Question regarding Pass X series

[georgehifi]

Nelson or if anyone else knows the answer, two of my freinds were arguing about the class of the Pass X or the XA series of power amps.
One was positive that they were push/pull the other was positive that they are single/ended. The single/ended guy said it looks like push/pull but it's not, the bottom transistors are constant current sources for the top ones, not having seen the circuit i could'nt correct either one of them, so does anyone know?
So i can declare a winner.

Cheers George

[uli]

The X series is balanced push-pull.
The XA series is balanced single ended, but with a
current controled current source instead of a ccs.

Uli

[thomasfw]

I ask the "Local Agent", the answer is :

X : will be discontinued soon
XA.5 : Class AB
XA : Class A

I think only Mr Nelson Pass can tell us the true answer !


Thomas

[uli]

Originally posted by uli
The X series is balanced push-pull.

added: X-Series is Class AB
X.5-Series is Class AB but SE Class A to a higher power than X

The XA series is balanced single ended, but with a
current controled current source instead of a ccs.

XA-Series is Class A

This info can be easily distilled from NP´s info on www.passlabs.com

Uli

[Nelson Pass]

The current X amps are becoming ".5" amps, which is the
same model # and specs but with some tweaks in the
power supply, gain stage, and output stage. The most
discussable change is the small amount of single-ended
bias applied to the output stage, which makes each 1/2
of the amplifier operated SE Class A for a couple watts.

The XA amps are staying the way they are for the time
being, and the introduction of the XA60 looms near.

As I have said before the phrase "balanced single-ended
Class A" is an oxymoron thought of by someone else but
aptly describing the result of balancing two SE circuits.

The result is 3rd harmonic, not 2nd due to the cancellation
of the 2nd harmonic, but we find that you get a better
result when you start with SE circuits than when you start
with PP circuits. Apparently the character of PP circuits which
are then balanced shows the compounding of two 3rd order
characters, and balancing SE circuits sounds better (IMHO).

[metalman]

Nelson,

I have a question on the X2 service manual you recently released at PassLabs. In your articles on supersymmetry you imply that a supersymmetric circuit when driven single ended shows no advantage over the equivalent circuit without supersymmetry. But in the X2, the balanced signal is converted to single ended before it is delivered to the gain stage. Doesn't this arrangement cancel the benefit of the supersymmetric feedback in the gain stage, or is there something inside the mysterious UGS modules that still makes the supersymmetry beneficial? I've been trying to wrap my head around this and have only succeeded in turning circles

Cheers, Terry

[tschrama]

Dear Nelson,

I have an idea...

Could it be possible to make some sort of a SE folower output stage .?.. based on a active current source like in the Aleph.. This change a X-serie amplifier with a PP output stage to a SE with minimum modification ?


regards,
Thijs

[thomasfw]

Dear Nelson,
I have same question what the Terry asked when I studied the X2.
Would you please explain more detail about this issue !!!

Best Regards !


Thomas

[stefanobilliani]

Originally posted by metalman
supersymmetric circuit when driven single ended shows no advantage over the equivalent circuit without supersymmetry. But in the X2, the balanced signal is converted to single ended before it is delivered to the gain stage. Doesn't this arrangement cancel the benefit of the supersymmetric feedback in the gain stage, or is there something inside the mysterious UGS modules that still makes the supersymmetry beneficial? I've been trying to wrap my head around this and have only succeeded in turning circles

Cheers, Terry

Well , I do not see the feedback in the schematics of the X2 version 1 ,

Supersymmetry is essentially the symmetric feedback around the differential pair . So I believe that SUSY is not applied in the first X2 .

[zinsula]

Originally posted by Nelson Pass
....As I have said before the phrase "balanced single-ended
Class A" is an oxymoron thought of by someone else but
aptly describing the result of balancing two SE circuits.

The result is 3rd harmonic, not 2nd due to the cancellation
of the 2nd harmonic, but we find that you get a better
result when you start with SE circuits than when you start
with PP circuits. Apparently the character of PP circuits which
are then balanced shows the compounding of two 3rd order
characters, and balancing SE circuits sounds better (IMHO).

This is very interesting. In the X Series, the output stage is PP. So the statement you are making here make here resulted in the X.5, at least for the first few watts?