Web search said they are absent in trade. I ended at the diyAudio Store to discover the depletion of its offering of LS JFETs. But; the article AN105 therein talked about converting these JFETs to voltage controlled resistors.Thanks to a nice person in Japan I have a few 2SK78B and 2SJ78B, SIT
complements, a couple hundred volts Vds, 0.5 amp and higher power.
Unfortunately, I do not know how to obtain more, otherwise they would be
sitting in a DIY project right now.
Thanks Mr.Pass.For the most part, Schade is the reference - local feedback which simulates
a triode.
Just for grins and perversity, I ginned up a version of Nelson's preamp using readily available J113 and J176, which have far lower transconductance than the 2SK/LS parts. Surprisingly, the simulation balanced up fairly well without trimming using EWAG resistor values just thrown in. I'll show the results in another thread once I get through playing with the optimization. I suspect the simulation results will be fairly decent, but inferior to what one could get with higher transconductance devices. I may also throw in a version similar to Juma's using the 2N4401 and 2N4403 for the cascode positions rather than using fets.
BTW, if you try to buy the 2SJ74 these days from E-prey, you're likely to get a re-marked J175 or J176 anyway (fakes abound!), another perverse reason for trying this dodge. Last time I looked, NXP still offered at least the J113 in a leaded package. I've been able to score large quantities of NOS J175 and 176 - who would try to fake them?
BTW, if you try to buy the 2SJ74 these days from E-prey, you're likely to get a re-marked J175 or J176 anyway (fakes abound!), another perverse reason for trying this dodge. Last time I looked, NXP still offered at least the J113 in a leaded package. I've been able to score large quantities of NOS J175 and 176 - who would try to fake them?
In spite of my surface jocularity, I am perfectly serious about every circuit.
IMHO, none of them sound bad, they are merely different from each other.
Often I choose simplicity as an important criterion just because I am trying
to get you guys to actually build something, and this lowers the barriers. I
figured this out with the Son of Zen, which seems to have been very popular
because it appealed to guys who know how to weld and machine and saw
and tear engines apart (and put them back together) but who are
intimidated by the little 3 legged critters.
You will find a more sophisticated (and certainly better measuring) circuit
based on the same ideas from Scott Wurcer elsewhere in this site.
(I am too lazy to find it for you)
One of the reasons I've been looking at this circuit is that it looks to have superior performance compared to the single-ended folded cascodes I've been looking at for line amp/RIAA 2nd stage duty over the past few years, though I admit that I probably haven't pushed those circuits as far as I could in the time I have available. The cheapo version of this preamp using the lower transconductance fets may actually sound quite nice, though it most likely will not measure as well. If the harmonic distribution turns out similar to Nelson's version (2nd, with a touch of 3rd for taste) it may be quite listenable even with higher THD.
Exercises like this may motivate me to add a negative supply to my test bed so I can mess with them witjhout too much trouble. I've been getting by with a single +40V supply for years.
Exercises like this may motivate me to add a negative supply to my test bed so I can mess with them witjhout too much trouble. I've been getting by with a single +40V supply for years.
Just to show what is possible, I simulated Nelson's preamp circuit with proletarian devices J113 and J176, old fets too humble to fake (so far), and also very rough complements. The circuit and sim results are attached, and are not at all shabby for a high level open loop circuit. Gain is around 9X, which could be pushed down by increasing the degeneration applied to the input fet pair, hopefully paring down the distortion further as a result. More extensive discussion will occur elsewhere if there is significant interest.
Attachments
Yes, a very versatile circuit indeed - here is a Chris Hornbeck's proposal to use it as a phase splitter (post #148):
http://www.diyaudio.com/forums/tubes-valves/189153-phase-splitter-issue-3.html#post2802454