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Old 5th December 2002, 08:38 PM   #1
DJG is offline DJG
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Question My Aleph 5 isn't working

Hello!

I have made a testing PCB for my Aleph 5. I have completed the soldering and connected the wires.

The problem is, that when I increase the input signal, it starts clicking in the 6.5Ohm speaker. Control LED also starts to blink and PSU drops from +/-31V to +/-27V. It's almost like it would go into clipping.

I have 31V-0V-31V PSU with 2x47000uF/elco and 4.7uF/bipolar.
When the load is 8Ohm speaker the critical point is a bit higher, but when the load is 8Ohm 2-way speaker it's a bit lower.

It looks like it would start short-circuiting.

Does anyone have any measurments that are critical and I could made them as well?

best regards,
DJG
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Old 5th December 2002, 08:44 PM   #2
MikeW is offline MikeW  United States
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Diconnect your speaker. Check your DC ofsett at he output. It should be a few miilivolts. Then go to your shematic and check to see if you have the proper voltage drops. Both of the problems I had with my Aleph 5 were from blown up transistors Q1,Q2, or Q5.
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Old 5th December 2002, 08:50 PM   #3
DJG is offline DJG
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Hello, MikeW!

Could you send me your schematic, because I don't have one with voltage drops on it. Please.

thx,
DJG
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Old 5th December 2002, 08:54 PM   #4
MikeW is offline MikeW  United States
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Go to the Pass Labs homepage. They have the Aleph service manuals that you can download.
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Old 5th December 2002, 08:58 PM   #5
DJG is offline DJG
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OK, thank you. I will get on it right away.
In case of any possible solution, please report them here.
I will report about the measurment results.

Best regards,
DJG
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Old 5th December 2002, 09:23 PM   #6
DJG is offline DJG
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All the measurments are OK - except the voltage on 1Ohm/3W output resistors. In service manual is written 4-5V, but I have only 0.22V and 0.27V. DC offset is OK - aprox. 60-70mV.
Any thoughts?

DJG
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Old 5th December 2002, 09:59 PM   #7
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Hi,

You don't have to have 4-5 volts across that resistor! The Collector-Emitter voltage has of Q4 has to be 4-5V. If you take a closer look, you will see, that the voltage must be .5V. And that is fair for 0.5 amps/mosfet pair. Take a look at the upper mosfet's source resistor's voltage. If it is the same low value, then maybe the current source is not working correctly.

Try looking at the transistor's base-emitter voltage. It has to be close to 0.6V.

Regards,
Miki.

Ps. I don't have experience with Aleph5, so maybe I am wrong.....
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Old 5th December 2002, 10:36 PM   #8
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What 10 ohm resistor?
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Old 5th December 2002, 10:44 PM   #9
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I think he is reffering to 1 Ohm resistor not 10 Ohm, it is because of the no-space and big O ;-) 1Ohm

Trigon.
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Old 5th December 2002, 11:53 PM   #10
grataku is offline grataku  United States
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For someone that would signal the time to get reading glasses.
Mybe it was an oppttttiiiicccaal illusion.
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