Sound Quality Vs. Measurements

[Pano]

Originally Posted by tvrgeek

I finally got the picture using two meter probes as a delay line and a 1/2 meter as the trigger.

Clever!

[tvrgeek]

Standard remote control IR runs between 36 and 56 Khz carriers with a few odd-balls running as high as 70K. What the actual diodes can do I have not looked at. Considering that are talking about 10Base Ethernet being piped over the LED overhead lights, I would suggest there is some room there.

[a.wayne]

Err, can i interupt a bit here, Sy and others are you saying that a/ab SS amps don't suffer from Temperature induced distortion, when temperature tracking ..?

[DF96]

Which matters most: chip surface instantaneous temperature, or junction instantaneous temperature? A bit of dynamic thermal modelling would give a connection between them, but a zero result from aiming an IR diode at the chip surface is not sufficient to show that nothing is happening at the junction (in the absence of such a thermal model). At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.

[SY]

Originally Posted by DF96

At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.

That gets back to my original observation about the lack of distortion rise with lower frequency.

[Wavebourn]

Originally Posted by DF96

Which matters most: chip surface instantaneous temperature, or junction instantaneous temperature? A bit of dynamic thermal modelling would give a connection between them, but a zero result from aiming an IR diode at the chip surface is not sufficient to show that nothing is happening at the junction (in the absence of such a thermal model). At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.

Right. And junction itself is the best tool to measure own temperature directly. Chemist SY knows physics well. But moderator SY wants the show to go on, I suppose. All topics where he participates are usually hot and long.

[Wavebourn]

Originally Posted by SY

That gets back to my original observation about the lack of distortion rise with lower frequency.

Very strange observation, SY!

Use one common emitter stage, with stiff voltage bias, no emitter degradation, no feedback, feed signal from zero volt source directly to the base, and measure what you get on collector. Then come back and let's talk about observations.

Proposed apparatus: opamp follower with output connected directly to the base of a common emitter stage. Bias applied to the input of the opamp follower.

[SY]

Anatoliy, could you sketch out the circuit you propose? I *think* there's a fundamental problem with it, but it may just be my interpretation of what you're proposing.

[Wavebourn]

Originally Posted by SY

Anatoliy, could you sketch out the circuit you propose?

I can't. No convenient drawing software for Linux.

1. NPN transistor. Emotter to ground, resistor in collector.

2. Opamp. Output to inverting input (follower). Output of opamp directly to base of transistor.

3. Voltage divider, 1 resistor from + rail and one trimpot to ground. Whipper of the trimpot to the non-inverting input of the opamp.

4. Signal from signal generator to the non-inverting input of the opamp through coupling capacitor.

For measurement first set 1/2 of B+ on collector of the transistor adjusting trimpot.

Measure. Enjoy. The junction itself is the best indicator of it's temperature.

The fundamental problem is, how to tell which distortions are thermally induced on background of huge distortions of the stage itself.

[Pano]

Originally Posted by SY

That gets back to my original observation about the lack of distortion rise with lower frequency.

OK, but I'm still interested in brief signals that are 20dB or more greater than the average level.
Does running the output devices and drivers at room temperature or above the boiling point of water make any difference? How could you tell and how could you separate any difference found from other causes (PSU, or other)?