DEF Amp

[Nelson Pass]

I am going to start this thread around the circuit shown at BAF 2016,
seen at the end of the talk on the video, and attached here in simplified
form.

I am calling it DEF, which stands for Depletion / Enhancement Follower.
It is a self-biasing push-pull output stage which has some interesting
characteristics, not the least of which is low temperature drift which allows
stable undegenerated operation.

 

[Zen Mod]

oh boy ...... here we go again

I'm outa here and outa electronics

not just that I can't keep up with Papamps .......... what's more important - I can't keep up even with just 2% of kwayzee Papawittyness

 

[Dennis Hui]

Watching this with great interest. Thanks Papa!

Dennis

 

[xrk971]

Very cool. Thank you for the new toy Mr Pass.

What parts can you recommend for the interested student to try out at home? The video shows a voltage divider on the gate of the P channel to balance offset. What values go there?

 

[riksu]

Superb

 

[Soundhappy]

Papa go from to
😀

 

[needtubes]

...I am calling it DEF...

Eh?? 😛

Very interesting, though it will be a challenge to find enhancement P-channels whose Vgs matches that of available depletion parts... The IXYS parts all hang around -2V for reasonable bias (<2A), so maybe the 2SJ201 could work. The USCi and Infineon JFETs all require very negative (<-7V) bias, though. Perhaps, once again, the Semisouth part is just special...

 

[dimkasta]

An externally hosted image should be here but it was not working when we last tested it.

Thanks for all the fun 🙂

 

[wdecho]

Some of you young whizzes fill in the blanks with some available parts and I will build. I already have some heatsinks, 20V transformer and PS section ready to build while waiting the BAF and a buildable project.

 

[rideht]

Great, thank you so much, i am interested in this 😀

 

[flocchini]

Thanks Nelson

I knew there was a reason to hold on to those R085s 😀
Standard PSU is already available 🙂

Thoroughly enjoyed your talk. As always learned a tremendous amount and it was a real pleasure to listen to this amp

 

[2 picoDumbs]

oh boy ...... here we go again

I'm outa here and outa electronics

not just that I can't keep up with Papamps .......... what's more important - I can't keep up even with just 2% of kwayzee Papawittyness

Papa is evil.

Hahaha

 

[vallickad]

Can't we do with a depletion mode mosfet?

 

[Soundhappy]

@ Mr Pass

In follower V2 resitors help selfbiasing for unmatched part's
do they resistors other function in the same time ?
Example schade feedback on enhancement IRFP240 for triode like character ?

 

[2 picoDumbs]

Source follower not common source

 

[Attila I]

maybe this combination could work?
http://www.mouser.com/ds/2/205/Viewer-707752.pdf
and
http://www.mouser.com/ds/2/205/Viewer-707752.pdf
they are as close (vgs-wise) as i could find at a quick search
cheers a.

 

[Zen Mod]

two same links/pdfs

 

[Attila I]

sorry!!!
http://www.mouser.com/ds/2/205/DS100025B(IXTA-TH-TP96P085T)-238149.pdf

 

[Antoinel]

@ Mr Pass

In follower V2 resitors help selfbiasing for unmatched part's
do they resistors other function in the same time ?
Example schade feedback on enhancement IRFP240 for triode like character ?

Hello soundhappy. You made an interesting point. A follower using an N device which has a pentode-like characterisic [R085], and P- device which has a triode like characteristic; be it a Schaded FET or a SIT; say 2SJ28. What will the resultant subjective sound be due to mixing a pentode and a triode characteristics?

 

[EUVL]

...... It is a self-biasing push-pull output stage which has some interesting
characteristics, not the least of which is low temperature drift which allows
stable undegenerated operation.

The low temperature drift only occurs when the Id-tempco of the PMOS is smaller than that of the NJFET, correct ?

Am I right in saying that it will have more noise than e.g. a Source Follower using a matched pair of NJFETs ?


Patrick