My Aleph 5 isn't working

DJG · 5th December 2002, 09:38 PM

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

MikeW · 5th December 2002, 09:44 PM

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.

DJG · 5th December 2002, 09:50 PM

Hello, MikeW!

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

thx,
DJG

MikeW · 5th December 2002, 09:54 PM

Go to the Pass Labs homepage. They have the Aleph service manuals that you can download.

DJG · 5th December 2002, 09:58 PM

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

DJG · 5th December 2002, 10:23 PM

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

dodonoid · 5th December 2002, 10:59 PM

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.....

Nelson Pass · 5th December 2002, 11:36 PM

What 10 ohm resistor?

trigon · 5th December 2002, 11:44 PM

I think he is reffering to 1 Ohm resistor not 10 Ohm, it is because of the no-space and big O ;-) 1Ohm

Trigon.

grataku · 6th December 2002, 12:53 AM

For someone that would signal the time to get reading glasses.
Mybe it was an oppttttiiiicccaal illusion.

5th December 2002, 09:38 PM	#1
DJG diyAudio Member Join Date: Aug 2002 Location: Slovenia	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

5th December 2002, 09:44 PM	#2
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	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. __________________ MikeW

5th December 2002, 09:54 PM	#4
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	Go to the Pass Labs homepage. They have the Aleph service manuals that you can download. __________________ MikeW

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5th December 2002, 09:50 PM	#3
DJG diyAudio Member Join Date: Aug 2002 Location: Slovenia	Hello, MikeW! Could you send me your schematic, because I don't have one with voltage drops on it. Please. thx, DJG

5th December 2002, 09:58 PM	#5
DJG diyAudio Member Join Date: Aug 2002 Location: Slovenia	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

5th December 2002, 10:23 PM	#6
DJG diyAudio Member Join Date: Aug 2002 Location: Slovenia	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

5th December 2002, 10:59 PM	#7
dodonoid diyAudio Member Join Date: Oct 2002 Location: Hungary	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.....

5th December 2002, 11:36 PM	#8
Nelson Pass The one and only Join Date: Mar 2001	What 10 ohm resistor?

5th December 2002, 11:44 PM	#9
trigon diyAudio Member Join Date: May 2002 Location: Canada	I think he is reffering to 1 Ohm resistor not 10 Ohm, it is because of the no-space and big O ;-) 1Ohm Trigon.

6th December 2002, 12:53 AM	#10
grataku diyAudio Member Join Date: Dec 2000 Location: -	For someone that would signal the time to get reading glasses. Mybe it was an oppttttiiiicccaal illusion.

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