Does the heat an amp puts out have any effect on the sound quality ?


Does  how hot an amp runs have any effect on sound quality ?
Or is this only a concern for the longevity of the amp? I have an old Harmon Kardon
amp that supposedly puts out 60 watts at 8 ohms and has 30 amps of current.
when purchasing I was comparing it to  an onkyo with 120 watts. They were driving
a pair of jbL monitors. It flat out smoked the onk. Probably twice the volume.
I decided On a minor upgrade down the road to a Yamaha as-500 at 85 watts.
Years later I got tired of the brightness of the Yamaha. Decided to hook up the Harmon
kardon just for kicks. Instantly the mains came back to life. Much cleaner an  better bass  maybe
a little more volume. Its almost like harmon Kardon put a wrong part in this amp. Making it sound much better than it should. My only concern is how hot it runs. It doesn't seem to effect anything even
at long listening periods. Should I be concerned at how hot it runs. It has given me no problems.
Any one have any opinions ?
jcb1957
No reason to be concerned. Many amps run hot,especially class A amps.Enjoy the amp and don't worry about it!
Thanks Y
I think heat is a byproduct of the amp design.  With a Class A amp each output device conducts both half waves, so it runs full out all of the time, dissipating what current is not sent to the speakers as heat.  The higher the speaker output, the less the heat output.  The heat itself will probably not be an issue, but I once had an OTL amp that put out so much heat that it eventually damaged components inside the amp, so it was a reliability issue.  Most amps are well enough designed to avoid this problem.  You probably found through your amp experience that watts are not necessarily watts and that current is the real factor that affects how loud the system will sound.  I would bet the HK to have a much more robust power supply and it probably weighs more.
I recently upgraded my speakers to a model that is less efficient than my previous speakers.  I have been noticing that my amp although warm before is hotter all the time now as it has to work a bit harder into the speakers with lower efficiency.  Probably welcome come the colder months!

The more "within reason" heat (at idle) an SS amp puts out, usually means the more Class-A bias is on it. And should equate to better sound on "that" same amp running cold. But there are many other factors that should be considered for high bias class a, power supply ability, heatsink area, etc etc. 

Cheers George
Size, heat, and cost I'm afraid are not reliable ways of determining the musical enjoyment you'll have with any particular piece of gear. 

There are some who insist on all three being maximized, but those of use without friends, or who don't care what they think are less interested in that as much as what our own ears enjoy listening to.

You can make good, and terrible sounding Class A amplifiers (well, at least I can make terrible one's) or amps that are poorly matched to your speakers, as well as for Class D or class H.

For me the win is in finding something truly great that is cheap, small and cold. :)

Best,


Erik
Does how hot an amp runs have any effect on sound quality ?
Or is this only a concern for the longevity of the amp? I have an old Harmon Kardon
amp that supposedly puts out 60 watts at 8 ohms and has 30 amps of current.
when purchasing I was comparing it to an onkyo with 120 watts. They were driving
a pair of jbL monitors. It flat out smoked the onk. Probably twice the volume.
I decided On a minor upgrade down the road to a Yamaha as-500 at 85 watts.
Years later I got tired of the brightness of the Yamaha. Decided to hook up the Harmon
kardon just for kicks. Instantly the mains came back to life. Much cleaner an  better bass  maybe
a little more volume. Its almost like harmon Kardon put a wrong part in this amp. Making it sound much better than it should. My only concern is how hot it runs. It doesn't seem to effect anything even
at long listening periods. Should I be concerned at how hot it runs. It has given me no problems.
Any one have any opinions ?
jcb1957
The 60W/ch HK has a max current limit of 30A that it will output under extreme conditions such a huge transient in the music or if you (in error) short the amp output terminals. It's a hint on how robust the power supply is. Just to be clear it is not outputting 30A of current during normal music playback. I got the feeling that you were equating the 30A of current to how hot the HK amp got. That 30A current limit's got nothing to do w/ how hot the amp is running during routine playback. that is dependent on how the designer biased the output stage transistors (I'm assuming this is a solid-state HK like the PM655 since you did not say it was a HK Citation II) & whether or not the designer intended it to operate in class-A for all 60W or for part of the 60W (& then slide into class-AB mode).

Check the manual (if you have one) how hot this amp is supposed to run. Maybe it's designed to run hot all the time? For eg, certain older Threshold amps (from Pass Labs) were designed to be full class-A & their heat-sinks needed to measure +54C to indicate proper operation. My class-A amp heat sink also measures +54C after it has warmed up. So, running hot could be normal for your HK amp....

In general, if the amp is designed to dissipate the heat it generates (by having adequate heat sink size & vents on the top, side & bottom) then it should have a long life (assuming that the designer knew what he/she was doing & is operating the output transistors in their safe-operating-area (SOA)). Also associated with this is what rlawry wrote - the surrounding components & the PCB should also be made such that they can withstand the heat generated by the output transistors otherwise components other than the output transistors will fail. One such component susceptible to failure is electrolytic capacitors - heat is the worst enemy of electrolytic caps. If you see caps with bulging tops, get them replaced ASAP. Make sure that you replace them with the same temperature spec as the original. For eg. if you had a 4700uF, +85C electrolytic, make sure the new one is also +85C or higher (which will cost more $$).
If the amp is not designed to dissipate the heat it generates, it will shorten the life of the output transistors & as they gradually fail, you will lose output power & will experience increased distortion.
I dont know how old your HK is but one thing to do is check the electrolytic caps for bulges & check the thermal paste under the output transistors. This paste looks white & over the years of heating & cooling the paste becomes chalky & if touched flakes off. If this is the case, it's become dry & probably is not doing a good job of connecting the output transistor case flush to the heatsink. This in turn means that the output transistor is not dissipating its heat into the heat sink efficiently & is getting more-than-necessarily hot. If you are handly you can disassemble the power amp, remove the power transistors & reapply the thermal paste & reassemble the amp. Or, have a technician do it for you. I dont know if you have spare output transistors as back-up should they ever fail but if you dont & this amp has not been serviced in a while this might be a good thing to check because if you fry an output transistor you might be done for good unless you can find the exact replacement. iow, spending $$ on maintenance could save your amp in the long run esp. since you seem to like it quite a bit....  
Does how hot an amp runs have any effect on sound quality ?
A definitive answer can’t be provided without knowing if how hot the amp is running is normal or abnormal for the specific design. If it is running abnormally hot for some reason, in other words hotter than it was designed to run, then yes, its sound quality may be affected. By both whatever is causing the abnormal temperature and by the abnormal temperature itself.

