Aleph30 biased lower than Aleph3!

claes

Member
2001-11-12 8:49 pm
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
 

rtirion

Member
2000-11-24 12:02 am
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!
 
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.
 
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?
 

rtirion

Member
2000-11-24 12:02 am
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
 
I have another ( I hope last) question. I feel lack of space or details of the sound.Of course the matter could be in the speakers ( but I am not sure with thisALR Jordan Take 2) or somewhere else. Which are the most critical points of this amp ( quality of the electrolyts,bias or so ...)? Thanks for angellic patience.