Aleph J illustrated build guide

Another observation. When turning on the amp I am getting temperature reading evenly on Q5 Q6 Q7 and Q8 on the left board. This board is testing OK. 81 degrees F soon after power on.

The right amp board mosfetts are also the same temp on Q5 and Q6 of 81 degrees.
However Q7 and Q8 read 89 degrees. These are inconsistent with all the others.

Also what is the relationship between Q1A and Q1B to Q56 and Q78?
I am assuming the Jfets are now working.
 
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KP,

I don't think your potentiometer at R7 is the issue to be honest. But you can replace it and see if it works or remove it and check and see if the pot is damaged by testing it with a DMM.

Did you check with the amp turned off, that each of the 3 pins on each of the MOSFETS does not have a connection to ground? Did you remove any burrs on the back of the MOSFETS with sandpaper so that they don't pierce through the Keratherm and accidentally short to the chassis? Remember the back of the MOSFET is connected to the drain pin and accidental shorts are common.

The temperature reading differences between the MOSFETS are small and I wouldn't worry about them too much. There are going to be minor differences in conducting current and because they are at different locations on the heatsink the dissipation will be slightly different as well.

For your 'relationship' question, read post 6735 and study the schematic carefully. You will see that the JFETS (Q1A in particular) must conduct correct, in order to create 4.3V which will turn on the MOSFETS Q7 and Q8. Similarly Q4 (ZTX450) must conduct so that 4.3V is created for the CCS MOSFETS Q5 and Q6.

Best,
Anand.
 
KP,



I don't think your potentiometer at R7 is the issue to be honest. But you can replace it and see if it works or remove it and check and see if the pot is damaged by testing it with a DMM.



Did you check with the amp turned off, that each of the 3 pins on each of the MOSFETS does not have a connection to ground? Did you remove any burrs on the back of the MOSFETS with sandpaper so that they don't pierce through the Keratherm and accidentally short to the chassis? Remember the back of the MOSFET is connected to the drain pin and accidental shorts are common.



The temperature reading differences between the MOSFETS are small and I wouldn't worry about them too much. There are going to be minor differences in conducting current and because they are at different locations on the heatsink the dissipation will be slightly different as well.



For your 'relationship' question, read post 6735 and study the schematic carefully. You will see that the JFETS (Q1A in particular) must conduct correct, in order to create 4.3V which will turn on the MOSFETS Q7 and Q8. Similarly Q4 (ZTX450) must conduct so that 4.3V is created for the CCS MOSFETS Q5 and Q6.



Best,

Anand.
Yes I did remove the boards and used 2000 grit sand paper for any potential burs on the mossfets and the heat sinks.

When adjusting the R27 potentiometer nothing changes at R18.

I did notice on the board the grounding hole for Q1A , middle pin, was missing that ring. Flipping the board over it was still on the back side.
View attachment 958085
 
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Are you able to prove that the voltage across R7 is 4.3V or more to be sure that the JFET Q1A is conducting and hence there is enough voltage to turn on the output MOSFETS?

See posts 6730 and 6735. The voltages to check are explained there as well as in the schematic he supplied.

The repeated soldering/desoldering that occurred with the JFET Q1A can harm the board so be careful.

Best,
Anand.
 
Are you able to prove that the voltage across R7 is 4.3V or more to be sure that the JFET Q1A is conducting and hence there is enough voltage to turn on the output MOSFETS?

See posts 6730 and 6735. The voltages to check are explained there as well as in the schematic he supplied.

The repeated soldering/desoldering that occurred with the JFET Q1A can harm the board so be careful.

Best,
Anand.
I will check again tonight. I think it measured 5.8 volts.
 
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I did notice on the board the grounding hole for Q1A , middle pin, was missing that ring. Flipping the board over it was still on the back side.
View attachment 958085

Your photo is not showing up. (Invalid attachment)

Anyway, it seems the trace connecting the gate leg (middle leg) of Q1a is on the bottom. Can you please make sure that leg is well soldered at the bottom of the pcb?
 
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Your photo is not showing up. (Invalid attachment)

Anyway, it seems the trace connecting the gate leg (middle leg) of Q1a is on the bottom. Can you please make sure that leg is well soldered at the bottom of the pcb?
Photo of Q1A Screenshot_20210607-134853_Gallery.jpg
 
Member
Joined 2002
Paid Member
Thanks Dennis. So I assume that would run between the two outer terminals?

Not sure where my reply went...

Anyway, yes., the fixed resistor will go between the two outer terminals.

Please also check the voltage across your zener diode since you measurement
of 6.5V across R8 doesn't sound right. Please also check the value of the
R5 resistor.
 
KP,



I don't think your potentiometer at R7 is the issue to be honest. But you can replace it and see if it works or remove it and check and see if the pot is damaged by testing it with a DMM.



Did you check with the amp turned off, that each of the 3 pins on each of the MOSFETS does not have a connection to ground? Did you remove any burrs on the back of the MOSFETS with sandpaper so that they don't pierce through the Keratherm and accidentally short to the chassis? Remember the back of the MOSFET is connected to the drain pin and accidental shorts are common.



The temperature reading differences between the MOSFETS are small and I wouldn't worry about them too much. There are going to be minor differences in conducting current and because they are at different locations on the heatsink the dissipation will be slightly different as well.



