Aleph30 biased lower than Aleph3! - diyAudio
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Old 22nd November 2001, 08:12 PM   #1
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Hi!
According to my calculations, the Aleph30 idles at about 80w per channel and the Aleph3 at about 100w (the output stages that is..). Maybe because of the cheaper and smaller heatsinks of the Aleph30? This must be the reason for the decreased output in 4ohms. Or am I missing something here?

Regards,
Claes
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Old 22nd November 2001, 08:19 PM   #2
hifi is offline hifi  Sweden
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souds logica...but have you really taken into acount that there is 3 mosfets on the A30 each at 0,37 and on the A3 only 2 at 0,5....?

just my 2c....

btw to much nietzche? =)
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Old 22nd November 2001, 08:52 PM   #3
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yep
In A30 the mosfets are biased at 0.25/0.47 = 0.53A each and in the A3 0.5/0.47 = 1.06A, or am I wrong? This should mean 1.59A total in the A30 vs. 2.12A total in the A3.
Claes
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Old 22nd November 2001, 09:48 PM   #4
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Claes,

You are right, ALEPH 30 idles at about 1.5 amps and the ALEPH 3 at about 2 amps. Not accounting for losses, this would mean 75 Watts for the A30 and 100 Watts for the A3.

However, i feel that decreased output into 4 ohms is largely due to the smaller supply in the ALEPH 30.
ALEPH 30, 30000 uF per supply rail, for a total of 60000 uF and probably a smaller transformer(225 VA or 300VA for stereo). Compare this with 88000 uF per supply rail, for a total of 176000 uF and probably a larger (500VA for stereo) transformer for the ALEPH3.
I have build an ALEPH 3 with a 500 VA tranny and this works very well. Cool running transformer etc. Sounds perfect to!

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Old 23rd November 2001, 05:04 AM   #5
Sud is offline Sud
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Now, this is something that's been confusing me.

The static part of constant current source in the A30 is the same as for the Aleph 3, except for the transistor.
Eg
A30 A3
R17 R111 (1.5K)
R18 R112 (1.5K)
R19 R113 (47K)
R20 R115 (1K)
R34 R120 (0R47)

I can't see why the A30 should idle at 0.25V across the 0R47 and the A3 0.5V across the same resistor.

The Aleph 30 I'm building idles at 0.4v across the 0R47, using the parts listed in the schematic. I swapped in the A3 transitor, and it didn't change the bias current.

Can anyone explain why the A30 should have only 0.25V across the 0R47? Idling at about 0.9-1.0A per output pair fits with Nelson's comment in the A30 manual that they have 'run the bias up a bit' compared to the A3.

I'd be interested in hearing your thoughts.

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Old 23rd November 2001, 10:46 AM   #6
Koy is offline Koy  Czech Republic
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Ha,ha,ha. I discovered the same. On 0.47 I have about 0.4V, together less than 2A per channel. There is some mistake we did not noticed. Alpeh 30 resistors are 3(!!)x0.47 ie 0.156ohm not only 1x 0.47ohm. Having 0.28V on this resistance the total current rises to cca ( I have no calculator here) 4A per channel. And it is much more than Aleph3. I made the same mistake. Now I try to rebuild it. I believe it could be the cause of bad sound ( I am not satisfied with the sound - loss of details). What is you oppinion? How sounds your A30?
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Old 23rd November 2001, 05:35 PM   #7
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What about R114/R21? They are NOT the same value in A3 and A30...
Koy: 0.25/0.157 = 1.6A per channel.. not quite 4A.
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Old 23rd November 2001, 07:09 PM   #8
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Koy, Claes

I hope I am way off but I feel like a little explanation:

If you examine the ALEPH 30 schematic you will see the power part of the current source surrounded by a dotted line. You can also see X3 (which means times 3) in the upper left corner of the dotted rectangle.
Simply consider this a separate assembly that you will have to build three times.
So
-assembly 1 consists of R28,Q6,R34
-assembly 2 consists of R29,Q7,R35
-assembly 3 consists of R30,Q8,R36

These three assemblies are simply put dead parallel.
So the three drains connected, 3 sources connected, 3 R221 second wire connected, etc. You will have 3 IRF244, 3 0.47 Ohm resistors and 3 221 Ohm resistors.
Since the three 0.47 Ohms are parallel the equivalent resistance will be 0.47/3=0.156 Ohms
0.25 Volt over 0.156 Ohms works out to 1.60 amps quiescent current.
A similar explanation could be given for the power gain stage.
So an ALEPH30 has 6 IRF244's and an ALEPH3 has only 4.

This explanation is not meant to be offending in any way. But I feel like the ALEPH30 schematic could lead to a slight misinterpretation.

If I offended any of you, please accept my apoligies.

Cheers
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Old 23rd November 2001, 07:55 PM   #9
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Thats the way I interpretated the schematic as well. But, it's still unclear why the Aleph30 is biased at less current than the Aleph3 (at least according to the schematics).
Claes
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Old 23rd November 2001, 08:30 PM   #10
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Naaah....

They draw the same current, which is 2 amps out
of the wall. The service manual voltages were
rounded up for the 3 and down for the 30, 'cause
I drew the schematic before they went into production.
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