small / downgrades Aleph for active speakers

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Hi,

where to start ?

I have 4-way active speakers, and would like to build Alephs for them.

Aleph3 is the smallest one, right ?

8 x 100 W = 800 W = too much :(


The mini-Aleph may be is a little too small.

Can I downgrade the Aleph3 by reducing the rail voltage and what else ?

So that I get 15 W output and 50 W dissipation per channel, that is 400 W total and ok :)

My active filters are full of op-amps, do theese degrade the Aleph qualities ?


Bernhard
 
Bernhard said:
Hi,

where to start ?

I have 4-way active speakers, and would like to build Alephs for them.

Aleph3 is the smallest one, right ?

8 x 100 W = 800 W = too much :(

The mini-Aleph may be is a little too small.

Can I downgrade the Aleph3 by reducing the rail voltage and what else ?

So that I get 15 W output and 50 W dissipation per channel, that is 400 W total and ok :)

My active filters are full of op-amps, do theese degrade the Aleph qualities ?


Bernhard

Aleph

Bernhard,

A30 is the smallest @ 30W per channel.

You might consider running the Mini Aleph in bridged configuration.... i'm not 100% if this will work but it should and it would give you the power you need.

As suggested above, Zen-Aleph is probably also worth considering as it outputs 35W but if you decide to go this path, i'd wait for the remaining 2 parts of this articles where the zen will gain a 47k input impedance and have it's upper frequency response refined.
 
ok, one idea:

the Aleph3 can drive a 2 ohm or a 4 ohm load.

If one uses only 8 ohm speakers, it should be possible to go with only one pair of IRFs, instead of two, so it is half power consumption, just 50 W :) instead of 100 W.

Also if only a tweeter or midrange which needs less power is driven, maybe a 4 pair design can run on just one pair and the output voltage remains the same.

Just the damping gets worse :(

But that is may be not so important for tweeters and midranges...


Bernhard
 
You want more power out of a Mini-A?
Run it at a higher rail.
Just mind the increasing heat dissipation, and you might want to increase the bias current if you intend to drive low Z loads. There have been a number of threads about fiddling the bias on the Alephs.
Yes, they'll bridge.
Again, bear in mind that a bridged circuit (any bridged circuit) is a current hog. Increase bias accordingly.

Grey
 
If I have understood the information you have given above, and both transformers are identical (350VA each).

Well, 30VAC will rectify to between about 36V and 42V depending on loading etc.

And the current capacity of each transformers is

350/30 = 11.67 Amps

Given that you shouldnt use a transformer above 50% it's nominal rating, that leaves you with about 11.6Amps of usable current.

Now you've got 1 transformer per channel (left/right), and 4 amplifiers for each transformer so

11.6/2 = 5.8 Amps
11.5/4 = 1.45 Amps

So each amplifier must draw less than about 1.45Amps from the transformer.

As for how much musical power you get from that, it depends on the resistance of each of the speakers you have.

Assuming 8ohms and the efficiency of an aleph,
If my calculations are correct,
idle current would be about 550mA
and output power would be about 6.6W per amplifier
and about 3W into a 4 ohm load.

But if your rails were lower and current capacity higher, efficiency and output wattage could be improved somewhat. +/- 20V rails or there abouts, would be far more suitable given the very low output wattage.
 
thanks for the calculation, :)

which means, my transformers are useless... :(

Your calculation says 6,6W x 8 = 53W

I did not know, that I must have double nominal transformer power...

But still the output power seems to be so small...


The manuals of Alephs say:

250W gets 60W / 8 ohms A3

300W gets 120W / 8 ohms A5

500W gets 200W / 8 ohms A4

so, my 350W should get 140W / 8 ohms, if compared to A4/A5 and 84W / 8 ohms, if compared to the A3



What would You suggest for each of the two transformers ?

I like to get 15W for the tweeter, 15W for the midhigh, 15w for the midlow and 60W for the woofer from each transformer.

So the 15W channels must run with the same rail voltage, as the 60W channels, is that possible ?


Bernhard
 
Bernhard said:
thanks for the calculation, :)

which means, my transformers are useless... :(

Your calculation says 6,6W x 8 = 53W

I did not know, that I must have double nominal transformer power...

