Delay....

[chaco1]

I've owned an XPA-2 for a few weeks and to say I'm pleased with the purchase is an understatement. It is a wonderfully powerful and clean amp and drives my MMGs beyond any SPL I care to experience for any length of time. I've noticed a slight delay in the response of the output meters on my XPA-2. The transient response is there but delayed by a very small fraction of a second.

Is this a flaw in what clearly is a remarkable piece of equipment or am I being excessively nit-picky?

[Deleted]

The meters on the XPA-2 and 1's are slow, which is perfectly normal and there's nothing to worry about.

[Boomzilla]

There are meters?

Just kidding - I've flickered the meters using my DefTech speakers, but with my Klipsch Cornwalls, I've never even seen the first LED beyond the pilot.

[chaco1]

Man, do I understand that. Even with the inefficient MMGs I had to crank the volume to uncomfortable SPLs to see the meters move. For most of my listening they just remain there staring like two beady blue eyes.

That reminds me, does anyone know at what point the XPA-2 switchs from Class A to Class A/B or is it always in A/B?

[Deleted]

Jun 19, 2013 14:59:48 GMT -5 chaco1 said:

Man, do I understand that. Even with the inefficient MMGs I had to crank the volume to uncomfortable SPLs to see the meters move. For most of my listening they just remain there staring like two beady blue eyes.

That reminds me, does anyone know at what point the XPA-2 switchs from Class A to Class A/B or is it always in A/B?

All A/B amps use a few watts in class A before switching over but IMO it doesn't make a difference.

[geebo]

Jun 19, 2013 14:59:48 GMT -5 chaco1 said:

Man, do I understand that. Even with the inefficient MMGs I had to crank the volume to uncomfortable SPLs to see the meters move. For most of my listening they just remain there staring like two beady blue eyes.

That reminds me, does anyone know at what point the XPA-2 switchs from Class A to Class A/B or is it always in A/B?

I seem to remember Lonnie telling a few of us at Emofest it was less than a watt.

[KeithL]

The XPA-2 transitions from Class A to Class A/B operation at around one watt; however, the exact point will vary depending on how warmed up it is and several other factors.

Again, though, I would like to correct the misnomer that this amp (or any Class A/B amp) "switches" between Class A and Class A/B.

The reality is that the bias remains at a fixed point. When the signal level is low enough, then the amplifier operates in Class A mode, which means that the output transistors connected to the plus and minus supply rails operate symmetrically (when the current through one set of transistors goes up, the current through the other set goes down an equal amount). Once the signal level goes above the "transition point", then the output transistors no longer vary symmetrically. At this point, the amplifier is no longer operating in Class A mode. There is no "switch" involved, and the only thing that "changes" is the amount of signal being output.

[The "transition point" is simply the amount of signal required to cause the amplifier to start operating outside Class A mode. On the XPA-1L, the "Class A" switch moves this transition point higher by increasing the bias to a much higher level. Again, though, the switch doesn't determine at any given instant whether the amplifier is operating in Class A or Class A/B; what it does is to change the point at which the amplifier will transition between modes IF the signal level causes it to do so. With the switch in the "Class A" position, the XPA-1L will continue to operate in Class A mode until a much higher power level before "transitioning" than it would with the switch in the other position.]

Jun 19, 2013 15:32:42 GMT -5 geebo said:

Jun 19, 2013 14:59:48 GMT -5 chaco1 said:

Man, do I understand that. Even with the inefficient MMGs I had to crank the volume to uncomfortable SPLs to see the meters move. For most of my listening they just remain there staring like two beady blue eyes.

That reminds me, does anyone know at what point the XPA-2 switchs from Class A to Class A/B or is it always in A/B?

I seem to remember Lonnie telling a few of us at Emofest it was less than a watt.

[arthurz]

So at which point does the XPR-1 transition from class A to class A/B? And what about XPR-5?

[pedrocols]

Jun 19, 2013 16:18:58 GMT -5 arthurz said:

So at which point does the XPR-1 transition from class A to class A/B? And what about XPR-5?

I think the XPR amps are not A/B but H....

[arthurz]

AFAIK, it's still fundamentally A and then A/B (the Emotiva marketing materials support that: "Fully discrete, quad differential, fully balanced, high current, short signal path Class A/B Differential Reference power amplifier with Optimized Class-H™ power supply topology".

[mgbpuff]

The XPR amps operate exactly as do Class A/B amps. Class H is a classification that was given to Class A/B amps with switchable rail power (or tracking rail power).