audioguru said:
Hi Nigel,
Figure that a Class-AB amp has a max efficiency of about 60%. It won't be driven to full output all the time (rock music does), will it? Calculate your power transformer's suitability from there.
The problem is I don't know the rating of the transformer, and yes! - my daughter plays rock music, songs at the gig will include their own songs, plus songs from AFI, Greenday, Muse, plus bands I haven't heard of :lol:
I've been running it for the last couple of hours, at fairly high volume (into dummy loads, with a speaker tapped off the bottom). I've got the chassis out, and the heatsink (just an aluminium plate) with the two original 2N3773's on, plus the two I added, is running at 77 degrees centigrade, 170 degrees fahrenheit - pretty damn HOT!. Still it's survived!, and (hopefully) it's had a LOT more hammer than it will at the gig?.
The transformer seems happy, you can rest your hand on it and it feels warm, not hot - touching the heatsink (never mind the transistors!) isn't a good idea :lol:
For my daughter, I would use a wideband TL071 opamp and let her and her friends hear the sizzle. :lol:
It's not a question of friends, it's a question of the audience at the gig, we've no idea how many might be there, we only know it's arranged by the Derbyshire Youth Service, who wanted an all girl band?.
Opamp changes are in the list of 'things to do', but for now it sounds fine, I've also got an older 300W mixer/amp, which doesn't use opamp's in the input channels (only for the mixer itself) - but the inputs don't seem as good as the 741 version, and although it has a hi/lo switch on each channel, it doesn't alter the input impedance, just the gain (I drew the circuit out the other day).
I'll be taking this amp as a backup :lol: