[mudihan]

In a simple CMOY (12v or 18.5v, I have two PSUs), what is the difference in sound between these chips? Has anyone compared? I need high current. AD8397 is hard to deal with, so I am thinking about OPA552 (gain =11). But sound alawys comes first! Thanks.

 

[Andrea]

The OPA551 is a strongly underrated chip IMO. It sounds great. I still haven't tried the OPA552. Note that being faster doesn't mean that it'll sound better. But with a gain of 11, I'd certainly give it a try.

 

[mudihan]

Thanks!

One more thing, the phones i need to drive "well" are im716, Koss A250, and AKG K240DF. I listen to the K240DF the most.

 

[Andrea]

It should be 600 ohm, right? Then you're going to need a high voltage power supply. 24V should be fine - the OPA551/2 can work with up to +/- 30V

I wouldn't recommend the AD8397, as its upper voltage limit is only 24V.

 

[mudihan]

DFs are 600ohms. And that's my worry. Is 18.5v enough to deliever the voltage swing? Is a 24v PSU with a rating of 100ma enough for a CMOY with OPA552s?

 

[jcx]

if a quick google is correct the akg 240df are 88 dB/mW

with 600 Ohms this is insanely insensitive

dynamic peak spl for real world music can exceed 120 dB, if only for seconds per hour

to get to 120 dB spl with the 240df you would need ~ 44 V pK

this would require balanced drive from 2 amps running off of +/- 24 V supplies - not exactly cmoy

yes you can listen to headphones without having that much dynamic headroom, in fact most pop recording's huge compression means you could easily deafen yourself with 100 dB spl without clipping the amplifier - the "music" production engineer has already done (clipped) it for you and 6 dB average to peak ratios are not uncommon

 

[Andrea]

Quote:

Originally Posted by mudihan DFs are 600ohms. And that's my worry. Is 18.5v enough to deliever the voltage swing? Is a 24v PSU with a rating of 100ma enough for a CMOY with OPA552s?

18.5V means, for the OPA551/2, a +/- 6.25V output swing in the worst conditions i.e. @ 200 mA output current. Which in turn means a 260 mW min. output power on 600 ohms. That means a 112 dB sound pressure level from your 88 dB/mW K240DF.


It definitely IS enough

edit- 24V @ 100mA is sufficient to start with, provided that you don't exaggerate with the volume..

 

[jcx]

Wrong #s Andrea

opa552 specs output swing to within 3 V of ps rail @200mA, 2 V @ 10 mA

I'll use your 6.25 V (split 18 V - opa552 sat V ?)

6.25 Vpk / 600 = 10.4 mA pk

6.25 V * 10.4 mA = 65 mW pK

since both Ipk, Vpk to rms have a factor of 1/sqrt(2)

65 mWpk /2 = 32.5 mWrms

10 * log( 32.5 mW / 1 mW) = +15 dB power re 1 mW

88 + 15 = 103 dB spl max before clipping

again even 103 dB is more than loud enough - On Average but simply inadequate Peak spl for well recorded music with 20 dB dynamic range

I really wonder how much of the subjective ranking of various op amp's "sound" here is infulenced by their saturation/clipping and recovey behavior rather than any linear frequency response differences you might expect from commonly posted "weak bass","dark", "bright", ect comments

 

[Andrea]

I was not (at all) clear about the peak vs. RMS thing...


But the output voltage swing (not peak but RMS I think?) is specified as 3V less than each of the +/- supplies (again in the worst condition, sourcing 200 mA to the load). So, with 18.5V, it's +/- 6.25V that is 12.5V.


So the output power will be somewhat better than that... I'd say roughly an average between my and your figures

 

[Andrea]

Quote:

Originally Posted by jcx I really wonder how much of the subjective ranking of various op amp's "sound" here is infulenced by their saturation/clipping and recovey behavior rather than any linear frequency response differences you might expect from commonly posted "weak bass","dark", "bright", ect comments

Perhaps it's just me... but I've never heard any (any, even the AD823) op-amp clip.