DAC AD1862: Almost THT, I2S input, NOS, R-2R

Vunce, I had a look at your schematic.
Place a 'base stopper' resistor between the two sections if OPA860, right on the input of the output buffer. After the filter cap! Like 1kohm..

Try the 1k, it can help ...

Also, the input stage base would need some hundred ohm (called Rs in the data sheet). (if You look carefully, the datasheet prescribes these 'damping' resistors at both places (Rs - 20ohm-250ohm), at the OTA input stage base; at the input of the buffer stage.

Ciao, George

This resistor should be small, let the I/V to see as smallest impedance as possible ... the simulation is working good with these changes (the R7 is only for simulation)
 

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Miro,

If we want splitting hairs, yes the input Rs contributes to the impedance into the emitter.. but as You know it gets divided by Beta of the diamond transistor..
An order of hundred ohm will result in less than 1ohm extra..

We have more losses otherwise. And instead the damping effect in the base results less inductive response in the emitter branch. (Which could then resonate with input stray capacitances)

Ciao, George
 
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A picture is worth 1000 words, thanks Miro 😀
In order to do this modification it’s a little more tricky without cutting a trace on the board. The Opa860 pin3 (Base) is directly connected to GND.
I will figure a way though 😉
 
Has anyone compared OPA1612 or another common OPA to more exotic active IV choices mentioned here?
OPA1612 ranks best out of a few other common op amps ( LM4562, NE5532, OPA2134) but still has slightly unnatural and compressed sound compared to passive, on the other hand passive is too lean sounding and this has become difficult to ignore.
Considering some of the high speed AD OPAs but they are expensive...
 
Hi laserscrape,
I’ve been using the opa1611, single version of 1612, it’s not bad. I like the LM6171AI better though.
Your description of the opa1612 is similar to what I hear also. My biggest gripe is the soundstage seems to shrink.
 
Has anyone compared OPA1612 or another common OPA to more exotic active IV choices mentioned here?
OPA1612 ranks best out of a few other common op amps ( LM4562, NE5532, OPA2134) but still has slightly unnatural and compressed sound compared to passive, on the other hand passive is too lean sounding and this has become difficult to ignore.
Considering some of the high speed AD OPAs but they are expensive...


OPA1656: High-Performance CMOS Audio Op Amp


I really think opa861 is an non exotic choice and if not one of the best and known from 15 years for that I/V task. Buffer is an other story and one should always precise what either task.
For driving a pre/amp, opa861 is certainly good enough diret after its I/V job and don't need buffer. However why not try a simple good enough discrete as buffer ? Matched LSJ74/LSK170 and voilou, walla, valhalla - pronounce like you 're able to-