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-   -   At last, My Aleph 2+ (http://www.diyaudio.com/forums/pass-labs/17365-last-my-aleph-2-a.html)

Brian Donaldson 6th July 2003 06:36 AM

At last, My Aleph 2+
 
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Now that my darling bride is out of town, I've been hard at work. The first of my Alephs is up and running. I let a little magic smoke out before I bought a variac. I must admit, I was worried that I sunk $700 into a project that may never get finished. I replaced 5 shorted fets (yes they failed shorting drain to source) and a few source resistors and powered up slowly.
First was some 60 hrz hum , then sound. I inched it up and it became clearer and the line on the scope sharpened.
I worked the voltages up to +- 40 then cranked the bias to 5 amps total and the line on the scope became razor sharp and dead straight. And the sound! Beautiful clear and focused.

Thanks to everyone
Hardvarian and BrianGT for the boards
Damon for the new soldering station
Mark for the insperation
And the countless other posters (I've read them all over and over)

Brian Donaldson 6th July 2003 06:43 AM

Now for hard numbers
Source resistors are .8 ohm x 8 fets @ .5 volts
Total bias 5A
Supply is running (humming along) +- 40 V
Total dissapation 400W
Heat sink temp 156 Degrees F
Sound to die for

There'll be no sleep in here tonight
I've got to get to work on the other channel

Brian Donaldson 6th July 2003 07:06 AM

I have .2v of ripple on the supplies and you can see the music signal superimposed on it. I thing I'll add inductors between the banks of caps and bypass the second bank with some film caps.

And Shame on me
I neglected to give the biggest thanks of all to the man that made this all posible... Nelson Pass, My hero!

JOE DIRT® 6th July 2003 11:02 AM

congrats!!! Brian:cool:

DIRT®

mefinnis 6th July 2003 11:42 AM

Now that's what we like to see ....... really serious hardware :)

cheers
mark

moe29 6th July 2003 11:23 PM

Brian,

So you added 2 more fets to the Gain and CC boards? Seeing
that the Aleph 2 needs about 45 volts on the rails, i would think
your amp would need close to 50 volt rails (??) Or can you get
away with 40 volts because you upped the bias?

was just wondering - in no way am i any kind of expert!, just
trying to soak everything in.

very nice what you've done here.


m.

Brian Donaldson 7th July 2003 02:01 AM

Well the 40 volt rails was an accident. The surplus transformers I bought were 60Vct 20 A. I decided I could live with slightly less voltage because my speakers are 4 ohm. So I've upped the bias so I still have over 100 watts rms at 4 ohms. I also bought a 22 amp variac (pictured) on Ebay for $40 that I'm thinking about installing in a power conditioner for the amps so I can juice it on up for louder listening or turn it down to save elecrticity for background. It's not the electric bill that I'm concerned over, My A/C is undersized and overworked and one extra kw of heat will make it run almost continuously on a hot Houston summer day.
I've noticed that to bias decreases as the voltage increases. I think I want to put a pot for r19 and a bias meter on the front panel. I like knobs an buttons and meters.

Brian Donaldson 7th July 2003 03:56 AM

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Her's some more pics

This is semi complete chasis. I still need to anodise front, top and back. I'll leave the bottom raw. All but the heat sink is surplus 1/4" aluminum cut with a skill saw

Brian Donaldson 7th July 2003 03:58 AM

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The feet in previous pic are 2.25" x 1.25" solid bar stock (surplus)
It'll also make nice knobs for apox.

Brian Donaldson 7th July 2003 04:02 AM

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I know, it's a MESS now, but I want to run it before I pretty it all up inside. Plus I'm going to do some of the tweaks in the ultimate Aleph thread.


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