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Old 28th July 2008, 10:33 PM   #21
juma is offline juma  Germany
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Quote:
Originally posted by Zen Mod

use fb arrangement as in inverted OP amp , then you'll loose one cap ;
I don't like that, it messes up the input impedance - especially when you have to put pot/attenuator in front of the preamp.
Also, we want to be consistent with CFB idea - feedback goes to source, not to gate
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Old 28th July 2008, 10:40 PM   #22
Zen Mod is offline Zen Mod  Serbia
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yup ; every path have it's own compromises .....

anyway - here is just as illustration - HK725 , discrete OP with Jfet input ;

possible to use whatever is in drawer

another option - Jfet XblahCSblah BOSOZ ......
again - choice for parts is ...... even BF245C , or my fave J309/310,,cascoded with any TO92/TO126/TO66 critter from drawer ........

I know that all these ideas needs optimisation .... but I'm lazy these days ;
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Old 28th July 2008, 10:49 PM   #23
juma is offline juma  Germany
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(entering Michel Caine mode)

Parts count, old chap, parts count .....

(exiting Michel Caine mode)


You really like LTP, don't you ?
(not a big fan of D. Self type of circuits myself)
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Old 28th July 2008, 11:08 PM   #24
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by juma
(entering Michel Caine mode)

Parts count, old chap, parts count .....

(exiting Michel Caine mode)


You really like LTP, don't you ?
(not a big fan of D. Self type of circuits myself)



me likey there good old SN7 , PSU either shunt reg or without reg but with heavy bleed , da toob scorched with bias ........ with hard cathode degeneration ...... for F5 we don't need mucho gain

or same with both halves of 6DJ8 , with even more miliamps than 6SN7



or make few tricks with J310 :

first stage source resistor biased , then current mirrored drain to next vertical current mirror string .

output in a middle of string .

plenty muscles to drive even Zen amp ,not sissy F5 Jfet input
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Old 28th July 2008, 11:18 PM   #25
juma is offline juma  Germany
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Yeaah, da toobz...
I wasted my youth waiting them cathodes to heat up...
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Old 28th July 2008, 11:25 PM   #26
lineup is offline lineup  Sweden
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Quote:
Originally posted by juma
Here is another idea that I've been playing with. It's based on J. Broskie's Aikido tube design. I used FETs that are cheap and abundant.
--------
no P-channel FETs needed, and IMHO, it sounds good
Heve you ever tried using JFET like Tubes, but in SRPP arrangement ?

It uses almost the input stage of your posted circuit.
But Instead of upper NJFET is pure current source, CCS,
it should be coupled as SRPP ( Shunt Regulated Push Pull ).

SRPP is frequently used in Tube Preamplifier stages.
They are a kind of PUSH-PULL, but with two N-polarity devices.
Because of the similarity between JFEts and Valves
we can try Shunt Rgulated Push Pull for JFET, too.


See my Attachment of a line amplifier.
The bottom 2 tubes are in SRPP.
This gives lower distortion than using your circuit.

But only if you can find one SWEET SPOT, for Shunt Reg Push-Pull.
This sweet spot should be arranged and setup while condering The Load impedance as one parmeter.
At least this is what I read about it

Lineup
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Old 28th July 2008, 11:29 PM   #27
juma is offline juma  Germany
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Quote:
Originally posted by lineup
....
At least this is what I read about it
Lineup

Yes, there's a lot of reading involved...
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Old 28th July 2008, 11:33 PM   #28
lineup is offline lineup  Sweden
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Quote:
Originally posted by juma
Yes, there's a lot of reading involved...
No actually NOOOOO!
You do not have to read about it at all.
Just setup your circuit using 2 N-JFET and use the SRPP way.
Then you listen to the sound and compare.


Forget about reading all stuff !!!!
But be open to try all good ideas.
you may find a goldmine of nice things, if you are LUCKY


am I right or .. Zen Mod
Less reading and more learning by doing. Pleeeeeeeeeeeeeeeeeease
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Old 18th September 2008, 06:31 PM   #29
juma is offline juma  Germany
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Bored by a rainy day I decided to try JFET-CCS-BOSOZ (schematics in attachment) as a preamp for F5. Yes, it has 1k Zout, but that's without significance when driving F5 (100k Zin).

2SK170 are of V type (12mA Idss). CCS gives 20mA. Gain is 6dB (2V/V).
+/- 18V PS is made from F5's PS by means of 7818 and 7918.
Output cap is 1uF MKP + 100nFMKS and it doesn't leave any imprint that I'm aware of.

Preamp is very neutral, nothing is changed in music presentation compared to F5 without preamp, signal is just amplified to level that drives F5 to full power.

I don't know if I like this preamp more than previous one, it's in nuances, so it will take more listening to make a decision. Anyway, circuit is simple, parts are easily obtainable, topology is nice, F5 is light load, it's simple enough to make it p2p, and this preamp sounds better than its' cousin with MOSFETs - what more could a man want to give it a try ?
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Old 18th September 2008, 08:18 PM   #30
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by juma
Bored by a rainy day.........

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