If "warm" amplifier makes difference ..

[voodooless]

I think @solderdude hit the nail on the head. There are only two possible answers to this question:

- bad design
- imagination

Some temperature variation is always measurable, but the performance difference should never be audible.

 

[charleski]

Since we're in hifi land, I think it needs to be said: while there definitely are a variety of temperature-dependent factors that affect amplifier performance, these are all well-understood and can be compensated. A well-designed amp shouldn't exhibit any significant shifts in performance after being turned on for a minute.

It's easy to find people who claim they get better sound by leaving their gear on 24/7, but this is either a) nonsense or b) evidence of very sloppy design. In either case it's a gross waste of energy and adds to our carbon footprint. Such people should not be surprised if their great-grandkids do a Tenet and come back to the past to exact revenge.

 

[Martini]

This is not the case with Benchmark.
From their manual:

No Warm-Up Required​

Unlike most power amplifiers, the AHB2 reaches its full rated performance very quickly. Full rated performance is reached in less than one minute. For this reason, there is absolutely no reason to keep the AHB2 powered on when not in use. The feed-forward error correction circuits in the AHB2 keep it very stable over a wide range of operating temperatures.​

 

[Grumpish]

I think @solderdude hit the nail on the head. There are only two possible answers to this question:

- bad design
- imagination

Some temperature variation is always measurable, but the performance difference should never be audible.

Agreed on that - I can, and have, measured electrical changes that have occurred while an amplifier has been warming up, but have never heard any differences.

 

[egellings]

Maybe when cold, voltages & currents in a device may not yet have reached their stable quiescent operating points yet. After the device is on for a while, these parameters drift into their final designed values, and it's possible that there is a sonic signature to that in some equipment.