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Old 11th December 2011, 01:16 PM   #18951
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by Bonsai View Post
Back to the earlier noise discussion, the best way forward I think is to use an agreed cartridge inductance and series resistance.
So, what do we standardise upon?

Some of us use J-Fets or Tubes and we would probably like a lot of L and R like the old Shure and Pickering MM carts to make our designs look especially good next to those inferior bipolar designs.

Meanwhile the manufacturers who use Bipolar inputs may wish to not use any MM's at all as model and instead concentrate on high output MC's which are often between 100 and 200 Ohm to show how their excellent designs are superior to those inferior Fet or Tube designs.

I'd give it up as a bad job in any case.

Most modern Phono stages are sufficiently quiet to not have noise constitute any issue when playing vinyl. And that is what really matters.

Ciao T
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Old 11th December 2011, 01:23 PM   #18952
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Quote:
Originally Posted by SY View Post
If it were my magazine, I'd report the shorted input, but then repeat the same measurement with a standard source (say, 400R + 0.5H or something) representing a MM and/or 5R representing a MC. Then show the standard source data compared to an ideal noiseless preamp with the same gain and frequency response curves on the same graph so that the reader can see what the preamp is actually adding, compared to theoretical limits determined by the source. These are easy measurements to do with the sort of setup that Stereophile has and give a readily understandable and graphically dramatic indication of what the real world noise of the preamp is likely to be.
That's an intriguing suggestion. I have pondered for a long time if I should load the preamp input with something that resembles a real MM or MC cartridge - Noel Keywood in the UK used to use an actual cartridge - but the question then becomes what would be most representative; a Grado or Shure MM, for example, which are very different electrically.

The shorted input becomes the default condition because of its consistency.

And thank you for your comments on Stereophile's incorporation of measurements in its reviews. I have always believed that reviews must be anchored with measured data since I first started reading audio magazines in the mid-'60s. I have made no secret of the fact that I have modeled Stereophile's reviews on those by John Crabbe and Ralph West in the 1960s-vintage Hi-Fi News, which did a great job of balancing the two worldviews.

John Atkinson
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Old 11th December 2011, 01:24 PM   #18953
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Quote:
Originally Posted by janneman View Post
In choosing medium-to-high-level technical content and no ads for Linear Audio I am condemned to breaking even at best.
I could never make a living from it.
But the upside is the high quality of authors you can get.
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Old 11th December 2011, 01:29 PM   #18954
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" the Krohn-Hite amp schematic is available on Dick's site at:

http://burwenaudio.com/Krohn-Hite_UF-101.pdf


Regards

Giorgio


Wow, that is weird, i have not run into anyone who knew what those were.
I have a pair of them that "someday" i plan to clean up.
One worked fine, the other had a problem.
Anyway, thanks for the memory jolt.
Best,
Tom Danley
Danley Sound Labs
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Old 11th December 2011, 01:29 PM   #18955
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John,

Quote:
Originally Posted by StereoEditor View Post
That's an intriguing suggestion. I have pondered for a long time if I should load the preamp input with something that resembles a real MM or MC cartridge - Noel Keywood in the UK used to use an actual cartridge - but the question then becomes what would be most representative; a Grado or Shure MM, for example, which are very different electrically.

The shorted input becomes the default condition because of its consistency.
I use 10 Ohm as "default MC" and a dead Shure V15 with it's cantilever assembly removed as "default MM" for measurements that are not shorted.

I would suggest that as the V15 is representative of most real MM's and one of the few "High End MM's" it fits the bill well, the 10 Ohm for MC also hit a spot somewhere in the middle...

Ciao T
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Old 11th December 2011, 01:34 PM   #18956
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Quote:
Originally Posted by StereoEditor View Post

The shorted input becomes the default condition because of its consistency.
How about using both shorted input and R +jwL simulations of MM and MC. Similarly as dummy load when testing power amp loading.
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Old 11th December 2011, 01:40 PM   #18957
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Quote:
Originally Posted by StereoEditor View Post
The shorted input becomes the default condition because of its consistency.
The problem is that you've gone from a simulation that satisfies some to a simulation that satisfies none. If you pick a model (the numbers I used in my earlier post were extracted from my hindquarters) that's somewhere in the middle of the pack, it will not be dead-on for anyone, but it will be Close Enough for most. As an intro to the new measurement methods, you can do a one-time measurement of several cartridges that are on the high and low side of the chosen resistances and inductance and show those as an envelope- this way, a reader can understand where his cartridge falls, and how to use the "standard" measurement to predict whether or not he'll hear the preamp noise over the basic thermal noise of the cartridge.

There's an analogy to the standard speaker load you use for amplifier tests ("But what if I have Quads?")- that simple addition to your test suite is superbly useful and was a great choice on your part. I have confidence that you could be just as clever in measurements on the other end of transduction.
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Old 11th December 2011, 01:49 PM   #18958
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Quote:
Originally Posted by ThorstenL View Post
I use 10 Ohm as "default MC" and a dead Shure V15 with it's cantilever assembly removed as "default MM" for measurements that are not shorted.

I would suggest that as the V15 is representative of most real MM's and one of the few "High End MM's" it fits the bill well, the 10 Ohm for MC also hit a spot somewhere in the middle...
I'll try these suggestions out. (I am sure Michael Fremer must have a long-unused V15 somewhere in his cupboard!)

John Atkinson
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Old 11th December 2011, 02:00 PM   #18959
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Except that Parasound did not run any ads, in this or most other magazines. Some dealers that sell Parasound do run ads. I don't even know who they are.
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Old 11th December 2011, 02:14 PM   #18960
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Looking last night at various phono cartridges that MIGHT be used with the JC-3, I think that 500mH with 500 ohms might be a good reasonable worst case. The VERY OLD Shure V15's might have had more inductance, but this limits the frequency response too much for anything of quality. This is because the electrical resonance has to be balanced with the mechanical impedance resonance to create a flat output. In the old days, 1H was typically used, but rarely, today.
For the record, however, the Ampex AG440 analog tape reproduce used an equivalent reproduce head inductance of 1H, and we used high quality ($0.12) bipolar transistors on the input, with more difficult reproduce noise conditions than the RIAA reproduce might provide. Thousands of successful recordings were made with that combination.
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