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.
26 responses Add your response
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.
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.
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?
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 wouldnt 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 its always possible that something could go wrong. If so, dont get excited, just
relax. Its really aggravating when something like this doesnt 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
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. Dont 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.
Its pretty simple: If the meter isnt 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
I know this thread is old , I own a XA30.5 and XA100.5 mono blocks with my stero Amp at turn on is different than my mono blocks the Bias needle on the XA30.5 is a little to the left of center and stays close to the middle even when playing very loud, but my XA100.5 at turn on are to the right of center then slowly move to center as they warm up I am wondering if the Bias is out of adjustment on my Xa100.5 Does anyone know ?