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OPA1656: High-Performance CMOS Audio Op Amp

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#701
Markw4 said:
We tried OPA1612, OPA1656, NE5532, and Muses 8920 opamps in Rohm BD34301EKV Evaluation Board (which came with 5532's installed). OPA1656 sounded worst, Muses 8920 sounded best. IMHO the outcome was mostly decided by how the opamps responded to the RF coming out of the dac chip. For the case of AK4499 the preferred opamp might have been different, perhaps due in part to some difference in the particular dac output RF noise. Therefore I would suggest to try and see what opamp you think works best with a particular dac chip.
Click to expand...
How did you measure the RF?
 
#702
Spectrum analyzer and E-field probe is all I bothered with. Did more extensive scope measurements of AK4499 clock signals buried in noise at I/V opamp outputs. So what? It doesn't tell me how it will sound, only that there is garbage present which I already knew would be the case.
 
#703
Markw4 said:
We tried OPA1612, OPA1656, NE5532, and Muses 8920 opamps in Rohm BD34301EKV Evaluation Board (which came with 5532's installed). OPA1656 sounded worst, Muses 8920 sounded best. IMHO the outcome was mostly decided by how the opamps responded to the RF coming out of the dac chip. For the case of AK4499 the preferred opamp might have been different, perhaps due in part to some difference in the particular dac output RF noise. Therefore I would suggest to try and see what opamp you think works best with a particular dac chip.
Click to expand...

How did NE5532 sound?
 
#705
Markw4 said:
2nd best
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That's interesting, because in my little opamps rolling experiment it did not do very well. I listened to OPA2134, LM4562, and NE5532, and OPA2134 sounded the best. Load was 1k but I'm planning on changing that to something easier like 2k and retesting NE5532 just for fun.

I'm still waiting for OPA1656 in the mail. But once it comes, I'm excited to try to listen to that.

I wonder how the sound of CMOS would compare to the JFET? Since jfets are said to sound warm and tube-like...
 
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#706
Wouldn't expect opamp preference to be the same for every dac. The nature of the noise would be expected to be in part of function of the modulator design. Other inadvertent signal leakage my also be a factor, such as the clock signal buried in noise coming out of AK4499.
 
#707
Got OPA1656 delivered few days ago. Today had a chance to swap it into my amp and give it a listen.

In my opinion it sounds the best at close to max volume.

Sound is cleaner comparing to OPA2134. But the warmth in mid frequency (1k-4k) is gone.

Great for piano/violin or metal / electric guitar. I did not like it too much when listening to edm / electronic music.

With this IC I can instantly tell the difference between good mastering/mixing tracks vs not so good and muddy.
 
#709
Does anybody know the max differential input voltage of the OPA1656? The common mode input can go to the supplies, but funny enough, the data sheet doesn't mention the max diff input voltage.
Being a FET input I think it would be the supply voltage, but the fact that they don´t mention it makes me suspicious.

Jan
 
#710
Take a look at the functional block diagram in section 7.2 of the datasheet and figure 43. There seems to be ESD protection diodes connected between the input terminals, so the differential input should be close to 0.
Unlike e.g. OPA2191, where the differential input can be anything within the supply rails.
 
#711
JensH said:
Take a look at the functional block diagram in section 7.2 of the datasheet and figure 43. There seems to be ESD protection diodes connected between the input terminals, so the differential input should be close to 0.
Unlike e.g. OPA2191, where the differential input can be anything within the supply rails.
Click to expand...
Yes, but those protection diodes are also limited in current (iirc 10mA) so you still have to take some precautions in the circuit. In this particular case I am upgrading an existing PCB so have to live with what it is.
The OPA1642 for instance has a diff input voltage max to the supplies.
I'll check the OPA2191, thanks for the heads up.

Jan
 
#720
peufeu said:
Its low gain bandwidth makes OPA1642 a nice option for retrofits, it will work fine on an oldskool PCB. Ideal when taking trash like RC4558 out of vintage amps... 50MHz opamps like OPA1656 (to stay on topic) are risky on single sided boards.
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I generally agree with you and think this is a prudent move. On the other hand, I modified a one sided (poor layout) Carver C-2 Preamp to 1656s and had no stability issues, albeit I carefully soldered in .1uF caps as close as I could to the new opamps. One sided boards have really terrible grounding schemes (if you can even call it that).
 
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