I just measured mine. 1K signal, 1W into 8 ohms (~ 2.82VAC). Amp not warmed up.
0.04% THD, 0.07% THD+N, measured using Keithley meter.
1.7A bias per channel.
Sorry...no spectrum info.
0.04% THD, 0.07% THD+N, measured using Keithley meter.
1.7A bias per channel.
Sorry...no spectrum info.
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I am suspecting the JFETs as well - eBay. I just ordered the matched ones from DIYA store.
J74/J74 Stereo Differential Kit – diyAudio Store
I do want to get to the bottom of this. I hope this fixes it.
Thanks for doing that Dennis Hui - gives me hope that when running properly it’s relatively low.
J74/J74 Stereo Differential Kit – diyAudio Store
J74/J74 Stereo Differential Kit – diyAudio Store
I do want to get to the bottom of this. I hope this fixes it.
Thanks for doing that Dennis Hui - gives me hope that when running properly it’s relatively low.
J74/J74 Stereo Differential Kit – diyAudio Store
A few possible areas to investigate
1) Bias of output stage
2) AC Current gain of Aleph CCS
3) Current limiting circuit
1) Bias of output stage
2) AC Current gain of Aleph CCS
3) Current limiting circuit
I think I have looked at all of the above with guidance from 6L6. Except not sure what is to be checked for (3)?
There are exceptions. I remember that there is a chap from Israel who sells match pairs, but I think he ran out of BL. Spencer of Fet Audio is also a reliable source for original Toshiba. However, all of very much at "market price" of the real deal.
IDSS is the quick test, but trace the transconductance curve should also be done. Many moons ago, it started with jfet disguised as 2SJ74 that passed the IDSS measurement but failed the curve tracing, then jfet not matching IDSS, then not even a jfet!!!
IDSS is the quick test, but trace the transconductance curve should also be done. Many moons ago, it started with jfet disguised as 2SJ74 that passed the IDSS measurement but failed the curve tracing, then jfet not matching IDSS, then not even a jfet!!!
I did not measure before installing (only Vgs). But the remaining ones I have from same shipment measure from -11mA and -12mA at -10v.
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Alwieit is the Israel fellow, his are real, but yes, I believe he is out of BL as well.
Spencer at FET Audio | Hi-End Audio Projects has genuine BL, scroll down a few posts for info. He is expensive, but worth it if you want Toshiba.
Picodumbs - Who is the seller Papa endorsed? I'd love to know in order to point people in the right direction.
Of course, all the matched Linear Systems Jfet in the store are real, work beautifully, and have been matched by yours truly. 😀
Spencer at FET Audio | Hi-End Audio Projects has genuine BL, scroll down a few posts for info. He is expensive, but worth it if you want Toshiba.
Picodumbs - Who is the seller Papa endorsed? I'd love to know in order to point people in the right direction.
Of course, all the matched Linear Systems Jfet in the store are real, work beautifully, and have been matched by yours truly. 😀
Pretty sure it was seller punkydawgs from Sacramento. Or at least that was my interpretation at the time and I bought a matched quad for future use.
BK
BK
Using the Borbely tester circuit modified for p Junction JFET:
I got -10mA for Idss and -2.13V for Vp.
Using the formula from Borbely Transconductance is approximately = -2 Idss/Vp I get about 9.4 mSiemens.
The Toshiba 2SJ74 datasheet says forward transfer admittance per the graph at -10mA should be 40mSiemens.
Did I do the calculation right, and does this show that the part is fake?
I got -10mA for Idss and -2.13V for Vp.
Using the formula from Borbely Transconductance is approximately = -2 Idss/Vp I get about 9.4 mSiemens.
The Toshiba 2SJ74 datasheet says forward transfer admittance per the graph at -10mA should be 40mSiemens.
Did I do the calculation right, and does this show that the part is fake?
The 2Sj74 Vp should be around 0.4 to 0.5 Vgs for 10mA IDSS. You can double check your work by taking readings at two different points then its the change in Id/change in Vgs. At higher drain currents the gm increases.
BDP
BDP
Calculation ok, part behavior similar to J270/271, not 2SJ74 any grade. No wonder your build has anomalous distortion, I was rather astonished by your spade connector comment. I can imagine a dark and flat presentation compared to correctly populated build.
Yes punkydawg.
Apparently Papa personally knows this guy.
I would still like to find the post though.
I purchased 2 matched quads.