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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
icorem
icorem OP
146 posts
 
onemug

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.
hgeifman
1,193 posts
 
Icorem: As I noted above, http://www.il-audio.com/ is a Pass Lab retailer located in Israel. Can you take the unit to this retailer?
jr_w
27 posts
 
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.
onemug
784 posts
 
Icorem,
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?
elberoth2's avatar
elberoth2
1,219 posts
 
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)
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