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

[dreamth]

Originally Posted by BesPav

Use LM6172, add BUF634 or any preferred buffer. It needs because 1796 output current are a bit on the high side and you better to decouple opamp crystal from relatively high I/V resistance.

I never forget the 100 ohms series resistor with the feedback integrating capacitor...50 ohms might work too...AD797 datasheet is often ignored...lm6172 is way too fast to be certain that your buffer will not loose the phase response. That huge iout current is not needed.
This is , i think, the least understood wrong practice of buffering dacs to get the most out of them ignoring that you need to buffer that voltage further and even decrease the output by 4...8x to get a clean line out.

Higher i-out dacs are used to improve the SNR ratio , but then you loose that original SNR to poor CMRR and PSRR in the filters and buffer stage because of unity gain stages and resistor dividers or rlc filtering devices used to further filter the i/v stage output.
The most common effect of these stages is adding noise because most of the unity gain high bandwidth op-amps aren't great at current noise specs and some not good enough at voltage noise either.
Making the i/v stage output smaller, the high frequency noise is decreased, the clipping is softer at lower rail supply voltages, the thermal behavior and added nonlinear distortions are improved and i can use old days cheap ultra low noise audio use(lower bandwidth) op-amps with a little bit of gain after the i/v stage.

I started my own little research a few months ago and i found that even the standard 2vrms is too much output and i don't get more than 0.5...1vrms out of any dac just to give a gain to the output op-amps buffers.This way , any i-out dac will sound better, even those well known for bad sounding...


You might find out that you don't even need high Q ultrasonic filters if you're using high bandwidth op-amps all the way down to your speakers because those op-amps are not producing their own artifacts which seem to be the real culprit in high frequency noise endangering the audio equipment .The speakers themselves will kill that HF noise and your ears will never hear anything, but the music.

[Monte McGuire]

Originally Posted by dreamth

I tried ada4898-1 on a pcm1701 output(less than 1ma max iout) at +9v/-12v suply and in one minute was melting ...dead.

The ADA4898-1 uses a die attach pad, which must be soldered to a pad on the PCB that is attached to V- (the datasheet shows the details). If you use a proper footprint, they run quite cool and are lovely to use. Too bad for me, their distortion is a little on the high side, with a surprising amount of 2nd harmonic. But, you absolutely need to deal with their die attach pad - they idle at 8mA each, and that's 0.24W at ±15V.

[dreamth]

I know...i had quite a big radiator attached...there must have been some sort of oscillation unless its sensitive to unbalanced rails...it's weird, but i think that these op-amps should be used at +-6v max...I'm thinking of a different strategy , to use bootstraped rail supply with ada 4899 which has its pad at ground.

[diyralf]

NE5532

[diyiggy]

lol

In this case of vintage choice I would more try NJM 4580D : bipolar, very neutral, simple scheme... smal slew rate though. Certainly worth to try instead the NE5532 which is a little dark and veiled... But I disgress..."These days" asked the op.

So if no AD844 or OPA861 as per Georgehifi older post choices, perhaps todays

opa1642, opa1656, opa1671, opa1678, opa826, opa827, opa2810...are more on topics ?



OPA1656: High-Performance CMOS Audio Op Amp

[dreamth]

njm4580 isn't as powerful or stable as ne5532, not even lower noise...

[diyiggy]

Sure, but I like it more... in D grade.

[dreamth]

well...there are better njm old chips in d grade for this purpose, like njm5532D

[diyiggy]

despite it's bipolar I don't find it "neutral" sounding... You're with diyralf in an off topic 5532 plot

[dreamth]

There are three old chips that are better than ne5532 as i/v stage, but there's no discussion whatsoever on DIYaudio about them and i won't ruin the secrecy tradition mainly because one of them was reactivated after 15 years for a short period of time at Mouser and is programmed for EOL, the stock being limited.I will only tell the fourth , which is njm2114.It was highly disregarded as it wasn't as good as ne5534 in phono preamps because of its lower input impedance, but for i/v circuits is quite good.
It looks like there are small conspirations here and there cause expensive chips need to be sold...

As a separate issue, no matter how stupid it sounds, i think that there's a real conspiration in the whole electronics industry about the use of op-amps in inverting topology as attenuator as there's not a single book or application note on talking about its performance.You can only find some small talks here and there about that finding that you can easily make a NON-stable op-amp working in a negative gain stage with better performances than in a 10x gain as noninverting op-amp...
For example this all that Analog Devices have to say about it:
https://www.analog.com/media/en/anal...q-issue-56.pdf
When we actually had Soundcraft mixers...and many ultra professional products using it!
First they'd tell us that it's too noisy, then they show us circuits that never meet the noise criteria we really need in exchange for ultra low distortions that we never needed!