Aleph-X: High-Power Version

I have read Aleph-X threats now for 8 hours and I have to admit that I am not yet through with everything. But even with extensive usage of the search functionality I have found some comments how to come to a high-power version of an Aleph-X, but I am not sure if they included all information to be considered. Therefore I would like to collect some of your experiences on that topic as I can imagine that there are some more DIYs out there who have planned to go for an Aleph 2, changed now there mind and want the same thing in terms of power, but with advantages of the Aleph-X.

Here now some thoughts / questions:
- Heatsinking: Also when utilizing now IRFP044 under very different voltages, we are in the same ballpark with the Aleph 2, right ?

- Voltages: Instead of 45 VDC, we are looking now for 15 VDC in the schematics I have seen. Will this hold to be true if raising the IRFP044 from 4 pcs/channel to 12/channel ( The Alephs raised voltages with growing number of fets ?)?

- Components to be trippled: When now coming from 4 044 up to 12: Will really only the fets be trippled or all components around them as well ( what my understanding is right now): In Grey's schematic this would be r7, r5, q1, q2, r6, r9. What about the circuit around the mpsa18 which drive q1 ? Will this drive as many IRFs as I put in parallel or has it as well to be trippled ?

- Are there any other issues to be considered, why in some threats is has been stated that the time is not yet there to go for a high-powered version ?

Regarding Components: What would be your recommendation: IRFP240 (which gives me the option to go back to the Aleph 2 if the Aleph-X is not my pair of shoes) or thhe IRFP044N (which cost me the same, but if have read somwhere the the N-Version is not that suitable for audio; the superior 044 VErsion is diffcult to get though).

Regarding separate PSU for the driver-stage: Do the same comments on the Aleph apply here (meaing not possible as part of the concept) or could this be an improvement ?

THanks & Best Regards

Choke-Input ?

Variac,

I have not yet simulated this in PSU-Designer, but I would consider a choke-input-setup, where you have a anyhow a much lower VDC compared to a pi-filter (in theory instead of VDC= VAC*1,414, it would be VDC=VAC*0,9). MArk Levinson has used this in his Cello-Amplifiers as it reduces power-supplier-noise (smoothes the spikes produced by a pi-filter)and gives nice regulation. The trick is to calculate the inductance correct, which is quite small here compared to tube equipment. So, in the case of 28 VDC with 4,350 A it would be 6,5 mH (more is no problem). If you still have to much VDC, have another RC-filter to follow (so you end up with an LCRC-Filter).

Best REgards

Jens,

I just found a threat around Aleph X-Biasing:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=4758&highlight=aleph+bias+calculation

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.

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 ?

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 ?

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...

Correction

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