John Curl's Blowtorch preamplifier part II - Page 1152 - diyAudio
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Old 18th March 2011, 08:38 PM   #11511
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Quote:
Originally Posted by hitsware View Post
Even with 1000's of them in parallel ?
With such current draw, some tubes will do better.
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Old 18th March 2011, 09:39 PM   #11512
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Higher noise than I remembered. 50nV/rt Hz.

I had pretty good luck with some old Siliconix switching FETs with low Rds(on). I think they were 2N5114 or 5116. As a demonstration of their quality control, the last batch I bought all had the wrong pinout. Quiet, though, worked great as an input buffer for a phono stage.

The problem with high gm devices like the Toshibas or LS is the high input capacitance. Some MM cartridges don't care but some do (mine unfortunately being one of the latter).
I would also be cautious about using devices like that as the input stage for an MM preamp. In my view, an MM preamp does not have to go that low in noise, anyway. This is a perfect example of my caution about going for unnecessarily low noise at the possible expense of other aspects affecting sound quality.

Cheers,
Bob
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Old 18th March 2011, 10:31 PM   #11513
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Parts like that, today cost a few tens of cents. Why bother?
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Old 18th March 2011, 11:44 PM   #11514
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Because they work? Seriously, is high cost a desirable feature?
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Old 18th March 2011, 11:53 PM   #11515
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Because they work? Seriously, is high cost a desirable feature?
Depends. Am I selling or buying?
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Old 18th March 2011, 11:59 PM   #11516
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Good parts usually cost some amount of money, if you want performance. Just like auto tires. By the way, SY what was the pin out that looked wrong?
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Old 19th March 2011, 12:07 AM   #11517
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SY the 5114 and 5116 are P channel PS geometry. I used them in the Levinson JC-2 for the line amp driver. The pin out is like a bipolar transistor. They are too noisy for this sort of input.
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Old 19th March 2011, 12:49 AM   #11518
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Actually, for the MM input, they were pretty quiet- they were used in an unusual source follower configuration with the input tube to extend bandwidth and drop input capacitance. I don't know that this would be true for every batch- the noise spec is pretty mediocre, maybe these were outliers.

The pinout was literally wrong. The gate and drain leads had been switched internally. Ooops. So much for quality control. Once I figured out that the problem was the FETs and not my wiring, and swapped the two leads, everything was fine.
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Old 19th March 2011, 01:06 AM   #11519
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Originally Posted by Joshua_G View Post
With such current draw, some tubes will do better.
Well then their ya go ! .......
A vacuum is a quieter
space than a solid ! ........
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Old 19th March 2011, 02:50 AM   #11520
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In actual fact, SY, this is a VERY poor choice for an input fet. It is relatively noisy, a very old design, with lowish Gm. This is because it is a P channel. IF you switched to the NC geometry, its geometrical complement, you would get 10 db lower noise, and much higher Gm, which in a follower, means lower distortion.
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