Dear fellow Pass builders,
After several years of excellent performance, one of my DIY Aleph 2 mono-blocks got defective.
The strange thing is that it fires up well and it stays well at idle as long as it does not get an input signal or even a wire attached to one of its inputs (either RCA or XLR), because then the fuse (I already went to 4A slow,230 Volt) blows.
I already checked some voltages. On the G and the S of the output 240’s there is with all 12 of them a voltage of about 4,12 Volt. The PSU voltage on the rails is +48 and -48 volt. There is only 12 mV DC on the speaker terminals (without any load). So this seems to be ok.
I have to add that in the PSU there is a slow-start module, but that too seems to be working fine.
Before I start deassembling everything, does anyone have a clue into which direction I should look?
Any advice dearly appreciated!
Best wishes,
Lucas
After several years of excellent performance, one of my DIY Aleph 2 mono-blocks got defective.
The strange thing is that it fires up well and it stays well at idle as long as it does not get an input signal or even a wire attached to one of its inputs (either RCA or XLR), because then the fuse (I already went to 4A slow,230 Volt) blows.
I already checked some voltages. On the G and the S of the output 240’s there is with all 12 of them a voltage of about 4,12 Volt. The PSU voltage on the rails is +48 and -48 volt. There is only 12 mV DC on the speaker terminals (without any load). So this seems to be ok.
I have to add that in the PSU there is a slow-start module, but that too seems to be working fine.
Before I start deassembling everything, does anyone have a clue into which direction I should look?
Any advice dearly appreciated!
Best wishes,
Lucas
Pass DIY Addict
Joined 2000
Paid Member
Hi Lucas,
Check out the circuit explanation that is posted on my Aleph-X page. The Aleph-X amp is essentially two Aleph amps running in parallel and the circuit and components are described on my page.
Hope this helps a little.
Eric
Check out the circuit explanation that is posted on my Aleph-X page. The Aleph-X amp is essentially two Aleph amps running in parallel and the circuit and components are described on my page.
Hope this helps a little.
Eric
Can you post your schematic as everyones render of these amps is different.
In Erics schematic you would be looking at R30 and C4.
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Pass DIY Addict
Joined 2000
Paid Member
I'm sorry that I don't think I'll be able to help much more beyond this. Replacing elements in the feedback chain seems like an easy enough place to start...
Are there any particular circumstances that preceded the failure? Prior to the failure, did you move anything? Wires? The amp itself? Open the chassis? Disconnect anything? Just looking for some clues that might suggest a course of action. Do you have a scope or any other measurement equipment?
Are there any particular circumstances that preceded the failure? Prior to the failure, did you move anything? Wires? The amp itself? Open the chassis? Disconnect anything? Just looking for some clues that might suggest a course of action. Do you have a scope or any other measurement equipment?
My first idea is to check the pair of 9610.........
Because I can imagine more a failure of the active components first, possibly followed by a failure of passive parts....
I do not know the current through the differential pair in the input, but let us say it is about 20mA so there should be about 4V over the 221 Ohm feeding the differential pair.
Am I correct?
But your idea with the Zener is also a good idea!
Because I can imagine more a failure of the active components first, possibly followed by a failure of passive parts....
I do not know the current through the differential pair in the input, but let us say it is about 20mA so there should be about 4V over the 221 Ohm feeding the differential pair.
Am I correct?
But your idea with the Zener is also a good idea!
Yes. there is maybe one: a friend of mine has used them with a pair of 10m long unshielded! balenced cables. Maybe this has led to oscillation and damaged some parts in the input section?
Q1A5 is a 20mA Constant Current Sourse for the input pair Q1A1 and Q1A2.
It should be impossible to blow this up as the CCS by its own nature will only deliver 20mA even if you short the output to GND. Therefore you should see about 4V at the Sources of Q1A1 / Q1A2.
I've just confirmed, the IRF9610 is a 200V device so even shorting Q1A1 or Q1A2 to the -ve rail shouldn't cause the demise of Q1A5.
Does the mono-block blow its fuses if you put a shorting plug at its input ?
Best way to confirm that CCS is working is to measure 4.5V across R3 (in the Aleph 4 diagram), if that's wrong then one of the actives around the input stage has failed.
I think the 4V at the sources of Q1A1 / Q1A2 must be relative to PWR GND.
It should be impossible to blow this up as the CCS by its own nature will only deliver 20mA even if you short the output to GND. Therefore you should see about 4V at the Sources of Q1A1 / Q1A2.
I've just confirmed, the IRF9610 is a 200V device so even shorting Q1A1 or Q1A2 to the -ve rail shouldn't cause the demise of Q1A5.
Does the mono-block blow its fuses if you put a shorting plug at its input ?
Best way to confirm that CCS is working is to measure 4.5V across R3 (in the Aleph 4 diagram), if that's wrong then one of the actives around the input stage has failed.
I think the 4V at the sources of Q1A1 / Q1A2 must be relative to PWR GND.
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Hi Lucas,
do you refer to the manual of Aleph2 or Aleph 4 because in both manuals Q3 means a different Semiconductor....
when the IRF are o.k. I would look next for the Q5 the MPSA18 (nomenclatura of Aleph2 manual)
you see we are all eager to help you.....
not building myself anything at the moment...
You need to compare your diagram with the one that I posted at Post 11.
If anything is wrong around the outputs I would expect it to blow fuses all the time, not just with an input.
The IRFP9610s are easy to spot on the PCB, they are the TO220 devices as opposed to the TO92 MPSA or ZTX devices that control the ouputs.
Q1A1 and Q1A2 will be very close to each other.
The part numbers that I am referring to are for the Aleph 4 at Post 11.
If anything is wrong around the outputs I would expect it to blow fuses all the time, not just with an input.
The IRFP9610s are easy to spot on the PCB, they are the TO220 devices as opposed to the TO92 MPSA or ZTX devices that control the ouputs.
Q1A1 and Q1A2 will be very close to each other.
The part numbers that I am referring to are for the Aleph 4 at Post 11.
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Hi Lucas,
do you refer to the manual of Aleph2 or Aleph 4 because in both manuals Q3 means a different Semiconductor....
when the IRF are o.k. I would look next for the Q5 the MPSA18 (nomenclatura of Aleph2 manual)
you see we are all eager to help you.....
not building myself anything at the moment...
I might be wrong, but dont the two MPSA's just control the quiescent currents by measuring the voltage across the Source resistors ?
I would have thought a failure here would cause fuses to blow at power on ?
Yes KatieandDad you are right,
I did not reflect that a damage in this place would cause more visible mess...I was inspired by his comment of oscillation and because the caps stopping oscillation are in this area I was so free to suggest to look for this place in second order....
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