DIY build of the Pioneer C-21 preamplifier

[mlloyd1]

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/pdf/Series915_preamp_man.pdf

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

mlloyd1

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

 

[ThorstenL]

Hi,

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/pdf/Series915_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

 

[mlloyd1]

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

 

[ThorstenL]

Hi,

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/pdf/SE-100_preamp_man.pdf

Ciao T

 

[rjm]

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.

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?

 

[ThorstenL]

Hi,

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

 

[morrosco42]

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

 

[rjm]

Well, there you go. I just might be building a C-21 replica yet.

 

[Madaudio]

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.