extreeme LF aleph-X

[elviukai]

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

 

[harryeng]

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

 

[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.

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

 

[Alain Dupont]

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.

 

[Netlist]

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

 

[elviukai]

I bought 52 pieces of theese diodes-

http://www.irf.com/product-info/datasheets/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.

 

[Nelson Pass]

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.

 

[elviukai]

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?

 

[Nelson Pass]

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.

 

[steenoe]

, 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

 

[elviukai]

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.

THanks Mr. Nelson again..
in the prototype amp(16v 10A bias arround 600w dissipation in both channels) transformer is 1.5kW per two channels. in monoblocks will be 2kW trannie per monoblock. or should I go ratings?

its interesting why aleph x input is slightly less sensitive practicaly (it has the same impedance and sensitivity like aleph 5 I think) I tried to up sensitivity increasing both 100kohm resistors to 130kohm but speakers(testing) get some DC arround 15V to speakers.

 

[elviukai]

Any chance to see a pic?? 60Kg of heatsink must be quite a sight

Steen

Yap, I will do some photos. but some of the well respected DIY audio members and moderator stricly slating my kichen during building process. so I'm litle bit shy now

the heatsinks itself also are very long and lastly I get some space to take away trasformer from circuit..

 

[wuffwaff]

Hi,

nice project you´ve got there! Just out of interest:

Where do you get 2kW 18v transformers (55A per secondary)?

I´m looking around for non humming transformers and a few manufacturers told me that at 1000VA (1kW) they couldn´t do 18V windings (even using two wires i parallel).

You could use schottkys for your rectifiers. These will halve the dissipation (and heat).

William

 

[elviukai]

hi nice project is zen v4 or gainclone. this is heat project
all my trafos I orders custom in my country. 600w trafo 30eur. 1,5kW 40eur 2kW trafo costs 50eur. 2kW transformer has 2 secondaries(4wires) but in one wire there are 4 wires. with diameter 2-3mm in 1.5kW trafo 3 wires in one wire the same diameter.

I will use IRF hfa ultrafast ultrasoft recovery diodes, a year ago in this forum this was recomended part.