Aleph J-X Amp Project

[SCAIFF001]

Originally Posted by h_a

Well, you should really go to the beginning and test with the actual amp disconnected and only one cap as reservoir - and work from here.

To your original post - it is unclear to my why one would put fuses right after the bridges before the actual caps, as that is the high current highway. Uncharged caps are almost perfect shorts if only for milliseconds.

Fusing is done on the primary and usually combined with thermistors to handle inrush current and avoid tripping the main breaker. Some also fuse the rail from the caps to the actual amp to avoid killing the amp in case of a short at the output. However, I would certainly use a bleeder resistor for the caps in this case to ensure that the caps can sufficiently quickly discharge when the fuse blows. Also keep in mind that your speakers might not be happy with the signal they'll get when the fuse blows, so I would use them with caution.

Also, the standard fuses are not much of a practical use; they're more of a 'don't burn my house down' sort of safety feature.
if you read in detail about their ratings you will find that an 8 A fuse does not blow at 8.1A, but more like at 16 A after 10 seconds or so. In practice if used to close to their rating they will fail sometimes even if there was no overcurrent.

Finally, the transformer ratings are generally continous values with the internal heating used as limit. In practice they can give much larger currents for short whiles (as they typically do when recharging the caps), don't forget that the caps are only charged at the top of the rectified sine, so one can easily see 100A for a few milliseconds.

I would use thermistors+fuses for the primary and CRC filtering to get the inrush down if necessary.

I hope this helps a bit.

Hannes

PS: this is something more for the PSU forum, you would likely get also more response there.

Hi,

Thank you for your help, I was able to find the problem with your help, I wired the positive and negitive backwards out of the bridge rectifier through fuses(my synptom of the problem with the blown fuses which I have now moved to the power supply output with two 6amp quick blow fuses, these are not blowing now.

Now when I turn on the amp I get no music untill I turn the power off, then I hear the music for 2 seconds. I have not set my bias yet, could this be the trouble ?

Thank You for your Help

Ian

[kroyin]

I give up :-) I know information is there but after reading through 100+ pages of 85c & 105c capacitor, CLC or CRC, am a wee bit nervous.

I have 8 ohm speakers (so bias current requirement is low) and I don't want 100 watt/ channel (J-X pls). I need 40~60 watt / channel.Unlike Papa I don't like flooring the accelarator & crusing at 55mph (happens with 5% of my low gain music on the J)

So keeping bias intact 900mA/1A (4 or 8 mosfet???) per mosfet what would be the rail voltage (without any significant component change)

If there is no easy answer :-) guess I have to troll F5x & AX threads :-)

[kroyin]

As per Peters Wiki http://www.diyaudio.com/wiki/Aleph_J-X

With 1.8A bias per side is about 180 watts per ch.

Is this for J-X or the J. If I put the values in the Aleph X excel (8 mosfets biased at 900mA each reaching a dissipation 173 watt.) it gives me ~50Wx8ohm so i guess it is for the J

[anilva]

Originally Posted by kroyin

So i guess there is no easy answer
Aleph J-X is 100 watts/channel
And as per Peter's wiki
"With 1.8A bias per side is about 180 watts per ch."
This means that with 8 MOSFETS each source resistor will have around 900mA across it (right/wrong pls?)

If i use the Alpeh X calculation excel and i put 24V rails 5.6A bias (900mA across 8 source resistor) it gives 173 watt dissipation but 50W into 8 ohms.

The same excel for 24V,7Amp bias reaching 120Wx8 ohm gives 330 watt dissipation

Kroyin,

Aleph J-X is not a formal Papa's design but an adaptation. Aleph J is complex enough compared to F5 and Aleph JX is lot more complex with the daughter card etc. If you are like the sound of Aleph J, just build one and use it. If you want higher power amp, build a F5T V3 rather than a JX. My two cents.

Cheers.

[derwhalfisch]

Kroyin - upping the bias won't make more power available if it takes higher than your rail voltage to get that current into the 8ohms.

[kroyin]

I already have the J, i didnt like F5 (i had one, must have been a bad implementation).
My F5T v2 is couple of weeks away but i have a sneaky feeling that i won't like it (though i am better prepared with Arta & Soundcard to tweak with P3 ).
So if i get to like the F5T, i'll stop there.

Worst case scenario i am thinking X-ing two mini aleph J (16V rails with 1A bias) hopefully reusing the F5T chassis

[kroyin]

Though I have no clue about how much power I'll end up with (x-ing 2 16 v 1a minis)

[kroyin]

Originally Posted by Peter Daniel

I don't see any problems with that, the main boards will be exactly AJ circuit, and I simply add pads to mount daughter board (3 pins on each side for the gates, out and ground). The front end circuitry will be inside marked area and for X version not installed. The balanced input goes directly to the daughter board (the X amp will also work with unbalanced signal), the daughter board is powered with separate wires from main supply, output is taken from between output boards. That could be the best X amp ever

One thing that eludes me is how do I power JX.
The daughter board doesn't have any inputs from the PSU while the two output boards have their individual +-V supply.
So do I power both the output boards and wait for some magic

[Zen Mod]

both main boards need to be connected to PSU

daughter board will have power delivered by Divine Force itself

[permaneder]

Originally Posted by Zen Mod

both main boards need to be connected to PSU

daughter board will have power delivered by Divine Force itself

Divine, indeed...