Supertex dn2540 CCS Rset trimmer value

[roger57]

Hi,

Can anyone tell me how they believe this circuit operates? I refer to the DN2540's in the cathodes of the E88CC LTP.

http://richardsears1.files.wordpress.com/2011/06/figure-8-6as7-current-balanced-pp-amp-sch.jpg

There are no external connections for gate drive, so the circuit appears complete. I've tried modelling this in LTSpice, using the Supertex part library, but it appears not to function.

Can anyone point me to a successful application of DN2540 cascoded devices in a long tail pair? I understand that the 10M45 is in the ballpark performance with the DN2540, so a rendition of that would work for me too. I've searched over the forum but have been unable to locate anything complete.

Thanks!

 

[BigE]

Here are a couple. They are copies of the CCS circuits in the letters after the regulator 101 article in audioxpress. The article suggests 60 ohms for the source resistor (Rset) to acheive 38 ma, but the sim shows that 30 is the actual value.... what gives?

you need the supertex.lib from the web site. I can't seem to upload more than one file.

 

[1audio]

For low currents use these cascoded with the Depletion mode Mosfet: Linear Systems || Current Regulating Diodes

They are selected Jfets in specific current ranges. They are not high accuracy but most audio designs should be tolerant of the variations (+/-20% or so- listed on the datasheet). Much easier than fiddling with an IC to do the same thing.