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More FET noise measurements (for EUVL)
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Old 9th October 2010, 04:02 PM   #11
juma is offline juma  Serbia
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Patrick, you are right about noise - if you want to chase the last nV of it.
Thermally, i find BF862 very easy to handle - gate pin collects the heat and it is always soldered to copper surface that takes the heat away. My prefered range of use is at 100-130mW (10V x 10-13mA) so it's an easy task . Taking into account the availability/price/performance ratio, I personally find BF862 unbeatable.
Of course, I support your efforts and I'm thankfull to Mr. Wurcer for valuable measurements.
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Old 9th October 2010, 04:59 PM   #12
EUVL is offline EUVL  Europe
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The Idss of BF862 is 10-25mA.

Depending on batch, very few of them falls below 14mA, unless you use source degeneration, which adds noise.

If you look at the datasheet in detail, the thermal resistance quoted by the datasheet are based on PCB copper area which is not realistic. So you need to do something else to get the heat out.

Don't get me wrong. I also use BF862 a lot, and I do get the heat out. You only need to look at the B1 Turbo thread.

B1-Turbo on a Chip

But for most, the 2SK372 is a very easy device to use, and is widely available.


Patrick
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Old 9th October 2010, 05:26 PM   #13
PMA is offline PMA  Europe
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2SK370 would be a choice as well, for low noise input stage.
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Old 9th October 2010, 05:47 PM   #14
AndrewT is offline AndrewT  Scotland
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Juma,
considering what I said comparing the f862 to k170, it seems there is no contest with respect to noise. The k170 is noisier.
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Old 9th October 2010, 07:46 PM   #15
juma is offline juma  Serbia
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Quote:
Originally Posted by EUVL View Post
The Idss of BF862 is 10-25mA. ...
Datasheet says so - I bought a batch of 500 and about 95% of them are with Idss in range from 12 to 14 mA.

Quote:
Originally Posted by EUVL View Post
...If you look at the datasheet in detail, the thermal resistance quoted by the datasheet are based on PCB copper area which is not realistic. So you need to do something else to get the heat out. ...
You saw my small adapter PCB for BF862 - with Pd=150mW temperature on the JFET's surface is 18 degrees C above ambient. I consider that quite good.


Quote:
Originally Posted by AndrewT View Post
...The k170 is noisier.
True. We are also aware of some nice MC preamps designed with k170 that produce no noise that can be heard even on highly sensitive speakers. Well, k170 is certainly good enough, but BF862 and k372 are better.
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Old 10th October 2010, 02:32 AM   #16
EUVL is offline EUVL  Europe
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> I bought a batch of 500 and about 95% of them are with Idss in range from 12 to 14 mA.

Then you are lucky.
I had a batch of 500 which was 80% > 18mA.

At least we all agree 2SK372 is better.


Patrick
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Old 12th October 2010, 11:57 PM   #17
EUVL is offline EUVL  Europe
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Some more details of the measurement circuit :

http://www.diyaudio.com/forums/solid...ikoflexor.html


Patrick
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Old 13th October 2010, 10:14 PM   #18
iko is offline iko  Canada
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More FET noise measurements (for EUVL)
Quote:
Originally Posted by EUVL View Post
But for most, the 2SK372 is a very easy device to use, and is widely available.
Patrick
Any place you know of that sells them at prices similar to the BF862?
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Old 14th October 2010, 04:56 AM   #19
EUVL is offline EUVL  Europe
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Ampslab, at 1USD each, min. 20x.
BF862 is cheaper, but noisier.

Patrick
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Old 18th October 2010, 04:23 PM   #20
EUVL is offline EUVL  Europe
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As promised :

http://www.diyaudio.com/forums/solid...ml#post2336629

Patrick
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