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
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
Member
Joined 2003
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.
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.
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.
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.
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
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
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.
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 said: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
OK, if DS1666 scares you that much, how about a DS1669. It has a linear resistance, but maybe it can be "law faked"? This would have greater headroom than DS1802 as it can use +/-4v supplies.
Or how about MAX5440? This would almost be a perfect "micro-controller-less" volume control, but it only has 32 steps and is limited to +/-2.7v supplies.
Maybe I will try them all. 
An externally hosted image should be here but it was not working when we last tested it.
Dear the Anonymous1,
I'm not scared
This time U really got to the point!
Whether DS1669 or X9511 or H9510 or... don't remember them all... are very good and easy-to-make solutions. Just buffer them with nice OpAmps and make a proper supply.
MAX5440 is perhaps a nice one but it is a bit tiny.
Please, also keep in mind if your certain digipot has nonvalatile wipper setting. This can be a matter.
I'm not scared
This time U really got to the point!
Whether DS1669 or X9511 or H9510 or... don't remember them all... are very good and easy-to-make solutions. Just buffer them with nice OpAmps and make a proper supply.
MAX5440 is perhaps a nice one but it is a bit tiny.
Please, also keep in mind if your certain digipot has nonvalatile wipper setting. This can be a matter.
If you are serious about digital pots for audio then you need to consider:
http://www.analog.com/UploadedFiles/Data_Sheets/AD7376.pdf
or
http://www.analog.com/UploadedFiles/Data_Sheets/AD5290.pdf
The AD7376 looks to be the better of the two. I have been toying with the idea of using the AD7376 to do digitally controlled analog filters. You avoid a lot of heartache by staying away from any and all pots that work on less than plus/minus 15 volts.
Best Regards,
Carl Huff
http://www.analog.com/UploadedFiles/Data_Sheets/AD7376.pdf
or
http://www.analog.com/UploadedFiles/Data_Sheets/AD5290.pdf
The AD7376 looks to be the better of the two. I have been toying with the idea of using the AD7376 to do digitally controlled analog filters. You avoid a lot of heartache by staying away from any and all pots that work on less than plus/minus 15 volts.
Best Regards,
Carl Huff
I think my first experiment will be with the DS1669S-10.
I will use input and output buffer op-amps and will "law fake" it with a 3k resistor between Rw and Rl.
Whats wrong with non-volatile wiper settings? I would figure this is a good feature as it stores the last wiper setting. Even with around 30 EEPROM writes a day it will last ~5 years.
I will use input and output buffer op-amps and will "law fake" it with a 3k resistor between Rw and Rl.
ybserge said:
Whats wrong with non-volatile wiper settings? I would figure this is a good feature as it stores the last wiper setting. Even with around 30 EEPROM writes a day it will last ~5 years.
Good question. I imagine it's because if you've already got a microcontroller in your project, you may as well integrate it all. The PGA2310 really isn't that difficult to control. For example the ATtiny13 for $1.36 has a built-in SPI interface. Still not totally trivial to set it up properly, but it should not be difficult.
If you need code, I would be willing to protoboard a setup and write some simple code to read pushbuttons or a rotary encoder and control the PGA.
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