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OP AMP Capabilities in Supporting 24 bit bandwidth

Hello Everybody

Iam in the market in search of a Minimalist Preamp and got pulled towards Morrison ELAD, I saw this piece of message in Don Morrison Website:
(The most important thing about it is that its circuitry is designed around the Analog Devices AD797, a highly advanced op-amp made with a fully complementary IC process. This complex device, consisting of 60 transistors, settles to a full 16-bit resolution in under a microsecond, has a noise spec equivalent to a 50-ohm resistor from 10 Hz to 1MHz, and achieves lower THD + N levels than any discrete audio circuit that has come our way. The preamp consists of two AD797's with associated circuitry - including separate volume controls for each channel)

Looks like it can handle 16 bit resolution at ease, but, how about handling higher bandwidth signals at 24 bit resolution?

Any advice is highly appreciated.

Thank you

sivamayam
eldartford
4,262 posts
 
I don't know anything about this particular OP amp, but..

1...Every OP amp circuit I ever saw had about 60 transistors.
2... Every OP amp circuit I ever saw had a complementary circuit topography. (That's part of the reason for so many transistors).
3... "16 Bit resolution" is a roundabout way of saying it has a dynamic range of 96 dB.

It may be a good preamp and a good OP amp, but I get a bad feeling when specmanship is evident.
con
1 posts
 
Hi
You seem to have locked on a bit of information presented for those digital engineers that have a problem in the analogue realm. Looking at the full spec sheet for the 797 you will find Slew Rate and two listings. 1 for "12.5 volts per microsecond" and one for "Settling Time to 0.0015%--10 volt step --800 nanoseconds" The 0.0015% is the precent value of the LSB for a 16 bit DAC, hence the 16 bit settling time. Analogue folks would have simply divided 1 microsecond by 12.5 volts and multiplied that by 10 and found that 800 nanoseconds was the time that the 797 required to respond to a 10 volt step. Now the difference between a 16 bit audio system and a 24 bit system is dynamic range NOT frequency responce, that depends upon the sampling rate. The full power bandwidth of the 797 at a gain of 10 is 8 MHz, much more than sufficient for any audio system. Back to dynamic range. A standard CD as a maximium dynamic range of 96 db, 6 db per bit, a 24 bit system then should have a dynamic range of 144 db but due to noise limites of the recording and playback loops you will find that the best units specify a range of 110 to 115 db. The 120db noise limit of the 797 exceeds those values by a fair margine and will add no audible noise to any system on the market.
Thanks.......Con
svenss1
2 posts
 
I completely agree with cornelius. 24 bits is a dynamic range issue, not bandwith. The 797 was designed before 24 bit digital audio existed as a regular format, which explains the published information from Analog Devices (and the ELAD spec's). I suspect you may be asking about sampling rate - 96kHz or 192kHz which are also non issues with the 797. It's bandwith exceeds the requirements of 192kHz sample rate by many times.
On a more subjective note, I've had a chance to use an ELAD and it is completely transparent. If you want minimalist, it's a good pick.
eldartford
4,262 posts
 
I checked out this preamp, and find that it has only 6dB gain, with a switch option for unity gain. It is easy to get distortionless ("transparent") performance from a low or unity gain amp. The trick is to do it with about 30 dB or more gain. I guess you could call this item a "straight wire without gain".
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