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Old 24th October 2011, 07:57 PM   #1
tmblack is offline tmblack  United Kingdom
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Default Line preamp for JLH/PLH?

I'm looking for a line preamp for a receiver, and the ouput amp will require a single voltage supply, it maybe a JLH design or not.
It should run on 12V (no -12V), use up to 3 transistors and be single ended and have gain up to 20x.
So BOZ is out, way too high a voltage and current.

Any good circuits from Threshold/NP/ to diy ideas?

Last edited by tmblack; 24th October 2011 at 08:02 PM.
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Old 25th October 2011, 11:00 PM   #2
tmblack is offline tmblack  United Kingdom
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I'm starting with a single BJT CE circuit with no bypass capacitor on the emitter resistor.
Not bad, but hums and not as much detail as even an op amp.
Am I asking too much from a single voltage power source?
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Old 26th October 2011, 05:12 AM   #3
Zen Mod is offline Zen Mod  Serbia
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NS10
or J310 BOZ ( search for Juma's posts )

then you'll find his BF862 preamp , too
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Old 26th October 2011, 09:16 PM   #4
tmblack is offline tmblack  United Kingdom
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Which do you like better?
I think the NS-10 should sound smoother and the J310 BOZ or k170 is brighter with more distortion.
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Old 30th October 2011, 11:26 AM   #5
Zen Mod is offline Zen Mod  Serbia
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they're different

build both and decide
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Old 31st October 2011, 05:57 PM   #6
tmblack is offline tmblack  United Kingdom
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K170 BOZ sounds like a little gem.
Solid bass, brash cymbals.
With Idss=6ma,17V in original circuit, I get almost all 2nd harmonic distortion 1% @0.3V output with 1kHz signal.
Should be very good for guitar preamp as well!
But I want less distortion.
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Old 31st October 2011, 06:56 PM   #7
knutn is offline knutn  Norway
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Maybe you should try it with "indirect feedback"...Indirect feedback with FETs
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Old 31st October 2011, 07:17 PM   #8
tmblack is offline tmblack  United Kingdom
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Very interesting design knutn.
Have you built one up? And with source resistors?
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Old 31st October 2011, 07:23 PM   #9
knutn is offline knutn  Norway
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No, I haven't, but I would think it is worth a try. Alex Nikitin (x-pro) has tried it. Dependent on matching, it is wisely to use small source-resistors. The output is high-impedance, so you will also need a source-follower.
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Old 1st November 2011, 04:37 PM   #10
tmblack is offline tmblack  United Kingdom
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I built the variations of JFET BOZ, first with feedback to reduce gain.
Tighter bass, treble still too crisp.
Then added JFET current source in place of drain resistor.
Even better bass, treble better but still too crisp/harsh.
Distortion is mainly 2H 0.1%.
Good but I like to get rid of harsh treble.
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