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Old 5th December 2014, 03:51 PM   #401
pinnocchio is offline pinnocchio  Canada
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There's no documentation available for this BUT using the IRF610-9610, I inserted a digital multi-meter in Amps mode (in my case, 10A mode) in between the positive supply rail to see the current draw. I figured that the best sound was around 230-240mA current draw by rail. You will need good size heatsinks. Some people have reported the same results based on my recommendations. Naturely, if you use different Mosfets, you will need to test and also read the specsheet.

Ciao!
Do
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Old 5th December 2014, 03:55 PM   #402
takis1969 is offline takis1969
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thank you again my friend
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Old 5th December 2014, 03:58 PM   #403
pinnocchio is offline pinnocchio  Canada
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Quote:
Originally Posted by takis1969 View Post
thank you again my friend
No problem!

Enjoy! it is a very fine preamplifier!

Do
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PREAMPs : Bal AMB α10 + JC-80 | Bal DCB1 | Bal LDR3x | AMPs: AMB β24 | USSA3 & 5 | FO v1.4 | TGM8 | VZ Audio NS OPS | NX Amp | FC-100
DACs : TPA Buffalo II + OPC's NTD1 I/V | JLsounds | Mirand AK4490 + Discrete Output Speakers : Troels Gravesen ATS-4 | Sagwee LT V3
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Old 11th March 2017, 02:55 PM   #404
RobertHaze is offline RobertHaze  United States
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I picked up a pair of nice looking JC-80 PC Boards with DC servo circuits from EBay. These are the red Chinese boards. I should have researched the design more thoroughly before buying; unaware that parts availability was an issue. . The seller provided a parts list which recommends the use of matched 2SK170BL/2SJ74BL single JFETs in place of the nearly unobtainable 2SK389/2SJ109 dual JFETs. Has anyone tried this approach?
I can buy U.S. matched sets of the single FETS which look quite reliable. However all the Hitachi dual FETs I see come from China and appear far less reputable. There is a fellow in Taiwan selling matched sets of duals, but the details of his matching technique are sketchy.
I have built a cheap JC-2 kit which did not even have the original JFETS with it. The FETs had been subbed with low-noise bipolars. I ended up putting 2SK170/2SJ74 FETS in it, as well as upgrading all the capacitors.. The results were still less than anticipated. I hope to have better results with the JC-80 boards.Any help from the forum would be appreciated.
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Old 12th March 2017, 01:24 AM   #405
ammel68 is offline ammel68  United States
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Originally Posted by RobertHaze View Post
However all the Hitachi dual FETs I see come from China and appear far less reputable.
I didn't know Hitachi made the dual JFETs. All I've seen were made by Toshiba.
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Old 12th March 2017, 11:31 AM   #406
AndrewT is offline AndrewT  Scotland
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The jFETs inside the Toshiba or Linear dual package are not matched.
They are guaranteed to have a Idss ratio of better than 0.9:1
If the internal jFETs are not matched, then one can NEVER get pairs that are matched.

What does the JC circuit require?
a.) matched jFETs in the N side and matched jFETs in the P side?
or
b.) accurately selected Idss in the N side and in the P side?
or
c.) reasonable selection of Idss in the N side and a different reasonable Idss selection in the Pside?

a.) is not available from the 389/109 package
b.) is unlikely to be available from a 389/109 package
c.) can be met with the genuine 389/109 package

a. b. and c. can all be met with 170/74 package if you have a group from which you can choose.

But the Thermal coupling in the 389/109 package cannot be met with the 170/74 package.
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Last edited by AndrewT; 12th March 2017 at 11:33 AM.
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Old 15th March 2017, 11:15 PM   #407
RobertHaze is offline RobertHaze  United States
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Thank you both for your help.
I assumed the dual FETs were Hitachi. My error. I've been dealing with Hitachi MOSFETs with similar numbers.
I am not sure which are the most critical parameters for the JC-80 circuit.
The matched quads of 2SK170BL/2SJ74BL are all selected for 10ma Idss. they should meet all criteria but the thermal tracking issue. I hope that thermal drift has only a minor effect on the circuit. Hopefully the DC Servos can compensate for that.
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