An Idea

[gettestudios]

I know as an engineer the ultimate console would be a fully automatable analog console. IE: Offering the same extensive automation found in DAW's. Such as EQ and Comp auto.

The question is: Outside of Cost factor, How would the use of VCA's (such as That 2181/2180A) in every Pot position on a desk (IE: EQ Section would have a VCA for gain, VCA for Q, VCA for freq) effect signal quality? An example Desk CH with the typical Pre/Gate/Comp/EQ would have 23 VCA's (excluding the AUX sends)
How would the "collective effect" of that many VCA's sound?

Obviously, the creative aspects of this kind of control is endless, just curious to your thoughts on it...

Joel

[mediatechnology]

That's a good question.

I think I would include in that design the use of digi-pots for some things (e.g. makeup gain, threshold etc in the dynamics) where you're potentiometrically controlling DC. For the preamps and line inputs a 1570/5171 combo might be included since VCAs wouldn't lend themselves well to controlling mic preamp or line gain. I did a universal input that used a 1570/5171 that had continuous gain control from about -60 to +60.

The EQ section would seem to be the most VCA-intensive since a single state-variable EQ section would require two for frequency control, one for level, and another for Q.

[JR.]

I know as an engineer the ultimate console would be a fully automatable analog console. IE: Offering the same extensive automation found in DAW's. Such as EQ and Comp auto.

The question is: Outside of Cost factor, How would the use of VCA's (such as That 2181/2180A) in every Pot position on a desk (IE: EQ Section would have a VCA for gain, VCA for Q, VCA for freq) effect signal quality? An example Desk CH with the typical Pre/Gate/Comp/EQ would have 23 VCA's (excluding the AUX sends)
How would the "collective effect" of that many VCA's sound?

Obviously, the creative aspects of this kind of control is endless, just curious to your thoughts on it...

Joel

While I don't accept your premise that digitally controlled analog would make the "ultimate" console, I have given this a great deal of thought and even have some related circuits I am not ready to publish (they might actually be worth something).

As Wayne pointed out, VCAs are not the only technology. The well respected Gamble console uses digital pots.

I am an old analog dog, but i have yet to hear a credible explanation for the bad reputation digital summing gets.

I do not doubt there is a market for this. I have as a mental exercise scratched out a variant on outside the box summing, where I use digitally controlled analog, in combination with an old invention of mine from the '70s that reduces bus noise gain (current source summing). In my ideal Dig controlled analog OTB, I could accept and pass analog signals but with digital control of faders and pans (automation is too useful to dismiss).

My only concern about investing time and money into such a product is that a well executed digital box could (should) perform as well (well maybe not quite as well, but close enough) .

JR

[gettestudios]

Some great Idea's!

Wayne- I am already looking at 1570 as a good front end. Looking for a very transparent low component count design, this ic seems to meet that. BUT How did it sound to you? Do you have any suggestions on where i can find info on the other solutions you suggested?

JR- I will look into the digital Pots that gamble used. I will also do some research on the topologies you have mentioned, do you have any suggestions on were i may find it?

Thank you both for your replies...

oh yeah i miss-spelled Bus on the other forum thank you for the correction JR...

[JR.]

There is another thread here already where I have described a VCA based fader and pan pot replacement that feeds into a current source sum bus topology.

Digitally controlling VCAs requires D/A conversion for every analog control voltage. Use of digital pots cuts out the middle man, so to speak, as you can directly control them with a simple digital word, while there are issues with step size and zipper noise.

I think there is also a discussing of interfacing digital control to VCA elsewhere around here (at least I recall answering some questions).

I have seen a few of the the gamble schematics in connection with my work over the years, but nothing that I can share.

JR

[gettestudios]

JR- Just did a simple search on Digital pots. I was quite surprised on the amount available and there relatively low cost. Since i admittedly have never even breadboarded a digital pot, what kind of resolution do you think it would need to not be able to hear zipper noise... Hmmm.

