Do all amplifiers sound the same? No, Unquestionably, to my ears. For those demanding some sort of objective test, please do not read on - this will be a bunch of static and not worth reading.
For the rest - here's the scenario. I just got new speakers. They are revealing to the point of being holographic. Inadvertedly, I fried my main amp and had to use an integrated Audiolab that retailed for about $1,000 in 1996. It is rated at 65 wpc and has a preamp-circuit bypass, so I was using the power section only, with a separate pre.
Two nights ago, I listened to Norah Jones, Come Away with Me, which is a very special CD. I was astounded by the spaciousness and clarity of the sound. The speakers completely disappeared from the room. I know this is somewhat cliche, but when you get it right, they really do.
The speakers have a neat feature that allows you to bi-amp. My original (and ultimate) plan is to use the integrated as the second amp to the speakers. I had the idea of bringing my garage amp and using it for primary duties, and sending the integrated to it's planned function as second fiddle. The garage amp is a respectable, though inexpensive NAD that claims 30 wpc and retailed for around $300. It is nearly new and is in perfect operating condition.
Last night, I was using only the NAD. I listened to the same CD and the magic was gone. Sure, just about all the same sounds were there, but the precision, textures, and tangibility were not. The most objective and noticable difference was a pronounced treble rolloff. The soundstage was condensed and overall immersion lost. Upshot? The Audiolab is going back into main duties until I get the broken amp back.
Setup was identical, except that I was using nice Naim cabling for the NAD and stuff I made from Lowe's for the Audiolab. Both events were at similar volume and well within the limitations of both amps.
This was not what I expected at all. I thought these amps would be fairly comparable, with the Audiolab possibly having a slight edge with its higher power rating and somewhat superior pedigree.
After all the exchanges over this, a small corner of my mind was doubting whether amplifiers actually DO sound different. That minority view has now completely been quashed. No question whatsoever. Don't hold your breath waiting for an old amp shootout test, there isn't one coming.