Look at it this way: that output delivers an output current. If you connect a resistor between that collector an ground, that current will develop a voltage that you can use as output voltage.
As you lower that resistance, the output voltage gets smaller and smaller of course. Until the resistor is zero and the collector is effectively at ground, and Vout is also zero. But as far as that collector is concerned, it's all the same. It will faithfully deliver that current, into the ground node, and consequently its collector voltage is thus zero.
Jan
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He simply used each half as two LTP's and took the output from the compensation node. You can do that with the AD844 or AD744 too. The noise in the BAS article was exemplary, even better than the JC-2 but I could not find a spec on the data sheet (was there a graph?)
Using only the npn's would make the speed much better, at first glance this looks like a nightmare to stabilize.
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Ah yes from the days of lateral PNPs.
I have to go back and read the BAS article again, as yesterday I was in a rush to get a friend's dog to the vet, yet couldn't pry my eyes from the piece. In particular I did see something about the "white noise" generator going out to a MHz or something, and an inverse RIAA network, and the criterion being that the preamp output still sounded white?
It would be interesting to determine the correlation between that perception of noise, and the DUT's overload margin measured in a conventional way. Also, as Otala's TIM was the big new thing around that time, was it really involved?
The AGI 511 was a seriously engineered product, but it could not be very quiet. The final feedback resistor limits the minimum noise to 4nV all by itself. We used 60 ohms. However, the AGI was FAST! Faster than the JC-2 phono stage, for sure. Was it necessary? It did help, but it was probably 'overkill'. The JC-2's phono stage had a slew rate limit that was lower, mostly because of the difficulty in driving the RIAA network (60 ohms) rather than 1000 ohms like the AGI 511.
You must be referring to the Citation I pre amp.
It would also be interesting to see how the various
top of the line pre amps measure up and compare.
And a repository created for comparisons and for future
generations.
We also have to consider that we are probably the last generation
who's going to be able to document this. Maybe the last
generation able to work on and restore this gear.
How to measure the gear is going to be important.
How to create the process that is both repeatable and consistent
and shown to be in statistical process control, including the
upper control and lower control limits.
Also Who's going to test, what parameters, how much fine tuning
while testing allowed, etc, etc. and how to schedule and ship all
the gear to be tested....or have a couple of sites/locations to
perform the tests under the same controlled conditions.
If two locations are different, then how do we identify those
differences and adjust the data to correlate with other sites.
It seems to me it might be easy to say hey the information
is already here, or out there..but where is it all in one place
easily assessable, etc.
There is just a lot of behind the test information that is important too.
for example, if testing the preamps, how do we ensure the same quality
of tubes, transistors, ICs, opamps etc?
OR
Do we just want to gather up the published data and say it's good enough?
It seems a trifle strange that the S/N doesn't change more with a 1k source impedance. And although a cartridge was used for some of the tests, what would have been interesting would have been an inductor in series with the 1k of order the same value as the cartridge, since this would increase the high frequency noise from the termination R and input parallel noise. Of course the weighted measurements would conceal this to a great extent.
Scott,
Would you be kind enough to send me the complete measurements
of all the gear?
Ackerman says that the site, at Homan Square, is but one of Chicago police practices that "echo the much-criticized detention abuses of the ...[link unavailable]
But I found this:
http://www.davidreaton.com/pdfs/holman_aes_paper.pdf
Cheers,
Would you be kind enough to send me the complete measurements
of all the gear?
Ackerman says that the site, at Homan Square, is but one of Chicago police practices that "echo the much-criticized detention abuses of the ...[link unavailable]
But I found this:
http://www.davidreaton.com/pdfs/holman_aes_paper.pdf
Cheers,
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Yes, if one cannot get high OL out of hollow state, something is very wrong.
I recall someone insisting that phono preamps require a 36dB OL margin to avoid clipping (?) on dirt clods and their ilk. But what happens in a system after that? It reminds me of a sci fi story, iirc titled You Were Right, Joe---I've forgotten the author but it was in a collection. [EDIT: hah here it is! https://archive.org/stream/galaxymagazine-1957-11/Galaxy_1957_11#page/n31/mode/2up ]
The narrator and protagonist has been sent into some alternate-time reality by "Joe", but manages to communicate with him. Things are going well, with predictions of Joe vindicated. But at the end, the interloper is discovered and informed that there was going to be a problem---a certain back-reaction that would be akin to a cosmic rubber band snapping back into Joe's realm. The narrator expresses some concern, but is confident that Joe will figure out how to cope with the probable cataclysm.
Saul was the first and his EQ would represent the known EQ being used at that time.... especially mono EQ and which were the most popular EQ's of the day based on LP sales of music and on which label.
There are other brands beside H-K who later added other EQ settings after Marantz success with his Audio Consolette and Model One. It became a neccesity or Must Have feature until everyone got on-board with RIAA.
We should measure the S. Marantz curves and publish them..... or has that been done already and long ago?
THx-RNMarsh
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I agree. Many of these are important issues. I address many of them in my VinylTrak preamp article published awhile back in Linear Audio.
Cheers,
Bob
The JC-2 that was measured was defective. Levinson did have a problem with the J110 input jfets at some point. I was not notified at the time. Later, I spoke to Ed Oxner about it, and he said the process was changed.
I noticed the subjective ratings did not follow S/n or thd... some better specs than JC got rated Good while the JC was Excellent.
Nothing has changed since then in the measured vs sound quality debate, it appears.
However, over time, JC designs have been consistent in their subjective ranking by a wide variety of people and groups. Could it be then, JC actually does know what else is needed but we arent listening or asking the right questions?
THx-RNMarsh
Nothing has changed since then in the measured vs sound quality debate, it appears.
However, over time, JC designs have been consistent in their subjective ranking by a wide variety of people and groups. Could it be then, JC actually does know what else is needed but we arent listening or asking the right questions?
THx-RNMarsh
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Are you sure, or taking the word of Saul as the truth? I've seen a lot of mentions of variable eq from before 1952 when he launched his first amplifier. It may have been the first, but would be nice to find out.
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