Using digital pots (DS18xxx) as audio attenuators

[JPK2300]

Hi all,

I am looking for any hints how to use a digital (IC) potentiometer to control the audio volume (attenuation).

My setup contains two parts:
- audio source provided by a line out (RCA) or headphones jack (e.g. TV)
- active speaker system (2.1) with amplifier, the volume is controlled by a mechanical pot placed on the input wire

I would like to replace the mechanical pot with an digital since I need to control it remotely.

I have tried with DS1807 and DS18030, but I am not able to get the same behavior as by the built-in mechanical pot. I get some attenuation, but the sound gets "corrupted" and noisy when the "wiper" is set to higher attenuation values.

I connect the signals directly to the ICs, perhaps I need to add some DC offset before and remove afterwards - but I could not figure it out, nor find any examples showing how to wire signals correctly.

I found a couple of thread on this site mentioning this pots, but no concrete examples how to use them. So I am kind of stuck

I would be very grateful if anyone can point me in the right direction or maybe explains briefly, what I am doing wrong?

Thank you!

/Jairk

 

[tomchr]

The various digital pots were never intended for audio use. What you want is a programmable gain amplifier (PGA). There are many options. PGA2320 is quite popular. Personally, I'd look at the THAT2181.

Another alternative would be a motorized pot.

Tom

 

[benb]

I connect the signals directly to the ICs, perhaps I need to add some DC offset before and remove afterwards - but I could not figure it out, nor find any examples showing how to wire signals correctly.

Yes, on any chip the signal level needs to stay between the positive and negative power input voltages. That means shifting the signal level as you mentioned, or powering the chip from both positive and negative supplies. Did you see this thread?

http://www.diyaudio.com/forums/anal...problem-ds1802-digital-volume-control-ic.html

The various digital pots were never intended for audio use.

I suppose it depends - if you mean "high-end audio use" where the lowest distortion is The Thing I'll agree with you, but I suspect these have been used in millions of car stereos with what most people would consider acceptable results.

 

[JPK2300]

Thanks for your reply, guys!

I started with DS1807 since it was the cheapest option and easy to get through DigiKey in Danmark. The datasheet for the IC states that it is specially designed for audio applications since it has logarithmic way of changing the resistance. So I do hope there should be a way to get it working somehow

I did consider to use a motorized pot, but it would be an overkill - I've got an old speaker system, low-end, and I just want to replace the manual pot with a digital to support the remote control. That's how I found DS1807.

I have not seen the other thread with DS1802, seems very similiar to my problem, thanks for the hint. I will check it out and try to reproduce with op amps.

 

[00940]

Well, Maxim at least took the time to characterize the audio specs of their digital pots. So it seems they were indeed intended for serious audio : https://www.maximintegrated.com/jp/app-notes/index.mvp/id/2119

I've successfully used the ds1802 but you must indeed either use bipolar supplies (+/-2.5v) or bias the input and output at 2.5V. Another big problem of those pots is their limited voltage swing. It's best to keep the signal through the pot well under 1Vrms.

See for example: DS1802 Digital Stereo Volume Control

 

[davidsrsb]

These single 5V supply parts struggle with CD player with excessive output levels, all too common. This means that you are likely to have to start with a passive attenuator before input selection

 

[Juxtapos]

you could use the pot to control a path to ground through a cap

effectively making an actual attenuator cotrolled by the digital pot.

 

[Neil Davis]

This thread might help: DS1881 Digital Pot Volume Control

It sounds like a DC offset problem, and post #3 in that thread shows two different ways to fix it.

A long time ago I had a nice board that used those devices for a 2-way crossover with BSC and volume control, with a .NET program for controlling the board. It worked really well, but it's actually cheaper to use a DSP circuit instead. Those digital pots are a bit pricey, or at least they were about 5 years ago.

 

[nigelwright7557]

If the d-pot is run off 5 volts then the audio signal needs to sit on 2.5VDC.
If not the d-pot clips the signal to the power rails.