For your 'relationship' question, read post 6735 and study the schematic carefully. You will see that the JFETS (Q1A in particular) must conduct correct, in order to create 4.3V which will turn on the MOSFETS Q7 and Q8. Similarly Q4 (ZTX450) must conduct so that 4.3V is created for the CCS MOSFETS Q5 and Q6.



Best,

Anand.
Anand.

I am getting continuity from at least 1 pin on most all of the mossfets to ground for both boards. I did sand and clean each Mosfet and the heatsink prior to installing the first time. No burrs were felt on inspection.


Here are some measurements.

Zener. Right Board=9.14v
Left Board =9.15v

Right Board. R8= 8.45v
R7=5.65v

Left Board R8=8.48v
R7=4.89v

Are my mosfetts or / keratherm an issue because they have continuity to ground?

Im Still trying to get this thing up and running.

Thanks in advance to any one else who wants to chime in.


Keith
 
I am getting continuity from 1 pin on most all of the mossfets to ground for both boards. I did sand and clean each Mosfet and the heatsink prior to installing the first time. No burrs were felt on inspection.

Here are some measurements of key areas mentioned above.

Zener. Right Board=9.14v

Left Board =9.15v

Right Board..... R8= 8.45v, R7=5.65v

Left Board........ R8=8.48v, R7=4.89v

Right Board ......R17= 2.1v. (Problem)
Left Board........R17=0.4v.


Are my mosfetts or / keratherm an issue because they each have continuity from 1 pin to ground?

Im Still trying to get this thing up and running.

Thanks in advance to any one who wants to chime in.

Also R17 is overheating on the right board.
I replaced it the amp was powered on just a few minutes it started to smell and turn brown.

Keith

View attachment 958185
 
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Got it! Where I went horribly wrong was with the trimpots.
I must have had a senior moment when I soldered them in because I had them hopelessly mixed up. On one board I had three 2K trim pots. On the other I had two at 100K and one 2K and that was even in the wrong spot.
After rectifying all of that I am now listening to beautiful quad with bass going through the bottom Aleph and treble through the new one on top. It's the DIY biamp crossover.
The sound is gorgeous!
I'm christening it with Albert King. Awesome.
Thanks for all the thoughts and great vibes.
 
Got it! Where I went horribly wrong was with the trimpots.
I must have had a senior moment when I soldered them in because I had them hopelessly mixed up. On one board I had three 2K trim pots. On the other I had two at 100K and one 2K and that was even in the wrong spot.
After rectifying all of that I am now listening to beautiful quad with bass going through the bottom Aleph and treble through the new one on top. It's the DIY biamp crossover.
The sound is gorgeous!
I'm christening it with Albert King. Awesome.
Thanks for all the thoughts and great vibes.
Congratulations now fix mine too...lol
 
Here are some measurements of key areas mentioned above.

Zener. Right Board=9.14v

Left Board =9.15v

Right Board..... R8= 8.45v, R7=5.65v

Left Board........ R8=8.48v, R7=4.89v

Right Board ......R17= 2.1v. (Problem)

Left Board........R17=0.4v.

Are my mosfetts or / keratherm an issue because they each have continuity from 1 pin to ground?


Also R17 is overheating on the right board if amp is on for about 5 min.

I replaced it the amp was powered on just a few minutes it started to smell and turn brown.

Mosfetts measure


Across outer pins

Right board:
Q5=0.455v Q6=0.500v. ***
Q7=4.6v Q8=4.6v

Left Board:
Q5=4.48v. Q6=4.51v
Q7=4.45v. Q8=4.52v

I am getting continuity from 1 pin on most all of the mossfets to ground for both boards when the amp is off.
I did sand and clean each Mosfet and the heatsink prior to installing the first time. No burrs were felt on inspection.

Im Still trying to get this thing up and running.

Thanks in advance to any one who wants to chime in.
 
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Kingsportal,
I hope you get yours sorted. You've had a pretty rough trot.
Anyway I just checked my mosfets terminals relative to ground.
If you call the end of the board with the DIYaudio lettering the 'front' then the two mosfets at the front have the centre lug cont. to earth and the rear two have the rearmost lug cont to earth.
The way I found my stupid mistake was by going around with the multimeter without the amp powered up and measuring resistances to get an idea if I had fitted a wrong resistor somewhere.
I have the luxury of owning the other Aleph that I made a few years ago so that makes comparisons much easier, since you don't have to unsolder all the ends of everything, just get the same or very similar reading.
So I suggest you do this on either side of your trimpots to make sure you haven't made the same idiotic mistake I did. It becomes fairly obvious if you have a 100K pot or a 2K pot in there even though the readings are necessarily incorrect when it's in situ.
I used a solder sucker to remove the pots and then I held the soldering iron on one side of each hole while I operated the sucker on the other. This cleaned the solder out of those holes nicely and allowed all the swaps to happen seamlessly.
 
R17 is overheating because there is too much current flowing through it.

What is the voltage across R16?

If R16 is not overheating and the voltage across R16 is normal, then it is very possible that Q6 is defective.

Agree with Ben Mah. Thanks Ben! ;)

Perhaps the attached link of the schema of the IRFP 240 and link for testing NMOS type Mosfets will help KP. I would recommend testing be done of Q5 and Q6 after completely desoldering the pins from the board and/or complete removal if possible.

Best,
Anand.
 
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