Controlling pots digitally
in [Design]
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From: John Nagle on 13 Sep 2009 18:22 Barry wrote: > Hi, > > We have a pair of speakers which we need to control from a pc. ... > What ever the solution we choose, it should not introduce noise into > the circuit. One option that sometimes appears in high-end audio gear is a photoresistor/light source combination. The photoresistor goes in the audio path, and the lamp is controlled by a DC voltage from some external source. The minimum ON resistance is generally around 1K, and goes up to 2M when the lamp is dark. So if you can tolerate a minimum ON resistance of 1K, this could work. It's not expensive. Since there's no electrical connection between the audio side and the control side, and the lamp drive is DC, this shouldn't introduce noise. https://taweber.powweb.com/store/chansword.htm Controlling the lamp power level is a separate problem. Use a linear drive circuit, not PWM. A D/A followed by a power transistor should work. Motor driven pots are mostly for where you want to store the setups on a mix board and reset the sliders to stored values. In many modern audio boards, the audio doesn't go through the pots anyway; that's all done in the digital back end. John Nagle
From: Jim Thompson on 13 Sep 2009 18:21 On Sun, 13 Sep 2009 15:22:58 -0700, John Nagle <nagle(a)animats.com> wrote: >Barry wrote: >> Hi, >> >> We have a pair of speakers which we need to control from a pc. ... >> What ever the solution we choose, it should not introduce noise into >> the circuit. > > One option that sometimes appears in high-end audio gear is a >photoresistor/light source combination. The photoresistor goes >in the audio path, and the lamp is controlled by a DC voltage >from some external source. The minimum ON resistance is generally >around 1K, and goes up to 2M when the lamp is dark. So if you can >tolerate a minimum ON resistance of 1K, this could work. It's not >expensive. Since there's no electrical connection between the >audio side and the control side, and the lamp drive is DC, >this shouldn't introduce noise. > >https://taweber.powweb.com/store/chansword.htm > >Controlling the lamp power level is a separate problem. >Use a linear drive circuit, not PWM. A D/A followed by >a power transistor should work. > >Motor driven pots are mostly for where you want to store the >setups on a mix board and reset the sliders to stored values. >In many modern audio boards, the audio doesn't go through >the pots anyway; that's all done in the digital back end. > > John Nagle I have several pieces of JVC consumer-grade audio with motor-driven pots... like 15 year-old stuff... still working just fine. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | DEM Senator: "..thousands are losing their health insurance daily" Damn! Wonder if their unemployment has anything to do with it ?:-)
From: Vladimir Vassilevsky on 13 Sep 2009 19:21 Barry wrote: > Hi, > > We have a pair of speakers which we need to control from a pc. http://www.cirrus.com/en/products/pro/techs/T10.html Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: krw on 13 Sep 2009 23:24 On Sun, 13 Sep 2009 15:21:29 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Sun, 13 Sep 2009 15:22:58 -0700, John Nagle <nagle(a)animats.com> >wrote: > >>Barry wrote: >>> Hi, >>> >>> We have a pair of speakers which we need to control from a pc. ... >>> What ever the solution we choose, it should not introduce noise into >>> the circuit. >> >> One option that sometimes appears in high-end audio gear is a >>photoresistor/light source combination. The photoresistor goes >>in the audio path, and the lamp is controlled by a DC voltage >>from some external source. The minimum ON resistance is generally >>around 1K, and goes up to 2M when the lamp is dark. So if you can >>tolerate a minimum ON resistance of 1K, this could work. It's not >>expensive. Since there's no electrical connection between the >>audio side and the control side, and the lamp drive is DC, >>this shouldn't introduce noise. >> >>https://taweber.powweb.com/store/chansword.htm >> >>Controlling the lamp power level is a separate problem. >>Use a linear drive circuit, not PWM. A D/A followed by >>a power transistor should work. >> >>Motor driven pots are mostly for where you want to store the >>setups on a mix board and reset the sliders to stored values. >>In many modern audio boards, the audio doesn't go through >>the pots anyway; that's all done in the digital back end. A lot of digital pots have non-volatile memory, of one sort or another. In the applications you mention there is usually a DSP, or at least a PIC, that can easily remember pot settings. That's how we do it, so don't bother with the NV memory in the pot itself. >I have several pieces of JVC consumer-grade audio with motor-driven >pots... like 15 year-old stuff... still working just fine. Same.
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