irf o44's in aleph 30

[audionut]

I've just ordered some of Brian's boards for the Aleph 30. I've got 28-0-28 volt transformers (nice big signal transformers 5 dollars each) which will yield 34 volt rails under load.

My problem (besides the 34volt rails...aleph 30 is supposed to have 25 volt rails) is that I've got all these irfp 044's left over from an aleph x project that never got off the ground. The Aleph 30 is supposed to use irf 244's.

What do you guys think...irf 044's with 34 volt rails in an Aleph 30???

 

[pamaz]

I've got aleph 30 with irf044

I had the same doubt at the begining, but finally I am now listening to 2 aleph 30 made with 044 BUT be careful to the power supply: Lower the DC value to 25 vdc. In your case you can do it wit a crcrc or clclc filter after the rectifier bridges.

Ciao

Paolo

 

[dhole]

Hey Audionut What are those transformers ? Where did ya get them from ?
regards
dave

 

[MikeW]

The 044 are 60 volt. The 044n are 55 volts. If you exceed these voltages they will probably blow up. Then you can use 140's or 240's. Are your speakers under warranty?

 

[Blues]

You can keep your rails at +/-34V. Each power fet will have 34V across it. You can keep the Aleph 30 bias the same too...you'll just have an A30 that can swing to about 32Vpk as opposed to about 22Vpk for the regular A30.

 

[mpmarino]

Each power fet will have 34V across it

...is this true? I understood that the audio outputs basically 'drag' the voltage higher across the ccs, therefore creating a voltage change with respect to ground.(as one leg of the ccs is equivalent to ground at rest or idle) Therefore it is possible to have over 60v across the ccs devices. Please correct me if I am wrong as I would like a better understanding of the circuit...

Thanks,
Marc

 

[Hanzwillem]

You can keep your rails at +/-34V. Each power fet will have 34V across it. You can keep the Aleph 30 bias the same too...you'll just have an A30 that can swing to about 32Vpk as opposed to about 22Vpk for the regular A30.

In idle, yes. But the output can swing between plus and minus 32V in this case, so in maximum operation near clipping the output will go somewhere near +32V, that means the upper set of mosfets will have almost nothing to dissipate, while the bottom half has the rest to take care of, say 64V (I believe the rest is dissipated by the bias resistors).

If I am mistaken, please correct me as I am typing this without the schematics.

 

[MikeW]

At positive peaks the output MOSFET will have 70 volts minus losses. At negitive peaks the current source will have 70 volts minus losses. That is if the rails are +/- 35 volts.

 

[Blues]

Mike,

That would be the upper fets handling the positive peaks and the lower fets the negative peaks. With +/-35V rails you'll get a clean sine wave of about 66Vpk-pk.

 

[mpmarino]

Nelson...HELP!

I'm confused

 

[audionut]

how about using the irf 150's they are $1.11 apiece versus the irf 244 at $2.20 apiece. I'm building 6 channels of Aleph 30's so cost will mean something.

The irf 150 Spec Sheet says they are rated at 100 volts, and that they are 5th generation devices...(whatever that means)...I note that forward transconductance is 14 for the 150 and 6.7 for the 244...is this good or bad???