Thread: Valve preamp.
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Old 21st Jun 2019, 6:46 am   #60
Diabolical Artificer
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Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
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Default Re: Valve preamp.

Thanks Peter, I did think of using a CCS and as you said he mentions some of this in his blurb, even with the changes suggested I wouldn't use it because of relative complexity and component count.

I tried this circuit yesterday - see attached - this is the sort of circuit I like, no weird odd value caps, small component count etc. Anyway it worked ok on the 1 x 10 and 1 x 100 range of my sig gen with a quick test, but has a lot of top end. At 10khz amplitude is four times as big as 1khz, I will test it more thoroughly today and change some values on the FB path.

Regarding using FET's, I got a few of the 2SK369 low noise jobbies to try Pat Turners Rocket circuit ( without the paralleled caps!) but after reflection knocked it on the head - too many valves & overly complex. PT built his Rocket amp after reading Secrets of the phono amp stage by Allen Wright - attached. Audiof*ckwitery? It makes sense to use a low noise FET I guess with a following valve stage to get The Tone but most 2SK369/2SK170 phono amps I've looked at lean towards Audiow**kery and treat the FETS as sacred.

Thanks Al, wondered where you got to and how you were. They're ceramic wafers out of a scrap Tektronix 545B scope, used a lot in all the 500 series scopes.
Lasly there's lots of useful circuits in this - http://www.tubebooks.org/tubedata/RC30.pdf

Andy.
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