[sdiy] Best AVAILABLE OTA for building new designs?

[Mike Bryant]

I think you need to watch some videos of the late Keith Emerson.  He'd happily have twenty or more keys pressed on a Hammond, some of course held down with knives :-)

As for the mixing, this is a problem met on all modular analogue mixers where running the virtual earth of the summing node the whole length of the console is the weak point for noise injection.  Fortunately for the OP, he can probably mix signals for each octave locally using an op-amp adder, then sum all of these in a second stage of addition.

It might be worth (digitally) monitoring how many keys are pressed and reducing the gain by some sort of curve above a certain number of keys pressed.
________________________________
From: Jacob Watters <jacobwatters at gmail.com>
Sent: 12 August 2024 14:26
To: Mike Bryant <mbryant at futurehorizons.com>
Cc: Gordonjcp <gordonjcp at gjcp.net>; synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Best AVAILABLE OTA for building new designs?

"3) Will there be a problem mixing 48 key outputs together?  Will clipping be a problem?  Obviously, all 48 keys will never be played at the same time, but still."

What I did for a top octave synth that I made is I added gain control to the mixer. Then I could turn it up when playing mono or low polyphony, and turn it down when playing dual chords like an organ.

Another option is to aim for a max note count. The max notes likely to be played at once is probably around 8. Maybe plan for that, and adjust accordingly.

Jacob Watters
JacobWatters.com<http://jacobwatters.com/>


On Mon, Aug 12, 2024 at 4:45 AM Mike Bryant <mbryant at futurehorizons.com<mailto:mbryant at futurehorizons.com>> wrote:
Except for noise floor in a mic amp with the gain wound up to maximum where there might be a very slight difference, I'll do the same for a 5532 and any of these fancy op-amps :-)

Of course there are op-amps which do sound different - the ones with added distortion.  Maybe the BA662 also adds something that way ?
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org<mailto:synth-diy-bounces at synth-diy.org>> on behalf of Gordonjcp <gordonjcp at gjcp.net<mailto:gordonjcp at gjcp.net>>
Sent: 12 August 2024 09:13
To: synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org> <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Subject: Re: [sdiy] Best AVAILABLE OTA for building new designs?

On Sun, Aug 11, 2024 at 12:09:35PM -0400, Ben Bradley via Synth-diy wrote:
> I was thinking of the Roland chip (BA662A/BA662B) that hasn't been
> mentioned, and I came across this discussion that may be helpful. For
> high-quality "real VCAS" there's the chips from THATCorp, but they're
> of course quite expensive compared to OTAs.

If anyone can tell the difference between a BA662 and an LM13700 VCA in an honest double-blind test, I'll buy them the best Juno 6 I can find.

After they test clean for cocaine.

--
Gordonjcp

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