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Old 8th June 2012, 05:39 PM   #1
vputz is offline vputz  United States
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Join Date: Apr 2012
Default Source select and passive volume for microcontroller-based preamp?

I thought it'd be an interesting project to fire up Kicad and my mill and make a simple preamp using a little microcontroller just to deal with source select and passive volume control.

On the source select side, it sounds like most people are keen on relays; I'd be needing a small 5V-operated relay (or relay assembly), and sounds like I'd prefer one that "latches" (only needs 5V to switch so I wouldn't have to hold a line high). Is there a recommended part that folks really like use?

On the passive volume control--I've read great stuff about the Lightspeed LDR series/shunt idea, and I do really like it, but for simplicity's sake, what's the view on straightforward I2C digitally-controlled potentiometers like the Maxim 1804 series or some such? My interest is more from the hobbyist side than the audiophile side, so "cheap and straightforward as long as it sounds pretty good" is what I'm shooting for this round (ex-helicopter pilot, so "perfect reproduction" is probably wasted on me; I just like building things--don't want it to sound wretched, but it doesn't have to be incredibly awesome).
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Old 8th June 2012, 07:17 PM   #2
vputz is offline vputz  United States
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Join Date: Apr 2012
Okay, so something like the 1804 doesn't look like as good a fit as the 1882 (a dual channel log output audio digital potentiometer; looks like just the thing). Eh, if I can source the right relays and a line-out shift register or some such to toggle 'em, I may just build the thing to see what it sounds like.
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Old 21st July 2012, 10:21 AM   #3
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I'm also about to build me a source select and passive volume control. Have you made any more progress?

I've been looking around a lot and it seems that people here favor the PGA23XX digital pot for volume control. For the source select relays I'm going for Omron G6K 5V smd's which seem to work OK.

Which microcontroller are you going to use? I'm a die hard arduino fan and I'll probably use a Arduino Pro Mini if I don't make my own purpose built volume and relay boards with the microcontroller on it.
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Old 21st July 2012, 10:51 AM   #4
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Location: S.England
For the volume, I would take the principles of the light-speed attenuator and drive it from the output of a serial DAC (such as the MC144110 / whatever - the output of which may need a simple buffer arrangement to drive the light-speed). Simple IMHO, but VERY effective. (And some processors incorporate DtoA built in).

Personally, I have never been attracted to digital pots really.

For manual adjustment of volume, any crappy pot can then be used, the output of which can be taken to an AtoD input of the processor. Hell, you wouldn't even need a pot, can use two PTMs for volume up / down instead.

For the processor, use a PIC which is ideal for the hobbyist?

Interesting little project, GL with that!

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