Choosing transformer VA-IcePower 500A into Scintilla

Phisci

Member
2012-08-03 6:28 am
Hi guys, recently acquired a Class D 500A Mk2 Icepower amplifier module (2 mono units). A friend has an Apogee Scintilla that has an impedance that drops as low as 0.5R!

So the 500A amp requires a +75V power supply and we'd like to know what the best VA rating for a transformer should be. Please detail calcs if possible. Thanks guys!
 
I would say between 500-800VA. You only need a single supply for the H-bridge that is on the B&O IcePower 500A mkII and some +/- 12 volts for the driver circuit.

If you find a torodial transformer with dual 55 volt AC then you need to parallel these to double the current. Have in mind that a 800VA with dual sec. has 2x400VA secondaries.

55V AC should give you 77 volts after rectifier. And that should be okay with the 500A mk2

Most important is the capacitor. Here I would choose one large type like Kemet PEH200 series. 47.000uF 100V. ESR 7 miliohm @100Hz, 6 miliohm @100kHz Iripple [email protected], [email protected]Hz.

After you listen to Class D/ IcePower for some years (like myself) then some day you get bored and wanna go back to analog solid state :)

Cheers
Flemming
 

Phisci

Member
2012-08-03 6:28 am
Thanks Flemming. Could you detail the calcs behind your estimates?
I am thinking of modding the 500A to include a buffer and better caps. How would I use the 500A to drive headphones? Is it a simple case of connecting 100R in series with the amps output?
 
Hi, regarding headphone connection to Icepower 500A mk2, then you need to understand that the botn output terminals on the output connector, is at half Vsupply (37.5 volt, for 75 volt supply. I would not recommend to connect headphones to an IcePower amp this way you are thinking. You headphone normally share a common ground for left and right channel, and that would mess things up if two Icepower PCB was connected to that even through a 100 ohm resistor. Your cans will be toasted if somehow the 37.4 volt was let out to ground by accident.

I also think the IcePower circuits is designed to be loaded either 8 or 4 ohm(and less) to sound right! Not designed for 32 to 300 ohm headphones.

Well look at peak and rms currents for 4 ohm load.
With 77 volt on the Vsupply. The 500A might be able to deliver (guess) +/- 65 volt into 4 ohm. This is a peak current of 16.25 Apeak. Divide with sqrt(2) = 11.49 Arms

The 11.49 Arms x 55 volt AC ~ 631VA (approx)

And for two channels, 800VA should be okay. The capacitor will handle the peak current needed when the two channels connected to the same supply.

Cheers