Jfet BOZ

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#243
for Zen Mod

Here is what I have. All ASCII I'm afraid....
Click to expand...

No problem with ascii, just use the "PHP" button and :yes:


PHP: 
l Audiophile MC Pre-Pre
=======================


Folks, with just few resistors, one JFET, one output cap you can build a 
step-up device.

   12 Volts regulated or accumulator buffered supply
                     |
                     |
                    2k2
                     |
                     |---------0.47uF-----out------------>
                     |                 |
                   (drain)             |
---in---------(gate)JFET              100k
         |        (source)             |
        100R         |                 |
         |          47R                |
         |           |                 |
-ground--------------------------------------------------

The basic topology is that of the second step-up amplifier by "Maison de 
L Audiophile" of Paris/France.

The first 100R is the cartridge load, which must be adapted for the 
cartridge you use. Using a paralleled 1nF cap also makes the circuit immune 
against RF noise. The 47R resistor in the source is not necessary, if the 
JFET has an IDSS(on) of 2mAmps or less.

As the signals are very sensitive, the voltage must be very clean, a 100 000 
uF electrolytic cap for blocking power supply noise, computer grade 
favourably, is advisable. Suitable JFETS are 2SK170, 2SK240 (double JFET), 
2SK97 (double JFET), sorry only these japanese types are suitable, the 
European BC264 and BF254 and so on do not work here (I tried !).

All resistors must be big metall resistors, e.g. Beyschlag 1Watt, or 
tantalum resistors. No carbon resistors allowed here, tubes addicts.

The output cap is preferably polystyrene or polypropylene or paper-in-oil, 
as you like it, as they are different in sonic balance.

Pacific RIAA Pre - 24V Version
==============================

              o-----------------------------------o------------+24V
              |                                   |
             R2                                  R6
              |                                   |
              |                               D---o---C7---o
          D---o---C1--R3--o--------o------o---G           OUT
  o---o---G               |        |      |   S---o        o
IN   |   S---o          R4        |      R5      |        |
  o   |       |           |        |      |       |        |
  |   |       |        o--o--o  o--o--o   |       |        |
  |   R1      |        |  |  |  |     |   |       |        |
  |   |       |        C2 C3 C4 C5    C6  |       |        |
  |   |       |        |  |  |  |     |   |       |        |
  o---o-------o--------o--o--o--o-----o---o-------o--------o--- 0V

R1 = 100k C1 = 0.47 micro
R2 = 2.4k C2 = 15 nano (ideal C2 + C+ +C4 = 99.3 nF)
R3 =  27k C3 = 15 nano well my copy says 100nF
R4 =   3k C4 = 68 nano
R5 = 100k C5 = 22 nano here its 30nF total
R6 = 2.4k C6 = 6.8 nano
C7 = 2.2 micro

We build the Pre using both the Fet Pre Pre and the Pacific. PSU is 3 X PP3  
NIMH Recharables. The Pre Pre get's it's PSU via a dropper resistor and a 
2,200uF Decoupling Cap (Black Gate or similar) so that 12V are supplied to 
the Pre-Pre.

Later Thorsten

great thread guys, me ordered the missing parts for this thingy today...


cheers, LC
 
#244
mpmarino said:
Batteries might 'be cheating' but could you imagine this pre on batteries hooked up to a 12+12 marine battery mini A - into a set of Altec 19's.

:angel:
Click to expand...
Yep I can🙂 Mark you know, whatever I can imagine. I can do😀 Loads of ppl told me that I was c****, he-he. My philosiphy goes like this: If you can/will build it, go ahead. If not, shut the f*** up!
There are a few of the last category here on the board who think they contribute with something usefull!!😱 😱
Sorry if I stepped on anyones toes😀 Harsh guy, signing out😉

Steen 😎
 
#245
As steen is doing the hard job, I can concentrate on serious listening.
For unhappy few who did not buid the pre : a cat is a very good test instrument. Playing "interview with a cat"/Marcel Brodhaerth, for exemple. Watch the reaction of the cat.


If I am too much OT, tell me , I will be quiet, very quiet, vanishing...
manu
 
#246
Nope I am not doing any hard job, yet!! I just put together the circuit and relied on Mr. Pass's judgement and adjusted the input pots to half resistance😀 He-he that was the easy solution, but what do you expect from the Lucky L..... guy?? Fast and Furious:devilr: I will give it a more serious walkover later!!

Steen🙂
 
#247
steenoe said:
Nope I am not doing any hard job, yet!! I just put together the circuit and relied on Mr. Pass's judgement and adjusted the input pots to half resistance😀 He-he that was the easy solution, but what do you expect from the Lucky L..... guy?? Fast and Furious:devilr: I will give it a more serious walkover later!!

Steen🙂
Click to expand...


Do you have both the input pot from papa drawing and another one at the input for selecting the volume?

Not that there is anything wrong about it, I'm just curious.
 
#248
steenoe said:
I have no idea why you find this surprising???? Please elaborate on that. I was surprised by the sound of a simple circuit like that, but I dont think that is what you are aiming at?? What is your (ahem) aim??

Steen:att'n:
Click to expand...


Well, i tend to take your opinion about sound and in particular Pass circuits seriously. From your unbridled enthusiasm i got the impression this is the best you've ever heard. Should i not be surprised?


Zen Mod

Thanks for posting all the old info.
 
#250
Manu said:
If I am too much OT, tell me , I will be quiet, very quiet, vanishing...
manu
Click to expand...

No problem, just don't get too serious 😀

Hey...I was offline for a few hours and WOw I see that Steen is already listening to his preamp! Congratulations! Steen, are you using the exact Nelson's schematic? Did you change any resistor value?

Judging from Steen's experience, this is really going to be a "diamond" preamp!

We can only :worship: to Nelson!

Thank you guys for the support...now I have to hurry....gotta build that pre!!

Regards,

Vix
 

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#252
Hi,

Sorry Manu. Your experience counts as well. I was mostly interested to know how will Jfet Boz sound with F4. Steen was the first one to try that.
(Ok, Nelson was first....)

By the way, Nelson, are you listening to this combination right now? (even if you have something better, please don't tell us, at least not now!:clown: )

Regards,

Vix
 
#258
Here's my little mess 🙂

I get about 5.1v across the jfets. I went thru about 7 of them to get them close. Are they normally that badly matched??

Anyway - can't try it tonight it's a bit too late:bawling:
 

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#259
analog_sa said:



Well, i tend to take your opinion about sound and in particular Pass circuits seriously. From your unbridled enthusiasm i got the impression this is the best you've ever heard. Should i not be surprised?


Zen Mod

Thanks for posting all the old info.
Click to expand...

I wont go as far as to say its the best I ever heard.
Was I too enthusiastic? I dont know! The easy way for you to find out, is to simply build one for yourself😉 Takes almost 2 hours to get one in the air😎 Its not my fault that Mr. Pass sends out all those very well sounding circuits😀

Vix, I used the values as in the schematic except for the source resistor. Funny enough I was out of 10r's too, so I had to use two 27r's in parallel.
I will try and finetune the circuit this weekend.

Steen🙂
 
#260
mpmarino said:
Here's my little mess 🙂

I get about 5.1v across the jfets. I went thru about 7 of them to get them close. Are they normally that badly matched??

Anyway - can't try it tonight it's a bit too late:bawling:
Click to expand...

Nice work Marino. Not as messy as mine though😀
At some point I had a pair of J-fets with 4,3V and 5,6V, VDS. Quite a difference.

Steen🙂
 
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