Warm-up time: Can it really take days, and why?

[zenith2134]

I did a quick and dirty search of audiokarma, audioasylum, and head-fi on the issue of warming up solid state amps. I wanted to find out which types of amplifiers specifically need a long warm-up time before they sound accurate and correct. I DEFINITELY do not want any debate in this thread, just trying to have an intelligent conversation on the matter, and learn something in the process.

Currently, my solid state Kenwood 8100 integrated has been on since early yesterday afternoon after having roughly 2 months of down time due to the need for repairs. When I switched it on, my CD deck and computer DAC had already been running for weeks since I leave all digital devices on 24/7.

Well, I must say that the amp has opened up ever so slightly since yesterday. I used the Cars album, Candy-O, to test this. (BTW the album is a first-gen CD pressing with actual dynamics.) On the track entitled, Double Life, the echo around the singer's voice is much more defined and noticeable then before. Same speakers, same disc, same CD player.

My question is, will I notice any further change now that it is already up to operating temperature? Why do some manufacturers omit a power switch completely?

[As a technical side-note, I should mention that although the sound changed over the course of a day, the amp's bias has remained stable on both channels, and dc is at zero with no load on the speaker terminals]

Since the 8100 uses 20,000 uF per channel and is a dual-transformer design, I'm thinking maybe it takes some time for the capacitors to charge up? (Doubt it though since I've read even 1 farad caps charge quickly) Can anyone shed some light on this for me?

 

[Tangent]

I don't know any of the technical theory (and even if I did I would not expound on it, as per your request for no debate.)

I do have a friend who has a SS amp and he never turns it off. I think it's been on for around 10 years with no problems!

As for a listing of amps? I would guess "all of them" but that's just a guess.

 

[kcollins4]

IMHO, when an amp has been on long enough to make reliable adjustments, it's as warmed up as it's going to get. What I'm referring to, is adjustment procedures in service manuals. If I was instructed to let an amp warm up for 30 minutes to adjust the bias, I would assume under normal conditions, that's as warmed up as it's ever going to need to be. I believe Echowars' thread about DC offset mentions a 30 minute warm up for an initial adjustment, and wait 30 more minutes to re-check; something like that. So, in that case, basically an hour, and you're good, (if you choose to wait that long).

 

[EchoWars]

60 minutes and it is about as warmed up as it's gonna get. I can't imagine any real benefit to leaving it on 24/7.

 

[stuartk]

I did a quick and dirty search of audiokarma, audioasylum, and head-fi on the issue of warming up solid state amps. I wanted to find out which types of amplifiers specifically need a long warm-up time before they sound accurate and correct. I DEFINITELY do not want any debate in this thread, just trying to have an intelligent conversation on the matter, and learn something in the process.

I'm not quite sure what exactly it is that you're after - given that you "don't want any debate."

 

[electroking]

Maybe it's your own body that has warmed up with respect to yesterday,
leading to 'ever so slight' differences in perceived sound quality! Just my two
cents' worth.

 

[SPL db]

Do you suppose that older power supply caps that haven't been used in a while might take longer to come up? :scratch2:

Meaning a full on cap replacement would minimize the time needed to warm up? :scratch2:

Maybe even getting more of a full charge since the cap is new? :scratch2:

Sorry, we are thinking out loud here aren't we?

Scott

 

[avionic]

Since the 8100 uses 20,000 uF per channel and is a dual-transformer design, I'm thinking maybe it takes some time for the capacitors to charge up? (Doubt it though since I've read even 1 farad caps charge quickly) Can anyone shed some light on this for me?

My DIY amps have 48,000 µf/per rail or 96,000µf/channel and I would bet they are fully charged in 17-34ms.The outputs and drivers are probably thermally stabilized in 5 min.- 10 min. max.

 

[zenith2134]

So maybe it is the fact that the caps are old. It is certain that the amplifier sounds better to these ears after a full day.

Stuart, I am not looking for trouble. I apologize if it appeared otherwise. Just kind of interesting that there is some difference with extended warmup times.

What about pro/high-end amplifiers which are designed to stay on 'round the clock? Why would a manufacturer suggest this, and why do so many enthusiasts note the same results? :scratch2:

 

[Bigerik]

So maybe it is the fact that the caps are old. It is certain that the amplifier sounds better to these ears after a full day.

Stuart, I am not looking for trouble. I apologize if it appeared otherwise. Just kind of interesting that there is some difference with extended warmup times.

What about pro/high-end amplifiers which are designed to stay on 'round the clock? Why would a manufacturer suggest this, and why do so many enthusiasts note the same results? :scratch2:

I understand where you are coming from. Very interesting question and one that can easily turn into a flame war. However, this is a safe spot on AK for any type of discussion.
I never easily dismiss what another person says they hear.

 

[shelby1420]

Maybe it's your own body that has warmed up with respect to yesterday,
leading to 'ever so slight' differences in perceived sound quality! Just my two
cents' worth.

Interesting point to an interesting question!! This very question wasasked ver on the Bottlehead forum...which warms up--the gear or your ears? I say both--I have had days where the first 45 minutes or so- ss or tube are horrible to listen to....I have had other days where I think every piece of gear I have is the best in the world and days where I think its all shit....thinkin the gear does not change that much so gotta be my ears no??

 

[Tangent]

Ears? Maybe.... maybe it's the brain?

I know a guy who had never heard the Allman Brothers. He bought the MFSL of Brothers and Sisters. He didn't like it.

I then convinced him to listen to it again - you have to be in the right mood to hear some laid back country-southern rock. He did and he loved it.