But still the output power seems to be so small...


The manuals of Alephs say:

250W gets 60W / 8 ohms A3

300W gets 120W / 8 ohms A5

500W gets 200W / 8 ohms A4

so, my 350W should get 140W / 8 ohms, if compared to A4/A5 and 84W / 8 ohms, if compared to the A3



What would You suggest for each of the two transformers ?

I like to get 15W for the tweeter, 15W for the midhigh, 15w for the midlow and 60W for the woofer from each transformer.

So the 15W channels must run with the same rail voltage, as the 60W channels, is that possible ?


Bernhard

I'll try to address each point in order.......

The power output is so small because from a power requirements point of view, we are driving around about a 2ohm load per transformer so for a given transformer VA rating, we require many more amps and less volts (something the stated transformers are not designed for ie. voltage too high, current too low).

The power requirements you stated above for various Alephs is 1/2 the minimum transformer VA rating.

If you want only 2 transformers, i'd recommend that you use one transformer to supply the 6 x 15W channels and the other to supply the 2 x 60W channels as this is by far the most efficient way of meeting your requirements. You could run the high and low wattage amps off the same rails but the power wasted becomes very large indeed (and heat also :D)

Given the above and assuming all drivers are nominal 8ohm resistance, the 2 transformers should be rated thusly.....

6 x 15W into 8ohms is from a power standpoint the same as 90W into 1.33ohms

So,

90W/1.33 = 67.5
sqrt 67.5 = 8.22Amps
8.22 x 1.4142 = 11.62Amps
11.62 + bias current = 18Amps

and

90W/1.33 = 67.5
sqrt 67.5 = 8.22Amps
8.22 x 1.33 = 11Volts
11 x 1.4142 = 15.5V

So accounting for mosfet and diode losses, rails of about 20Volts would be most suitable.

If it were me, i'd probably go for secondaries of between 16V and 18V depending on what is available to you.

So the transformer must have 2 x 16-18VAC @ 18Amps secondaries which fits fairly neatly in with the other Alephs power requirements.

This would mean each amp would have bias of about 1.07Amps and an output of about 15W into 8ohms.

2 x 60W is an Aleph 5 which has rails of +/-34V and current draw of about 9Amps.
So, 28VAC @ 600VA is probably about what i'd go for there which translates to 2 x 28VAC @ 11Amps secondaries.

Hope all this helps ....

Regards AudioFreak.

ps. this is a total of about 590W power consumption
 
Ok, could I use my transformers for Aleph5 Monoblocks ?

One 2x30V / 350VA for the left channel, the other one for the right channel ?

Maybe if the railvoltage should be a little to high, I could put a coil in series to reduce it...


And for the 15VA Minis, use the circuit of the Mini-Alephs or make a small Aleph5 ?

Would it be better to have seperate transformers for each Mini ?


What I like to have, is: All 4 channels in one classic-Aleph-design-housing.



It is possible that I let make 2 custom transformers with 2 windings 28 Vac and 6 windings 17 Vac, each.

Is that a good idea ?


Anyway, I will watch what happens around the Mini-Aleph tread...


Thanks,


Bernhard
 
Yep you should be able to use your current transformers for A5 Mono's if you use coils / power resistors / power diodes of the correct value to lower the rails.

Yes you could have transformers wound as per your description but they may cost a bit given the number of windings required. Also, each chassis would require about the same as an Aleph 2 or a little more.

As Grey already stated, if you ramp up the rail voltage, the Mini-A should do the trick nicely for the 15W amps. Make sure you use the latest schematic and not the original :D and then fiddle the bias current to suit your needs.
 
Bernhard said:
Also, each chassis would require about the same as an Aleph 2 or a little more.

With chassis, You mean transformer or the whole 4-channel-amp ?

Bernhard

Chassis refers to the housing/case that the 4 channel amp is within.

I also note your post in another thread re: downsizing the Aleph 3 ..... this is precisely what i have done in my above calculations... my 15W alephs are effectively Aleph 3's with only 1 set of ouput devices not 2 and can be easily built this way.
 
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