Rollover - A Decent Amplifier with JFET in and MOSFET out

[lineup]

Uses LSK189 for input.
Buy at mouser.com: https://www2.mouser.com/ProductDetail/Linear-Integrated-Systems/LSK189-TO-92-3L-BK?qs=T%2BzbugeAwjjUrS49wFak%2Bw==
Uses ECX10N20 and ECX10P20 for output.
Buy for example at: https://gb.profusion.uk/uk/audio/transist/lateral-mosfets

The input JFET pair can be other JFET, too.
Bias in output is set to 300mA.
THD is 0.00026% with the LSK189.

 

[jxdking]

3 differential stages, may be too much for my tast.
LSK189 can withstand 60V on paper. Did anyone tried it on 100W amplifier, as the input stage? Sometimes, transistors behave weird around their limits.

 

[PMA]

Loopgain analysis, phase margin and gain margin should be posted.

 

[njswede]

What's the deal with the unequal gate stoppers?

 

[minek123]

What's the deal with the unequal gate stoppers?

Post in thread 'LatFet Amp Based on Philips AH578'

2021-02-09 11:20 pm

>tcd1963

1) Exicons have Zeners built in. No need for gate protection Zeners here.
There were several discussions about this here on DIY, and it was confirmed several times already.

2) The role of caps on GS is to equalize input capacitance on both devices (P and N).
Usually N device has lower capacitance than P device, so some designers ADD extra cap on N device to make them equal.
Example: Rod Elliot's P101.
If capacitances are not equal - that may cause oscillations.

Another way of dealing with this issue, is by using DIFFERENT gate stoppers, using formula RC = constant, where R is...

• minek123

 

[njswede]

That was fast and crystal clear. Thanks! I’ve never worked with LATFETs…

 

[minek123]

Same applies to hexfets...

 

[njswede]

Ok. You rarely see that in schematics, though. Or have I just missed it?

 

[minek123]

Most popular hexfets (IRFP240/IRFP9240) have very similar Ciss, so there is no need for different gate stoppers.
With some other fets that might be not the case...
E.g. Onsemi FQA N/P fets differ more.

 

[njswede]

I guess that's why all the IRFP(9)240-based builds I have filling various rooms with music haven't blown up yet. 😀 So I wasn't completely wrong in my initial statement, since the difference in capacitance is negligible if you stick to "bog standard" FETs. Still learning all the finer nuances of component selection...