It applies to both AC and DC applications.
Taking your last post as an example it can be reworded to become:
If it's significantly measurable, the wattage rating of the resistor is too low. It's important in both AC and DC applications like measurement bridges.
Otherwise, TCR can be ignored, unless engineering was ignored.
Full details in the Linear Audio article and the Blowtorch thread. There absolutely is thermal distortion on AC! Shows up as you sweep the test frequency.
No need to repeat one of those threads, there is not that much to be learned from bad engineering. BTW I came across a paper that claimed the seconds were intermods of the fundamental and the thirds caused by the heating (TCR) explaining all the excessive distortion on thermals alone i.e. no rectification.
Last edited:
That would nicely explain why no 4th harmonic. However there still is a chance some resistor somewhere does have some rectification. But I would consider that a defective sample.
Now if we didn't repeat the same stuff over and over and over.... There would be a lot less DiyAudio..
What are the time constants for resistor temp? Are they fast enough to matter? Need to be faster than about 25 ms? ( 20hz). Seems rather fast but would like to see the numbers. And for a music signal ( not a LF sine wave )the TC would probably be at least an order of magnitude higher. In other words, the temp. of a resistor dosnt change fast enough ( compared to the time between signal zero crossing ) to matter.
At low audio frequencies the thermal cycling can be slow enough for distortion to show up in some resistors. It's easy to measure in 1/8W carbon film resistors, or even 1/2W devices, but I've never detected it in metal films, even 1/8W devices (it might show up with very large amplitudes, if you can generate them). Carbon comps generate so much voltage-coefficient distortion that it swamps thermal effects if they exist.
But the topic is "sound quality." Whether or not this is relevant to audio kinda depends on where something is used in a circuit and what the circuit looks like, right? (Yes, I know you know this, it's a pedagogical point)
Sorry for being unclear. I mean as the power in the resistor increases on the peaks of the waveform, and decays around the zero crossover, if the frequency is low enough then the temperature has time to track the signal and thereby introduce distortion. At hgher frequencies the signal changes too fast for the temperature to track the changes, so it becomes constant, steady-state.
Yes. The easiest way to accomplish that is... increase wattage. That assumes that the effect in a given situation is enough to cause a circuit to audibly misbehave (see the article I've cited many times, "The Sad Tale of a Half Watt Resistor").
The other way is to use more resistors to share the thermal load. If I correctly recall a lecture AD gave mumble decades ago it was a std precision analog practice to use multiple resistors in a string both from an accuracy perspective and a thermal perspective.
Memory failing, but they also pointed out that IF you are worried about that sort of thing affecting your circuit then the dissipation and thermal gradients of the entire circuit including any airflow needed to be taken into account in the design.
Oddly enough not much in domestic audio is designed according to the 'precision analog' principles that were first enshrined over 30 years ago (and I will admit I have forgotten most of that in that time). But it would be heresy to suggest that there are things out there that need to be measured more accurately than the human ear can detect.
Memory failing, but they also pointed out that IF you are worried about that sort of thing affecting your circuit then the dissipation and thermal gradients of the entire circuit including any airflow needed to be taken into account in the design.
Oddly enough not much in domestic audio is designed according to the 'precision analog' principles that were first enshrined over 30 years ago (and I will admit I have forgotten most of that in that time). But it would be heresy to suggest that there are things out there that need to be measured more accurately than the human ear can detect.
Most would, but sometimes it's worth looking at things from another angle. Analog Devices : Rarely Asked Questions (RAQs) : Resistors in Analog Circuitry (and apologies if this has been quoted before on this thread) contains bits of that late 80s lecture, but sadly missing the part about multiple resistors. Worth a scan to see how easily from a 'precision' standpoint you drop resolution.
Or we just accept that audio is not a precision discipline but some fun that allows us to sniff some solder fumes.
Or we just accept that audio is not a precision discipline but some fun that allows us to sniff some solder fumes.
Hi,
Yeah, sure. I should have added that in my small field of electronics the exact R value is of no great consequence for as long as it is close enough to ideal. Of course, it should be a stable R and not be impacted by whatever signal or current is sees during normal usage.
Far too many people consider passive components as being just Rs, Cs and Ls and that's where the links comes in as an eye opener for sure.
I think it was DF96 who mentioned earlier on the importance of knowing RF to some extent to gain insight on what and what can not be of influence in AF design. At this day and age I'd say you can not do without it and many of the better designers apply this to audio to good effect. Obviously so, I'd say.
Cheers,
Yeah, sure. I should have added that in my small field of electronics the exact R value is of no great consequence for as long as it is close enough to ideal. Of course, it should be a stable R and not be impacted by whatever signal or current is sees during normal usage.
Far too many people consider passive components as being just Rs, Cs and Ls and that's where the links comes in as an eye opener for sure.
I think it was DF96 who mentioned earlier on the importance of knowing RF to some extent to gain insight on what and what can not be of influence in AF design. At this day and age I'd say you can not do without it and many of the better designers apply this to audio to good effect. Obviously so, I'd say.
Cheers,
- Status
- Not open for further replies.