Scaling the Aleph-X

[AudioAngel]

Hello!

I'm new here and I hope you can help me with some questions.
Because I have already built several hifi electronic projects I decided to build an aleph-x-clone. Losing the plot in the Aleph-X-High-Power-Thread I don't know which power configuration I should choose for my Aleph-X.
I'm using diy-loudspeaker: Odin. You can see it here: www. seas.no by using the link "kits" or here: www.intertechnik.de. But I don't use the shown configuration, instead of the tweeter my Odin has an airmotion-transformer (Eton ER4).
So, would it be a good idee to built an Aleph-X with a power output of 90W into 4Ohm nominal impedanz to drive my Odins?
Increasing the power up to 150W or something like that I'm taken fright at the produced heat by the amp. I don't want to be in a sauna every time I'm listening to music.

G.
AudioAngel

P.S. Sorry for my bad English it is not my first language so I make very often some mistakes.

[GRollins]

There's no way around it--an Aleph or Aleph-X will dissipate roughly three times its RMS output in heat.
As for how much power you'll need, that's not a question anyone can answer for you. It depends on what kind of music you listen to, and how loud. 'Live' levels for chamber music aren't going to be as demanding as 'live' levels for a full symphony orchestra. Rock doesn't (barring synthesizers) go very low, but people typically listen to it loud, etc. You'll have to estimate your power requirements on your end.
As a practical matter, speakers usually blow from the amp clipping, not from too much power.
To put the heat output from a class A amplifier into perspective, think in terms of a hair dryer. They're usually in the range of 1200-1500W. Ever tried to heat a room with one? Doesn't work too well. Yes, eventually the room will warm up, but it's not the kind of thing that will happen in thirty minutes.

Grey

[jwb]

Perhaps I'm mistaken but I thought the Aleph-X was about 33% efficient, meaning it would dissipate about twice its rated power as heat, not three times. At least, I've worked out the numbers on my 49W-into-8Ω monoblocks, and they dissipate 89W heat continuously, which is actually a bit better at 36%.

[AudioAngel]

Ok,

at first thanks for your replies. My preferred kind of music is classical (baroque) music (Bach, Händel etc) especially orgen music. Therefore I thought 90W into 4ohm would be a good compromise concerning produced heat, dimension of heatsink and avialable amplifier power, isn't it?

G.
AudioAngel

[wuffwaff]

jwb,

this is a question of how you define efficiency. An Aleph normally has a bit below 50% (with 50% ac-current-gain), meaning that for an output of 50W max your amp will idle at 100 watts. So maximum efficiency is defined at full power!
At 1 watt output, efficiency is only 1%.

The 33% could come from defining efficiency as max power @ 8 ohms / idling power consumption with an amp that has it´s power max around 6-7 ohms.

william

[AudioAngel]

Noone who can help me?
I'm a little bit confused about estimating the power I need. Grey wrote it depends on what kind of music I listen to so I described it but now the question is: Are 90W into 4ohms a good choice?

AudioAngel

[wuffwaff]

yes,

90 watts would be a good choise if you have 87dB and no less than 4 Ohms.
Dont overestimate the difference between power outputs! I think that it is difficult to tell if an amp has 60 or 90 watts max. This is only 1.8dB louder before clipping.

I think it´s more important that you design the the amp to have it´s power maximum at 4 ohms be it 90 or 60 or 45 watts.

william

[roddyama]

I'm assuming that your speakers are similar to these:
http://www.madisound.com/odinmk3.html
(I know there are slightly different versions of these around the world.) These have a sensitivity of 89db/Wm which is good. 90Watts should be fine as William indicated in the last post.

[Zapped]

Hi Wuffwaff:

In your post, you said: "I think it´s more important that you design the the amp to have it´s power maximum at 4 ohms be it 90 or 60 or 45 watts." How does one go about this?

On my old Leach amp, or similar AB designs, I expect to see more power into 4 than 8 ohms--one reason my Magnaplanars really open up with that amp (even if the sound quality and finesse really ain't so hot). But with my Zen this doesn't hold, and with the Aleph- [fill in the blank] I plan to build I am not sure whether I will invariably have less oomph at 4 ohms than 8 ohms. One of the spreadsheets I looked at seemed to suggest that some permutations of the Aleph would put out more into 4 ohms, before dropping off at lower impedances. Other evidence seems to contradict this. Head hurt....please explain.

Is there a simple way to think of this relation?

Larry Wright

[Panelhead]

Originally posted by Zapped
Hi Wuffwaff:

In your post, you said: "I think it´s more important that you design the the amp to have it´s power maximum at 4 ohms be it 90 or 60 or 45 watts." How does one go about this?

On my old Leach amp, or similar AB designs, I expect to see more power into 4 than 8 ohms--one reason my Magnaplanars really open up with that amp (even if the sound quality and finesse really ain't so hot). But with my Zen this doesn't hold, and with the Aleph- [fill in the blank] I plan to build I am not sure whether I will invariably have less oomph at 4 ohms than 8 ohms. One of the spreadsheets I looked at seemed to suggest that some permutations of the Aleph would put out more into 4 ohms, before dropping off at lower impedances. Other evidence seems to contradict this. Head hurt....please explain.

Is there a simple way to think of this relation?



The relationship between the idle current and rail voltage is where the best speaker impedance is found. If you run low rail voltages and high idle currents the amp will supply more power into 4 ohm loads than it will into 8 ohm.
Example, 50 watts consumption. Two amps

#1 20 volt total swing and 2.5 amps. Divide 20 by 2.5 and you get 8 ohms.

#2 10 volt swing and 5 amps, Divide 10 by 5 and best is at 2 ohms.

The first example can deliver into 8 ohms, 2.5 x 2.5 x 8= 50 watts.

The second at 2 ohms 5 x 5 x 2 = 50 watts.

Both will deliver 25 watts into 4 ohms.

To maximize power into 4 ohms with 50 watt delivery it will take
14.14 voltage swing and 3.535 amps idle.
This is all purely in theory, it neglects losses due to output impdeance and other losses involved. But this relationship is what determines what impedance a class A amp delivers the most power into.

George
Larry Wright