Is it possible to extend dynamic range of audio volume control IC?

[NQ21HT449]

Hello, I'm trying to replace a volume control IC that has 80 dB of dynamic range, but I think 66-70 dB would be enough for my application.

I don't have SPI bus, the device has to be fully analog and be controlled by a log potentiometer. MAX5440 is one of the few analog options, but only has 60 dB of dynamic range. I suppose I could build a comparator circuit to mute it when the potentiometer is at towards the end position, so my attenuation would jump from 60 dB to 90 dB. Shouldn't be a problem with hysteresis circuit.

I checked other chip manufacturers and their volume control ICs are fully digital as well. Are there any other options, other than running a SPI line or creating a glue CPLD logic to translate log pot to digital? Can I somehow cascade two MAX5440 to extend their range?

Do I even I need a volume control IC if I could build the similar circuit with op-amps?

 

[betwixt]

Cant you use the log pot directly as a volume control. That gives infinite adjustment and maximum dynamic range with no additional components at all.

Brian.

 

[dick_freebird]

It's possible that a different resistor network could get you more
range - but the question becomes "what does the mfr know that
I don't?". More amplitude at the big end likely means distortion,
less amplitude at the little end worsens SNR.

Seems like a "try it, and see" bench exercise, you do have a
bench golden-ear-ometer right?

 

[NQ21HT449]

Cant you use the log pot directly as a volume control. That gives infinite adjustment and maximum dynamic range with no additional components at all.

Brian.

I haven't done much design at audio range, so I'm not sure. I thought about just building attenuator circuit (like pi-pad) but I assume it has drawback, the one of them is stability.

 

[crutschow]

Sorry, but the MAX5440 also has a 2-bit digital input, usually from a rotary encoder.

I suggest you change the log pot to a rotary encoder, unless you can do what betwixt suggested.

Op amps, by themselves, cannot control volume (gain), which is a non-linear function.
You would need something like an analog multiplier for that.

 

[KlausST]

Hi,

I've not tried this ... but what about connecting two linear pots in series. Then you get a quadratic function.
I expect it to work better than a single linear pot.

Klaus

 

[FvM]

Did you check if attenuation range below -60 dB has any practical relevance for your application? I would be more concerned about coarse attenuation step of 2 dB which is maintained when cascading two MAX5440 devices.

--- Updated Sep 29, 2023 ---

For volume control with professional audio performance, you may check other vendors, e.g.

Volume control ICs product selection | TI.com

Select from TI's Volume control ICs family of devices. Volume control ICs parameters, data sheets, and design resources.

www.ti.com

--- Updated Sep 29, 2023 ---

I missed the analog control requirement in post #1. MAX5440 has however position enconder rather than analog control input.

 

[NQ21HT449]

Sorry, but the MAX5440 also has a 2-bit digital input, usually from a rotary encoder.

I suggest you change the log pot to a rotary encoder, unless you can do what betwixt suggested.

Op amps, by themselves, cannot control volume (gain), which is a non-linear function.
You would need something like an analog multiplier for that.

Alright, so can I use one of the log stable op amps to control the gain with log pot, like they shown in these MIT papers?

https://www.analog.com/media/en/training-seminars/tutorials/MT-077.pdf

https://www.analog.com/media/en/training-seminars/tutorials/MT-078.pdf

I like the alternative of putting log pot to the voltage divider of driver amp better, but still I don't understand if this was an acceptable solution, why would anyone bother putting volume control IC in the first place???

 

[FvM]

I don't understand which relation do you see to log amps. They are not suited as variable gain amplifier (VCA) for audio.

 

[crutschow]

can I use one of the log stable op amps to control the gain

Those log amps are to compress that gain with amplitude to get a wider dynamic range.
They do not have a control input to vary the gain.

why would anyone bother putting volume control IC in the first place?

Good question.
Perhaps it's to avoid having to run the audio signal through shielded wires to the control where it might pickup noise or hum.

So the old circuit was controlled by a DC voltage from a log pot?

 

[FvM]

There was a series of audio VCA available many years ago (SSMxxxx series) but it's obsoleted since long. There may be still analog volume control IC on the market, but I'm not sure.

--- Updated Sep 29, 2023 ---

Amendment: Some SSM chips are resourced for special applications, e.g. analog sound synthesizers: https://www.soundsemiconductor.com/

 

[dick_freebird]

I think that an op amp with a log-taper pot in the feedback
might give you the profile, but question whether there is a
4-decade log taper pot to be had. Have to look at datasheets
or selection guides.

A linear taper and an exponentiating stage, fed to a VCA, might
do. Might achieve more decades that way. An analog multiplier
is one VCA, do not know if old timey VCAs like CA3080 (?) are
still made.