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Old 23rd October 2009, 12:28 PM   #31
juma is offline juma  Germany
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Quote:
Originally Posted by ucciopino View Post
....
Well, then this should be the circuit in accordance with the PCB?....
Thanks Giuseppe,
yes that's the circuit - there's an error on the sch. - C14 (in the +V shunt) is the wrong way around but it's OK on the PCB.
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Old 23rd October 2009, 03:06 PM   #32
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Originally Posted by juma View Post
Thanks Giuseppe,
yes that's the circuit - there's an error on the sch. - C14 (in the +V shunt) is the wrong way around but it's OK on the PCB.
True ...... thanks Juma.
Could you make a sound comparison with other pre NP?
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Old 23rd October 2009, 06:22 PM   #33
juma is offline juma  Germany
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Originally Posted by ucciopino View Post
True ...... thanks Juma.
Could you make a sound comparison with other pre NP?
I suppose I could - but I don't want to
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Old 24th October 2009, 08:28 AM   #34
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Originally Posted by juma View Post
I suppose I could - but I don't want to
Ok ..... I realized

Last edited by ucciopino; 24th October 2009 at 08:35 AM.
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Old 24th October 2009, 04:37 PM   #35
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Juma have you used bf selected?

The 470r (grid stopper) is only in the adapter ...... and not in a preamp PCB?

thanks
Giuseppe.
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Old 25th October 2009, 02:33 PM   #36
juma is offline juma  Germany
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Quote:
Originally Posted by ucciopino View Post
Juma have you used bf selected?
No, they are all pretty much close in Idss (12-14mA, most of them about 13mA)

Quote:
Originally Posted by ucciopino View Post
The 470r (grid stopper) is only in the adapter ...... and not in a preamp PCB?
Right
You can use lower value for gate stopper, Scott Wurcer says that even ferrite bead is enough
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Old 25th October 2009, 03:45 PM   #37
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Originally Posted by juma View Post
Scott Wurcer says that even ferrite bead is enough
Ferrite in audio applications? .... Never use it for distorction and dinamic reduction.
On the Psu cable? ...... Never.

thanks Juma.

Last edited by ucciopino; 25th October 2009 at 04:03 PM.
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Old 10th November 2009, 10:11 PM   #38
tessier is offline tessier  Canada
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Originally Posted by juma View Post
Intrigued by good reports (Scott Wurcer and EUVL) on BF862 JFET I also got some. The idea was to build a preamp based on JBOZ and B1 concepts with gain of 2 (enough to drive F5) and ability to drive 5K next stage impedance. Also, 6-7 V of undistorted output signal is needed.
This is what I ended with and it's all I hoped for, it sounds great, better than 2sk170 in same topology - I suppose it's due to much higher transconductance and smaller parasitic capacity. The only "problem" is that BF862 is an SMD part but that's easily cured with small adapter PCB.
This is the preamp and PSU schematic:
Hi

I have a bunch of 2SK170.

Can I use my 2SK170 as drop-in replacement of the bf862, in this bf862 preamp or do I need somes mod to do ?


Thanx

Paul
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Old 11th November 2009, 11:54 AM   #39
juma is offline juma  Germany
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Originally Posted by tessier View Post
Hi
...Can I use my 2SK170 as drop-in replacement of the bf862....
Yes, if you have 2sk170V. BL grade needs minor adjustments (because of lower Idss). If your JFETs are GR grade only, you can use them here too (with adjustments and/or paralleling them maybe) but with sub-optimal results.
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Old 11th November 2009, 03:04 PM   #40
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Alas, Old Age (and its consequences) is keeping me from this project. If you go to post #10 you will see a strip of miniature PCB's made for the BF devices used in this project. I have one of these strips and the BF862's to go on the strip.

I have made numerous attempts to solder the devices to the strip but poor eyesight and shaking hands keeps success at bay. Believe me, this is not a one or two attempt scenario but a concerted daily ongoing trial and error thing that creates suicidal tendencies!!

There are 14 pads on the strip as shown in post#10 . What I seek is an individual with the ability and courage to solder these together,with a barter deal of some sort to show my gratitude. It would be best if that (wonderful) person were in the US to keep it more manageable.

I can furnish solder and a flux pen for the job.
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