Aleph-X: High-Power Version

[Blitz]

Jens,

I just found a threat around Aleph X-Biasing:

Aleph X bias current

It seems that your cals are right for one side of the Aleph-X, but as we have two (per channel), the current needs to be doubled, so for 150 W into 8 ohms it would have to be 8,66A @ 34,6 V. Sorry, just found these formulas a minute ago. So, let'S do some calcs with them:

8 ohm:

60 Watt: 21,9 V, 5,4 A
100 Watt: 28,3 V, 7,1 A
150 Watt: 34,4 V, 8,6 A

6 Ohm:

60 Watt: 19 V, 6,3 A
100 Watt: 24,5 V, 8,2 A
150 Watt: 30 V, 10 A

4 Ohm:

60 Watt: 15,5 V, 7,7 A
100 Watt: 20 V, 10 A
150 Watt: 24,4 V, 12,2 A

Well, how much Fets should I use now to get the power desired ? From Mr. Pass we learn that he uses his devices at 18 Watt dissipation, 2 Amp each and max 70volts (I wonder from where these 70V should come from). On the other hand he states that he gets 200 Watt from 32 fets. If I get this right now, for 100 Watt we would need not the originally planned 12 fets, but 16. If you want to go for 150 Watt. this would be 24...wow.

[Variac]

woohoooo we're off!!

Blitz: Ironically about 6 months ago, after bothering lots of people here, I got the message about the inductor being first in line lowering the voltage. This was to use my 37 volt transformers in a Son of Zen. I had been looking forward to using them in a more conventional pi configuration in an Aleph 2.
But now suddenly now that the Aleph X is the hot ticket, I'm back to the same problem. Oh well, I guess I'l just leave them in the SOZ (stll not hooked up- but verry close) I believe Nelson says even 2 mH does a great job filtering- but for the
LC arrangement you are prob right! Thank you


HAppy holidays

[hifiZen]

Just remember that a choke-input filter needs to be loaded with a minimum current at all times, otherwise the output voltage will rise, possibly exceeding the rating of your caps! *kapow!*

That would <i>not</i> be pretty!

[Cobra2]

Now we are getting somewhere...

I have read almost all of the documentation, but silly me, do not understand more than half... And these treads spreads, and tend to get very long...
So I really appreciate when scaling info is posted, with examples.
And the "X" have hold me back from assembling the "2", witch I otherwise would have asked for help for making into a "1,6" (something inbetween the 2 and 1,2).
Yes, I woud probably be happy with 100W, If I did not know...

ArneK
NORWAY
(With europeean all time high price on el-power coming...)

[Blitz]

OK, reading further does not necessarily help to avoid confusions...I am studying not the Aleph-X-Thread and just have found some calcs from GRey which look quite different:

The voltage has to multiplied by 0,8 and the current is only half of the current which was stated in the link above, so Jens would be in the right ballpark again.

Is this now the right formular ?

[Blitz]

OK. It does not become clearer when looking into the XA-200 Owner's manual:

http://www.passlabs.com/pdf/xa200man.pdf

There it is stated that the xa-200 powersupply with +-35 Volts at 30 Amps ! This is quite different from the 30 Volts at 5 Amps stated somewhere in the threat. So do we have to double now the current or not ?

BTW: The XA-200 has about 400000uF on board. Wow.

The comment on the choke-input is absolutety correct, that is especially true for tube equipment, if you have not heated the tubes and they don't draw any current yet. Voltages raise and your capacitors can blow, if you have not a bleeder resistor which always draws some current. But with SS ? Should draw current all the time, or ?

[Variac]

fortunately with class A especially I think the coils are always loaded. Now if the mosfets blow? then no current then the caps go bang? On my Son of Zen this might be an issue with only 2 Mosfets per channel but balanced, so if one blows, current shuts down! Luckily I used higher voltage caps.

This brings up a point: A huge cap supply is cheaper with the lower voltage X aleph since lower voltage rated caps are a lot cheaper. BUT you wouldn't want to do the coils right after the bridge topography with the lower rated caps- rather you should use the "correct" transformer

As always, p;lease correct me

[Blitz]

Well, with PSU-Designer you can see nicely what the voltage after the choke would be. If you set the inductance higher then needed you have enough headroom, even if one mosfet would blow up. As well it has been reported that the oversizing of the transformer has not to be done like you normally do it: This seem to become very clear when you look at the current spikes generated in a pi-filter. Most Transformer are heavily oversized for normal operation, but the spikes are so huge, that any reserve to handle them is appreciated and improves the sound. With a choke-input you have no spikes. So, you have solved the problem at its root...

[diyman]

Based on Blitz, to have an output of 150W at 8 ohms, we need a +/- 34.4V @ 8.6A power supply. At this voltage which is more than double the original +/- 15V supply, do we need to rescale the values of the other resistors in addition to those used for bias adjustment?? If we do, can I use those values of the Aleph 60 that runs at +/- 35V ??
For bias current adjustment, the low value resistors will be calculated to give a total 8.6A as required.

ckt

[Blitz]

DIYman,

As stated above, I have read further through the threat's (not should mean now...typo...). Grey stated that the voltage has to be mupliplied by 0,8, so it is not 34,4, but 27,7 for 150 W at 8 ohms.

Still, we have a bit confusion: If I understood Audiofreak right we need 8,6 A (see link above). Grey clearly stated that half of this is enough (in the Aleph-X-Threat). So, let's wait and see if we can receive some feedback from them.

By the way: Grey has as well published a formular to calc the source resistor accordingly: Rs=(0,5/(I/2)) which in this case would lead us to 0,23 ohm for 4,3 or 0,115 ohms for 8,6.

Best Regards