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Vix 5th June 2007 04:11 PM

Jfet BOZ

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...



Nelson Pass 5th June 2007 08:37 PM

2 Attachment(s)
Maybe you would like to try this first.


mpmarino 5th June 2007 08:53 PM

That's way too complicated.


Vix 5th June 2007 11:23 PM


Originally posted by mpmarino
That's way too complicated.


Yeah, imagine this preamp combined with an F2 lite: the most "complicated" integrated ever made...hehehe... it strikes me as E=mc2 hehehe, too complicated :D

Just kidding, I didn't even think that 2sk170 could do a job alone!

Thanks Nelson!!!:worship:

lineup 5th June 2007 11:39 PM

Pass 2SK170 BOZ
2 Attachment(s)

Originally posted by Nelson Pass

Maybe you would like to try this first.

Originally posted by mpmarino

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 )


stefanobilliani 5th June 2007 11:53 PM

yeeeeaaahhh ! I will try this tomorow !


twitchie 6th June 2007 01:30 AM

50 Gain = F4 heaven
I will try this too ... eventually :D :D :D

mpmarino 6th June 2007 01:44 AM

Re: Pass 2SK170 BOZ

Originally posted by lineup

You must be joking, mpmarino ;)


Ya think? :)

please note the :clown: smiley in my post.

But can this thing really give good audio? I gotta try it too.

Should we have a groupbuy on the perfboard ? :clown:

Babowana 6th June 2007 01:50 AM


Originally posted by Vix

Thanks Nelson!!!:worship:

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 . . . ^^.


twitchie 6th June 2007 04:43 AM

my first layout
2 Attachment(s)
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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