But if we drive the VCA control ports differentially does that work out with simple unity gain inverter? 3 + 3= 6 ?
I recall last time I thought about this, issues with wanting low source impedance when driving the VCA (for lowest noise and distortion).
JR
Linearize 'log' VCA's response
Re: Linearize 'log' VCA's response
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Re: Linearize 'log' VCA's response
Yes it would. Forgot we were driving it differentially so 3mV/dB/port works out to be 6 mV/db single-ended.
And you do want low source impedance that's low over frequency.
An op amp output that's "non-inductive."
And you do want low source impedance that's low over frequency.
An op amp output that's "non-inductive."
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Re: Linearize 'log' VCA's response
Hi Wayne and John,
Thanks for your valuable comments. I'll certainly look at John's proposed economic solution; a good opportunity for me to further explore LT Spice.
I simulated the EDN-circuit with inverted reference current; applying +5V DC as reference voltage gives 0dB thru the VCA if the input voltage is +5V DC; lowering Vin linearly attenuates the signal thru the VCA (+2.5V DC = -6dB, +1.25V = -12dB etc...).
The automation system that I'm looking into is designed to work with SSL circuitry; they have chosen to have the VCA fully open (0dB) at 0V DC in, and gradually attenuating the signal as the input voltage raises up to +5V DC (VCA at max attenuation).
-How can the EDN circuit be modified to react to 0V in = 0dB out / +5V in = max attenuation?
-SSL uses the same control line which steers the VCA with 0 <> 5V DC to also read / reproduce the mute status; the ADC / DAC react to anything above +7.5V DC as a mute signal. What would be the least complicated way to have the VCA circuitry ignore any incoming DC voltage above +5V?
Thanks Gentlemen!
I am by no means an electronics designer; at best an analog audio maintenance tech. But full of enthusiasm to learn as I go
Igor
Thanks for your valuable comments. I'll certainly look at John's proposed economic solution; a good opportunity for me to further explore LT Spice.
I simulated the EDN-circuit with inverted reference current; applying +5V DC as reference voltage gives 0dB thru the VCA if the input voltage is +5V DC; lowering Vin linearly attenuates the signal thru the VCA (+2.5V DC = -6dB, +1.25V = -12dB etc...).
The automation system that I'm looking into is designed to work with SSL circuitry; they have chosen to have the VCA fully open (0dB) at 0V DC in, and gradually attenuating the signal as the input voltage raises up to +5V DC (VCA at max attenuation).
-How can the EDN circuit be modified to react to 0V in = 0dB out / +5V in = max attenuation?
-SSL uses the same control line which steers the VCA with 0 <> 5V DC to also read / reproduce the mute status; the ADC / DAC react to anything above +7.5V DC as a mute signal. What would be the least complicated way to have the VCA circuitry ignore any incoming DC voltage above +5V?
Thanks Gentlemen!
I am by no means an electronics designer; at best an analog audio maintenance tech. But full of enthusiasm to learn as I go
Igor
Re: Linearize 'log' VCA's response
Most VCAs are 0dB at 0V control voltage.Igor Dockx wrote: ↑Mon Jun 19, 2017 1:33 pm Hi Wayne and John,
Thanks for your valuable comments. I'll certainly look at John's proposed economic solution; a good opportunity for me to further explore LT Spice.
I simulated the EDN-circuit with inverted reference current; applying +5V DC as reference voltage gives 0dB thru the VCA if the input voltage is +5V DC; lowering Vin linearly attenuates the signal thru the VCA (+2.5V DC = -6dB, +1.25V = -12dB etc...).
The automation system that I'm looking into is designed to work with SSL circuitry; they have chosen to have the VCA fully open (0dB) at 0V DC in, and gradually attenuating the signal as the input voltage raises up to +5V DC (VCA at max attenuation).
To increase attenuation from increasing voltage wire the faders backwards... Ground at the top, +5V at full down. Of course and audio taper pot will not result in a useful control law that way.
don't know-How can the EDN circuit be modified to react to 0V in = 0dB out / +5V in = max attenuation?
You can clamp or detect and clamp for voltage above 5V..-SSL uses the same control line which steers the VCA with 0 <> 5V DC to also read / reproduce the mute status; the ADC / DAC react to anything above +7.5V DC as a mute signal. What would be the least complicated way to have the VCA circuitry ignore any incoming DC voltage above +5V?
I am unclear about what you are trying to accomplish... your original post sounded like you wanted to control a VCA from an audio taper pot. I provided a circuit to support that, albeit with +10dB gain at the top of the fader, typical gain structure for consoles. You can make the top 0dB by scaling the current in offset transistor.Thanks Gentlemen!
I am by no means an electronics designer; at best an analog audio maintenance tech. But full of enthusiasm to learn as I go
Igor
What kind of faders are used SSL with that automation? That may be the real difficulty.
JR
Cancel the "cancel culture", do not support mob hatred.