Do you measure component temperatures?

[Greg Erskine]

I have an InfraRed Thermometer and for the last year, whenever I have the top off one of my amps I take a look at the temperature of the various components. I am trying to get a feel for what is normal.

I realise the differences between classes and how hard the amp is being driven will make a difference.

On my AKSA 55 amp, the temperature of the components are what I'd expect. All active components are elevated a few degrees above ambient, maybe up to 10 or 12 degrees.

But...on some of my amps, some components (input pairs, some resistors) are over 50 degrees C and that's just sitting on my test bench.

Looking at the datasheets it indicates that these devices behave differently (sometimes better) at these higher temperatures. Do designers decide on an operating temperature of the various components? I suppose temperature is probably just a function of voltage and current (power) so there may be no need to focus on temperature.

regards

[Wavebourn]

I would love to have a camera based temperature measurement device, but it is too expensive yet for me to afford. Looking at the picture in dynamics is very revealing. For example, you can see oscillations of termocompensations that can't be caught easily; you can see how to improve layout, and so on.

I mean, something like this one:

http://www.mikroninfrared.com/Catalo...7b_8_24_1092_1

[Greg Erskine]

Thanks Wavebourn,

That Mikron M7800 Infrared Imaging Camera looks really cool.

I had never really thought of thermal imaging in relation to audio before. It would be interesting to see a movie of a complete amp goig through its heating and cooling cycle.

The only problem I can see would be, a normal temperature for an output devices might be dangerous for a capacitor. So the 'red' on the image would not always be a problem, but I guess anyone with experience could be able to work out the problem areas will little effort.

regards

[wrenchone]

I'm lucky - we have an $8k thermal imaging camera used to record temperature profiles for switching power supply prototypes. It's a little hand-held thing that stores data on a standard memory card. What makes it especially valuable is that you can use the software included with the camera to look over the image data at your leisure to scope out device temperatures after the fact. The thing has paid for itself already in uncovering problems with components where one would normally not think of pasting a thermocouple.

I haven't used the camera for any of my amp prototypes yet. I usually just let my fingers do the walking - 50C is ~10 sec uncomfortable, 55C is 5 sec uncomfortable, and 60C is "get your finger off right away". Your fingers are sensitive nonlinear thermometers developed over long years of evolution....

[Wavebourn]

Is it possible to borrow it somehow? I would bring my amps to take series of pictures.

[Mr Evil]

I use my thermal sensing digit. I have nine spares.

Designers should be paying attention to how much power everything dissipates, and also to where hot components are in relation to everything else, e.g. no heat sources near input stages.

[pacificblue]

Originally posted by Greg Erskine
On my AKSA 55 amp, the temperature of the components are what I'd expect. All active components are elevated a few degrees above ambient, maybe up to 10 or 12 degrees.

But...on some of my amps, some components (input pairs, some resistors) are over 50 degrees C and that's just sitting on my test bench.

When the amp is closed, those temperatures will be different. They will be higher in general and more similar to each other from component to component.

One of my profs gave the rule of thumb that at 25 °C ambient the inside of an enclosure with electronic components would heat up to between 60 and 70 °C. And that we should therefore always calculate the components for an ambient of at least 70 °C, better 80 °C for a safety margin. Higher, if the apparatus was to be exported to hotter countries. That was at a time, where surface mount did not exist yet, and the possible packing density turned out to lead to that temperature range. Heat dissipation for resistors is usually given at 70 °C. Coincidence?

We will probably have to raise that figure soon to make up for global warning.

Originally posted by Greg Erskine
Looking at the datasheets it indicates that these devices behave differently (sometimes better) at these higher temperatures. Do designers decide on an operating temperature of the various components?

[insert text block]Some do, others don't.[/insert text block] That could be one of the differences between good and bad designs, and the reason, why many audio components sound better, when they have warmed up.

[AndrewT]

Originally posted by Greg Erskine
On my AKSA 55 amp, the temperature of the components are what I'd expect. All active components are elevated a few degrees above ambient, maybe up to 10 or 12 degrees.

I think that is AKSA's design expertise showing through in a practical example.

I would expect, if second guessing Hugh is allowed, that he has taken account of many and various factors that affect sound quality and looked for methods that maximise SQ.

I would not be surprised if he came out and said that temperature modulation of semiconductor junctions and maybe to a lesser extent resistors too, do affect SQ and that minimising the temperature rise of each of the devices, particularly in the front end of the voltage amp stage also reduces temperature modulation.

My own thoughts are to run everything as cool as practical and fit heatsinks if significant heat must be dissipated, even in non power devices.

[Steve Dunlap]

For about the last 10 years I used thermocouples epoxied to the device to be monitored. Sometimes there could be as many as 20 thermocouples in one piece of gear. You then monitor the temperature with the component running normally, again in a 35C oven and again in a 50C oven. One hour at each temp is usually enough.

[Greg Erskine]

Originally posted by pacificblue
When the amp is closed, those temperatures will be different. They will be higher in general and more similar to each other from component to component.

One of my profs gave the rule of thumb that at 25 °C ambient the inside of an enclosure with electronic components would heat up to between 60 and 70 °C. And that we should therefore always calculate the components for an ambient of at least 70 °C, better 80 °C for a safety margin....%<

Thanks pacificblue.

Yes I understand about when the amp is closed, but the degree of change will be depend on physical design of the amp. In my case, the cases are 3U with lots of space between PCBs, the main heatsink is oversized and external. A lot of commerical gear seems to be more tightly packed and use internal heatsinks, so the temperature difference between closed and open will be greater I imagine. Also, equipment designed with fans may actually run hotter with the lid off, I know this applies to some PCs.

Thanks for your profs rule-of-thumb values, it gives me a little bit more confidence. It looks like everything I have measured so far is well within your profs rule-of-thumb.

regards