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Author Topic: Sunn Concert Lead PA  (Read 4981 times)

gbono

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Re: Sunn Concert Lead PA
« Reply #15 on: August 23, 2010, 01:37:29 PM »

I spent some time testing the preamp sections on this amplifier - Sunn used JFETS in the input stages of their design (Concert series). The original part is a "glob top" (preceded TO-92) package - 2N4304. I tried using Fairchild J201's and though they had the same PIN OUT and similar IDSS specifications they produced more 2nd order spurs (without change the circuit) - the PN4303 is still available and seems to give about the same results as the orginal part - FYI

I had to rebuild much of the signal path of the second channel including sourcing a new reverb pan.

Now to dial in the bias for the best distortion/power dissipation at idle.

Thanks for the help.
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