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Clone preamp section of JC-120
Clone preamp section of JC-120
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Old 15th September 2018, 03:10 AM   #11
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Quote:
Originally Posted by john65b View Post
I vaguely remember that the 2SK170 should not be used over 18 vdc rail...hmmm.....
Rated 40V breakdown.

Gate current WILL rise over a few Volts. In some audio circuits, that matters. In this one, it does not.

I'm not gonna offer any opinion on JFET substitution. If you know basic amplifiers, you can probably figure how to re-bias. If you have to ask, it may get frustrating.
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Old 16th September 2018, 03:30 PM   #12
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The 2sk117 came in different IDSS classification Y: 1.2~3.0 mA, GR: 2.6~6.5 mA, BL: 6.0~14 mA
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Old 16th September 2018, 05:10 PM   #13
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OK, so I left the three gain stages 2SK-117 GR, and put in the 2SK-170 GR in for the two buffers...

Just gotta make up the tone stack / volume pots now...
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Old 28th September 2018, 06:27 AM   #14
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OK so I have the preamp all soldered up and looking to supply the voltage from an ICEPower 200ASC 47VDC hanger header. I have quite a few 1N5354 17V 1W Zeners...can I do the following assuming I would only be drawing 10 - 20ma:
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Old 28th September 2018, 01:38 PM   #15
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Whoops, meant this...
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Old 29th September 2018, 03:59 AM   #16
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Yes.
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Old 3rd October 2018, 01:46 PM   #17
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Built the pre and it sounds about as clean and quiet as I ever heard. Me likes!

Only one issue - too much GAIN!. I know I have a 1 Meg Linear volume pot, and have a real hard time getting past 1 with bleeding ears... I don't think changing it to a Log pot would do me any good with all that gain. I am thinking of pulling Q4 or modding Q4 to reduce some of the gain...any thoughts?

Hate to bastardize a known loved and proven design, but maybe the output section of the real JC-120 NEEDED all that gain to operate correctly? Clearly I don't.

For the hell of it, I put this JC Clone preamp into the Amp input of my effects loop of my Fender Hot Rod Deluxe and I was floored! This thing ROCKS.
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Old 3rd October 2018, 06:53 PM   #18
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The "Audio taper" pot will get you off "1".

This preamp is made to go to a POWER amp, not an effects loop.

Yes, in many setups Q4 may not be needed/wanted.
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Old 3rd October 2018, 07:05 PM   #19
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Understand, guitar into preamp, preamp out into amp in connection on effects loop. I do not have the entire preamp in the effects loop. I am bypassing HRD preamp section using jc connected this way.

I will remove Q4....thanks!!
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