How to assess compatibility with speakers?
I recently built this amp: DIY Class-A 2SK1058 MOSFET Amplifier Project
. For now I'm using a SMPS rated at about 4.5amp, not the 5amp spec'ed in the project. It's quite enjoyable really!
Now I'm wondering how to determine what speakers it would be safe to drive. In short, I've driven Vandersteen 1Cs (6.5 ohm, 89-90dB but supposedly still a difficult load), Ohm E (? I think - 3-way ported box), RTR and a DIY pair of Pass BOFU speakers safely and quite nicely.
But now I've lent the amp to a friend to demo, and he has some Totem speakers (Mani-2 I think) that are 4 ohm/85dB or so and EXPENSIVE. I don't want him to fry his beloved speakers, so I'm wondering if it's a safe match (the Totems go down to 1.5 ohm or so)? Nevermind the efficiency issue...
What I really want to know, though, is how to evaluate the compatibility of ANY amp with speakers. I understand the impedance matching issues a little, so I'm more concerned with 1) how to calculate output impedance of an amp like this, and 2) what other concerns I need to keep in mind (e.g. current draw and capacity, etc. etc.). I don't so much mind if the amp fries as it cost me little to build. I'm more concerned about my friend's speakers...
Thanks a ton for any input on what to consider under such circumstances.