Parasound JC3 Phono

[SY]

Originally Posted by john curl

Well, page 426, the leakage graph of the 2SK170 shows: 10V-10pA, 12V-100pA, 14V-1nA, etc. 'Toshiba SMALL SIGNAL TRANSISTORS '92'

That graph isn't on their datasheets. What are the test conditions, specifically Vds and id?

[john curl]

It is really simple. They apply a voltage between the source and the drain. Then they measure the gate leakage, apparently at Idss, or they may have another DC voltage to control Id. They call it Igx-Vds.
I just spoke to a manager at Linear Systems, and they claim to meet or BEAT the leakage spec of the 2SK170, and we discussed that something might be wrong on their spec sheet.

[SY]

Yes, I understand that. For the test conditions you're citing, what's Vds and what's id?

[john curl]

Why don't I send you the pdf data sheet that I just took off line with a Google search? What is your E-mail address these days? For the record, Id varies from 1ma to 10ma. The differences are minimal with current, for the most part.

[SY]

I have the datasheet resulting from a Google search. It specs gate leakage at Vds = 0, but with varying Vgd, which ignores the mechanism that creates excessive gate leakage at high Vds. If you have something which has more info (especially ig at Vds = (say) 10V and id at 1ma, 10ma, or something like that), I'd love to see it. Email addy is my initials at syclotron.com.

[SY]

Got the datasheets from you. The LS doesn't show much, the Toshiba is much more useful. Public thanks!

[Joachim Gerhard]

lab page

[IngemarR]

What I was trying to say, John, was that it is possible for DIYers to get some 2SJ74:s even today. A DIYer does not need to have 1000s of JFETs. Thus, most JFETbased amps can still be built.

Erno has closed his business last year already.

Originally Posted by john curl

Go for it, IngemarR. Build it and love it. Better yet, buy the kit, if they are still available.
I build with the SAME parts, even today.
However, we have 50,000 already in house, and an inside track to vendors. Charles Hansen, my esteemed competitor, purchased 500,000 J74 devices for his future use. Perhaps you have access to a few to put something together and would like to share them with your friends and colleagues. '-)

[ThorstenL]

Werner,

Originally Posted by Werner

The Kiseki was low output, as all Kisekis were. They used another brand name, Milltek, for their (cheaper) high output MCs.

The Denon DL-304 is most certainly low output: 0.18mV.

The "bird" I believe goes to Ortofon, MC7500 is 0.12mV and the MC-1000 & 2000 where 0.1mV and 0.05mV (not certain which way around).

The MC7500 is the cartridge I get to Demo my Phono with, in Hong Kong and China (as the distributor carries only Ortofon and Benz and the MC7500 is pretty much the only one that sounds good on that NA Table they give us).

I find a Phono Stage with -145dBV Ein (e.g. my one) works fine with the MC7500 and the 0.1mV Ortofon, but I have not tried the 0.05mV pickup.

Ciao T

[Bob Cordell]

Originally Posted by scott wurcer

Which is even more non-linear with voltage than the capacitance, and it varies with both drain current and Vgd.

Bob - I'm surprised at your statement. Compute the nonlinearity caused by say a 1mV MC signal (with Rs = 10 Ohms) on top of a -1V Vgs with a 240pF capacitance with standard 1/3 power voltage variation. Then compare it to the open-loop distortion of the FET.

Hint: 240pF becomes 240.072pF

I get ~14ppm @ 10kHz

Hi Scott,

The main point I have been making is the concern about device capacitances in use with MM cartridges, where the impedance levels are much higher, and indeed the signal levels are much higher. My main point is that input stages designed for extremely low noise by using multiple paralleled JFETs are not a good idea for use with MM cartridges.

Your calculations with Zs = 47k and 5mV signal level will probably yield a bigger number.

Cheers,
Bob