Bernhard said:

**thanks for the calculation, **

which means, my transformers are useless...

Your calculation says 6,6W x 8 = 53W

I did not know, that I must have double nominal transformer power...

But still the output power seems to be so small...

The manuals of Alephs say:

250W gets 60W / 8 ohms A3

300W gets 120W / 8 ohms A5

500W gets 200W / 8 ohms A4

so, my 350W should get 140W / 8 ohms, if compared to A4/A5 and 84W / 8 ohms, if compared to the A3

What would You suggest for each of the two transformers ?

I like to get 15W for the tweeter, 15W for the midhigh, 15w for the midlow and 60W for the woofer from each transformer.

So the 15W channels must run with the same rail voltage, as the 60W channels, is that possible ?

Bernhard

I'll try to address each point in order.......

The power output is so small because from a power requirements point of view, we are driving around about a 2ohm load per transformer so for a given transformer VA rating, we require many more amps and less volts (something the stated transformers are not designed for ie. voltage too high, current too low).

The power requirements you stated above for various Alephs is 1/2 the minimum transformer VA rating.

If you want only 2 transformers, i'd recommend that you use one transformer to supply the 6 x 15W channels and the other to supply the 2 x 60W channels as this is by far the most efficient way of meeting your requirements. You could run the high and low wattage amps off the same rails but the power wasted becomes very large indeed (and heat also

)

Given the above and assuming all drivers are nominal 8ohm resistance, the 2 transformers should be rated thusly.....

6 x 15W into 8ohms is from a power standpoint the same as 90W into 1.33ohms

So,

90W/1.33 = 67.5

sqrt 67.5 = 8.22Amps

8.22 x 1.4142 = 11.62Amps

11.62 + bias current = 18Amps

and

90W/1.33 = 67.5

sqrt 67.5 = 8.22Amps

8.22 x 1.33 = 11Volts

11 x 1.4142 = 15.5V

So accounting for mosfet and diode losses, rails of about 20Volts would be most suitable.

If it were me, i'd probably go for secondaries of between 16V and 18V depending on what is available to you.

So the transformer must have 2 x 16-18VAC @ 18Amps secondaries which fits fairly neatly in with the other Alephs power requirements.

This would mean each amp would have bias of about 1.07Amps and an output of about 15W into 8ohms.

2 x 60W is an Aleph 5 which has rails of +/-34V and current draw of about 9Amps.

So, 28VAC @ 600VA is probably about what i'd go for there which translates to 2 x 28VAC @ 11Amps secondaries.

Hope all this helps ....

Regards AudioFreak.

ps. this is a total of about 590W power consumption