The others have made very commendable attempts to answer your question as thoroughly as possible, especially in the post just above, but we might be able to provide answers that are more focused if you would tell us what the model number of the amp is.

Regards,
-- Al


Thank you all for your input !
       Keep listening J.
It will not do that.
So for the sake of Almarg's question of the model amp, we can use mine. I have a Accuphase E-600 Class A with Harbeth C7ES3 speakers. Overkill yes, but a path to upgrades for an integrated lover. I don't find the Accuphase to run overly hot. I believe class A running hot is a blanket statement pople throw out there for all class A amps.

Don, the relevant specs on your equipment are:

Speaker impedance:  6 ohms nominal, described as "easy to drive."

Amplifier:

Rated Continuous Average Output Power (both channels operating simultaneously, 20 - 20,000 Hz):
150 W/ch 1-ohm load (1-ohm operation possible with music signals only)
120 W/ch 2-ohm load
60 W/ch 4-ohm load
30 W/ch 8-ohm load

Power Consumption:
160 watts idle
260 watts in accordance with IEC 60065
200 watts for rated output into 8 ohms

Maximum Dimensions:

Width 465 mm (18.31”)
Height 191 mm (7.52”)
Depth 428 mm (16.85”)

Weight:

24.7 kg (54.5 lbs) net

Consistent with what you have found, I would not expect an amp having size and weight as substantial as the E-600 and dissipating (consuming) roughly 200 watts to get particularly hot.  The same dissipation in a much smaller package would be a different story, though.

Regards,
-- Al
  
well, for the sake of discussion then......

I've a vintage Yamaha CA-2010 integrated which has a switch on the front to toggle between Class-A & "Normal" (which is Yamaha speak for class-AB). in class-A it is also a 30W/ch into 8 ohms just like donjr's Accuphase E-600. in my particular case, the amp's heatsinks (in the middle of the amp) become really hot. In the manual i read that the quiescent bias for the output stage is stepped up to 300mA in class-A while it is just 25mA in class-AB. The amp has no forced cooling & it is vented on the top + bottom + back. I suppose that Yamaha intended to operate with this sort of heat dissipation....
Could it be possible that the Yamaha's heatsinks are much smaller than the E-600's hence the higher heat??
The dimensions of the amp are quite similar to the E-600 & it's just 8-9 lbs lighter.  
Bombaywalla, here are internal photos of the Yamaha CA-2010 and the Accuphase E-600:

CA-2010 internal view

E-600 internal view: On page 3 here.

There may be somewhat more heatsinking on the E-600, which perhaps contributes to the weight differential, but it’s hard to tell for sure (in part because the height of its heatsinks isn’t apparent in the photo).

Perhaps more significantly, though, I see that the CA-2010 is specified here as being capable of providing:

2x 120W (Class B, 8 Ohm, 20Hz...20Khz, 0,03% THD)
2x 130W (Class B, 8 Ohm, 1Khz, 0,03% THD)
2x 140W (Class B, 4 Ohm, 20Hz...20Khz, 0,03% THD)
2x 180W (Class B, 4 Ohm, 1Khz, 0,03% THD)
2x 30W (Class A, 8 Ohm, 20Hz...20Khz, 0,03% THD)

And has having power consumption as follows:

600W / 700VA (USA / Canada)
900W (EU)

I see three relevant implications in those numbers:

1)Although the test conditions upon which the CA-2010 power consumption numbers are based are not explicitly specified, all of those numbers are far greater than the numbers for the E-600.

2)The relatively small increase in the power capability of the CA-2010 into 4 ohms vs. 8 ohms would seem to indicate that it is not designed in an especially robust manner, which would seem consistent with a greater rise in internal temperatures compared to a more conservative design.

3)The fact that the CA-2010 is specified to operate in class B at much higher power levels than in class A would seem to suggest that its internal B+ and B- voltages are likely to be much higher than in the E-600. Which in turn would seem consistent with its much higher specified power consumption.

Best regards,
-- Al

there is no doubt in my mind that the E-600 is a better designed integrated & it is also accordingly priced. These 2 amps come from a different eras of audio - 2009 for the E-600 & 1977 for the Yamaha.
yes i did see that the specs of the CA-2010 indicated a not very robust power supply for hard-to-drive speakers. Luckily for me the speakers it is driving are almost flat 8 Ohms; so, very little stress on the amp.
thanks for taking the time to research these 2 amps & compare their specs......   
Heat good...cold bad !  
For me it does. I would love to have a little powerhouse amp that ran cold, but I like a warm sound signature and class D doesn't give me the even order harmonics that I enjoy.
Class D certainly offers its own unique sound, runs very cool but my preference is more towards conventional designs. Anyway I think heat is good for transistors, as they warm up they sound better but definately not if they go into thermal run-away.
My Krell gear sounds best when pushed hard...4ohm loads or lower bring out a sweeter sound!