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Old 1st February 2012, 04:17 AM   #41
mlloyd1 is offline mlloyd1  United States
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Thorsten:

I might be misremembering; what you describe here makes me think of the phono preamp in the old Hafler 915 preamp.
http://www.hafler.com/techsupport/pd...preamp_man.pdf

Curiously, never hear about anyone "cloning" this ...

mlloyd1

Quote:
Originally Posted by ThorstenL View Post
Hi,
...
If you use a 2SK170BL at Idss you get around 40mA/V transconductance... Use a second J-Fet as Active load and you can easily get 1MOhm load, giving a "near DC Gain" of around 92dB, which if you use this 1M Load as LF determinant of the RIAA EQ allows 72dB Gain. Add a third J-Fet as buffer/follower and you are done.
...
Ciao T
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Old 1st February 2012, 11:04 AM   #42
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Hi,

Quote:
Originally Posted by mlloyd1 View Post
Thorsten:

I might be misremembering; what you describe here makes me think of the phono preamp in the old Hafler 915 preamp.
http://www.hafler.com/techsupport/pd...preamp_man.pdf

Curiously, never hear about anyone "cloning" this ...
There are parallels but the Haffler phono uses feedback Equalisation, my suggestions works feedback free...

Incidentally the Hafler SE-100 or 915 Preamp Schematics show very seriously high performance FET Circuitry. It is a shame this stuff is underappreciated.

The designs are by Jim Strickland (ex Acoustat), to who'm I doff my hat in respect, it is rare that we see simple, innovative and high performance circuitry the way he did his designs.

Ciao T
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Old 2nd February 2012, 02:55 AM   #43
mlloyd1 is offline mlloyd1  United States
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i agree. i always liked the 915 line stage preamp, but never had a chance to hear the phono section. i also never heard the SE-100.

mlloyd1
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Old 2nd February 2012, 05:41 AM   #44
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Hi,

Quote:
Originally Posted by mlloyd1 View Post
i agree. i always liked the 915 line stage preamp, but never had a chance to hear the phono section. i also never heard the SE-100.
The SE-100 is basically a 915 with all the electronic jiggery pokery switchery replaced by honest to god mechanical switches:

http://www.hafler.com/techsupport/pd...preamp_man.pdf

Ciao T
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Old 16th February 2012, 07:10 AM   #45
rjm is offline rjm  Japan
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I just wanted to say thanks for the JFET op amp circuit you posted. Back-of-a-napkin it may be but it's sufficient. I get the idea, and certainly the small parts count make it attractive.

Quote:
Originally Posted by ThorstenL View Post
I have a load of 2SK170/2SJ74 pairs selected for this kind of Job.
This is a bit of a problem. I've been looking at the current status of through-hole JFETs and, yeah, it's not looking good: End-of-life, not-recommended-for-new-design, out-of-stock, discontinued, not stocked, part number not found...

Mouser right now is down to about a dozen TO-92 n-channel JFET models that are bone-fide active, not OEL. Everything is "low Rds on for switching applications".

I mean, I'm sure I could track some of these down, at least in personal use quantities, but are there any useful-for-audio JFETs still around if one wants to stick with widely available and easy to source parts?
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Old 16th February 2012, 08:05 AM   #46
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Hi,

Quote:
Originally Posted by rjm View Post
I mean, I'm sure I could track some of these down, at least in personal use quantities, but are there any useful-for-audio JFETs still around if one wants to stick with widely available and easy to source parts?
Nelson (Pass) uses 2SK370 / 2SJ108 which appear current and are similar to the K170/J74 pairing, but use a different process AFAIK, so performance is not identical hence a new number.

They should be close enough for government work though.

Ciao T

Last edited by ThorstenL; 16th February 2012 at 08:13 AM.
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Old 21st August 2012, 08:52 PM   #47
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I own a C21 that got in eBay.
I changed all caps with high quality modern caps
I bypassed in signal path all caps wit polypropillene.
C. 21 is extremely good sounding preamp that gives a run
to preamps costing more than 5000€ including the preamps I own
(Threshold fet 10/e, Coda fet5, Parasound JC2.
Maybe his simplicity is the origin of so good sound.
I like DIY but always keeping in mymind to get a better sound
Out of this target all the chating about transistors, feedback, etc etc
is irrelevant,
By the way the Spectral DMC 10 that I own do not sounds better than
C-21.Is not more defined or delineated is just thinner.
C 21 is more difined , better panorama and specially MORE MUSICAL.
Maybe engineers in Pioneer had also good taste for music
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Old 24th August 2012, 02:22 AM   #48
rjm is offline rjm  Japan
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Well, there you go. I just might be building a C-21 replica yet.
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Old 10th July 2013, 01:27 PM   #49
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Quote:
Originally Posted by rjm View Post
Well, there you go. I just might be building a C-21 replica yet.
If you ever come across a full version of c21's service manual, please let me have a copy.
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