What's the best dual I/V opamp these days???

If I take your 2 matched transistors and change the room temperature 3°C, then they are no longer matched.

This could be cured by a very slow acting servo.

These pseudo-symmetrical discrete circuits are not as symmetrical as one might think, so matching NN and PP is not the dominating problem, its the NP matching of dynamic parameters.

IMO, such CFB circuits make more sense on an IC with very careful design like AD844 or AD846-(RIP) or very interresting:

The LT6275, which shares the advantages of CFB (Virtually no slew limiting) and VFB (high input impedances)
 
Careful design of the surrounding circuitry is even more important.

In case you add a PI-Filter (with large PP or C0G caps up to 100nF) to the input node, you can easily come away with a good, but cheap audio OPA like OPA1642 or the like, because this filter unloads the I/V Converter from the speedy current transients, overloading the input stage, which can cause momentary slew limiting in traditional VFB designs.

The added noise gain (leading to a rise of noise outside the audio band), the succeeding aliasing filter stage can cope with. A second order filter may be enough, since you (overall) get a 5th order response.

I successfully adopted this trick as an upgrade for the SONY SCD-1 SACD-player, whose "bitstream" current DACs are very demanding regarding the I/V-Converter. The original LM6172 was even not fast enough in the original design, but after the PI filter change a LME49720 was more than sufficient regarding speed and provided a nice boost in sonic transparency.

You can easily monitor your success of this trick by measuring the inverting input at 0dB fs D/A-converted 20kHz sine wave with a scope. If the voltage spikes remain below lets say 20mV, you are likely safe.

NOS-Multibit and true one bit DACs are more demanding here.
 

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The trick may work with Hi-Z output dacs, but not with ESS Sabre or AK4499 where dac output impedance is very low. In the latter case the dac outputs need to be held at a precisely fixed output voltage by the I/V opamp or distortion rises unacceptably. Passive filtering before the I/V opamp allows the dac output voltage to be less tightly regulated and or causes frequency peaking issues in the I/V opamp. The differential summing opamp is a different matter of course. Passive filtering before it can be useful.
 
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Thanks Jon Lord,


A noob question if I may, please.


Using multibits old dac chips, lowering the impedance output is very important.


Is this shematic is what you suggest after a oap I/V stage and also act as a buffer ?


For instance : a 1612 as I/V conversion than your shematic and then a buffer oap, or a low pass to attack for illustration a 25k input pre amp ??
As I have trimming so no serie caps nore traffo output in my dac (I/V opa861 made), I drive the pre with a serie 150 ohms after the buffer (reversed opa861)... is you shematic could be an improvment after the I/V stage please ?
 
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I/V input filter before I/V stage

The trick may work with Hi-Z output dacs, but not with ESS Sabre or AK4499 where dac output impedance is very low. In the latter case the dac outputs need to be held at a precisely fixed output voltage by the I/V opamp or distortion rises unacceptably. Passive filtering before the I/V opamp allows the dac output voltage to be less tightly regulated and or causes frequency peaking issues in the I/V opamp. The differential summing opamp is a different matter of course. Passive filtering before it can be useful.

I see your point with the AK4499 etc. It seems to me the passive filter idea might be useful with a PCM1792A where the output Z is much higher. This may be a pretty good tradeoff given the fast edges.
 
@Gopher,
Not really. Sometimes people have no good reference to know what a recording is supposed to sound like, so they choose an audible result that seems to help compensate for other audible shortcomings of their systems. For example, if speakers are a bit muffled sounding, then a bit of bright opamp distortion may sound more 'right.' It may produce a more 'balanced' sound. In such cases it doesn't mean opamp preferences are random, nor does it mean all opamps sound the same. Besides, we can often measure differences that strongly suggest one opamp is likely to be more suitable for IV as verses some other one.

Its just that what you get in forums often tends to consist of a bunch of personal opinions. Some are likely to be more accurate than others, but figuring out which are which can sometimes be difficult.
 
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Hello Mark

When I said its down to personal taste I included the rest of the playback system in that. What sound great in one system may not in another and vice-versa. But there is also an element of how people like their music to be reproduced and even what kind of music they mostly play.

If YOU like the sound in YOUR system, then it's the best I-V op-amp for YOU.