My simple search did find this, Anologe devices AD5293 1,024 step digital pot. That would work on a -/+15 volt supply. Am i going the right direction here?

Current source sum bus topology. Would this be something you can/willing to share?

Or should i do more searches in the forum before i put my foot in my mouth?

Thanks for your time

Joel

[JR.]

JR- Just did a simple search on Digital pots. I was quite surprised on the amount available and there relatively low cost. Since i admittedly have never even breadboarded a digital pot, what kind of resolution do you think it would need to not be able to hear zipper noise... Hmmm.

I am just now getting into my first design using DPOTs to control an audio path so ask me next year.

The audibility of zipper noise depends very much on the context of the signal.. i.e., if path is quiet there is no zipper, also gain changes could be coordinated with zero crossings to mask them. I am thinking of several different strategies.

My simple search did find this, Anologe devices AD5293 1,024 step digital pot. That would work on a -/+15 volt supply. Am i going the right direction here?

Most cost effective DPOTs have less bits of resolution and less operating range, but IIRC the Gamble used high voltage parts. I am inclined to finesse that for a more cost effective solution.

Current source sum bus topology. Would this be something you can/willing to share?

Or should i do more searches in the forum before i put my foot in my mouth?

yes and yes...

I first published my current source summing in an article I wrote about console design back in 1980. While I published the concept I never published actual schematics. I used current source summing in the AMR consoles I designed for Peavey (late '80/early '90s) and those schematics were in the owners manuals so published and out there somewhere. I don't have copies.

The concept is simple, replace the resistors in a virtual earth summing bus with current sources. In theory this completely wipes out the N+1 noise gain buildup, that not only increases bus noise, but loop gain margin related phase shift and distortion. In practice, the practical synthesized current sources i used gave me 20-30 dB of improvement over conventional.

As i hinted I have some new ideas that do better that I don't wish to publish just yet, as I am trying to talk my friends with an analog console company into maybe using my new design.

Thanks for your time

Joel

I mean no disrespect, but it seems like you don't know what you don't know... designing a big dog console, is a little like designing a car... the individual parts are no big deal, but they all have to work together harmoniously or you have problems.

I fear you will be disappointed in this pursuit, and I am not convinced the world wants or needs a box like you have specified. The majority of people are just trying to give you good advice. I will point you in the right direction but I won't teach you how to design consoles from scratch, or do any design work for you.. You have a lot more research to do before you start in earnest, and IMO if you learn enough from you research, you should convince yourself to take another path.

Good luck

JR

[gettestudios]

I hear ya, and fail or succeed at least i gave it my all in the end. I will be a better engineer for it. I hope i was not giving the impression i was looking for a "console-by-the-numbers"

My intent was not to build a desk for the market only ever planed to just build one.

[juniorhifikit]

I know as an engineer the ultimate console would be a fully automatable analog console. IE: Offering the same extensive automation found in DAW's. Such as EQ and Comp auto.

The question is: Outside of Cost factor, How would the use of VCA's (such as That 2181/2180A) in every Pot position on a desk (IE: EQ Section would have a VCA for gain, VCA for Q, VCA for freq) effect signal quality? An example Desk CH with the typical Pre/Gate/Comp/EQ would have 23 VCA's (excluding the AUX sends)
How would the "collective effect" of that many VCA's sound?

Obviously, the creative aspects of this kind of control is endless, just curious to your thoughts on it...

Joel

Not to be a wet blanket, but what you've described is a Euphonix console. They're not bad - I just mixed an album on one. These days you can probably pick one up for less than the cost of the parts.

[JR.]

Joel has posted his questions on several forums and the discussion has gravitated to a thread here-

http://www.prodigy-pro.com/diy/index.ph ... =40053.100

I think checking out the Euphionix series was already suggested there.

I have a passing interest in this, but this is not a good use of time for a one off...

JR