Chip amps as I/V converters

[oon_the_kid]

Hi,

I was wondering if anyone evertried using a chipamp as the IV converter of a Sigma delta DAC (for example AD1853). Then use the differential output of the IV converter to drive the speakers directly. It would be sort of a bridge amplifiers.

Volume control would be implemented digitally. of course somewhere along the way somebody has to upsample the 16 bit to 24 bit.

Of course you would need a much higher resistor in the I/V to implement the gain stage. Any thoughts on that?

PowerDaC of sorts.

Oon

[jan.didden]

Originally Posted by oon_the_kid

Hi,

I was wondering if anyone evertried using a chipamp as the IV converter of a Sigma delta DAC (for example AD1853). Then use the differential output of the IV converter to drive the speakers directly. It would be sort of a bridge amplifiers.

Volume control would be implemented digitally. of course somewhere along the way somebody has to upsample the 16 bit to 24 bit.

Of course you would need a much higher resistor in the I/V to implement the gain stage. Any thoughts on that?

PowerDaC of sorts.

Oon

I think you have it worked out. Don't see any reason why it shouldn't work.
Not sure about stability, with the LM3668 (for example) not being unity gain stable, but I don't know how that works out in an I/V config.
Maybe just try or sim?

jan didden

[qusp]

I do the same thing, but with a transportable headphone amp, i only need about 1.5x differential gain though, so the IV resistor can stay pretty small for lower noise. i use opa1632dgn on the output of a sabre 9018 and use the dacs digital volume. it works really very well. of course you would want an additional current gain stage.

[abraxalito]

Originally Posted by oon_the_kid

I was wondering if anyone evertried using a chipamp as the IV converter of a Sigma delta DAC (for example AD1853).

Haven't actually tried this myself but have played with the sibling part to the AD1853 into various I/V opamps. Given the minimum gain of the chip amp (26dB is it?) you'll find yourself rather quickly running out of slew rate. But don't let that put you off....

Volume control would be implemented digitally. of course somewhere along the way somebody has to upsample the 16 bit to 24 bit.

AD1853 has a rather neat volume control capability which doesn't look to be digital - you can vary the reference current. Think its good for around 40dB range.

[Ipanema]

Opamp I/V converter works as unity gain and most power opamps are not stable at unity gain. Won't work except for OPA549 etc.

Power opamp tends to be noisier than small-signal opamp.

A scaled up version of Pass D1 or Zen will work well as power I/V having low noise and without stability issue.

[willysan]

As far as I know, the input pin of chipamps is the non-inverting one. However, an IV converter uses the inverting input. I see some problems with input impedance.

[abraxalito]

Chipamps can be configured as inverting or non-inverting. Both + and - pins work fine as inputs. The main problem, as Ipanema mentions is the lack of unity gain stability. A 'gain stealing' network could be used but this would probably compromise settling performance rather badly.

[oon_the_kid]

Originally Posted by abraxalito

Chipamps can be configured as inverting or non-inverting. Both + and - pins work fine as inputs. The main problem, as Ipanema mentions is the lack of unity gain stability. A 'gain stealing' network could be used but this would probably compromise settling performance rather badly.

Technically, the I/V is a openloop inverting amplifier rather than unity gain voltage amp. Not sure how stable a chipamp in a that configuration, but I believe most op-amps used for I-V conversion are probably not unity gain stable either. However there is the DC issue that must be taken care off too I believe... since most DACs are run off single supply hence a DC output will probably exist...

Oon

[oon_the_kid]

Originally Posted by Ipanema

Opamp I/V converter works as unity gain and most power opamps are not stable at unity gain. Won't work except for OPA549 etc.

Power opamp tends to be noisier than small-signal opamp.

A scaled up version of Pass D1 or Zen will work well as power I/V having low noise and without stability issue.

Having a thread on the Pass side

Oon

[oon_the_kid]

Originally Posted by abraxalito

Haven't actually tried this myself but have played with the sibling part to the AD1853 into various I/V opamps. Given the minimum gain of the chip amp (26dB is it?) you'll find yourself rather quickly running out of slew rate. But don't let that put you off....



AD1853 has a rather neat volume control capability which doesn't look to be digital - you can vary the reference current. Think its good for around 40dB range.

Did you manage to try the volume control? Can I just put a variable resistor in series with the the reference resistor and that will do the trick?

Oon