Pass Labs Amplifier Meter meaning?

On the XA series, it appears to have no meaning. I never got any movement on my meter while playing music. Someone said if it starts moving you are close to clipping. If you get the answer from Pass, let us know.

I used to own the X250 amp and if I remember correctly the meter indicated the mode of operation. So up to the 12 o'clock position the amp is running in class A. Beyond the 12 o'clock position it is running in class A/B. Not a 100% sure about that though.

That makes sense as the XA is pure Class A.

I was told by Pass Labs that it reflected/measured bias. When changing from class A to class A/B the bias meter "bounces".

X.5 series amps - meter stays still means amp is operating in Class A. Usually that stand-still is at approximately 11 o'clock meter position. Once the meter starts moving, it means the bias is switching to A/B.

On XA series amplifiers, the meter, as far as I know, is there for looks only, since the XA series amplifiers are pure Class A operation only.

Given the reputation of Nelson Pass, I am amazed and a little disappointed to hear these meters are cosmetic only.

Agreeing that the meters look great, and in fact, are more than a small part of my lifelong desire to own a pair of Pass mono blocks.

But why not add some functionality? What a bummer.

I was "told" that it is current draw. The harder I drive my X-250, the higher up the scale the needle moves.

It would seem the meter is of no practical purpose to an end user other than to verify that the amplifier is in "operate" mode.

It means more expense and more things to go wrong.

I received a reply from a knowledgeable source who chooses to remain anonymous:

In the XA series, the meter measures bias. From a practicality standpoint when the meter begins moving, it's an indicator the amp has reached rated output.

I think Zippyy is right, if my memory serves me right. My X250 runs class A for the first 40 watts, then switches over to A/B. The meter needle moves slightly in class A mode. I had the needle up to the 12 o'clock position once, and it was alot more than 40 watts, and so loud the sonics were terrible in my room, which is approx. 15x27x9. I think it just measures current, whether it be class A or A/B. I guess they figure since you're paying alot, you may as well have something to watch, even if it doesn't move very much.

Surely someone must have an operators manual for it.

Hey, it's okay to have a little eye candy in your system. The meters look cool....even if they are unecessary.

All amp mfgs could put the things in black boxes and call it a day. Nothing wrong with having aesthetics in a system. Look at the car you drive.... is that metallic paint and the custom wheels really necessary?

Ecclectique, I have a manual, but it has no mention of the meter in it. Must figure it doesn't need an explantion.

Maybe I should rephrase. According to Pass Labs, my 600.5 amps stay in class A to 110 watts. Once a 600.5 amp reaches 110 watts, it switches to class A/B and it is indicated by the movement of the bias meter. Peter at Pass Labs called the meter a bias meter and said that it wasn't an indicator of current. Just "Passing" on what I was told.

I own the Pass Labs X-600 monoblocs. The explanation for the meters below was taken from the manual posted on the Pass Labs website.

---------------

You are ready to play music.

The meters read current through the output stage in the X1000 and X600 and total supply
charging current in the X350. At low levels, they should stay pretty constant and if the meters
are bouncing around at a moderate or low listening level, it might indicate that you are driving a
very low impedance load or even a dead short. If your speakers are not known to be very low
impedance, say less than 4 ohms, then you should check this out.

Do everybody a favor and try not to have shorted output cables. It happens accidentally all the
time, and the amplifier is designed to survive, but I wouldn’t bet the farm on it.

With the X350, you will see some meter bounce if the AC line is not constant. This is normal,
and simply shows the different charging rate of the power supply capacitors, not the actual
current going through the audio circuitry. You will also note on the X350 that the meter shows
the draw of both channels. We had only one meter.
Of course it’s always possible that something could go wrong. If so, don’t get excited, just
relax. It’s really aggravating when something like this doesn’t work, we understand, but it will
get fixed. At Pass Labs, we go to a lot of trouble to make products reliable, and the failure rate
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of our amplifiers is almost non-existent. This is small comfort to the few, but take it easy and
give us a call if you have problems.

Now that the channels are up and running, we can take a moment to note a few things. The
meter lights are blue, subtle lighting in daylight, a little more dramatic at night. The meters
themselves read the amount of current going through the amplifier, and that is why they sit
near the half-way point, reflecting the bias current we run through them to get low distortion.
The bias current seen by the meters will vary slightly, going down a bit as the amplifiers warm
up. Two channels will not always be at exactly the same position. Don’t worry about it. If they
drift upwards or vary dramatically from each other, give us a call.

Later, as you start listening to music at higher levels, you will start to see the meters move up
above the bias point. Basically, the amplifier will be operating in pure Class A at current levels
that do not cause the meters to move. As the current to the speaker exceeds the bias level,
you will see the meter bounce upward from the idle reading.

It’s pretty simple: If the meter isn’t moving, you are still in pure Class A mode. You will
probably be surprised how loud you have to play it before the meter moves.

The meter has been calibrated to reflect the 600 watts idle draw of the amplifier, which is about
one-third full scale for the X1000 and X600, and one-half for the X350.

The meter is intended
as a general indicator of the status of the amplifier and has not been calibrated to reflect any
particular values.

Thanks for all the replies.

Re "The meter is intended
as a general indicator of the status of the amplifier and has not been calibrated to reflect any
particular values"

Maybe EKG's would be just as useful if they simply showed that someone's heart is beating, without worrying about any particular "values."

Cheers,

cwlondon

Are the above ten year old responses still the same for the current X and XA point 8 models?

@tubesrule yes

Pass explains this pretty well...

And yes, this is still what he says at Burning Amp.

https://www.passlabs.com/press/leaving-class

I've had an X350 for about ten years. Other than on and off I've never seen the meter move. Driving ML Ascent Is.