Do external DAC & headphone amps need "burn-in"?
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Solved by Spuriae,
There are slight advantages to warm-up even on solid state devices, but don't expect the changes to be significant. It's more about having stable operating conditions than a real burn-in phenomenon. Off the top of my head,
- Oscillators are fairly temperature sensitive. Very expensive ones (unrealistic for normal consumers) will be temperature controlled (the IC contains a heating element and insulation), while cheaper ones will decrease in phase noise slowly as temperature stabilizes.
- Most multibit DACs have better even order linearity and lower switching error around 50C. In general R2R designs are going to be very susceptible to temperature changes since the error on the most significant bit needs to be very low. A drift of 0.001% starts eating into 16 bit resolution; 0.00008% (less than 1C at 100ppm/C) is 20 bits. High-end oscilloscopes specify warm-up time and provide temperature calibration for this reason, as they too require a very accurate MSB.
- Lots of components used to set operating points have surprisingly large drifts with temperature. The LM334, often used as a current source, is variable enough to be advertised as a temperature sensor. Zener diode temperature coefficients are all over the place. These effects can be compensated for but rarely are since they aren't that big a deal for most people (after all, it's just bias and not directly in the signal path).
- Even though they aren't as temperature dependent as tubes, transistors still drift a decent amount. Though it's a higher order effect, it's roughly a linear 0.5-1% difference in gain per degree at reasonable temperatures depending on device.
Take a look at these measurements of the Yggdrasil taken at ~2hrs on vs ~2weeks. Note especially the improved jitter and midscale error. Keep in mind also that these are small effects. For amplifiers the practical warm-up time is probably on the order of minutes.
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