[pddjsteve]

Well, I got my Pimeta basically done last night, and it sounds great so far. The only thing left besides casework is setting up my jfet cascode for class A. I have a bunch of 2N5484 that I measured/sorted for Idss according to Tangent's writeup. Would it be appropriate to choose two that measured 4.3mA as Q2 and two that measured 2.1mA as Q1? I have a couple other matched sets at values between those.

 

[MisterX]

Yup...Q2 must have a higher IDSS than Q1


http://tangentsoft.net/audio/opamp-bias.html

Quote:

The harder way is to buy many of one type of JFET and test the IDSS of each one, sorting them into small groups of JFETs with similar measured IDSS values. Then you pick Q1/Q2 pairs so that Q2 comes from one of the high-current groups and Q1 comes from a low-current group. The exact values don't matter so much, just so long as Q2 is higher in value than Q1.

 

[pddjsteve]

Quote:

Originally Posted by MisterX Yup...Q2 must have a higher IDSS than Q1 http://tangentsoft.net/audio/opamp-bias.html

Thanks! That was the info I was going off, and I'm glad it actually was that simple. I just wanted to double check, because I've been having the worst luck with stuff the last week or so and I don't quite trust my middle of the night judgement

So the current difference between Q2 and Q1 doesn't really matter, as long as Q2 is higher?