Aleph 30

[swede]

Transformer?

Hi,

I tried to find more information on the forum about the transformer, but I couldn't find any.

Will I be home safe if I build an Aleph30 using a 300VA transformer with two secondary bindings of 18V for both channels? (=> sqrt(2)*18 - 0,5 v = +/- 25 volts)

Best regards,
//magnus

 

[Freddie]

swede,

The Aleph 30 draws about 200W so one 300VA transformer for both channels is a little bit to small for my liking. I would use a >=500VA transformer. 2*18V secondary windings is good.

I use one 2*18V 600VA transformer per channel in my Aleph 30, the rails are at +/-25V. However one 600VA per channel is overkill.

I bought my toroid transformers at www.elfa.se

/Freddie

 

[swede]

I can go for a 500VA instead, but what is a good theoretical value? Or should I go for two 200VA (one per channel) instead, or 300VA per channel?

//magnus

 

[Freddie]

swede,

Perhaps these articles about power supplies is interesting to you.
http://www.passlabs.com/pdf/powersupply.pdf
http://sound.westhost.com/power-supplies.htm

From Rod Elliot's article.
"VA Rating - Class-A
The minimum VA rating suggested is 5 times the amplifier power. A 20W Class-A amp therefore needs an 100VA transformer, or 200VA for stereo 20W Class-A amps. Larger transformers will again provide a "stiffer" power supply, and this will be beneficial. Nelson Pass suggests the ratio should be 7.5 times the amp power [2]."

/Freddie

 

[swede]

Gazongas!

Phew, that calls for a really expensive piece of hardware...

No wonder hifi equipment is really expensive. The transformer cost more than anything else in the amplifier.

Thanks a lot for the links!

Best regards,
//magnus

 

[swede]

I decided to build two monoblocks with a 300VA transformer each. Hope it is enough.

Best regards,
//magnus

 

[Freddie]

swede,

300VA per channel is enough.
Good luck with the project.

/Freddie

 

[swede]

Just about to power up...

Hi,

I'm just about to power up one channel for my Aleph30 for the very first time. Mostly to get some measurements.

Wish me luck! I'll post pictures in a couple of days.

Best regards,
//magnus

 

[swede]

Ok, fired it up...

...and it seems to work. Runs VERY hot, due to my small heatsink. I'll change it tomorrow, to another small heatsink (though a little better). Now I have to make friends with someone at a junkyard, so I can get heatsinks cheap.

I got -0.078 volts on my output post. Is that way off, or within margin?

Best regards,
//magnus

 

[Freddie]

Referring to the servicemanual the DC offset should be <100mV.
So it's ok. I have a DC offset around 10mV after an hour or so, on my Aleph 30. When the amplifier is cold it's a little bit higher.

/Freddie

 

[mefinnis]

The service manuals are not DIY projects. You
will get an extra merit badge for navigating the
treacherous waters of any service schematic drawn
by Pass.

With the greatest respect to Nelson, where's my badge ????

Cheers, Mark

 

[till]

question to you who built aleph 3 or 30:
how many caps did you use? the manual aleph 3 says 8*22000u , for aleph 2 its only 4. How much will i need? because it looks like these large caps are the most expensive part of the projekt.

 

[Freddie]

till,

The Aleph 30 uses 6*10000uF per channel. I wouldn't use less capacitance than that. I use 24*10000uF per channel in my Aleph 30. Capacitors are indeed quite expensive.

/Freddie

 

[till]

thank you Freddi. the cheapest way is instead of 8*22000u for example 36*4700u. or instead of 6*10000u 14*4700u

Are there disadvantages for such a solution?

 

[fcel]

capacitor source

http://www.apexjr.com/capacitorsR.html

I have bought computer grade Phillip brand 26,000uf/75V at only $6.95 each from the above link. I have not used it yet, so I don't know how well it'll perform ... but it's CHEAP!

 

[swede]

It's alive!

Hi again!

Now I have tried the first board on my Aleph30. It works! Thanks a lot to all of you! Especially to Panos (panos29) and (of course) Mr Pass.

How much bigger heatsinks should I get for each channel?

I didn't get it to go very loud (fairly loud, but not VERY), but I think that has more to do with me using an attenuator instead of a pre amp. I measured the input (from the attenuator) to be +/- 2 volts max.

It runs very hot, so I don't think the heatsink vill do. It gets almost too hot to touch after just 5 minutes.

Well, now I have to build a really nice enclosure.

See ya!

//magnus

 

[swede]

Heatsinks

Hi all,

Now I got my monster heatsinks (big, huge, fat *** heatsinks), but my Aleph 30 still runs pretty hot. Actually I found them in a dumpster!

I read somewhere that 55 degrees C is the limit where it is no longer comfortable to touch a heatsink. Well I believe I run it hotter than that. I'll do some measurements on my amp, but I'm in the middle of packing all my stuff down in boxes. The next month or so will be amp-less, since I'm moving to Schwizerland on tuesday.

Isn't it so, that oscillations can heat up the output FET's pretty much? I'll scope my amp and see what happens.

I finally got two pieces of 300VA transformers (2x18 V). Will post pictures as soon as I can.

Best regards,
//magnus

 

[swede]

Heatsinks again

By the way,

Should I put heatsinks on the IRF9620 FET's as well?

//magnus

 

[Asen]

As I can see there are no heatsinks in the original amp.

Take a look for yourself:
http://www.audio-logic.com/images/pass_a30i_800.jpg

Regards

Asen

 

[Asen]

BTW how much voltage do you have on your PSU? I'm not sure but I think the voltage must be +/- 20V (not 25 as in the manual). May be this is the reason for the big heat dissipation.