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-   -   Digital pot used in audio preamp (http://www.diyaudio.com/forums/chip-amps/111502-digital-pot-used-audio-preamp.html)

marthaman 7th November 2007 04:18 PM

Digital pot used in audio preamp
 
A semiconductor company’s website provides a sample analog circuit for an audio preamp that features a digital log potentiometer with push-button volume control. The circuit appears novel, at least compared to other conventional audio preamp circuits that I have seen.

There are some posts on this forum that refer to the digital pot chip (DS1802). However, with respect to a preamp, the posts only indirectly refer to its major feature (a Wheatstone bridge) and/or suggest some webpages that are no longer accessible, I wonder if anyone has built and tested this preamp circuit, or has any comments on it.

Are there any better preamp circuits that are simple and use this (type of) chip?

The webpage is:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/161

DcibeL 7th November 2007 08:18 PM

I've yet to see a digital pot with a wiper current rating higher than 1mA, so you'll have to make sure your current will be very low when using this device.

In my opinion, a better solution would be a digital volume control like PGA2311 or WM8816. There have been several preamps designed, built, and liked by other members of this forum using these ICs.

marthaman 7th November 2007 09:27 PM

Indeed, op amps are included in their sample schematic. The vendor writes, ".....The operational amplifiers are required in this circuit because the DS1802 has a relatively high wiper (output) resistance. Without buffering, the DS1802 can only drive a 1mA load."

I pursued some of the good leads you provided, that led to another (typical) link that does comment on one limitation of this digital pot, perhaps compared to others. "The main issue is that the IC is powered from a single 5V supply, which will result in gain/headroom problems...."

But, I'm still intrigued if anyone has tried this circuit.

Carl_Huff 8th November 2007 04:34 AM

The MAXIM 1802 part is a 5 volt part. That makes using it in common bipolar circuits a chore if not impossible.

You'd find life much easier using the TI PGA2320 and a simple PIC to drive it. The TI solution is a more complex solution but so much better.

Check out ... http://www.littlefishbicycles.com/preamp/index.html

The PGA2310 described in the project has been superceded by the improved PGA2320. The new part drops in place of the old without issues.

Best Regards,
Carl Huff

marthaman 8th November 2007 05:45 AM

I'm humbled, if not overwhelmed.

Carl_Huff 8th November 2007 06:17 AM

Yea me too.

She did an excellent job designing that preamp/controller.

Best Regards,
Carl Huff

m-tech 8th November 2007 07:48 AM

I'm using DS1802 with dual power supply. http://www.pedjarogic.com/spot/index.html

Sound is great.

ybserge 8th November 2007 10:47 AM

U have to obey at least two things:
- to buffer your digipot with nice OpAmps
- to use dual power supply
Then, U're a success. Let PGA stay where it is.

theAnonymous1 8th November 2007 12:15 PM

I have some DS1666 I plan to play around with soon. I think this will be sort of a middle ground between PGA2320 and DS1802.

The DS1666 has better headroom and more steps than DS1802, but needs more than simple push buttons to work. The logic control should be a bit easier than whats required for a PGA2320, but I have to admit I'm not sure where to start.

BTW, why aren't there any simple projects out there for the PGA2320? They all seem to be a bit too complicated with things like input selectors, displays, balance, etc. I would like to see a bare minimum project for just volume up/down and maybe mute.

ybserge 8th November 2007 12:52 PM

Since it requires MORE THAN push button control DS166 doesn't seem to be a simlier solution. Think hard before U dare get on it:bawling:


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