I should have thought that the optimum sound quality would only truly be possible if the preferred sound was in agreement with a flat transfer, and with no aberrant behavior at the trafo (i.e., no overshoot...). That one might prefer the mojo version to a dull, if pure, version is a familiar claim. But the purer version which is also exciting would be superior to either of the other two.
You may recall that the A80 R meter bridge has termination switches on the front (similar to the ones on the rear of the ATR I/O module, except the Ampex ones are slide switches and the Studer's are flip switches†), and these seem to be 600 Ohms only, just like the ATR's...
The Studer manual cites the maximum output with a 600 Ohm load. Possibly this is just for reference, due to the historical place 600 Ohms has in studios, and possibly it may be in fact a specification that this load _must_ be used in order to achieve the maximum possible output for the 30 Ohms output, _without overshoot or re-eq.
Again, it does say that the load seen by the A80 has to change if the eq standard changes.
But through e-conversations with some heady techs (ex-CBS), and, evidently, DC seems to agree, I have gathered that the A80's compensation networks should already be buffered from load effects external to the machine's output connector by design. So, why, indeed, would the manual ever say to feed a multimeter the output with a 200 ohm resistor in parallel, if measuring the CCIR performance - or a 600 Ohm one, if NAB? How does it know? If it's just a matter of level, can't that be adjusted adequately at the trimpots?
The ATR man does not mention a need for changing the load based on equalization. But I believe that it _does_ indicate that when _not_ driving devices which are already 600 Ohms, to flip the switch, thereby rendering the net load, close enough to the 600 target (Rpt =
1
_____________
1/Rp1 + 1/Rp2).
At least that's in the section for calibration of the I/O module.
What to do with the ATR overbridge in Helsinki? Besides throwing it in the Gulf. (; CCIR works better with modern formulae, according to Jay McKnight, btw.
Please vote:
1) Don't terminate the ATR (or A80, be specific, please, as they do, indeed, use different trafos - Thanks, JohnR) if voltage matching, and forget it?;
2) epoxy the termination switch in the On position?; or,
3) make two pairs of short, extension cables (labeled NAB and CCIR, respectively) which have the target loads soldered across the pins... always using them with the matching standard, unless the given load is already at the target Z?
Andrew
† Does anybody know a good source for the little plastic sleeves that go over metal flip switch throws? Such as on an electric guitar? I'm looking for black, but I might be persuadable, if the color is good... Mood sleeves?
* (are there any? ...like a working museum studio? I know of one that is in a incubation phase right now, locally, but it hasn't reopened, yet)