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biju55 7th September 2016 07:59 PM

Nice work Salas , lovely.

buzzforb 7th September 2016 08:02 PM

Wow. This snuck by. I appreciate another project, as if....

Salas 7th September 2016 08:15 PM

2 Attachment(s)
It can be done capacitor coupled output too but I don't recommend it. Everything is audible, very simple signal path, very fast circuit. Couplers spoil it.

(build example by V George)

Bonsai 7th September 2016 08:40 PM

Very nice Salas! Looks like a awesome design!

Salas 7th September 2016 08:42 PM

2 Attachment(s)
I had question about using 2SK389-V Toshiba. Answer is yes it will work. J3 (with R3 as degeneration) fixes the JFET LTP total current at about 5mA so the IDSS of the monolithic chip won't matter as long as it is >3mA tested per element. What will happen is THD will go 0.00025% but the flat trend will go rising trend. I know because I have tested K170BL and V matched pairs. LSK389 does not go such so much because it has less pF. I have tested that too. Its elements curve matching is visibly worse than uPA though. The NEC behaves closer to 2SK117. Pins order is compatible to Toshiba 2SK389. Don't connect the sub pin to anything or it will hum.

Salas 7th September 2016 08:45 PM


Originally Posted by Bonsai (
Very nice Salas! Looks like a awesome design!


evanc 7th September 2016 08:50 PM

Any good/recommended source for the NEC parts?

pchw 7th September 2016 08:52 PM

Is the Nec uPA68H easier to source than the 2SK389?

Salas 7th September 2016 08:56 PM

Far more easier. Forgotten part by DIY. I got mine from ebay. There are fat and slim ones. Will take picture for you.

pchw 7th September 2016 08:58 PM

Then start loading them up before the rate hike :D

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