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Old 4th December 2009, 09:46 AM   #1
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Default Bride of Zen as a preamp for F2?

hi guys,
i just finished a pair of Sachiko speakers (fostex FE206E in a BLH) and am going to build an F2 for them. i also need a preamp, and am wondering if the BOZ is a good match? will there be any impedance mismatch?
thanks
mymindinside
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Old 4th December 2009, 05:44 PM   #2
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Hi,

Years ago, I built the BOZ, but with some slight modifications to the power supply. Very nice sounding preamp.

I never used the BOZ PCB I got from AudioXpress.com and right now I've almost got a cascode version of the preamp working using the stock PCB. It uses 4 BF862 JFETs cascoded with an IRF510 Mosfet per channel.

I accidentally adjusted the bias potentiometers wrong which put too much voltage across BF862 JFETs and fried all of them.

It's kind of a G.Rollins SSTART preamp, but biased differently with different JFETs and it uses voltage feedback. Measures nicely in SPICE ... should sound good, but we'll see.

I'll post the schematic later, when I have time if you like?
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Old 5th December 2009, 05:39 AM   #3
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yes please...that would be great
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Old 5th December 2009, 05:45 AM   #4
shaan is offline shaan  India
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Have you considered the DoZ pre? I am using it and is quite a great sounding preamp for class-a designs. One drawback, it does not have comlementary inputs, only non inverting. It's a current feedback pre so is exceptionally fast too! it's made from cheapest parts available... see if u can give it a try. Simulations shows flat response up to about 300MHz.

Click the image to open in full size.

The dual supply version is here-> Minimalist Discrete Hi-Fi Preamp
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Last edited by shaan; 5th December 2009 at 05:48 AM.
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Old 5th December 2009, 05:49 AM   #5
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hey shaan,
you are based in india aren't you?did you source the semiconductors for this locally?how much did the project cost you? did you do it p2p or on a pcb?
what poweramp are you driving with this?
i just need a basic pre for my F2.

cheers
mymindinside
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Old 5th December 2009, 06:18 AM   #6
shaan is offline shaan  India
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Quote:
Originally Posted by mymindinside View Post
hey shaan,
you are based in india aren't you?did you source the semiconductors for this locally?how much did the project cost you? did you do it p2p or on a pcb?
what poweramp are you driving with this?
i just need a basic pre for my F2.

cheers
mymindinside
Yes ALL semiconductors shown in the circuits are commonly available, sourced locally. Two of the preamps cost me about Rs.300(quite cheap isn't it?). I made them on dot board. I am driving a pair of MOSFET follower with them. But the preamp can be used for any kind of amp/power followers.
And if you really need a "basic" preamp for your F2 then this is the exact thing you are looking for. Plus, its performance is on par with other exotic preamps. Highly recommended!
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Last edited by shaan; 5th December 2009 at 06:20 AM.
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Old 5th December 2009, 06:41 AM   #7
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sounds good shaan will try it out on breadboard and can make it neater if it is good...
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Old 5th December 2009, 06:43 AM   #8
shaan is offline shaan  India
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Old 5th December 2009, 07:54 AM   #9
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Hi,

Here's the circuit, as modeled using the Linear Systems LSK170C, though I'm actually using the BF862. I've haven't got it working again yet since I fried my JFETs last time. So, this is an untested and not listened to circuit. I plan on getting it wired up again soon maybe this week.

Click the image to open in full size.

That DoZ looks nice and is simpler and easier to wire up. I might also try that. Thanks Shaan.
Attached Images
File Type: png Cascode_BOZ2.png (4.5 KB, 571 views)

Last edited by Johnloudb; 5th December 2009 at 07:58 AM.
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Old 5th December 2009, 01:30 PM   #10
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Hey mymindinside,

The highgain BOZ is totally wrong as F2 has a sensitivity of below 1,5Vrms.

What is the output of your source?

It might be enough with a volumepot at the input, if you only run a CDP.
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