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Old 12th May 2006, 08:47 AM   #1
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Default extreeme LF aleph-X

hi all, I am about redesigning my aleph x. I already bought heatsinks which is indecency big and weight almost 60kg
because of heat I will build 2 separate monoblocks. each has 1,6kW transformer with 18v secondaries and 400 000uf. also I will use 2 refricters per monoblock IR ultra fast ultrasoft 25A 600V. actualy with my mini prototype of 50w rms at 8ohm and 100w at 2 ohms with total dissipation of both channles at about 700w. after 50seconds playing (2x 35A rectifiers mountened on separate big heatsinks)wires soldered out because of heat! I soldered again but they soldered out again. now I tide them to legs. I am litle bit afraid what will happen with my 25A ultrafast ultra soft recovry diodes..

here my calculations =

Voltage after the rectifier 22.0
Voltage at the Fets 21.0
Bias 12.5
Ac current gain 50%
Number of fets 16
Peak current 12.50
Power 8 Ohms (RMS) 90
Power 4 Ohms (RMS) 162
Power 2,3 Ohms (RMS) 180
Power 2 Ohms (RMS) 156
Dissipation for one channel (complete) 591
Dissipation for one channel (fets) 525
Dissipation per fet 32.8

is this ok values? my spekers has 6ohm impedance but I am targeting at 2.5-3ohm at low frequencies.

I already buil mini verion with 8 fets with 16v biased at 10A. ant it plays very well inspite 50w power. and lastly I hear some bass from my speakers. very tight and clean bas by the way


the question - do i need change any other values when paraleling devices?
the question nr2 highly biased aleph x has some discortions at high frequencies. especialy whern volume is higher.
question 3 I will wire mosfets irectly to hetasinks. is there some rules to wire,except that wire should be short as posible
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Old 12th May 2006, 09:49 AM   #2
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Hi Elvuikay,

I won't comment on the design, as I did not finish my own X yet.

I am going in the same direction as you are: I wanted an bi-amp system with Aleph 5 for high, and an adapted Aleph X for low. ZV9 has slowed things down; I want to finish a ZV9 before I go any further

The reason I react is the following: Did you measure your woofer impedance? It seems very low. The measurements I did on my system (6 Ohm nominal) gave a lot higher impedance. (4.5 Ohm minimum @ 170Hz)

Another thing: going to active cross-over will double the power you will get to your woofer...

Greetings, Harry
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Old 12th May 2006, 11:48 AM   #3
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thanks. however with my wilson audio watt puppy 6 alepx x has absolutely no low bass. with biased aleph x its provide +6db at 25-35hz/ comparing with a5, but at 50 hz where I have impedanse peak it lacks punch. aleph 5 is better in that respect.

but aleph x bass is much more controled comparing with a5.

today I will end heatsinks. they are 4 pieces (650x200 with 26 fins 100mm) I calculated threy can disspate arround 1200w total.. the only thing it can make trouble its diodes. I have no ideal how thy get hot at 20A
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Old 12th May 2006, 01:15 PM   #4
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elviukai,

Did you use thermal grease to mount the rectifiers, and
what are the references of the IRF bridges?
Plus the size and caracteristic of the bridge heatsink...

Regards.

Alain.
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Old 12th May 2006, 04:05 PM   #5
Netlist is offline Netlist  Belgium
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I'd be inclined to add another couple of mosfets.
20 instead of 16.
Make sure you mount the gate resistors directly to the mosfets.

/Hugo
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Old 12th May 2006, 04:38 PM   #6
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I bought 52 pieces of theese diodes-

http://www.irf.com/product-info/data.../hfa25tb60.pdf

thay are rated at 600v 25 a, but in tube amp they blow at 400V .

I use separate enlosures heatsinks (250x 400 5mm aliuminium. for rectifiers but they get very hot. when I run amp at 10 A with 21secondaries they was fine. now with 16V and 20A they got really hot.

I have bunch a irfp 240 but at lower voltages - 20V maybe I should buy irfp044? thry can be biased more than 240.
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Old 12th May 2006, 05:12 PM   #7
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Quote:
Originally posted by elviukai
thanks. however with my wilson audio watt puppy 6 alepx x has absolutely no low bass. with biased aleph x its provide +6db at 25-35hz/ comparing with a5, but at 50 hz where I have impedanse peak it lacks punch. aleph 5 is better in that respect.
I suspect you have a flaw in your Aleph X. The X amps all have
better execution of the bottom into Watt/puppies than the Alephs.
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Old 12th May 2006, 05:56 PM   #8
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the only flaw I can imagine is prety high ofset and it is varying. also voltages across source resistors are pretty diferen- 0,47-0.49v. and even 0.42v few. thats no good i think . I will fix it in nearest time remaching 5% tolerance source resitors.
aleph x is pretty sensitive to transformers secondaries - for example my secondaries are 14.5 and 14.6V and it flows all the time about 0.3v. when conecting trafo to aleph x theese transformers spoils things and dc ofset flows.

I runing power amps directly throught DACT passive regulators and aleph 5 is better than x in this mode. and I feell that aleph 5 sensitivity is bigger than aleph x(to achiewe the same output aleph 5 needs less line output from CDP,DAC) maybe there is a problem with aleph x bass. ???


I conecting trafos this way- both secondaries has its own rectifiers and afrom one rectifier I take + from other rectifier I take - and wire together + and - and take zero potential.

am I wright doing this? there is other conection when secondaries wired in serial. whaty method is better?
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Old 12th May 2006, 09:47 PM   #9
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The bottom end of the Aleph X is not very sensitive to
transformers, as it has a constant draw from the transformer.

It's certainly true that the amp draws a lot of current, and if
you have a low powered transformer, it will load down a lot -
but the issue will affect all frequencies by virtue of low power
supply.

The matching between devices is also not critical, at least not in
the range you cite.
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Old 12th May 2006, 11:23 PM   #10
steenoe is offline steenoe  Denmark
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Quote:
, I am about redesigning my aleph x. I already bought heatsinks which is indecency big and weight almost 60kg
Any chance to see a pic?? 60Kg of heatsink must be quite a sight

Steen
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