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

Showing 3 responses by sean

When i first read about the ELAD, i was reminded of the old AGI 511A, which i'm still very fond of today. Both products took a very straight-foward and scientific approach to audio circuit design and utilized IC's as the main source of gain. In effect, i'm quite certain that the design of the AGI was influential in how Morrison approached the ELAD.

Quite honestly, i think that David Spiegel of AGI is the Father of high speed, low noise, wide bandwith, high linearity audio circuitry i.e. the "straight wire with gain" school of audio design. Many before him set out to build products of that nature, but i think that Spiegel was the first to achieve the mass majority of those goals within the confines of one simple product. I just wish Spiegel would have actually produced the prototype amplifiers that i read about way back then. I'm certain that they too would have been very forward-thinking in terms of their design, implimentation of circuitry and sonic performance.

As far as the ELAD goes, it would probably be a nice piece for a very basic system. It is limited in terms of quantity and type of inputs and is very small in physical size. While it uses "good" quality parts, those parts can be bettered. Personally, i think that the sonics would improve along with upgrading those parts, but this is strictly my subjective opinion.

Other than that, Cornelius did a very nice job of summing things up. Svens1 also pointed out that the IC used has the bandwidth capacity and noise level below that of most commercially available gear, BUT, that doesn't mean that all of the support circuitry is up to the same capacity of the IC itself.

As Steve at Empirical will tell you, one can take the same circuit using the same exact parts and lay it out in various manners. Even though you've got the same circuit and the same parts, how it measures, performs and sounds could be very different due to the varying impedances involved. That's because impedances affect power transfer characteristics, transient response, crosstalk between channels, the residual noise floor of the circuit, etc...

As a side note, Stereophile had an article comparing the actual measured performance of several different IC's from various manufacturers a few years ago. I'm not certain, but i think that Ben Duncan wrote the article and provided the test results. Ben has done quite a bit of interesting audio related research and had stumbled across FM distortions within cabling. That is another matter for another thread though : )

Even though the IC's shared the same part number and should have been identically interchangeable in a circuit due to sharing industry spec's, some brands tested FAR inferior to others. Going out of memory, i think that some models had a noise floor of -145 dB's ( PHENOMENALLY good ) to where other so-called "identical" IC's of the same part number measured in at -85 dB's. This is a HUGE difference of 60 dB's While the "bookworm" type of engineers will look at those spec's and say that both are well beyond the audible limits, i have to resort back to the earlier comments made about circuit design and lay-out.

If you start off with a "noisier" part, and then install that into an inferior circuit design and / or poorer circuit lay-out, you won't even be able to reach the full potential of that "junky" part. As such, the difference between an optimally configured -145 dB part in a really good circuit and the much noisier -85 dB part configured in a poor circuit with a bad lay-out can become even wider than the aforementioned 60 dB's. Whether or not this is audible is still subjective, but to my way of thinking based on past experiments and experiences, i personally think that it is.

With all of that in mind, i think that The Audio Critic actually tested and measured an ELAD. From what i can recall, it did quite well on the test bench, demonstrating excellent spec's in most every category. Obviously, whether or not this unit will deliver what they want sonically is a matter of personal tastes and system synergy. Cosmetically, the unit doesn't have much going for it, but then again, neither did the AGI. Both units were built with form following function, so looks were a secondary consideration. For as much of a "straight wire with gain" design as Spiegel set out to make the AGI, it was a tremendously versatile unit. The ELAD is a much more bare-bones approach and lacks much of that versatility / switching arrangements.

As a side note, Morrison also produces some interesting speakers too. I've never heard them, but they make use of a relatively novel and complex to build bass alignment that was developed by Stuart Hegemann many years ago. I've always wanted to experiment with this type of a bass alignment, but never gotten around to it. I can see it having multiple benefits, especially if using a woofer with a high impedance peak at resonance. Then again, i would avoid ever choosing a driver like that to begin with, so i don't know how beneficial this approach would be using a higher quality driver to begin with : ) Sean
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El: That's why i said "bookworm" engineers i.e. those that design things so that they look good on paper according to the theories and formulas in their textbooks, but really have no idea as to how things will work under various operating conditions in the field. These are the kind of idiots that should be made to use their own products that they design. Then they could see how we as end users have to deal with all the flaws, glitches, quirks during normal use. After that bit of education, then they should be forced to repair these items once they fail. Just going through the process of having to figure out why it broke, how to repair it and how / where to get the necessary parts would blow their mind. I think that both their design philosophies and design prowess would both change for the better i.e. less "design revisions" and more getting it right the first time.

Other than that, i've always thought that one should design and build for the "worst case" scenario. If you do that, any other type of situation is simply easier on the gear. Then again, something that has to strain to keep up or get the job done obviously won't work as reliably in the long term and / or may provide less consistent results in the short term. At the same time, keeping things simple also helps as there is less to go wrong. More unnecessary features, functions and gadgets only means a longer signal path with more connections and things to go wrong. In that respect, the ELAD is based upon several different tried and true design premises. Sean
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I agree that everything has to be factored in. Then again, if EVERYTHING is built "gonzo", nothing is left to go wrong : )

As to regulation circuits, most are piss poor. This is why there is a lack of dynamic headroom in regulated amps. That's because the regulation circuit is both too small and too slow to pass the necessary amount of current that the circuit requires on a dynamic basis.

Since the entire amp would be pulling juice through the regulation circuit, the regulation circuit itself should be sturdier with more capacity than both channels of the driver and output stages combined. I've never seen a regulated amp built to anywhere near this level, let alone heard anyone ever discuss such things. Sean
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