What can you build with 2n5457 and 2N5460 JFET's

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#2
Those are the two most difficult devices to buy, in the Parts List of Richard Marsh's Headphone Amplifier. The project was published in Linear Audio magazine (volume 3), and one of our members sold kits-of-all-parts a long time ago. There is a discussion thread about the HPA, somewhere on this Forum; I've seen it but don't remember where.

Here is a link
 
#6
Too noisy for phono pre's.

Another line level examples :
XCEN Balanced to Single-Ended Converter Revisited
John Curl's Blowtorch preamplifier part II
I have used MMBF5457/5460 to replace 2SK208Y/2SJ106Y in those circuits.
Both of the above have less than 20dB gain.

If I were you I would match the 2.5k and sell them here as matched quads.
Or offer them to DIYA store and let them match.
You can then use the revenue to buy 2Sk170/2SJ74 for many applications, including phono pre's.


Patrick
 
#8
Thanks For the thoughts on what to do with the 2N5457’s and 2N5460’s
The JFET’s arrived a couple of days ago.

When I ordered these months or years ago I was looking at and playing with the Marsh Headphone Amplifier.

While these JFETs are here on the bench I do think that I will match up a small hand full to test some of the Marsh Compound-Complimentary and Diamond amplifier ideas. (with 2N5087 and 2N5088)

Thanks DT
 
#9
Hello All,

Going by recall here the book is not in front of me.

Dr. Marsh was concerned about heat and attempting to be near Temco when he selected 2N5057 JFET’s for his HPA.

Dr. Marsh used a 1k bias resistor and a target 0.85 voltage drop across the bias resistor.

E=IR. 0.85V is equal to 0.85mA.

Now that I think about it, it is sort of academic.

Giving the idea a little practical ingenuity why not fab a test circuit that is the design circuit and measure/calculate current at the expected real world operating conditions.

My expectation is that JFETS previously sorted to matching Idss values will settle into the test circuit, heat up and perform just the same as the next Idss matched part.

I like the idea.

Once you get close you can trim the circuit bias resistor and you have it nailed.

Now that sounds like Papa’s idea.

I like that idea even better.

Thanks DT

To be fair, DR. Marsh did put trim pots in his HPA project
 
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