Pass Labs heatsinks temperature

Hi all

I have Pass Labs xa60.5 monoblocks and they are always warm to the touch at the heatsinks and not as hot as other class A amps I'm familiar with. A friend from the US that has the same model visited my place and told me his amps ran very much hotter than mine. I got concerned and looked at the manual where temperature was estimated at 55 degrees Celsius. I estimate mine at around 40 Degrees. I'm concerned my amps are not biased to pure class A as they should be. I contacted Pass and while they repeated that heat should be around 55 deg. they had no idea if my concerns are valid and they sounded quite mysterious about it. Did anyone has a xa.5 series model ever measured its temperature or has an idea what can I measure without opening the amps (with a technician) that will prove that they are working only in pure class A ?
Thanks in advance
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).

I'm not a DIY guy - I hardly know what the word bias means :-)
Just wanna make sure that what I have is what I paid for my hard earned money. Thanks anyway
Couple of questions:

On your front meters, where do the needles sit when the amps are idling?

Do they bounce around much when you are playing music?
Then take them to your dealer or send back to Pass to check bias. It is definately set too low.
I guess I am begging the obvious, when I say take it to a tech who can talk to pass about the bias current spec, and have him make the adjustment. I assume there is no dedicated Pass service center you can get it to easily.
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.
Please see the web site below:

This retailer carries Pass Labs. Can they help you?
If anyone is in the L.A. area, I would be able to help them.

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.
Icorem: As I noted above, is a Pass Lab retailer located in Israel. Can you take the unit to this retailer?
My XA60.5 needles ran a little left of center at idle as well. If they're not moving, I wouldn't be too concerned. There is an article on the Pass site titled "Leaving Class A" that might be worth a read.
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).
I've had the same experience with James 123 and Map with my Pass INT-30A: warm to touch (including the beefy face plate), but not hot.

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.


Thanks for your input. I think that the front left part of each amp between the heatsinks is the warmest point. Was it there where you got the 120 degrees read ?
If I were you I wouldn't worry. Pass Class-A amps get less warm than most others.
Mine measure 150-152 degrees at the heatsink midway down its length. After 6 seconds, a touch definitely becomes quite uncomfortable. It is the same between the 2 amps. The heatsinks at the front and back are around 140 degrees.
Your 200.5s are a lot more amp than some being discussed here, Rtn. Could that be a factor in heat output?

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.
I am not using a baby thermometer, using an infrared. I've checked the temps up and down, front to back and all the different fins and the highest I got was the 119.8F. It's warm but not hot to the touch. I'm going to run them all day today and then check again just out of curiosity(sp?).
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.
I need to make a correction on my last statement; I meant to say that the hotest point is not towards the front panel but in-between the front panel and the rear, right about the middle and in-between the top and second fin. Sorry about that.