Self type 3 EF (hybrid triple)... any pointers ??

[ostripper]

I'm still at it ... trying for more power , better devices , and keeping it simple and reliable. While reading a little Douglas self (amp handbook), I ran across this statement :

"type 3 is as equally good as type 2 at reverse biasing the output bases, and may give even better HF turnoff as the carriers are "swept" away by a higher resistance connected to a higher voltage" "this remains to be determined..."

This seemed to deserve more investigation , and the best test was my new triple using njw0281/0302's (drivers) - njw21193/4's (outputs). The 21193/4's have HUGE dies (hefty Cob) , lower gain/Ft and killer SOA. After I plugged in the models for the 21193/4's , I noticed more Xover distortion even as I was driving them with smaller OP's. I then tried the type 3 driver config (1st attachment). This seemed to run most nicely in class A (attachment 2) , and to my surprise halved my THD20 ,plus reduced (considerably), the Xover artifacts being fed back via NFB.

This also brought up the question of model quality as the NJW21193/4's are newer to-3p ON devices and the models, (like the fairchild KSA's) seem to show the device in great detail (Cob , saturation "effects") versus "stupid" models - (mje340/50).

It was cool that the simulation showed what Mr. self predicted ,..smoother Xover from 10k up , rounded corners in the Xover region at HF ,and a nice class A driver region (70ma average).
Has anyone built something similar ??? I'd love to hear about it .
OS

BTW , WOW... what a improvement in the forum !!!

[homemodder]

Hi Os
That looks like a triple with the driver stage biased to the rails. It does show improved figures, scheme used by electrocompaniet and some others. Electrocompaniet goes further and uses a current source instead of resistors to bias which improves things further if youd like to try. Adreia Scafolli a Italian designer goes even further and biases the predrivers like that too, all show improvements THD wise, as for the sound youd have to try and listen to the sound of these schemes. The one you showed but using current sources gives a mighty kick in the bass but your amp better be quite fast or the bass will overwhelm. Carlos the destroyer didnt like it, I found no problems with it except the rest of the amp should be fast or the mids will sound slightly muddled.

[ostripper]

[QUOTE]Carlos the destroyer didnt like it/QUOTE]

That is a good sign !!

scheme used by electrocompaniet and some others. Electrocompaniet goes further and uses a current source instead of resistors to bias which improves things further if youd like to try. Adreia Scafolli a Italian designer goes even further and biases the predrivers like that too, all show improvements THD wise,

Ahhh, others have tried it... must check that out!
The FFT (attachment 1)shows the H3-7 almost goes away , even at full throttle. This looks a little like a diamond buffer in theory. I must say besides the already mentioned effects , the type 3 triple is far more stable as well.
OS

[homemodder]

Theres plenty one can do with output stages to improve the figures, use current mirrors instead of 2 current sources to get the currents in the collectors very close and it will show further improvement or even better use the current mirors but change the drivers to cfp s, I couldnt get this stable with BJTs but with mosfets it works great.

[roender]

Originally Posted by ostripper

This looks a little like a diamond buffer in theory...
OS

This topology is much better than DB where a CCS limited driver current is available for driving the output BJTs

[roender]

Originally Posted by homemodder

... even better use the current mirors but change the drivers to cfp s, I couldnt get this stable with BJTs but with mosfets it works great.

I was able to get this run stable, CFP drivers loaded by CCSs from opposite rail, and it sound very very good! The only downside is the complexity and the thermal dissipation from drivers and CCSs, because you need at least 100mA through each driver to run stable!
From my POV, this is the almost perfect class B output stage, as per Self OPS class definition.

[ostripper]

Is this what you guys meant ??? (attachment 1)

Roender - The only downside is the complexity and the thermal dissipation from drivers and CCSs, because you need at least 100mA through each driver to run stable!

In a non-CFP mode (EF) , I ran at 35ma with great results. Perhaps the CFP ,with local FB , contributed to this instability. As far as complexity and extra dissipation .. 2 more mje15032/33 drivers and 4 diodes is not bad !! 140ma extra current would be "swamped out" by the 4+ pairs of beasty 21193/4's.

Roender - This topology is much better than DB where a CCS limited driver current is available for driving the output BJTs

It is looking a little more "krill - ish".. BTW , at least in simulation , the CCS's dropped the THD20 in half again ...
OS

Edit : I thought it out , I could still use my 0281/0302's as the actual drivers, while using the mje's as separately heatsinked CCS's. That would make the CCS's independent of the main EF's Vbe..

[Rafael L]

Hi OS

I tried this topology "rail-to-rail", problem is requiring much current, you check Ib of output TRs, After you compare with Ib drivers.
PS: I used for the pre driver...

[ostripper]

by raphael - I tried this topology "rail-to-rail", problem is requiring much current, you check Ib of output TRs, After you compare with Ib drivers.

does not seem too bad ,If you use "fat" drivers (outputs... njw0281/0302)

at 4r /400w (see attachment 1) , the CCS's (green/light blue) are steady at 35ma +-2ma -the mje15032/33's with a small PCB 10watt/c heatsink would be slightly warm at most (happy ,cool transistors).

The drivers Ie (combined Ib of all outputs - Red/blue) is much higher , with a minimum 30ma ..peaking to 88ma. The drivers are outputs and will be on the same heatsink as the main outputs so this is not a real issue.

(pink/grey) is just the current (Ib )to one pair of outputs. The THD improvement (attachment 2)is the best I've seen at 4R and even holds at 2R !! No wonder the Electrocompaniet amps have such high damping factors !!
At these levels , a standard type 2 EF will drop dead (beta droop)...

The Ib of the drivers is (attachment 3) is less than 1ma , no sweat for the ksa's (predrivers) ,no heatsinking would be required.

OS

OS

[Lumba Ogir]

ostripper,

Self type 3 EF (hybrid triple)... any pointers ??

Yes, it gives you 3 (hybrid triple) bastantly nonlinear base-emitter junctions.

roender,

This topology is much better than DB where a CCS limited driver current is available for driving the output BJTs.

I cannot agree on that for a second.