I also have different days where I'm just not in the mood to relax and listen to music.

 

[dogscanskate]

There simply are too many variables to really assert how long it may take an amp to stabilize and settle in. Since it's connected to the speakers which have capacitors, inductors and resistors, who knows? The same goes for source components. they all depend on "electricity". I think it should be about a "system warm-up" lol.

What I have found is that later at night, my system really starts to open up and sound way better. This has been discussed before but with less demand per household, fewer companies sucking up the current, less grunge... it only makes sense that it should sound better.

Trying to devise a test that would isolate this issue is still dependent on the power utility and its users unless you make your own electricity. There are voltage swings in the hydro power we get, harmonics, phase errors... the list goes on.

 

[zenith2134]

Thats another good point we must consider: The power grid. I leave my CDP and computer DAC on along with the amp, but sometimes fear what would happen if there was a sudden power surge or lightning hit. I am not running a line conditioner at this time, so I'd probably lose it all. :sigh:

Some audio groups even suggest that loudspeakers and headphone drivers need a 'warm-up' time...This makes perfect sense to me since the VC's heat up ever so slightly say, after a couple of songs at moderate volume. I bet their parameters change too.

Again, this is a very subjective thing to discuss and everyone's opinions will vary. In the meantime, I'm going to try and figure this out for myself and try to determine how warmup affects my gear. Thanks for the tips so far guys. :thmbsp:

 

[stuartk]

Stuart, I am not looking for trouble. I apologize if it appeared otherwise. Just kind of interesting that there is some difference with extended warmup times.

I didn't think that you were looking for trouble or anything like that.

I just wasn't sure what you were looking for since you specifically said you weren't looking for debate.

It's very hard to talk about this kind of thing without at least some debate.

What about pro/high-end amplifiers which are designed to stay on 'round the clock? Why would a manufacturer suggest this, and why do so many enthusiasts note the same results? :scratch2:

I can think of one reason. If you leave your equipment on 24/7, it's going to wear out much sooner, so they'll be able to sell you another one.

Enthusiasts note all kinds of things... it's sometimes hard to determine why.

 

[outshined]

James Bongiorno once told me, in his inimitable way, that SS circuits stabilize, after power on, in a matter of micro seconds. He said that you might want to wait a few minutes before you turn off the amp to allow the caps to dissipate. Heat is any amps enemy, and leaving stuff on will only lead to their early demise. Bongiorno said he does not leave anything on when not in use. I think he would be someone who knows a great deal about such things.

 

[shimniok]

60 minutes and it is about as warmed up as it's gonna get. I can't imagine any real benefit to leaving it on 24/7.

I would think transistor response dependency on temperature is primarily at play but at the same time I can't imagine the transistors would still be cold after 30-60 minutes.

Based on advice I left my receiver (Sony STR GX800 ES) on 24x7. It's dead now (not sure that is why).

I won't leave the HK on especially with how hot it runs and how old it is. It does change sonically within an hour after power up...

Michael

 

[stuartk]

I won't leave the HK on especially with how hot it runs and how old it is. It does change sonically within an hour after power up...

Well, either it changes or you do.

Without controlled listening tests it's difficult to say what's going on.

 

[Arkay]

James Bongiorno once told me, in his inimitable way, that SS circuits stabilize, after power on, in a matter of micro seconds. He said that you might want to wait a few minutes before you turn off the amp to allow the caps to dissipate. Heat is any amps enemy, and leaving stuff on will only lead to their early demise. Bongiorno said he does not leave anything on when not in use. I think he would be someone who knows a great deal about such things.

There are not too many people out there who would know any more, so I'd be inclined to believe him! [:scratch2: I should ask my Uncle this question. He's one of the few people alive who might know more. But I would expect him to give the same answer as Mr. Bongiorno would.]

I think the effects of the power grid, as well as the physiological changes in hearing (morning, after sleep, versus evening, after a day of listening) would outweigh the differences you would get from leaving gear on those extra hours.

While in theory, the equipment should stabilize in milliseconds or seconds, there are a few reasons why it may take longer, in practice. For one, ti takes time to heat things up to a "steady state" where heat energy coming off of heat sinks matches the heat energy being put into them, etc... Humidity is another factor: it takes energy to evaporate off water (which is how sweating helps keep us cooler). Climate (humid or dry) plays a role here. Air circulation likewise plays a BIG role, which is why we sometimes add fans to gear.

Leaving gear on versus turning it off and on will affect longevity. Repeated heating up and cooling off of gear stresses solder joints, and can thus lead to solder-joint breakdowns. But otherwise the lifetime of many components is shortened by higher temperatures, which speed up chemical reactions that signal their decay. Caps, however, deteriorate from being too idle for too long... but also deteriorate faster when kept too hot. In general, you are probably shortening gear by leaving it on all the time, or by turning it on and off too frequently. The best solution is probably a compromise: turn it off overnight, but if you will be listening at regular intervals during the day, perhaps leave it on through that period, just with the volume turned down(?).

One possible solution would be to run the gear with a trickle of lowered voltage (say, using a variac) when not listening, but for some kinds of solid state circuits/components, that is NOT advisable. Works well for tube gear, though.

 

[wineslob]

I don't know about it being in a few miliseconds, but the Bedini amp I use takes about 30 min to stablize. Until it does, you can hear a slight wavering of the imaging from left to right, and back (it travels a bit side to side). It seems to come and go for the above 30 min. After that it's rock solid.
Oh, when I had the amp rebuilt the sound of it changed for roughly 2 weeks. It went from VERY warm sounding (overly) to neutral.