MOSFET follower headphone amplifier

[nicoch58]

 

[xrk971]

The amp build is over in this thread. So far, having issues with too much Ids and need to adjust source resistors on bottom half.

http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp-45.html#post4919251

 

[xrk971]

The amp build is over in this thread. So far, having issues with too much Ids and need to adjust source resistors on bottom half.

http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp-45.html#post4919251

Works now. Had a bad wire - sounds pretty good. Need to build second channel now for a real listening test.

 

[didiet78]

Works now. Had a bad wire - sounds pretty good. Need to build second channel now for a real listening test.

Did you matched those Jfet ?

 

[xrk971]

Yes, sort of, I matched them in-situ. After they were installed in circuit, i measured current across each one and they were within 5% (all JFETs from same reel). The outliers, I would remove and pop a new one in until the currents matched. Typically, there was 1 out of 4 that needed to be replaced.

In stereo now. Sounds great.

 

[woody]

In the previous picture of your board didn't you use one of the newer solid polimer caps ?
Is there any reason you changed to other capacitors ? And any reason why you decided
a 5% match was close enough for the jfets ?

 

[xrk971]

In the previous picture of your board didn't you use one of the newer solid polimer caps ?
Is there any reason you changed to other capacitors ? And any reason why you decided
a 5% match was close enough for the jfets ?

That amp has moved to this thread:

http://www.diyaudio.com/forums/head...f862-based-se-class-headamp-without-heat.html

I changed it to use larger value for deeper bass with lower impedance loads. 47R is for 250ohm headphones.

 

[mlackey]

Zout of original circuit

What is the output impedance (Zout) of the circuit in Post #1? Is it 50R?