Why does my SS amp need to warm up?

[topspeed]

I recently replaced my PS Audio HCA2 (switching amp) with a Pass X150.5 and was hoping someone can explain to me why the sound of this solid state amp changes so much as it warms up? Tubes need to warm up, I get that...but solid state? When I first plugged it in, I was concerned I'd made a mistake, but helpful advice from Mr. P and others assured me that 24 hrs of feeding it juice would make all the difference, and it did. Now I leave it in stand-by, but even then I've got to give it a good half hour or so before she brings her big guns out to play. I've never encountered this before in a ss amp. The nerd in me wants to know why this happens :)

[Feanor]

I'd like to know too. I also have a Pass X150.5 and agree that it takes a good 30-40 minutes to warm up close to potential from Stand-by. Maybe it's the transistors coming up to the temperature they need for stable operation, but that's only a guess. According to Pass, the X150.5 draws about 30 watts on Stand-by but 200 watts powered On but idle.

But I note the may Class D Audio SDS-258 required a warm-up time to sound best; in its case it was only 10-15 minutes but even so.

[topspeed]

I'd like to know too. I also have a Pass X150.5 and agree that it takes a good 30-40 minutes to warm up close to potential from Stand-by. Maybe it's the transistors coming up to the temperature they need for stable operation, but that's only a guess. According to Pass, the X150.5 draws about 30 watts on Stand-by but 200 watts powered On but idle.

But I note the may Class D Audio SDS-258 required a warm-up time to sound best; in its case it was only 10-15 minutes but even so.

The PS Audio consumed so little power while idling, I simply never turned it off. Warm up? What warm up? Gotta love that Class D efficiency!

[Mr Peabody]

My X250 also sounded better after 30+ minutes of play time. I can't explain it but I believe it has to do with the Class A type topology Pass uses. Coincidentally, my 532h sounds better after some play time. Now I wonder if it's a solid state thing where you need high resolution system to hear it or if it's just the character of certain amps. The 532h is quite a bit different topology. The Pass warm up time was more apparent to me, just like when I had my CJ tube amps.

[Hyfi]

Don't big Caps need to be charged all the way before optimum performance?

My Stratos amp as well as a Rotel Receiver both get louder and start sounding better after about 30 minutes.

[blackraven]

Don't big Caps need to be charged all the way before optimum performance?

My Stratos amp as well as a Rotel Receiver both get louder and start sounding better after about 30 minutes.

Yes, caps need to charge up but that takes a second to do so. It probably has something to do with the temperature as well as polarization.

TS, welcome to the Pass club. How do you like the amp? What are you using for a preamp?

[topspeed]

Yes, caps need to charge up but that takes a second to do so. It probably has something to do with the temperature as well as polarization.

TS, welcome to the Pass club. How do you like the amp? What are you using for a preamp?

Hi BR,

I like the Pass quite a bit. I had never purchased an amp before without auditioning it, but knew Nelson Pass has the same JBL's for his own system, so it was safe to assume they would be a synergistic match, which they are. Once warmed up (which is key), the X150.5 has terrific grip and extension on the bottom end while the mid band and treble are both very smooth without the slightest hint of grain or glare. It isn't as fast in transient response as the HCA2 and the edges are softened in comparison, but its not a matter of better or worse, just different. While both are rated at 150wpc, the Pass seems to pull harder (car-guy parlance). The greatest attribute is the complete lack of fatigue. It just makes you want to turn it up, which the JBL's love! Once she's really cooking, the sound has meat on the bones and the dynamics simply bloom. I'll spin tunes for hour after hour. I went from Porcupine Tree to Stan Getz to The Eagles and relished every second of it.

My pre-amp for now is a Marantz SR5010 used in Pure Direct with all room correction and audio/video processing shut down. Sometime down the road, I think I'll add a pre-amp/dac w/ theater bypass. Before I purchased the Pass, I was negotiating on a CODA CSX integrated that Mr. P spoke highly of, which would have saved me the trouble of finding a good line stage, but I've always wanted a Pass so that's what ended up in my room.

[blackraven]

Congrats on the Pass. You described the sound perfectly. My X250 has a soft top end but tremendous grip and bass extension. I find transients are very fast but I am using a BAT VK-51se preamp which is just an explosively dynamic preamp.

[Mr Peabody]

What I notice after some play time the sound seems to have less of a glare and opens up more, warmer sound. The Pass just gets into a more relaxed character and more open.

[topspeed]

What I notice after some play time the sound seems to have less of a glare and opens up more, warmer sound. The Pass just gets into a more relaxed character and more open.

The only time I've experienced anything resembling glare on the JBL's was when I had the Rotel inserted, which was a horrible match in my rig. With the Pass, after 30-45 minutes, the bass is a lot fuller while the mids come forward and, like you said, open up more. The difference, especially in the bass, is not subtle.

We need more nerds on this site! There has to be a technical explanation for why this solid state amp does this.

[blackraven]

The only time I've experienced anything resembling glare on the JBL's was when I had the Rotel inserted, which was a horrible match in my rig. With the Pass, after 30-45 minutes, the bass is a lot fuller while the mids come forward and, like you said, open up more. The difference, especially in the bass, is not subtle.

We need more nerds on this site! There has to be a technical explanation for why this solid state amp does this.

Send an Email to Pass Labs and ask them.

[Mr Peabody]

Maybe glare wasn't the right word, when first turned on the sound has just a coolness more so than compared to the sound after warming up. I say glare because after warm up it's more inviting to the ears, not that at first it isn't good, it just gets better.

[topspeed]

So 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. We both found it ironic that 30 years ago, you could fry a semiconductor if you got too close with a soldering iron, yet some of the chips today don't reach full potential until they've got 400 degrees of heat in them.

So there you go boys, the answer is heat.

[blackraven]

It is what I suspected.

[harley .guy07]

Well I jokingly tell people when they come over that I have a very good $6,000 space heater that doubles as a unit that makes my speakers sound good. I really love my Pass and have always wanted one even back in the Aleph days when they were a weird square. I have always loved Nelsons work even the Adcom designs in the 90's that were very affordable and good even though not a shade of good compared to Pass Labs. I know that the newer class D stuff is getting better especially designs based on the Pascal architecture that has been the newest thing which I heard is really good but I just can't get past the Pass sound.