Digital volume control

[day1118]

hi guys, I am wondering if it would be possible to take a chip such as the LM1036 which is a volume controller with treble/bass control too. Controls are analog inputs using a 47K variable resistor. I then want to swap on of the pots with a digital pot that I can control with a pic chip so I can have digital volume control and still have he tone control as analog. I was looking at a DS1803 which is a 50k digital pot.

Anu suggestions would be much appreciated!
Thanks.

[day1118]

Hey guys? any one have any idea as to whether or not this would work?

Any advice much appreciated!
Thanks

[breez]

The LM1036 is quite a bit noisier than say PGA2311. 80dB SNR for 0.3Vrms signal translates to 30uVrms noise compared to typical 2.5uVrms for PGA.

Depending on your power amplifier gain and speaker sensitivity you might get audible hiss from the speakers.

Example calculation:

Power amplifier gain: 30dB
Speaker sensitivity: 88dB/2.83Vrms @ 1m

Noise amplitude at speaker output:

(30 * 10^-6) * (10^(30 / 20)) Vrms = 0.95 * 10^-3 Vrms

Noise level at 1 meter:

20 * log (0.95 * 10^-3 / 2.83) + 88 = 18.5dB.

Conclusion: Not a problem for this scenario, but amplifier gain and speaker sensitivity variability can lift the noise over ambient noise levels.

[day1118]

Thanks for your reply. I dont know enough about audio to completely understand what your saying, but got the general gist. I am using a 40-50W amp, but dont know the sensitivity of the speakers.

Anyway, I just found the LM4832 which would do what I want perfectly! Any advice for or against this chip? I had a look at the store i get my electronics from, and not sure that they have many/ can get more. I checked ebay, but couldnt find any, can anyone suggest that its being discontinued ect, or where I could order them from?

Thanks heaps!

[gmarsh]

To keep signal quality up, I'd use a PGA2310/2311 chip for gain control.

These chips are much more clean than the LM4832 chip. I'm more concerned about the THD of the LM4832 than anything; 0.5% max THD is pretty bad (and audible), it might be better if the chip isn't driving a low resistance load but there's no data in the datasheet for that.

To do tone controls, I'd build a pair of active Baxandall circuits and use a couple of dual gang pots to control them. Info on that is here:

http://sound.westhost.com/dwopa2.htm

Also, the LM1036 is a pretty bad chip. I built a 250WRMS amp when I was doing EE, for powering large speakers for outdoor field parties. I used the chip for bass/treble/volume/"loud" control, it sounded pretty awful but hey, considering the (drunk) audience, it was fine.

[day1118]

Thanks gmarsh, Illl have a look at it.

Does that mean that there isnt really a good chip that has digital in to control volume, bass and treble? and also no good chip that does these with analog inputs?

Thanks

[day1118]

What do you think of the TDA1524? I have seen a lot of preamps that use this to include tone control.

Has anyone used the LM4832? what was the sound like?

Any suggestions much appreciated!
Thanks

[gmarsh]

Originally posted by day1118
Thanks gmarsh, Illl have a look at it.

Does that mean that there isnt really a good chip that has digital in to control volume, bass and treble? and also no good chip that does these with analog inputs?

Thanks

Though I haven't done an exhaustive search, I've got my doubts that you'll find a decent quality chip that does this. I think manufacturers have nailed down digital volume control because it's useful to have in various pro audio equipment, but bass/treble control tends to be the domain of cheap MP3 players, radios, etc. where audio performance is less of a design criteria.

Another option is to build a 3-band stereo equalizer circuit. Break the incoming audio into bass, mid and treble with op-amp filters, use PGA23xx chips to adjust the gain of each band, then sum them together. To adjust volume, adjust all three. To adjust bass/treble, adjust the bass/treble gain with respect to mid.

[day1118]

Another option is to build a 3-band stereo equalizer circuit. Break the incoming audio into bass, mid and treble with op-amp filters, use PGA23xx chips to adjust the gain of each band, then sum them together. To adjust volume, adjust all three. To adjust bass/treble, adjust the bass/treble gain with respect to mid.

That could work... I was told that the LM4832 clicks when volume is changed because it doesnt detect a low signal, so thats out.

What about using a circuit like the one you suggested

I'd build a pair of active Baxandall circuits and use a couple of dual gang pots to control them

then replacing the pots with digital pots if I latter decide that I want digital tone control? Could this work?

Thanks for your help!