2 picoDumbs, do you mean, for both amps 7.5mA - 8mA would be good? I'm still in struggle.What Idss grade uses Mr. Pass for his commercial FW amplifiers?
I've sent an inquiry to Jensen.
Russellc, do you use 7.5mA for F5 or you ordered for F6?
Yes, I saw your thread. But, did you use the same parts from F5 including JFETs for F6?
I wonder maybe use some transistor socket for JFETs to be available easily play with, e.g. compare Linear and Toshiba. But on the other side I'm not sure about contact issues. What you think?
I got them for F-6
Sorry for the confusion I am talking about sonic differences between the Toshiba and Linear Jfets not the F5 and F6. I didn't know there was s commercial version of F6...I thought it as strictly diy. I guess 6 moo's did review it! I just never saw it listed under "products" on First Watt page? Whoops, it is the first one listed!
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Yes, I guess I am just thinking of his release of it, and some how got to thinking it was released as Diy only. Also saw a review on "New Record Day" oh well. Can't wait for chassis to be restocked so I can finally finish mine.
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What about a transistor socket I mentioned above? Is it good idea? E.g.: 03-0518-11 Aries Electronics | Mouser
Woody, which event? This one?
Woody, which event? This one?
I have to find my own solution for chassis/heat sink, delivery of diyAudio chassis to my country will be million dollars!
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As I understand, it must not exceed JFETs 0.4 watt power rating. So if we calculate:
U*I<P
Idss<0.4W/23V=0.017A=17mA
Am I wrong?
I am really sorry, but someone please explain me.
P.S. The guy that sells quality JFETs wrote me that Idss doesn't matter.
No.
Don't exceed 1/2 the power rating. Don't exceed 200mW
I wouldn't be buying jfets from someone who spoke such rubbish.
Buy from the diyaudio store
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In terms of Vds yes, in terms of power dissipation NO. Don't exceed 200mW.
There is no degeneration on F6 jfets
Looks like he has 23V rails not 20V rails.
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I'll have a look but, this is F6 not F5.
1) F6 does not have degeneration on Jfets
2) F6 does not have drain resistors on jfets.
3) Toshiba jfets are unlikely to be used, I'm not sure the LSK/LSJ devices are as robust as Toshiba.
4) A couple of people have already experienced burnt out jfets, so clearly this is to be taken seriously.
5) I'm pretty sure Nelson has said on a few occasions not to exceed 1/2 power rating of jfets unless you are using heatsinks on jfets
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Directly from F5 Turbo article
"The average dissipation of the Jfets with a 32V supply will be about 28 volts times the operating current. A 2SK170 or 2SJ74 with a 10 mA Idss will operate at about 8 mA in this circuit, which gives a dissipation of about 220 mW. A quick calculation shows that its maximum junction temperature at 220 mW is reached with an ambient temperature of about 70 deg C. A wise DIYer will either select a Jfet with a lesser Idss (say 8 mA) and/or see to it that the Jfets gets some cool air or a little heat sink." Nelson Pass
So on F6 don't exceed 200mW, which means specifically don't exceed 8.5mA, for the reasons posted at post #32
"The average dissipation of the Jfets with a 32V supply will be about 28 volts times the operating current. A 2SK170 or 2SJ74 with a 10 mA Idss will operate at about 8 mA in this circuit, which gives a dissipation of about 220 mW. A quick calculation shows that its maximum junction temperature at 220 mW is reached with an ambient temperature of about 70 deg C. A wise DIYer will either select a Jfet with a lesser Idss (say 8 mA) and/or see to it that the Jfets gets some cool air or a little heat sink." Nelson Pass
So on F6 don't exceed 200mW, which means specifically don't exceed 8.5mA, for the reasons posted at post #32
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I will admit to thinking of the original documentation on the F6 which had degeneration resistors, as well as other options that are not available on the store version. I concede, you win
btw, how have you been?
Got busy riding/racing motorbikes (enduro).
I thought I had lost interest in this hobby, but I'm back and determined to build every amp idea I have thought of as well as finish off a few more Pass designs. Just getting the hang of PCB design software so be on the look out for dumb amp ideas. Hahahaha
Don't worry I have my eyes set on Vice President of ABFAB.Enduro bikes and afraid of a little Jfet heat
Hahahaha
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