Aleph-X: High-Power Version

[macka]

Brian & Blues,

Hope you don't mind me stepping in here...

A few months ago I did conversion for Aleph 2 to X Aleph.

Prior to conversion I ran the amp with only small side slit vents top and bottom with 3 mm aluminium un perforated top panel.

The heat sinks ran about 55 c and internal about 35 c as I recall.

After initial conversion heatsinks ran the same temp but internal now very hot, above 45 c without top on.

Why you ask?

Well the energy spent to raise the internal chassis temp came from the PS losses, the bridge rectifiers ran much hotter, the heat from the transformers (dual 300 va 24vac ) and heat from inductors.

Some if not all this energy is in the form of radiant heat. To remove the hot air I raised the chassis sides 6mm on washers off the base plate and mounted a Papst Vario flow fan in the top of the lid.

This solution seems to work for me anyway

Ian

[jlm]

Hello,

I constructed, there are some months, 2 monophonic Aleph-X,

http://www.passdiy.com/gallery/alephx-p4.htm

The schematic is the one of Blitz slightly modified with 24 IRFP240 MosFets.

Voltage: ±31V
Bias: 8A
Power 200 Watts / 8 ohms

With AC current gain: 50%
125 watts / 4 ohms
62 watts / 2 ohms
31 watts / 1 ohm

With AC current gain: 60%
200 watts / 4 ohms
100 watts / 2ohms
50 watts / 1 ohm

On the forum, Mr. Nelson Pass says that AC current gain = 69%, it is too high

It is the particularity of these circuits, the power decrease if the impedance of the speakers decrease. I wonder if it is true with the XA200 of PassLabs. There is perhaps a trick.

On the XA-200 Owners Manual, it is written: Max Output Current: ± approx. 15 A
How to have 15A with a bias of 8 or 8,5A without overshooting 69% of ac current bias?

With my Renaissance 90 INFINITY speakers (87dB and very low impedance 1 to 2 ohms mini) in a large room, the DC protection circuit of my Aleph-X clones operate. I would need more of power on low impedance

If someone has a solution!!!

Best regards

jl.m@tele2.fr

[jlm]

Hello,

Did someone make tests with different ac current bias ?

50%, 55%, 60%, 66%

What are the influences for the sound ?

Regards

jl.m@tele2.fr

[wuffwaff]

Jlm,

I started with 50% and then raised it to around 60% (Aleph5) to get my 90 watts at 4 ohms.
Bass got tighter and more important, clipping at higher volume settings was gone (my Thiels are 2.3 Ohms at higher frequencies).

The results will vary with the loudpeakers you use so I would just try what´s best for you.

William

[Blitz]

It is a shame that I started this threat and it seems that I am the last one to complete the Aleph-X as a high power version. Well, finally I am getting there...nevertheless there are some experienced in powering it up where I need your help folks, so please check the separate threat around firing it up:

Help needed: Firing up the Aleph-X100

Thanks & Best Regards

[Nelson Pass]

Originally posted by jlm
On the forum, Mr. Nelson Pass says that AC current gain = 69%, it is too high

It is the particularity of these circuits, the power decrease if the impedance of the speakers decrease. I wonder if it is true with the XA200 of PassLabs. There is perhaps a trick.

On the XA-200 Owners Manual, it is written: Max Output Current: ± approx. 15 A
How to have 15A with a bias of 8 or 8,5A without overshooting 69% of ac current bias?

The performance of an Aleph depends highly on the bias current.
If you bias the circuit to the full peak current (twice where we
usually set it) then you can pretty much set the AC current gain
wherever it pleases you.

Keep in mind that if you use the Aleph current source in an X
circuit, you have to bias each side, so that doubles the number
for the circuit as a whole. I am referring now to simply one
half of an X circuit, or an ordinary Aleph:

If the bias is set at 1/2 the peak output, then the optimal gain
for the current source is 50% from the standpoint of the
efficiency of the circuit, and I would say also from a sonic
standpoint, which is my subjective opinion.

If the bias is set at less than 1/2 peak output, and you
compensate by increasing the current gain beyond 50%, then
you will start seeing the current source cut off on negative peaks,
and it shows in the distortion curve.

The XA amplifiers don't have a trick - they decrease in power
output as the impedance declines below some arbitrary value.

The bias of an XA200 is about 9 amps (total) last time I looked,
and this means about 9 amp peak output - the 15 amp figure is
incorrect. The 9 amps implies a peak output of 486 watts into
6 ohms, which is 243 watts rms. This is the most you can expect
out of this amp, and below 6 ohms, the maximum undistorted
wattage will decline proportionately with impedance.

[Nelson Pass]

As a note, I am having the information on the web site
corrected in regard to the maximum current.

[elviukai]

Originally posted by Nelson Pass
Definitely goes both ways.

I used to wonder what all the fuss was about Watt/Puppies
until I hooked up an X600. Then I decided that both Alephs
and Wilsons were at fault.

I feeling the same way. looks like I will have to mate watt with aleph and puppy with some otheramp which delivers enought power in low impedanses. or make aleph which double wattages at low impedances

[elviukai]

Originally posted by vuki
What are Watt/puppies?

very expensive, audiophile-loved, two-parts floorstanders that have real trouble to play music. I listened them few times in various iterations and even with high-powered 600W/8R amps they sounded like small ineficient minimonitors on steroids - clean, sterile and dynamicly flat even at low volumes.

thr]ey do not need power. 30-40w is enought for them. the saund is like monitors. if there no low signal in music. but if it appear.. and if the amp is right. puppy require very musle amp in low impedanses. once I hook some kenwood amp which was able to deliver 100w8ohm 200w 4ohm and 400w 2ohm. that was wall shaking expierence- its pretty believable that puppy woofers has 29mm xmax. with aleph x puppy sounds like it is disconected

[Nixie]

Anyone have a rough estimate on the THD of the amplifier?