THAT2162 Dual VCA and THAT1286 Dual Line Receiver

JohnRoberts

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The dual VCA looks like a good building block for my current summing console. One of these per channel to perform fader/pan function (perhaps with selectable pan law).

The 3 pf that each VCA would present to the bus would add up across a large number of channels but using a variant on a MFB LPF in summing amp could easily tolerate that capacitance and more.

I always liked the idea of a large summing structure with no noise gain in the bus In fact with no noise gain on the summing amp, a VCA could be used there too for almost unlimited bus headroom (headroom would be the reciprocal of VCA cut capability). Of course then the MFB filter is out and the bus capacitance might degrade stability of summing VCA. I have some ideas but they would require melting some solder to confirm.

The beauty of using VCAs per channal is you wouldn't need to physically put a VCA on the master to apply global gain changes. Applying a gain offset to every channel VCA could give you a virtual bus VCA.

This might be commercially viable if this trend in mixing digital projects with analog mixers had some basis in theory and therefore legs. If it does, that basis escapes me.

JR
 

JohnRoberts

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I've designed consoles using synthesized current sources in place of summing resistors for Loft and at Peavey (AMR 800/1600/2400 series). The old Loft (late '70s/early '80) even had a dBx VCA (202 IIRC?) wrapped around a TL072 for the master sum amp .

I didn't use VCAs in channels because of cost, and I wasn't addressing an automation market, so it was much more cost effective just roll a simple bilateral current source.

The VCA based mixer is mostly a mental exercise, and it would also lend itself to throwing some automation hooks into it since all faders and pans are voltage controlled. This could be a digital controlled analog mixer that I suspect would appeal to the current fashion. Whether this is fashion or a credible market need stands to be seen.

I am not familiar with PAR, and I don't need another black hole for my time. I have seen plenty of anecdotal "digital mixers sound bad compared to analog" reports, but haven't heard a concise explanation for why digital combining would not live up to it's promise of improved performance over analog means. In principle it should be arbitrarily good, and certainly better than some of the names I've heard mentioned that were used in lieu of (probably mediocre digital platforms).

If there is really a "there" there (problem), I could design a simple analog mixer that is arbitrarily good (for analog), but I don't see the point if in my judgement properly executed digital should be better. There may be a disconnect between theory and practice, but that should be a interim hardware issue until MIPs or whatever grow into the task at hand.

JR

PS An old acquaintance is a very serious recording guy, I may need to just ask him. He is not hip to the nitty gritty of hardware design, but he knows what is going on at the cutting edge of SOTA for recording.
 

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