Get yourself two multimeters and bias it by yourself. On the scale form 1 to 10, I would rate it as 2 - easy DIY project. 15 minutes and you are done (then you will have to recheck in 1h or so).
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I suggest you call Pass Labs again and ask them how you can check to see if the amps are biased to pure class A as they should be. I am also not a DIY person so I suggest you take the amps to a local technician and request the amps bias be checked. Pass Labs should be able to explain how to do this (I hope).
You have to ask Pass Labs if the amps are not bias correctly, can the local technician set them correctly or do they need to be returned to the factory.
Do you have a local Pass Labs retailer who can help. A local Pass Labs retailer might be the best option.
meters are a little left than the middle and no bouncing around although I don't hear at high volume most of the time.
Hifigeek1 and Elberoth2
I'm from Israel so LA is a little far away and also sending them to Pass will be pricey if it comes out that nothing's wrong with them - I will be surprised if they will finance the trip back and forth.
Judging from your report, it "looks" like your amps are okay. The fact that they aren't bouncing means you are not leaving class A.
Seems like I remember my manuals saying the heatsinks should be "around" 50 degrees "F" above the ambient temp. Don't know what that converts to in "C". My heatsinks run a little hotter in the summer than in the winter. What is your room temp these days?
Icorem - I though you are from the US. If you are from Israel, sending them back for sth as trivial as biasing, would be a total waste of money and effort. Just take the amps to your local tech, or ask one to come over.
Here is XA-30.5 bias procedure for reference purposes only - it is really easy !
(pls note that you need XA-60.5 biasing manual to perform this task on your amps !)
1) Measuring across test points adjust bias for each channel to 125mV. Pay attention to DCO across the two speaker terminals and from each terminal to ground, aim for as close to zero as possible. (P1 and P2 on the socket mounted module adjust offset.)
2)Replace cover allow unit to warm up to 53 degrees C at the heatsink, which wil take a couple hours.
3)Final adjust which will take several attempts with time lapse to allow For stabilization of temperature, and bias which tracks temp as a NTC.
4)Target Bias is 135 mV, again paying attention to DCO, absolute and differential
PS. From what I remeber, I needed 4 Digital Multimeters (you can get the cheapest one you could fing from ebay - no name ones are ~ $10 each) to perform biasing on my XA-30.5:
- one to measure DCO across the two speaker terminals
- one to masure DCO from each terminal to ground
- one for each of two bias test points (A nad B)
Hi. Im not sure if this helps at all, but i have a pass xa30.5 and it just gets warm to the touch. After an hour or so the whole thing is warm, certainly not hot. even the whole thick metal front panel is warm as well as the fins. im no expert on amplifiers, but it seems fine and has always reached that temperature since the day i acquired it five years ago.
i observe that the sound quality is not optimal until it is warm. i would be very cautious about opening a piece of kit like that. i wouldnt attempt it.
I have had two XA30.5 amps and I can/could keep my hands
on the heatsinks for as long as I want/wanted. Not sure
what temperature they actually get/got to, but it definitely
is not as hot as advertised. My hot water heater is set
to around 120F and our hot water is much hotter (by the time
it gets to a faucet).
This thread got me a little curious so last night I measured the temp on the cooling fins on both of my amps(XA-100.5's). I could find no area that was over 119.8F, the amps have been in stand-by mode for several days and had been fully on and running for several hours. Not sure if this will help but thought I'd toss it in the mix.
Thanks for the measurement, Johngp. That's about 20 degrees above normal body temperature, which I'd expect to be experienced as pretty warm to the touch, but far from jerk your hand away hot. That's about what I feel on my INT-30A. I lust after your 100s, of course, though I'm loving the simplicity of an integrated.
All this temp measurement stuff has me thinking.
It is important in trying to get comparable data to take the data the same way using the same warm up procedures in the same location.
Sticking a baby thermometer up agains the fins is not the best technique. At work we measured hot chuck temperatures using a temp 'Puck'. A flat sensor connected by cable to a handheld device.
Some FLUKE meters can use a thermocouple, too. You just need the right 'type' so MV ouput matches the appropriate temp readout. A 'Type T' may be just the ticket.
Good. Now if others use similar equipment with similar competence, the data could be compared.
As it lies? Well, 3 or 4 others have measured, with unknown means and accuracy, while getting results which confuse me.
No relation to bias condition has been stated, though all are on 'a' amps.
I've read, on the Pass DIY site the bias setting procedure for a Pass designed amp, and it was thorough enough that I have trouble believing an amp could leave the Pass factory and be mis-biased.
Ok, I went ahead and rechecked again as promised, I wanted to be sure my first readings were correct.
I'm using an infrared thermometer and checked from front to rear and all fins in an attempt to find the hottest point on the amplifiers. The hottest point does seem to be near the front panel in between the topmost and second fin. The amps have been kept in stand by for days, I set my cdp on repeat, left the house and let them run for several hours at a moderate volume. I got a maximum temp of 121.4F.
FYI; This is a new pair of amps that are only about two weeks old and I agree; I doubt that Pass would let a set leave the factory without checking and double checking the bias.(As a matter of fact I believe they set the bias, run the amps for 24 or 48 hours and then recheck again.)My needle hovers just to the left of the center line and stays there unless the volume is turned to an unbearable to me level. Though I know this is not much of a scientific way of checking for correct bias setting I hope this helps out anyone with questions on their amps bias setting. To be honest I think that Pass Labs class "A" amps just run cooler than most other class "A" amps.
Good data...and taken after complete warm up.
Most people don't know the difference between heat and tempreture.
An iceberg has more heat than a red hot nail even though the nail is at 500c or whatever.
Pass labs have generous heatsinking and huge transformers. Those 60a monos weigh what......60 or 70lb each? More?
And even though you touch 'em after a good warmup and say 'Not too bad!' all you'd have to do is put em in a smallish room on a cool night and see just how much HEAT they reallly kick out.