New Audio Op Amp - OPA1622

[mige0]

Originally Posted by JohnYang1997

Let's forget about k701 now. I think we will get no where by discussing that.

Agree.

Originally Posted by JohnYang1997

Another evaluation boaed is High-Power High-Fidelity Headphone Amp for Current Output Audio DACs Ref Design (Rev. C)
http://www.ti.com/litv/pdf/tidu672c
Higher gain from opa1612 allows more feedback of 1622 allowing lower distortion.
If you use 1622 in unity gain configuration, distortion can be lower. Tested on o2 platform, very good.

Nice board, thanks for the link.
But there are two IMO major issues not addressed
- possible common mode errors of DAC chips
- different impedance seen at the OUT of the transimpedance amp stage

Originally Posted by JohnYang1997

4556 has 0.001% at 1khz but much higher distortion at lower and higher frequencies like a smiley curve. i won't talk about audibility of such distortion, but it's much better with opa827 the distortion goes under 0.0001% full spectrum 32ohm.

ok
I'm not after specs at all, so that point is mute for me.

[JohnYang1997]

Originally Posted by mige0

Agree.



Nice board, thanks for the link.
But there a two IMO major issues not addressed
- possible common mode errors of DAC chips
- different impedance seen at the OUT of the transimpedance amp stage




ok
I'm not after specs at all, so that point is mute for me.

On the last part. I wasn't talking about spec sheet. I was talking about real world measurements. If you want I'll show you.

[mige0]

I don't doubt any of your measurements.
Its just I don't care about distortion figures that much, at least not as a solely basis of decision making.

In audo there are always two questions to answer IMO
- how does it measure
- how does it sound

More often than not those answers do not go hand in hand, at least that's my experience so far

[soumyabanerjee]

Originally Posted by johnc124

OK, you didn't have to be patient very long! Here's a sneak peak of the precision version of my swan song project:

OPA2156 Ultra-Low Noise (3nV/rtHz), 25MHz, Precision (200uV), Rail-to-Rail Input/Output Amplifier | TI.com

Prototype samples of this version are available now. A more audio-centric version of this product will follow along soon.

Sorry for quoting an old post, but didn't find a dedicated thread for OPA2156.
Just wanted to say a colossal thank you to you and your team.
2156 is an excellent part, the best non-discrete dual I have heard ever.

Popped these in my Topping D50 I-V and LPF stage and one in FiiO A5.
Amazing tonality - such a sense of air, richness and sweet mids!

[chris719]

Originally Posted by mige0

Seriously, I don't need any more measurements if auditioning brings up such a bunch of crap. And I already traced it down to a fair degree if you have read my postings.

To add on the above list of shortcomings, the INA1620 isn't even capable to directly drive a AKG K701 without issues.
You will have to add output resistors to make that happen. Not what's advertised and no good in terms of audio performance as well!

Frankly, I'm not after "not bad at all" with a chip that is stellar specd and said to be for audio, but after outstanding sonic performance right away.

The INA1620EVM board doesn't do that any justice at all.


The INA1620 with its matched resistors for me were the main reason to give it a try.
All in all I've come to the conclusion that pairing the TPA6120 with LT5400 to form a "audio grade" symmetric IN / symmetric OUT instrumentation amp for driving cans would possibly be the route to go.

Sure, for the O2 headphone amp not being a symmetric design this point is mute.

Was it unstable? Why did you need series R?

[mige0]

Originally Posted by chris719

Was it unstable? Why did you need series R?

This was a lesson I had to learn when I first rolled to the OPA1622. Those are available for cheap on DIP8 adapter boards for plug in replacement.

Occasionally the OPA1622 at the plug in adapter board got into distortion mode with my AKG K701, some oscillation I guess.
Was not able to trace it down because it worked ok as soon as I hooked up my oscilloscope.

There are two measures one can undertake against oscillation / low phase margin
- decoupling capacitive load by adding OUT resistors
- http://www.ti.com/lit/an/slyt630/slyt630.pdf

Adding OUT resistors did the trick both for the OPA1622 and later on for the INA1620 and was the first choice for lazy me