Product selection: digi pots

[lpc32]

So what did you end up doing?

[linux-works]

I've spent a few yrs developing and testing analog audio attenuators.

first, let me point you to my (partner's) website that has kits and schematics for controller based vol controls: www.amb.org (look for 'lcduino' and 'delta1' as products).  the code is open-source and we support users on the amb.org forum.  what we have now is a relay atten and I'm happy to answer any questions about that.

the code also supports 2 other attens; one is a TI pga23xx chip and the other is a cirrus cs3318 chip.

the pga is a pain to deal with and its fussy about layout and power.  but its cheap and it can be an ok vol control for stereo.

my current fave is the more expensive (and harder to solder chip) cs3318.  its 8ch of analog vol control and its pretty much noise-free and distortion-free.  I have one in my current DIY home stereo and I plan to do a board for it, someday (right now its perf-board since I have not designed a pcb for it).

I would avoid digital pots.  they are not meant for audio.  I tried a few simple ones but you really want a buffer and that buffer to be gain controlled.  the pga/cs chips have both input atten stepped R's and also variable gain (feedback R) based on whether you are below 0db or in the gain region.

I also have done my share of motor pots and my code will support that, too (as will the lcduino) but running audio thru a mech pot is not so great.  l/r balance always sucks toward the low end of the pot and there's crosstalk as you go down in levels, too.  I now use digital control of analog-domain vol controls and swear by them.  or relays, if you can deal with the relay clicking


HTH

[linux-works]

oh, and as for LDR's, you don't want them.  they have distortion, they are a HUGE pita to match (and keep matched) and they are more of a 'fad' than true high end atten.

what they excel at is muting!  if you needed a soft mute (hard off/on, no middle states) they are great for that.

but to run LDR's for vol control is a mess.  no one seriously uses them (well, one company that I know of does; and they charge upwards of $20k for their preamp due to the HUGE complexity of making it all work well).  its the old audio alchemy guys doing that and I have no idea how big their sales are, but I've never known anyone to own a $20k preamp before

[magetoo]

I've been thinking along the same lines as the OP did (two years ago..) so this was an interesting read.

l-w, it seems like you are doing something pretty different (volume control/fading) from what he wanted to do.  I'd be interested to hear what you would use for a generic pot replacement that isn't a volume control.

I guess the correct answer for this sort of thing is "redesign the thing from scratch" and use DACs for control, but...