Your fast is your amp f rom 0-60 .?

My McIntosh MC240 sounds great within 5 minutes but it sounds even better about 1 hour later. I tested its biasing with a multimeter connected to the internal circuit and it settles down after about 30 minutes but the sound doesn't change much during that time. The output transformer takes about 1.5 hours to reach thermal stability.

It is only normal for SS to be slower to reach thermal equilibrium since they generally don't consume as much power. However, my experience with Gryphon Class A amplifiers is similar to tube amps: super hot in no time! Class D amps are at the opposite end of the spectrum.

Arthur

09-10-08: Aball
It is only normal for SS to be slower to reach thermal equilibrium since they generally don't consume as much power. However, my experience with Gryphon Class A amplifiers is similar to tube amps: super hot in no time! Class D amps are at the opposite end of the spectrum.

This has definitely been my experience. I got in the habit of keeping my high current SS amps on all the time, and am unsure how much that might have contributed to my electric bill. When I got in to playing guitars into tube amps, I was surprised how little warm-up time was required to hear the difference in tube swaps and the like.

My s.s. amp is ready to play in about 10 seconds from cold power up.
However, for it to sound good & re-confirm to me why I spent so many $ on it, it takes about 40 minutes.
FWIW.

Abal - any piece of gear sounds better after few minutes but sometimes it is combined effect of, for instance, speakers sounding better (tweeters' ferrofluid getting warmer etc). In case of the class D it probably achieves full temperature of output transistors faster than class A (smaller mass to heat-up) but it is not even relevant here since time (duty cycle) and not the voltage is important parameter here (before passive low-pass filter). Output Mosfets, if anything are slower (less accurate) with temperature.

Kijanki - I am getting a phd in Class D circuits and have witnessed variations with temperature in PWM waveforms first hand. Whether it is audible or not is a good question but the feeback loop really has to work to keep the duty cycle in check (mainly because the voltage feedback loop is very fast and few audio modules use the slower current control loop). Tracking a musical signal is tough work and beat frequencies are all over the place, some of which are thermal.

Also, depending on the level of switching frequency, it can take longer than expected to reach thermal equilibrium. It depends on the modulation scheme and signal as to what the duty cycle is but typically, it is 50%. In this case, I doubt that they will reach equilibrium faster than Class A. Those Gryphon amps would burn your hand in less than 5 minutes despite massive heat sinks, if they weren't playing music, whereas I have had thermocouples attached to switching devices and watched their temperature rise in real time and it took about 15 minutes for the curves to level off with an output current of 100A (multiphase buck). If the devices are attached to heat sinks in addition to the multi-layer PCB, it will take much longer still (lots of mass, little energy). You can look at a Class A amp as having 100% duty ratio and 10x the bias current. It will be hard for a Class D amp to beat that kind of energy level, regardless of the mass involved.

As a result of all this, I would leave a switching amp on all the time. Besides, it hardly uses any power.

MOSFETs are actually not as sensitive to temperature as BJTs. Voltage drive doesn't pay much attention to variations in circuit impedance - unlike current drive. Not to mention having positive temperature coefficients.

Just details but thought you might be interested.

Arthur