digital volume control chips

I'm starting this thread to be a reference list of suitable chips. This is supposed to be a fairly high quality volume control, useful for hifi setups or PA systems.

Basically, for controlling volume, you reduce the volume with the help of a potentiometer, and then you buffer the high impedance output of the pot wiper with a opamp or a transistor.

A digital potentiometer is a chip with a built in resistance that can be varied via a digital interface. There are lots of them around. These could be useful, but need additional opamps. I wanted chips with the opamp integrated, in order to simplify the design. (adding any opamp is not difficult, but choosing the right digital pot and opamp and getting rid of noise, THD, etc. might be not so easy)

So far I found 5 chips:

| chip | USD | supply V | interface | audio performance | comment | | - | - | - | - | - | - | | max5486 | 2.50 mouser or farnell | +2.7V to +5.5V | up/down pushbutton | SNR 90dB THD 0.01% | only SMD | | pt2257 | 2 ebay | 3 to 9V | I2C | SNR 90dB THD 0,07% | | | pt2259 | 3 at ebay | 4 to 10 V | I2C | SNR 95dB THD 0,07% | | | pga2311 | 10 at mouser or farnell | 10V (+/-5V) | serial | SNR 120db THD 0.0004% | | | m62429 | 5 at ebay | 5V | serial | SNR 85db THD 0.01% | creates its own ground ref V |

The chip "that2181" from http://www.profusionplc.com/index.php has superior audio performance, but no digital interface.

Power supply: This is not so trivial, because you can't just use the power supply of the arduino. The switching processes inside the atmega chip introduce small spikes in the Vdd rail, which will be audible.

Also, the volume chip needs a dual voltage power supply. The dual voltage requirement can be cirumvented in a fashion: because there is actually not much current flowing in and out of the ground, you can create a ground point with a voltage divider and an opamp used as buffer. Or you omit the ground alltogether and connect the inputs and outputs with capacitors. However the capacitors will affect frequency response, if not carefully selected.

A 5V power supply will allow a maximum output amplitude of roughly +/- 2V or 10dBu or 8dBV, which is enough for PA use or for hifi use. However there is no safety headroom left, since 10dBu is PA standard.

My plan for the power supply so far: Use one 9V or 10V power supply (depending on the chip) and filter this power supply with a low pass RC filter and possiby an inductance for the analog audio chip. This filter will take away some voltage, depending on the current drawn, but there will still be enough headroom left, if the resistor is not too big. The arduino will step the 9V down to 5V with its internal voltage requlator.

Any thoughts or suggestions for other chips?

BTW, there is a fully assembled board with a PT2259 or m62429 chip available, including voltage regulator, at ebay or other online stores, for around 10 - 20 USD.

This thread http://forum.arduino.cc/index.php?topic=244152.0 shows that it's possible to operate the board with an arduino.

P.S. My actual need is this (for guitar): http://www.pfeifferelectronics.com/products/leveler_volume_pedal.aspx However I need more than 8 steps, and I'm not willing to shell out USD180 + shipping + tax to Germany, and there are additional things supposed to go into the casing (LED metronome, effects bank switching)

Thanks for reading Thomas

Any thoughts or suggestions for other chips?

TDA7439 - Three-band digitally-controlled audio processor

PT2258 - 6-Channel Electronic Volume Controller IC

TDA7439 - I2C three band tone control and 4 input channel stereo mixer

not sure about PT2258, cant seem to make it work i.e. find it in i2c scanner code, shouldn't it acknowledge communication.

To make sure I am not doing something wrong, I have repeated connections many time (on breadboard)

also i got hands on another IC, same result, no device found in i2c scanner,

is there any ICs that dont show up in I2c scanner ?

I have decided to code for it and run that with volume low > wait > high and will check with audio source and amp

is there any ICs that dont show up in I2c scanner ?

Yes plenty, they all have one thing in common though, they don’t use the I2C protocol.

To make sure I am not doing something wrong, I have repeated connections many time

Looks like you are making the same mistake over and over then.

