Claude,
What do You mean, in the role of I/V for 4499, or some other application?
I have ordered a complete set of OPA1612 (which is a lot..) to try too.. But the 1656 output stage is just so well performing, that I stopped and never implemented the alternative set.
I have some experience from the past with 1612. At the end preferred other solutions, then, in that place. (output of an AK4490). Though for measurement purposes that is one of the best.
What do You mean, in the role of I/V for 4499, or some other application?
I have ordered a complete set of OPA1612 (which is a lot..) to try too.. But the 1656 output stage is just so well performing, that I stopped and never implemented the alternative set.
I have some experience from the past with 1612. At the end preferred other solutions, then, in that place. (output of an AK4490). Though for measurement purposes that is one of the best.
AKM uses OPA1612. OPA1556 might be a good choice. Only thing I see in its data sheet that has me wondering a bit is the EMIRR section on page 16. Don't know how OPA1612 compares in that regard. Obviously, RF in and around dac outputs can sometimes cause issues with opamps. Distortion is mostly what I am concerned with. Sometimes a little distortion can sound more clear or more detailed when in reality it is other problems that is causing the dac output to sound less clear than it perhaps otherwise should. In that case a little synthetic clarity from a little distortion may sound subjectively 'better.' Distortion from RF can be hard to pin down sometimes, although sometimes there are clues. In the case of the AK4499 eval board, I suspect there is some RF coming out, could be differential or common mode, I have seen both from dacs. I will leave off here before the measurement police come along.
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Something else Mark, nothing to do with DACs I am afraid, aim is in fact this time my RIAA amp, so really nothing to do here 
However, while listening to some op amps in various test rigs of mine to do a kind of preselection (that I defo won't discuss here!), I noticed that this op amp shone so far to my ears (adding 2 in a row in the chain to listen to degradation... revealed nothing), hence me asking if it could be a potential contender...
In fact, I am thinking tonight about it because it performed so far better than what I use for decades as op amp in my output stage (in my own DAC based around an AKM chip back in 2001), hence me wondering about it for a more modern DAC - should I want to play again with all that
Claude
However, while listening to some op amps in various test rigs of mine to do a kind of preselection (that I defo won't discuss here!), I noticed that this op amp shone so far to my ears (adding 2 in a row in the chain to listen to degradation... revealed nothing), hence me asking if it could be a potential contender...
In fact, I am thinking tonight about it because it performed so far better than what I use for decades as op amp in my output stage (in my own DAC based around an AKM chip back in 2001), hence me wondering about it for a more modern DAC - should I want to play again with all that
Claude
The I/V stage opamp for the 4499 needs to be comfortable driving low impedance loads whilst swinging significant voltage too. It needs to be able to source/sink the output current of the DAC whilst doing so linearly. There are plenty of opamps that have a short circuit current delivery way beyond the output current of the ak4499 but they start to show nonlinear current delivery way before getting near that. Capacitive load drive is also important.
Ultra low noise isn't as important as you'd think. Each half of the differential signal needs to be around 2.3uVRMS with respect to the 4.65VRMS to hit the 126dB non A weighted SnR figure (129dB differentially) with a 20-20kHz bandwidth. The OPA1611 would contribute only 0.43uVRMS to this figure so other factors dominate here. Of course a noisier opamp will degrade things but probably not by as much as you might assume. The OPA1622 would be interesting to try although only for lower distortion due to its ability to deliver loads of current and handle capacitive loads easily. If the 4499 is already the limiting factor with respect to distortion, when using the 1611, then going to the 1622 would only do one thing. Make it noisier whilst giving you nothing in return.
Whatever you decide to try measurements are mandatory to ensure you aren't botching things up. This is hard in and of itself though as the DACs distortion is ridiculously low. You might be going from 0.00007% distortion with one opamp to 0.0002% with another and never know if your measurements are limited to around 0.0005%.
Don't let us folks be intimidated here...
Your subjective impressions CAN mean a lot to others here, and the rest should just ignore them when it's not their cup of tea.
> Do you know of any Zen I/V implementiation that might suit the AK4499?
This is an interesting question.
Most (IMHO) good-sounding discrete IVs like the Zen IV use some form of current steering and without global negative feedback.
And they also mostly work in pure Class A.
With a differential signal current of 73mA p-p, One would need a bias of 150mA or more for the input stage alone.
And assuming that we want to have good PSSR and no coupling caps, we would need to use a cascode on top.
Something like the Loesch IV circuit published quite a while ago.
Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
For DC offset & bias stability, one would also want to use devices with negative tempco, e.g. lateral power MOSFETs for audio.
So here is one example of such a circuit.
I did not put in an additional buffer as Zout is very low at 82R for line level.
The key to low distortion are the two 250mA current sources.
They want to be DC stable (or at least track each other) to < 0.1mA.
And the dynamic impedance should be higher than 2k.
Not sure whether I want to burn 50W for two channels of balanced IV.
But that would be the price with such high output currents.
Cheers,
Patrick
.
This is an interesting question.
Most (IMHO) good-sounding discrete IVs like the Zen IV use some form of current steering and without global negative feedback.
And they also mostly work in pure Class A.
With a differential signal current of 73mA p-p, One would need a bias of 150mA or more for the input stage alone.
And assuming that we want to have good PSSR and no coupling caps, we would need to use a cascode on top.
Something like the Loesch IV circuit published quite a while ago.
Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
For DC offset & bias stability, one would also want to use devices with negative tempco, e.g. lateral power MOSFETs for audio.
So here is one example of such a circuit.
I did not put in an additional buffer as Zout is very low at 82R for line level.
The key to low distortion are the two 250mA current sources.
They want to be DC stable (or at least track each other) to < 0.1mA.
And the dynamic impedance should be higher than 2k.
Not sure whether I want to burn 50W for two channels of balanced IV.
But that would be the price with such high output currents.
Cheers,
Patrick
.
> and there will always be the '8 legs bad, 3 legs good' brigade.
I can only speak for myself.
I do DIY for fun.
Discretes are a LOT more fun than opamps.
Nothing to do with which is better than what else.
And in audio, everything is subjective.
Everyone is allowed to do what he thinks is best for him.
No need to convince others that it is so.
Cheers,
Patrick
I can only speak for myself.
I do DIY for fun.
Discretes are a LOT more fun than opamps.
Nothing to do with which is better than what else.
And in audio, everything is subjective.
Everyone is allowed to do what he thinks is best for him.
No need to convince others that it is so.
Cheers,
Patrick