Warm-up time for Pass amps?

Puma Cat

Puma Cat

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Hey gang,
I know many folks here love and enjoy Pass Lab amps.

Some of you may remember I built up two Nelson Pass-designed Amp Camp amps last summer.

I've set these up again over the long Memorial Day holiday weekend to get some real hours on them and on my (also DIY) GR-Research X-LS Encore speakers (which I recently found out need 400 hours of running in), and have an anecdotal observation that they seem to require about an hour of warm-up time to fully come "on song". When I listen to them as soon as I switch them on, they seem to be a bit thin and 2-dimensional sounding. Once they've been on for an hour so, though, they really do sound very good, especially when run as a pair of bridged monos.

Here they are set up on the floor in a quickie set-up configuration (sorry for the quality of the quickie iPhone 12 "snapshot")

DIY-Stereo.jpg


Is this observation consistent with your experiences? What do you guys that have a Pass Class A amp typically do? Do you leave the amp on all the time, or fire it up for listening sessions?

Lastly, I'm not telling you guys anything you don't know, but Nelson Pass is a genius.
 
Nelson Pass IS a genius!

Pass amps usually sound really good after about 20-30 minutes but I've found an hour or more really opens them up and makes them sing.
 
joeinid said:
Nelson Pass IS a genius!

Pass amps usually sound really good after about 20-30 minutes but I've found an hour or more really opens them up and makes them sing.
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Ah, great! Thanks, Joe! I figured you'd chime in with your experience with several Pass and First Watt amps, so many thanks.

Your observations are concordant with mine.

Cheers.
 
My old XA60.5 amps sounded superb after an overnight run in and even beat MC2301's for a lot less money.
 
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Puma Cat said:
Yeah, that doesn't surprise. I've heard great things about the 60.8s, too.
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Our XA60.8’s are killer good. They will drive anything. Their real world specs are actually double their rated specs.


Sent from my iPhone using Tapatalk Pro
 
I play one album as background before critical listening and don’t notice much change after that, so approximately 45 minutes. This has been consistent with a number of different Pass amps that I have owned over the years.
 
MPW said:
I play one album as background before critical listening and don’t notice much change after that, so approximately 45 minutes. This has been consistent with a number of different Pass amps that I have owned over the years.
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Great, thank you, Morgan. Very helpful. Anecdotally, it seemed like it was between 30 and 60 minutes.

Cheers.
 
I've always left my Pass Labs products on 24/7 unless I was leaving for an extended period of time (usually several days) or there was a storm rolling through the area. The couple of times I did listen from cold, the only thinness I noticed was in the XP-10 and XP-22, not the X250.8. But. like others have said, give it 30-60 minutes and that sound was gone.
 
I've been listening to my little Amp Camp amps as bridged mono blocks since the beginning of the long holiday weekend, and I have to say that now that they are getting more hours on them, they are starting to sound very good indeed. Nelson Pass, I tell ya what...

And...for 654 bucks, they're rather amazing.

ACAs.jpg


😻
 
X260.8's here, they sound great from the moment I feed them a signal and my mind convinces me they sound even better after the first LP or second dram, which ever comes first ! :woot:
 
Congrats!!!

The 260.8s is what I presently own as well. They get better and better.
 
I think George is just about spit on with the 4 hour warm-up.

Unlike George, I like to listen to mine as they warm. For the first 30 to 45 minutes the sound is a bit hard and constrained between the speakers. Then it suddenly opens and then gradually blooms over the next few hours.

When I do let them warm up unattended, I find that even if fully warm they only reach full potential after 30 minutes or so of playing music.

After 4 hours and playing music I don’t notice further improvement.

This holds true for all the Class A Pass Labs amps I’ve owned… XA 160.5s, XA 160.8s, XS 150s and XS 300s.
 
One of the forerunners of the current products were the Threshold class A and class a/AB amplifiers. In the owners manual of the Threshold S/550e amplifier, there was a graph of time (x) and temperature (y) which showed that the heatsinks temperature of that model stabilized at 50C in about 1 hours time. One of the ways to check the correct amplifier bias was to measure the heatsink temperature after that time had elapsed and adjust accordingly. I also owned a pair of the Aleph 2 class A mono blocks and they had a similar warm-up time. I never noticed much sonic improvement after that time.

The preamps I owned (X0.2, XP-20, Xono) took longer, and the XVR-1 crossover I still own takes 2-3 days for the sound to stabilize.
 
Audioseduction said:
My pair of xa160.5 takes 4hrs of being on before they sound their best. So I turn them on and wait at least 4hrs before listening to music.
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When I first got my Pass X600.5 amps I noticed they sounded best after being on over 24 hours. Now that they are a few years old, and broken in, they sound great after 6 hours of warmup.
 
I just turn mine on and start listening, hell I'm getting to freaking old to wait hours to listen to music. Nelson sad one hour in the manual. Also a user on another forum emailed Nelson and got this " I just talked to Pass Labs and he said the reason the amp sounds better is simple: Heat. The caps reach full capacitance quickly but the mylar needs heat to sound best. As the current and bias come up, the radiant heat affects everything in the amp... obviously in a good way. He mentioned that they can actually put a dead cold amp on the 'scope and watch the distortion curve deepen and then decrease as the amp warms up, which is why final tuning isn't done until the amps are at full boil. "
 
CPP said:
I just turn mine on and start listening, hell I'm getting to freaking old to wait hours to listen to music. Nelson sad one hour in the manual. Also a user on another forum emailed Nelson and got this " I just talked to Pass Labs and he said the reason the amp sounds better is simple: Heat. The caps reach full capacitance quickly but the mylar needs heat to sound best. As the current and bias come up, the radiant heat affects everything in the amp... obviously in a good way. He mentioned that they can actually put a dead cold amp on the 'scope and watch the distortion curve deepen and then decrease as the amp warms up, which is why final tuning isn't done until the amps are at full boil. "
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Yeah, that is what I find, too. They start to come "on song" at 45 minutes and are fully warmed up in an hour. Concordant with my experience.
 
I suspect that the Class A and A/B amps don’t warm up at the same speed. Further, the power output, number of chassis involved (1, 2 or 4), whether they’re stacked, racked, or separated from other components, and the ambient conditions in the room might all have an effect on time until “full boil” is reached.
 
I keep my XP-32 on all the time. And for my X600.8, I believe they sound pretty good at the time I turn them on, and become even better when fully warmup in less than 1 hour.
 
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