DS1807 digital attenuator use - diyAudio
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Old 26th October 2004, 08:17 AM   #1
djdamix is offline djdamix  France
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Default DS1807 digital attenuator use

Hello,

I'm trying to make a volume remote control for my amp, and so I'm using DS1807 (dual attenuator 5V supplied) . It works ok with positive DC voltage but I seems it doesn't support direct connection of the symetric audio signal on the digital pot (the negative part is limited to about 1v). I supposed I will have to polarize the input at 2.5V so the input signal will swing between 5v and 0v with +/- 2.5 V at the input. I've found nothing clear to me in the datasheet.

Has anybody ever done that ?? I'm looking for help ...

Thanks .
David
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Old 26th October 2004, 09:01 AM   #2
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STOP STOP STOP !!!!

Get the DS1808, it has dual 12V supplies and 5 V logic supply.
Being Dutch and all there, is one other, cheaper solution. Put capacitors both at input and at the output of the DS1807. Use bipolar caps, if you use electrolytics put them with the positive terminal towards the DS1807. Don't use the DS1807 as you do, since a negative input current on a CMOS can trigger an intrinsic thyristor on the chip, making it blow up due to uncontrolled currents.


Andreas
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Old 26th October 2004, 09:30 AM   #3
djdamix is offline djdamix  France
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thanks, but you mean I only need to add bipolar capacitor at the input and the output ? I'm ok it will stop the DC but AC negative voltage will still be there. Do I need to put VCC/2 at one of the pot. terminal ?

David
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Old 26th October 2004, 09:59 AM   #4
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Resistors to Vcc/2 are not entirely neccessary since the intternal diodes to vcc and gnd, these will center the DC. Especially if you have an unsymmetrical input wave, that is possible, you will gain a few dB headroom before clipping. The most McCoy solutions is of course resistors Vcc/2. These resistors have a drawback of inducing Vcc noise into the signal path though. The resistors can be 1 Meg. Remember to also have a capacitor to the common terminal of the potentiometer as well, so the potentiometer is able to float DC wise.

Andreas
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Old 26th October 2004, 12:02 PM   #5
djdamix is offline djdamix  France
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thanks for all Andreas, I've tried it and it works perfecly ;-)

David
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Old 26th October 2004, 05:11 PM   #6
Kermit is offline Kermit  Norway
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I see you solved your problem, but for reference heres a appnote describing how to use single supply digital pots for audio.
http://www.maxim-ic.com/appnotes.cfm...mber/846/ln/en
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Old 27th October 2004, 02:03 PM   #7
Oil is offline Oil  United Kingdom
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I have used the ds1802 successfully with a +/- 2.5 V supply - sounded very very favourable compared to an alps blue pot, using a simple dual tracking power supply from a 5v reference.
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Old 27th October 2004, 06:47 PM   #8
Nisbeth is offline Nisbeth  Denmark
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Another DS1802-design from Pedja

http://users.verat.net/~pedjarogic/audio/


/U.
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Old 27th October 2004, 08:00 PM   #9
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To use +-2.5V supplies is nice but you have to have get some problems regarding to interfacing to a microcontroller or PC or whatever. There has to be very sanitary constructions as to avoid noise from digital side. I use DS1808 with separate logic and analog supplies and grounds. It also handles up to +- 12V supplies for the analog section. Feels safe. For switches I use MAX335 also +-12V analog region. I ordered booth from Maxim, no prolemo.


Andreas
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Old 28th October 2004, 07:41 AM   #10
djdamix is offline djdamix  France
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that's what I was thinking about ... interface problem ... may need some transistors & resistors to adapt the level. I think I'll try the ds1808, since I don't want something to big for this board. I'll will also try to compare the sound with a motorized pot from alps.

David
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