Is 100VA per LM3875 good enough?

[uvodee]

I use that low current set up for testing only, I noticed also that when cranking the thing up, the transformers are not happy.

J-P

[Pjotr]

Hi,

Well point is how hard do you want to drive the chip? I’m driving it not too hard and I’m driving 90 dB eff. monitor speakers with it that gradually falls off at 60 Hz (closed box). The speakers have also a gentle impedance curve. In my case 18V transformers sound better than 22V transformers at moderate level. Have also tried 22V/250VA toroidals, the 18V / 50VA’s sound somewhat more relaxed. But honestly the difference is small. In the smaller trannie there are smaller but wider peak currents flowing because of the higher Ri.

And no I don’t use it for parties

[intotubes]

Ok that makes sense. I'm driving them pretty hard most of the time. Have them on large heatsinks so barely get warm. Even running hard, these are great sounding little amps. Beats the heck out of store bought boom boxes my kids have.

I guess I missed the point of the original posts.

Mark

[Circlotron]

Originally posted by Circlotron
i'm using a 120VA 2x25V EI for 2 channels. Works like a charm.

Mine makes a measured 44 watts rms per channel with 1 channel driven. (Didn't have time to measure both). It has 3 x 4700uf for each rail - none of this 1000uF stuff. For the pair of 89dB subs in my 4m x 7m loungeroom it is heaps powerful enough. I must be getting old.


/Circlotron - doesn't have a 50kw amp in his car either.