Jfet Bosoz?

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Nelson Pass

Nelson Pass

The one and only
Joined 2001
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It has a tremendous amount of potential.

While simply hooking up a 2sk389 in that topology actually
works well, it is easy to envision a fully cascoded and
constant current sourced version, with output followers
if you want to "gild the lily"

If there is any enthusiasm, I'll go dig up some of my curves and
get back to you next week.

:cool:
 
apassgear

apassgear

Member
Joined 2002
Nelson Pass said:
It has a tremendous amount of potential.

While simply hooking up a 2sk389 in that topology actually
works well, it is easy to envision a fully cascoded and
constant current sourced version, with output followers
if you want to "gild the lily"

If there is any enthusiasm, I'll go dig up some of my curves and
get back to you next week.

:cool:
Click to expand...


I for one would be very intresded in seeing such topology in action. Any posibility that you could post also a schematic? May be this is asking too much :xeye:

Thanks very much Nelson :cool:
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
You can chew on this if you like...

:cool:
 

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Zen Mod

Zen Mod

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Joined 2003
zenmod.in.rs/
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Vix said:





:) Almost. I wanted to use resistors instead of CCS. Just keep the gain Jfets. How could we call this circuit. Bride of F4? :)
Click to expand...


really depends on your power needs with F4.
if you need smaller swing,then resistors are good ;
for bigger swing you need CCSes and even higher PS voltages......and then even cascoding of jfets.

B200 still?
 
Vix

Vix

Member
Joined 2003
Zen Mod said:
B200 still?
Click to expand...

Yes, it's love and hate relationship. At the moment I put them in ML TL boxes previously used for Fostex FE206. That was Martin J.King project 5. http://www.quarter-wave.com/Project05/Project05.html

I used to fill the port with foam, (without it was sometimes boomy). So it worked more like sealed box, at least until I make my mind for an OB. On the other hand, Fostexes are waiting for a BIB. As things look now, I am going to have two setups, one with B200 's, OB in one room, and a BIB with FE206 in another. F2 is fine with B200, nice for easy evening listening, but not louder. ZV9 is better, overall. I am also using a pair of B&W's 601, with two sealed 12" sealed subs, just for reference, but I prefer the sound of fullrangers. B&w's are more calm, but sometimes boring.

Short explanation of the "items" on a picture: Top: ZEN V9 (used to be zen V3). CD -player: Rotel RCD-02. Below that is what looks like
JVC equalizer. It is not. It's a BOZ in a new enclosure. On top of it is a chocolate can that houses an active X-over for the two 12" sealed subwoofers. They are powered by a smallish amp at the bottom (looks like a satellite receiver, in fact is was a satellite receiver until I put an LM3886 in it).

Overall, I am getting good sound out of my system, but feel that with a little more work, it could be modified to sound better. Somehow I get an impression that, apart from the speakers that did not get appropriate "home" yet, BOZ is the "bottleneck". That's why I was considering building another preamp. I was wondering about BOSOZ, then almost decided on Aleph P 1.0 and then...this circuit:scratch: :confused:

So, most probably, this preamp would drive ZEN V9 with B200 on OB, but it would be nice to know that is has enough capacity to drive F4 in the future. Who knows....

Sorry for such a long post that appears to be OT, but I wanted to let you know what I use at the moment and what I'd like to do, so it could be easier for you to give a proper advice.

Big thanks to all of you, specially to Nelson. I could have never imagined that learning about amplifiers could be so motivating.

Regards,

Vix
 

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J

jupiterjune

Member
Joined 2006
Nelson-

I would love to see some measurements -- especially on a cascoded jfet BOSOZ. I fooled around with it for more than a year.....but gave up on it for various reasons (unbalanced to balanced conversion, implementing volume control for 5.2 channels)

To my ear, it sounded better using resistors for the CCS( 72v rails, 3000 ohms per CCS). No follower.

Using Jfet CCS's sounded similar to the resistors, but the "classic" CCS using a small signal bipolar transistor and a mosfet sounded edgy. I would be curious to get see if the meter shows a difference.....

I just drilled a few holes in my AudioXpress boards and plopped them in.
 

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G

GRollins

Member
Joined 2001
I have done a bit of fiddling with current sources versus resistors. Yes, sometimes a resistor sounds better, specs be damned. As for why, I'm not certain. I have long held a suspicion that part of the problem is high frequency compliance problems in current sources. A resistor, at least a decent one, is going to give pretty much the same performance at any reasonable frequency.
In practical terms, a resistor of 5-10k is usually sufficient to get good results from something like a differential. If you want to use a higher resistance you will get better performance still, but at the expense (sometimes) of having to provide a higher voltage rail.
The main problem you run into is when you need a lot of current. By definition that means a low resistance, which tends to negate the things that a current source is supposed to do. You also start burning a lot of power in the resistor.
Like many things, you have to think it through. In some cases a CCS is the best solution. In others, a resistor does as well...sometimes better.

Grey
 
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