However if you read How to use this forum not only will it tell you how to ask a question it will also tell you to start your own thread and not hijack others.

I mean, I2C ics not showing in scanner, but sure thing. I’ll follow the advice @new thread

I've had very good results from the PGA2311. I generated the +/- 5v rails using a Murata NMA0505SC DC-DC converter.

You also have the PGA2310 if you want to run higher voltages for more headroom etc.

A virtually identical chip to the PGA2311, is the Crystal CS3310. With both of these chips, bring the analogue +/- 5v rails up before the digital 5v, or you'll get SCR latch up and a very hot chip.

Ian.

does anyone have any experience using any of these chips just as potentiometers? I'm fairly new to electronic circuits, so please bear with me..

for example, what kind of pot would (if it even can) any of the chips emulate? like 100k pot, 10k, etc.. i imagine i'm lacking a fundamental understanding of pot's, as I hardly understand the meaning of different pot values, if i remember correctly, its going to be that the pot can reach a maximum resistance value of its rating from zero. so basically its a variable resistor, from 0 to 10k ohms. or whatever its rated for.

am I making any sense here?

thx in advance

o basically its a variable resistor, from 0 to 10k ohms.

No it is not. It is a 10K, or 100K resistor and the slider takes a tap off a point on that resistor. So at the halfway point on a 100K resistor you would have 50K between the slider and each end.

Their is another thing with pots and that is the "law" or how the resistance changes with the tap position. With a linear law the pot behaves like I said above, with a log law it does not, these pots are designed for things like volume controls so that equal movements of the slider give equal changes in pecieved loudness. Then their is the anti-log pot which are even more specialist. See:- https://en.wikipedia.org/wiki/Potentiometer

for a linear chip see:- https://www.arduino.cc/en/Tutorial/DigitalPotentiometer

P.S. My actual need is this (for guitar):

Guitars like to see about a 1M Ohm load so depending on the chip you may need to buffer the input.

Most pedals are buffered, or if your guitar has an active pickup, you can probably get-away with lower impedance, but if you want it to work with “any guitar, anywhere”, it should have high input impedance.

This is supposed to be a fairly high quality volume control, useful for hifi setups or PA systems…

…A 5V power supply will allow a maximum output amplitude of roughly +/- 2V or 10dBu or 8dBV, which is enough for PA use or for hifi use. However there is no safety headroom left, since 10dBu is PA standard.

Most PA systems have line & mic inputs (no guitar inputs). If you want to use a line-input, you’ll generally want some amplification (as well as buffering) or you can use a DI box into a mic input.

If you use a linear digital pot you can adjust the “law” or “curve” in software. The “steps” will be bigger (in dB) at the low (quiet) end but with 8-bits (256 steps) that might be OK. I assume most specialized volume-control chips have equal-dB steps.

I’ve got a prototype preamplifier running using a PGA2310, the 2310 improves on the 2311 by having the ability to run on higher analog side rails. At least the 23xx devices output show up as a low impedance - think opamp output, able to drive loads as low as 600R.

The benefit of analog rails having a higher voltage is more overhead, reducing the chance of overload. One caveat is that according to the data sheet the source signal on its input must be from a buffer with low output impedance. This range is actually made by burr brown and I can attest the sound quality is very good.

DVDdoug: I assume most specialized volume-control chips have equal-dB steps.

Most of the true volume controls are actually opamps with variable gain in the feedback loop from looking at the datasheets. Further the TI and muses hi-end ones are usually controlled in 0.5dB steps. They have very tight tolerance across channels. But they are expensive. With a pga2310 coming in at about £20.

hydrocontrol: A digital potentiometer is a chip with a built in resistance that can be varied via a digital interface.

Also....most of these 'digital potentiometers' have much more limitations on the voltage (potential) range on the "end-terminals". Classical potentiometers allow you to connect the end-terminals to whatever voltages we like ..... provided max power dissipation etc are ok. And classical potentiometers often have a whole line of similar looking items - but each having a specified end-to-end resistance -- allowing for pretty good choice of desired end-to-end resistance.