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preamp cable ? fet ?
preamp cable ? fet ?
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Old 27th January 2003, 03:30 PM   #1
partyjups is offline partyjups
diyAudio Member
Join Date: May 2001
Location: Denmark
Question preamp cable ? fet ?

I found this E. page . http://www.till.com/articles/PreampCable/

And I want to build a cable. I coudent get the fet at my local dealer he said that its an old type.

Does any one know witch fet will be best, most low noise.

for that type of circuit ??

If any idear, or even a better circuit.

I'll be happy to hear from you.

thanks jc dk.
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Old 27th January 2003, 09:21 PM   #2
P.Lacombe is online now P.Lacombe  France
diyAudio Member
Join Date: Jul 2001
Location: Orleans, France
Try 2N5457...

Regards, P.Lacombe
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Old 29th January 2003, 02:21 PM   #3
TheFettler is offline TheFettler
diyAudio Member
Join Date: Sep 2002
Location: south yorkshire, UK
partyjups ,

I have built this circuit ( or at least a very similar one ) using a 2N3819 j-fet in place of the J-201.

my observations:

don't expect much gain ( if any! ), the forward transconductance of the 2N3819 is about 5.5mS ( the 201 is even worse at <1mS) , so with a bit of luck you may get 3dB or so, depending on your resistor choices.

The thing works brilliantly as a high impedance buffer - you can increase the input resistor beyond 3Meg if you really want a high impedance input !

Don't try to drive the thing from much more than 12-15v if you use the 2N3819 or you'll risk it breaking down, some J-fets's will take a higher voltage drive. watch this if you are using Phantom power from a mixer board 'cos the standard level is 48v so you'd need a zener/resistor/cap to limit this.

the sound quality with the 2N3819 is quite impressive, I use it as a buffer for the expensive pickup in my acoustic guitar and it is completely noise-free when run off a 9volt battery.

you can get higher gain at the expense of a bit of noise and a slight hi-frequency roll-off if you bypass R3 with a cap of around 1 - 2 uF.

If you need more gain, try using the J309 which has a forward transconductance of about 10 mS

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