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-   -   Digital pots, better or worse than analogue pots ? (http://www.diyaudio.com/forums/parts/198748-digital-pots-better-worse-than-analogue-pots.html)

nigelwright7557 17th October 2011 08:59 PM

Digital pots, better or worse than analogue pots ?
 
Digital pots, better or worse than analogue pots ?

Opinions welcome.

I am about to start on a mixer with digital pots and controlled via USB from a PC.

kevinkr 18th October 2011 12:47 AM

:cop: Moved to Parts

Zero Cool 18th October 2011 01:43 AM

well I guess we should qualify what BETTER means?

I have heard some solutions that use Digital pots that sound very good. the channel to channel tracking tolerances are much tighter then conventional pots. yes as a DIY'er you could carefully select a well balanced pot that would work well. but with time pots get dirty and scratchy and the tracking over its range maybe good in some spots but not as good in others.

Digital pots have their issues too. static sensitive. requires the use of a microcontroller to work. and can jump from one setting to the next under certain "glitch" situations. requires the use of additional power supplies etc etc. they get pretty complex to implement well.

If you are building the ultimate no holds barred pre-amp. then the digital pot solution has advantages. But for the average DIY'er. a carefully selected pot i think is a much easier solution to implement well!

YMMV


Zc

counter culture 18th October 2011 02:44 AM

Without offering an opinion on the digital vs. analog issue, the PGA2310, 2311, 2320 volume controls from TI seem to be the best parts in this application, there's a Cirrus 8-channel part too, CS3308/18. They have quarter- or half-dB steps and have some gain as well as attenuation. The digipots I've looked at often have worse THD. You need to make sure the source is <600R or the THD suffers.

If you achieve the stated performance in practise these parts should be transparent.

benb 18th October 2011 05:47 AM

For the ultimate, these two aren't your only choices, and may not be your best. A "digital pot" might mean a mechanical rotary switch attentuator - very low distortion, very good tracking (with well-matched resistors), and for "digital control" could possibly be turned by a motor. The only disadvantage I can think of is high cost of the multiposition rotary switches. Also for digital control would be a set of telecom/reed relays switching appropriate fixed-resistor attentuators, and likely controlled by a microcontroller. This would be the most complex design, but it sounds like a "fun" project.

nigelwright7557 24th October 2011 01:31 AM

I knocked up a test circuit and used Microchips MCP4231.
They sound very good and adjust ok without any clicks.

Making a 6 channel mixer taht is controlled via USB from a PC.
The PC has a screen with 6 faders and a bargraph display, the mixer sends back audio peak detection for the bargraph.

tinitus 24th October 2011 01:38 AM

a chip vol/att is not digital, is it ?

nigelwright7557 24th October 2011 01:42 AM

Quote:

Originally Posted by tinitus (Post 2756291)
a chip vol/att is not digital, is it ?

It is digitally controlled via SPI (Serial bus) and it has 129 discrete settings.

If your suggesting teh audio is not in digital format then that is true.

http://www.ckp-railways.talktalk.net/digpot.jpg

JoelS 25th October 2011 05:10 PM

I have recently been working with the PGA2310 and I'm quite impressed with it. as long as you stay within the recomended parameters (low source impedance, not too low load impedance, supply voltage, layout considerations) then the performance is good. it is definitely more complicated to implement but if you can overcome the challenges there are several advantages. Zero Cool already mentioned the superior channel matching (+/-0.05dB matching according to spec sheet) that's way better than any dual ganged pot. Also, once you have digital control you can do things that could be really useful for a mixer like store and recall settings - like a snapshot, or control several chips together creating groups. remote control. many possibilities that conventional pots aren't suited for.

-Joel


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