Heat Kills. Right? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th March 2010, 07:29 PM   #1
diyAudio Member
 
Join Date: Nov 2004
Default Heat Kills. Right?

I just cleaned up and reserviced an old hitachi amp and while I was at it I put a 90mm muffin fan atop the heatsinks to boost the updraft. 12vdc fan running on 4.5vdc. Just enough cfm to work and really negligible noise. These are all tradeoffs, and for the purposes of the super high fidelity that most home equipment aims for, even the barest whisper of added noise is anathema to many. So this question is not for the purists.

With this little mod, the output transistors on the sink are much much much cooler to the touch (an unscientific but significant improvement).

My question is... to what extent is heat in an amp analogous to heat in an internal combustion engine? The engine is designed to perform optimally in a pretty specific range as determined in its design. Too hot is not good. Nor, less obviosly, is too cool. Is this at all true for electronics?

I would expect far better lifespan out of any amplifier given a little fan assisance regardless of how well it was ventilated or how large the heatsink to begin with. But do they actually perform better when 'warmed up"?
  Reply With Quote
Old 5th March 2010, 07:37 PM   #2
diyAudio Member
 
Join Date: Nov 2005
It really depends on the bias circuit, and older often implies simpler and not so accurate over a wider temp range, though not necessarily. A cooler output stage needs more bias drive for the same bias setpoint. Of course forcing air through the entire amplifier might mean that every transistor is running cooler, so you can shift the operating point through every stage of the amp. Over the years I've stuffed fans around almost every amp I've had, depending on how hard I was abusing it at the time. When you're really running an amp hard pretty often you're more worried about it blowing up than becoming underbiased, and the heat generated is still enough to keep things in the normal range even with forced air. When you're barely running the amp over idle you may as well leave the fans off.
  Reply With Quote
Old 5th March 2010, 07:40 PM   #3
diyAudio Member
 
event horizon's Avatar
 
Join Date: Feb 2008
Location: East Midlands, England
You can't compare an engine to a power amplifier

There is no such thing as "too cool" with a power amp. The cooler it runs, the longer it'll last. The big problem is with the output transistors that produce the most heat. What you have is a silicon die welded to a copper substate & these don't happen to expand at the same rate when things get hot & sticky or contract at the same rate when switched off.

Given so many cycles of being turned on & off & used, ran at high volume etc if it's a class B amp, the silicon die eventually starts breaking away from the copper base & this leads to the eventual demise of the transistor. If you can keep it cool then it'll last longer.

In a class A amp it'll last longer if the thing is left switched on permanently as there will be no thermal cycling, eventually though all transistors will die
__________________
"Never let your morals prevent you from doing what is right!" Salvor Hardin
  Reply With Quote
Old 5th March 2010, 07:48 PM   #4
diyAudio Member
 
cowboy99's Avatar
 
Join Date: Dec 2008
Location: Texas Hill Country, SSW of Austin
Quote:
There is no such thing as "too cool"....
Its' been said ....in Austin,Texas
Especially during August
__________________
I'm kinda curious about that myself........
  Reply With Quote
Old 5th March 2010, 07:51 PM   #5
diyAudio Member
 
Join Date: Nov 2005
Yes, thermal cycling is important to consider. This is why if you can rig it a thermistor on the sink to control fan speed is really boss. For lower cost class AB amps often the sink is too small to prevent big case temperature swings during a single song, no matter what the fan does. Also, in older amps, the relative dryness of the thermal grease is a big issue. But by far the biggest problem is the slope of max power dissipation versus die temperature. If you want maximum dissipation capacity you have to keep the temperature down.
  Reply With Quote
Old 5th March 2010, 09:26 PM   #6
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
In my high power amp in a pc case I use 3 fans.
One sucks air in and another blows it out the opposite corner.
I also have fan blowing air through the internal heatsink.

I found using a slow fan was useless, it just didnt pass enough air through the amplifier. So I use 3 large pc fans running on 12 volts dc.
  Reply With Quote
Old 5th March 2010, 11:01 PM   #7
diyAudio Member
 
Join Date: Nov 2004
Given the input so far, I would say.... EXACTLY!

There is no such thing as too cool, especially in Austin, Texas, except that most Texas Republicans, and that's most Texans outside of Austin, would say the Austenites are too-cool for the common school! But that's another matter...

So if cool is all good in electronics, unlike our internal combustion engine, and if my fan is significantly reducing the temperature of all elements, especially the output transistors (i wish i had some real temps to provide - maybe i'll measure them) and if (all these ifs) the fan noise is actually (and this is usually the case) below the ambient threshold produced by the road traffic, neighborhood kids, air traffic overhead, furnace and airconditioning, mice in wall joists, etc... then what's not to love about an aux fan in your integrated amp?

Thermistor control would be nice, and electronically basic enough to be within the means of most of us at diyaudio to employ, but not really necessary unless you were listening to very dynamic music, at very low volumes, at 3am deep in the countryside (or in your very own anechoic test chamber).

Last edited by peace brainerd; 5th March 2010 at 11:06 PM.
  Reply With Quote
Old 5th March 2010, 11:04 PM   #8
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
The Arrhennius equation applies to MTBF for output devices. I understand that MTBF approximately halves for each 11C rise in temperature, due to doping migration effects which 'age' and eventually destroy the transistor.

Thereforce, you'd expect the output stage to last longer at lower temperature, and if the bias temperature management system is well designed there will be little difference in bias current regardless of temperature, within certain broad limits.

I found that moderate air circulation yielded around three times the still air cooling capacity in a small, multifinned heatsink. I could easily push 175W into a 180 x 180 x 50 heatsink with just 28C rise above ambient. Without forced circulation, dissipation dropped three times for the same rise. An amazing difference. Try idling an auto in heavy traffic with a defective visco coupler on the fan; they overheat very quickly.
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com

Last edited by AKSA; 5th March 2010 at 11:08 PM.
  Reply With Quote
Old 5th March 2010, 11:21 PM   #9
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
All the above gets my vote too - it's also my understanding that temperature is the big thing, the lower the better is almost always a good thing to lengthen the average lifetime of components. But they will all die eventually - there are so many ways in which they fail.

In DIY a failed amp is a great opportunity to build a new one
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 5th March 2010, 11:27 PM   #10
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by Bigun View Post
In DIY a failed amp is a great opportunity to build a new one
For me I love the challenge of fixing an amp.

I have seen some horrible faults in my time.
One was after replacing blown output MOSFETs the amp still misbehaved.
In the end I took out all the semiconductors and tested every component.
In the end a MPSA42 had lost all its gain and had an HFE of 1 !
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
to much heat! kanifee Chip Amps 9 15th July 2008 10:34 AM
What kills an opt tranny? JojoD818 Tubes / Valves 28 3rd September 2006 02:45 PM
How do you deal with the heat?? Magura Everything Else 15 3rd June 2004 12:44 PM
Heat macka Pass Labs 1 11th June 2003 07:15 PM
Turn on surge kills 1 2nd winding of transformer? Cradle22 Parts 10 23rd April 2003 11:22 PM


New To Site? Need Help?

All times are GMT. The time now is 02:30 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2