Digital pots

[ipagel]

Do Digital pots exist (i know they must)

and does anyone know anything about them.
i would like to make a 8 pre-amp that can be remotley controlled.

thanks for any info

mark

 

[JohnRoberts]

I believe TI offers a mic pre chip that can be digitally controlled.

JR

 

[stickjam]

http://www.maxim-ic.com/products/digi_pot/

--Bob

 

[ipagel]

Thanks guys :thumb:

 

[gyraf]

But be aware of the drawbacks - limited voltage- and supply potential range.

They are by no means direct replacements for real potentiometers.

Jakob E.

 

[bcarso]

By coincidence I was looking for low-end versions early this AM. I have used Toshiba and knockoffs by Princeton (beware of the latter's ESD tolerance!), but it looks like a possibly better manufacturer, in terms of the range of products, is Renesas.

Check out as well Cirrus (their legacy products and extensions from Crystal), for higher-end stuff.

And as Jakob says, note well the limited voltage range on any part and the consequent limitations on noise and distortion. Also be cognizant of switching noise and step size---virtually all of the parts with acceptable resolution are digitally-controlled step attenuators, and some are quite coarse.

 

[Rochey]

for 30V swing, and use in volume control, you may want to check the PGA2320.

Most digitally controlled mic preamps on the market are moving to the PGA2500.

 

[mobyd]

[quote author="ipagel"]Do Digital pots exist (i know they must)

mark[/quote]

As well as the PGA devices already mentioned, there are many others -
Analog Devices AD711x range
Dallas DS1267 family
Crystal Semi's CS3310
Nat Semi LMC198x series (seems to have been ditched)
Various Xicor XC95xx offerings (beware, noisy)
I'm sure there are many more
M

 

[PRR]

DigiKey may carry motor-operated stereo volume pots. True pots, no odd chippy flaws. Can be manually operated, or remoted with a several-volt DC supply. Not expensive; fewer pins than most alternatives.

Ah.... only PNC100SY-ND 100mm slider $47 each.

SOMEone was carrying the $10 rotary kind used in less-cheap 1980s hi-fi.

 

[Crusty2]

[quote author="PRR"]DigiKey may carry motor-operated stereo volume pots. True pots, no odd chippy flaws. Can be manually operated, or remoted with a several-volt DC supply. Not expensive; fewer pins than most alternatives.

Ah.... only PNC100SY-ND 100mm slider $47 each.

SOMEone was carrying the $10 rotary kind used in less-cheap 1980s hi-fi.[/quote]

Mouser: http://www.mouser.com/catalog/631/572.pdf

If you don't need a control track(or run mono), these could be fun...

Another option could be a multiplying DAC?

 

[ipagel]

wow thanks guys lots of info.

the motor pots look cool and i guess would be easier to implement.
but will look at all options and try some stuff out.

have any of you guys ever tried a remote controlled setup before?



I think i better explain what i'm trying to do as well.

what i would like is to be able to change the controls off preamps like the green or the other diy preamps with a digital control which i could then setup to be controlled from a infared controller.

i do not want to really redesign the preamps ony the way they can be controlled.

 

[Samuel Groner]

The main question is the resistor range you need--if it's a transformerless preamp like the GreenPre it's for a full 0 dB to 66 dB about 100k to 2 ohm--which is pretty tough. A motor pot seems almost impossible, and the other solutions suggested are probably difficult to implement as well for this wide range (though I'd need to look into the details here). Relay-switched resistors are a possible, though costly solution. For sure it would be the most sonically transparent solution.

Samuel

 

[JohnRoberts]

I have actually been pondering this for decades and there is no simple. inexpensive, no-compromise solution. The gain law and pot taper for smooth mic pre control are difficult enough to get in normal pots let alone motorized faders. Digital pots work to a point, but are not a good fit for high performance mic preamps.

My suggestion of the TI part was not without consideration of all these points. The TI preamp chip will give decent gain law and good performance.

To incorporate digital gain control into an existing high performance design without degrading performance will require relays. I have several ideas for solid state switching but they get pretty complex to reduce the impact of solid state switches in the low impedance part of audio path.

JR

 

[mikep]

http://www.ams-neve.com/html/models/Outboard/Classic/1081R/

I was working for them when these came out. IIRC the "AIR" type had an array of FETs, each with a resistor to ground. I think I remember the other one using reed relays. microprocessor controlled. nice units actually.

mike p

 

[sonicmook56]

I just put together a little embedded computer complete with 7" console mounted touch screen for the neve remote racks. Now if I can only get Linux/Wine to run the software.......

The "Air" model uses a 74hc595 to drive a phototransistor to drive a fet. I don't really understand how this works quite yet to set the gain... the audio circuit is incredibly simple. The most used/requested preamp here by far.

1081 model indeed uses reed relays driven directly by a 74hc595. Nobody really likes the way these sound.

one microprocessor in the rack, that is controled via RS-485.

 

[tony666]

How about using Multiplying DAC's for this ? I was just reading some info on the Euphonix history on Wikipedia and from what I understand, MDAC's were used as variable resitor in their analogue consoles.

 

[gyraf]

Otari also does this for computer-control of the tape adjustment for their MTR100...

Jakob E.

 

[Carl_Huff]

Anybody have experience working with the Analog Devices AD5920 and AD7376 digital pots? They run off of +/-15 volts and as result can work with pro audio voltage levels. They come in single packs of 10k, 50k or 100k values. THD is reported to be 0.006% typical. No remarks as to their noise contribution tho ...

 

[JohnRoberts]

In general thd specs are thd+n so you can ballpark a s/n.

JR

 

[playboss]

I found this article once: http://www.edn.com/article/CA45967.html