John Curl's Blowtorch preamplifier part II

[Joachim Gerhard]

I had a long discussion with Burkhard Vogel and he told me that the Hitachis are not that good as advertised. He measured an rbb`of 14 Ohm. The lowest rbb`he measured was the Toshiba 2SC3329 with rbb`of 2 Ohm. The second best was the BFW16A, an old stablemate.
It has an rbb`of 4 Ohm at 25mA with hfe of 35. It translates into 0.28nV/qHz. fce is quite high at 250Hz. A circuit was shown in "Ultra-low-noise Preamplifier for MC phono cartridges " Nordholt & van Vierzen, 1980.

 

[john curl]

I have 100 ea. They were as good as advertised.

 

[Joachim Gerhard]

I believe that. I will do my own measurements. The jig is ready.

 

[scott wurcer]

Actually, no. I'm going by memory...used to play with waffle packs and wafers back in the 80's. So I lived dice..

If anything, it's faulty memory. I found some mat-02 stuff on my drive, I may be confusing the two...



I'm not sure, but I think the 194 and 394 are just different grades of the same die.

But I'n not sure if this is the die I'm thinkin of however..

Cheers, John

I meant the original story, Bob Pease said the part happened when he joked about just paralleling something like LM101 input transistors. Yes National used 1** ,2**, and3** as grades, runs you out of numbers faster.

 

[Steve Eddy]

You can tell I never use the things.

Yes.

Pity.

se

 

[hitsware]

http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/transistors/AN-222.pdf

Right ...... 194 and 394 are grades.
Anyways I still surmise power mosfets to
be quiet because they are comprised of
many 'cells' in parallel.

 

[john curl]

Hitsware, mosfets are very, very, noisy. Big time noisy, except at RF.

 

[Joachim Gerhard]

Here is the circuit i mentioned.

 

[Joshua_G]

We buffer with a 2N5564 pair used in follower mode.

Sorry, I'm not clear how you buffer the JFETs, are the 2N5564 used as CCS, or cascode, or as source followers?

 

[hitsware]

Hitsware, mosfets are very, very, noisy. Big time noisy, except at RF.

Even with 1000's of them in parallel ?

 

[Joshua_G]

Even with 1000's of them in parallel ?

With such current draw, some tubes will do better.

 

[Bob Cordell]

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

 

[john curl]

Parts like that, today cost a few tens of cents. Why bother?

 

[SY]

Because they work? Seriously, is high cost a desirable feature?

 

[simon7000]

Because they work? Seriously, is high cost a desirable feature?

Depends. Am I selling or buying?

 

[john curl]

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?

 

[john curl]

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.

 

[SY]

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.

 

[hitsware]

With such current draw, some tubes will do better.

Well then their ya go ! .......
A vacuum is a quieter
space than a solid ! ........

 

[john curl]

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.