Jfet BOZ

Hi,

Recently I bought some 2SK170 Jfets. Yes, the idea is to make Choky's variant of J-fet cascoded CCS-ed BOSOZ...(the one that Steen tested)

But, the first thing I was thinking about is the possibilty to modify the Bride of Zen, by cascoding 2sk 170 Jfet and IRF620. So I guess it would look something like downscaled ZEN V8. I need some help with a proper schematic though.

Choky, If you've got the time, could you please work around this?

I guess there should be an improvement compared to the "normal" BOZ...

Thanks!

Vix
 
Pass 2SK170 BOZ

Nelson Pass said:
Maybe you would like to try this first.
mpmarino said:
That's way too complicated.


You must be joking, mpmarino ;)

It is as simple as it gets!
Most of the time we wouldnt even need an input cap.

My question is only
shouldnt those resistor values be adjusted a little bit?
I mean the Drain resistor, 2k2 and Source resistor, 10 Ohm.

These are contributing to BOTH setting the current in
2SK170 (what variant of 2SK170 is it? They come in colours ... )

But GainV, by bipolar formula is:

Load // 2200 // 2200
--------------------------- = ???
10 Ohm

Say we have a of of 10000 Ohm (10k)
and the voltage gain is 991/10 = 99 ... for a bipolar

Still for a JFET, even at half this value, we get a gain of like 50
Isn't this too much. Or maybe this is supposed to be An input of a RIAA Phono amp?

What current will this variant of 2SK170, with 10 Ohm?


I attach here the nice BOZ schematic.
It is a good starting point for true Nelson type of preamp.
Wuth maybe a few small adjustments, depending of:
- input voltage level
- wanted output level
- source impedance
- load impedance

In attached image, we can see that suggested Voltage supply is 35 Volt.

As with all these simple a Straght forward circuits with minimum components,
we need a Good clean supply.
And Nelson has many such supply circuits.

( the rule is, what you do not put into amplifier itself, you need to provide in the surroundings
- if you want good audio )


Regards
lineup
:)
 

Attachments

  • n-pass_2sk170-boz_1.png
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my first layout

I know this one is simple enough that most people will try it P2P, but I figured this would be a good lesson in Eagle for me.

Anyway, I'm going to etch this and try it out with a regulated (LM317T) psu ... wish me luck, and any recommendations or comments are welcome.

Thanks to NP (Papa) for this :D

It's not labelled, but input is at the top (L&R) and output is at bottom. Large middle hole is +35V and large bottom hole is GND.
 

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Hi Twitchie,

I look forward to your completion and impressions. I'm sure I won't get to it for quite some time. Amongst the majority of the company on DIYA I'm a hopeless newb but I think you may want to make room on the board for 10uf film caps. I'm thinking that with so few parts - selection may be more important.

Please free to tell me I'm wrong and I'll happily crawl back into my hole:xeye:
 
Official Court Jester
Joined 2003
Paid Member
Babowana said:




You just got a great gift from Papa. Congratulations!
I already got Babo Zen that was much bigger than a small gift.
I wonder what Choky would get . . . ^^.


:darkside:

Papa already promised to me one X1000 case ,complete with hsinks
( that dreky box will be probably good enough for my next phono preamp), randomly throttle filled with small/medium/big jfet/mosfet goodies ;

he sez-because weight is slightly under 100 killos ,he will pay for shipping.......there is no need that I worry about trivia like this ........



:devilr:
 
Re: Pass 2SK170 BOZ

lineup said:

shouldnt those resistor values be adjusted a little bit?
I mean the Drain resistor, 2k2 and Source resistor, 10 Ohm.


If am not mistaken, it should be possible to increase the source resistor to get a lower gain. But I am not sure how this would affect the operating area of the Jfet.

Second, is it possible to operate this one from a higher supply voltage (60 v)? I see that 2sk170 max. voltage is 40v...

What if we increase the supply voltage to 60v, Drain and load resistors to 3,9 K and the source resistor to 33 ohms?
I know these are basic questions, but....:scratch: :ashamed:


Babowana said:




You just got a great gift from Papa. Congratulations!
I already got Babo Zen that was much bigger than a small gift.
I wonder what Choky would get . . . ^^.


:darkside:

Diamonds are small. :cool:

:)

Vix
 
Re: my first layout

twitchie said:

I know this one is simple enough that most people will try it P2P, but I figured this would be a good lesson in Eagle for me.

Anyway, I'm going to etch this and try it out with a regulated (LM317T) psu ... wish me luck, and any recommendations or comments are welcome.

Thanks to NP (Papa) for this :D

It's not labelled, but input is at the top (L&R) and output is at bottom. Large middle hole is +35V and large bottom hole is GND.


Here is a PNG image of your PCB suggestion.
I wonder if not The Master had intended source resistor = 100 Ohm
... what I can estimate, using my head only,
this would render a Lineamp with a Gain of like x5 - x7.

10 Ohm here, seems too little,
when the total Drain Lood impedance is like 1000 Ohm.

Gain is set by: 1000/(source resistor) x k
....where k maybe is something like 0.5-0.8

Let's see what comments Nelson himself has to give
( next time he can spare some time for www.diyAudio.com )
before we start decide for our Final Version.
Anyway, one resistor or two are easy to exchange ..
and for these circuits, will hardly be much smoke :D


Regards
lineup
:)
 

Attachments

  • sk170boz_pcb_twitchie-1.0.png
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Manu said:
The 170' are BL I suppose?
Manu


Manu
I dont know if I have 2SK170BL spice model, but I think ....

I know I have 2SK170GR spice models. They are the ones easy-to-find.
And this is the variant of 2SK170 I can easily buy in my country.

This evening I will set up Nelson's circuit in my Electronics WorkBench, EWB MultiSim.
I will post in this thread my findings:
- regarding my optimal values of drain & source resistors.
In Nelson's schematic those are:
- 2k2 coming from power supply
- 10 Ohm ... attached to ground, 0 Volt

I will also present a fourier analys: Level of 2nd 3rd 4th harmonics.
:cool: For one rudimentary No-feedback JFET circuit, like this one,
we can expect some 2nd harmonics and considerably less 3rd harmonics

Regards
lineup :)

=================================
APPENDIX, software used:
EWB MultiSim for FREE download:
MultiSim Download
There is also a free evaluation version from EWB website!
www.electronicsworkbench.com
But this eval. vers. has a almost no audio transistors in spice library.