modulation cab on my system, and sticking with the spacious and much more playable MU format with the audio path modules.

I think small "modulation panels" within MU systems, that embrace 3.5mm connections and dense circuitry are the way to go. Picture how some of the software VST synths (that emulate vintage synths, such as the Minimoog) have little "drawers" or "flaps" that conceal little densely populated controller sections. The CS80v VST is also that way, it has a ~cover~ that may be flipped up to expose a goodly supply of modulation resources.

This is the way to go. Picture devoting (let's say) ~roughly~ 8sp of a 44sp synth cab to Euro, which is devoted to modulation and 1v/oct processing and routings (stuff that deals with portamento, paraphonic splits, unison modes, etc ...) and all other modulations. Devoting 25% or so of the MU cab to a ~corner's worth~ of Euro ... 3.5mm Euro ... is practical ... in fact it's more than just practical, it's optimal.

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Post by duluthdack » Sat Jun 18, 2016 6:55 pm

:woah: :woah: Looks like a great module! More VCA, more panning CV! Love that idea! My DOTCOM pan is VERY boring!

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Post by VinceL » Sat Jun 18, 2016 9:09 pm

burdij wrote:
VinceL wrote: It seems that there are several MU manufacturers out there trying to cram as much functionality as possible into their modules. This results in having to use smaller knobs and tighter spacing of the knobs, jacks, switches, and buttons. :bang:

We are using MU/5U systems here people! :pan: They are big and spacious.

If you want your controls and jacks jammed together, go buy a Euro system.
When I got close to filling up my fourth 22 MU case, I began to realize the scope of the packaging problem with MU systems. In order to have more I had two basic options, another stack of cabinets (and 8 and 10 foot patch cables) or modules with more functions per module.
John,

I understand what you are saying and why you are increasing functional density. But, IMHO, if you want a well-populated 5U/MU system, then you need to be willing to pay the price to have lots of space for your system. If having many smaller cabinets or a few very large cabinets doesn't work for you (insufficient space, insufficient funds, whatever), then maybe a well-populated 5U/MU system isn't for you.

This is all my personal opinion. I know there are wigglers out there putting together 5U/MU skiffs who want maximum functional density.

I hope that packing functional density into 5U/MU modules is not the long-term trend. Unfortunately, it's not just you, John, who is tightly packing the functionality. I've been quite disappointed with Dotcom's recent modules with small knobs and tightly packed knobs, switches, and jacks. I can't believe these are from the same guy who brought us the Q110 Noise Source or Q116 Ring Modulator. :doh: :mrgreen:

OK, BIG MU rant over...
VinceL

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