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revintage 20th March 2009 12:52 PM

Three Pass-style sourcefollowers
2 Attachment(s)
These are the three versions:

Aleph style
kenpeter style
Lars PLH style

I am a little confused as they donīt sim as I thought they would.

The third one handles more load and also has the lowest 3rd order harmonic.

Fourier isnīt fully reliable in Spice but when comparing like here it usually can point in the right direction.

Can supply *.asc if anyone is interested.

Babowana 20th March 2009 01:01 PM

Thanks for the post.
All are very interesting.


revintage 20th March 2009 02:54 PM

2 Attachment(s)
Forgot the fourth:

Zen style

This one is SE, the others are PP capable of higher output power.

kenpeter 20th March 2009 06:04 PM

I tend to think of Aleph mostly as a base follower.
And to somewhat lesser extent, a collector follower...

Therefore, the impedance looking into the emitter
(my choice of input node) is quite reasonable.

Now imagine if you will:

Twin resistors spanning the base outputs of
complementary Alephs. Each tracking the same
input with opposing .66V offsets.

And a quiescent current inbetween.


Or Post#24 my other thread if you need a picture.

revintage 20th March 2009 07:00 PM

Hi kenpeter,

I am not into yours or the Aleph. The PLH buffer is the interesting one as it seems to do everything right. In theory that is;) !

At the same as it has lowest 3rd harmonic it is also capable of delivering power into impedances where the others fail with the same Iq.

Will build a proto together with Hoktuna with whom I built the SETOR triode/antitriode.

kenpeter 20th March 2009 07:01 PM

The resistor divider you've been calling kenpeter style, is really
Michael J Koster style. All I did was stick it under Nelson's Aleph
to see what might happen.

Now, direct coupling signal into Aleph's emitter... That might
be me. I'm still backtracking to see if its been done before.

Anything might appear to sim good with an ideal OpAmp.
The moment I see one, I begin to wonder if I can trust it.

kenpeter 20th March 2009 07:19 PM


Originally posted by revintage
it is also capable of delivering power into impedances where the others fail with the same Iq.
We call that Class AB.

PIFA Post#24 can just easily drive AB after Iq runs dry.
But distortion in AB is definitely loop feedback territory.
Probably overcorrection stored on MOSFET gate caps.
Stick your opamp on ECAlephs1, what happens then?

Maybe a series diode, or carefull selection of collector
saturation voltage could keep the gate from being
bled down any further than necessary to shut it off?

revintage 20th March 2009 08:00 PM

2 Attachment(s)
Kenpeter, spare me the AB b-s;)!

None of the three circuits can go into anything but A. But if the PLH works otherwise than the JLH I can be wrong.

But in the Alpeh and MJK/KP the modulated CCS clips on both the positive and negative side before the S-follower.

Think the absence of source-resistor in the PLH-buffer has something to do with this phenomena.

For those with Opamp allergy this could be the simple cure. Will not change much though:

kenpeter 20th March 2009 08:27 PM

Spare me the three circuits above (looped or not) as the only
ways to build a follower. Have you read P.I.F.A. post #24 yet?

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