sam's 300W or eti-466 : power supply

[bigpanda]

Hi,

I've put together the amp. at :

http://users.otenet.gr/~athsam/power_amp_300w.htm
or
http://www.alphalink.com.au/~cambie/ETI466Web.htm

Still having minor trouble (hopfully is minor, appreciate if anyone can give more advice to rectify them ) mentioned here :

sam's 300W or eti-466 :setting quiescent current

I started looking at the power supply. I use two 24-0-24V 3A transfromers in series to do my testing. 50-0-50V 6.5A ready made are not available here so I intend to send tailor-make order to some local manufacturer who claim that the transformer will be too bulky to be made. They suggest I should use 2 instead. I was wondering should I use two 50-0V 6.5A (/7A to be more insured) in series or two 50-0-50V 3.5A in parallel (or two secondaries each of 50-0-50V 3.5A )? Or even more work : two seperate sets of rectification+DC filtering

One last piece of info. I did had the Zobel connected now and also the inductor. I found a ready-made that is about 16uH.

My friend happens to have two spare 45-0-45V 4A toroids he can offer me. But that would mean a rail voltage of ~ +-63V. Would this cause any trouble because I am concerned about the 3 zeners in series. Would this drop of supply voltage do harm to the amp. ?


Any further advice will be much appreciated.

[amplifierguru]

Always use transformer windings in series on high current types. Regarding the xformer choice, why 50-0-50 at 6.5A? Surely a 500VA i.e. 5A would do. That's a popular size.

Where are you, HK? alternatively 2 xfs at 50V x5A in series. If you're concerned by a couple of volts over put high current dioded in the supply feeds.

[bigpanda]

Tks amplifierguru,

I am just following the instruction in the article : 300-350W for the toroid for a single channel. How to calculate what power we need?

Is there a reason to prefer series connection than parallel connection?

I am concern about lower voltage (if we use 45-0-45 AC, we have only +-63V DC). Any problem with that?

[amplifierguru]

Big panda,

Since the design supply voltage is 68V, allowing for say 1V ripple and .6V diode drop you need a 49V winding per side as this rectifies up x1.414. A 50V @say 5A is 50V under load so if the regulation is 5% it would be 5% higher under idle conditions - well above you're 68V.

Assuming you are using this for music with a high crest factor the transformer is never going to see continuous full power for any length of time. I would use the 3.5A one for 2 channels and enjoy the headroom of the higher supply. Then, later, if you wish, add a second supply to power the second channel ensuring freedom from crosstalk (a good idea in this case).

My Eidetic amplifiers 150W/channel from one 300VA transformer and had 2dB dynamic headroom making them seem the equal of a 250W stiff supply amplifier.