Aleph J illustrated build guide

[Kingsportal]

I retest by keeping the common probe on ground and tested both positive and negative sides and I did get a negative voltage reading on the negative side.
Any ideas why no voltage at r18.
Would it be possible that I have to turn r7 more than 10 x to get a reading?

 

[Kingsportal]

Kings...I don’t see minus voltage?

I also measure 20.3 volts at the speaker terminals, if that helps.

 

[Monk55]

Yes....make sure to adjust bias pot measuring voltage across R18....then use offset pot to achieve as close to zero volts across speaker posts

 

[Dennis Hui]

Kingsportal, can we try a few measurements?

Please measure the voltages across D1, R8 and R7. Also, what value are your parts R8 and R7?

 

[Kingsportal]

I am not able to adjust r7 at all. Its is reading 20volts at the speaker terminals.
R27 is reading 0 volts across r18.

 

[Kingsportal]

D1 measures 9.18 v
R8 measure 8.67 v

 

[Kingsportal]

D1 measures 9.18 v
R8 measure 8.67 v

R8 is 1k ohm
Zener doide for D1 9.1vols 1.3 watt on package

 

[Kingsportal]

R8 is 1k ohm
Zener doide for D1 9.1vols 1.3 watt on package

R7 is potentiometer.

 

[Dennis Hui]

You can measure the voltage across R7 at the holes on each side of the R7 pot.
That voltage is important and should be in the 4 to 5 volt range. If it's too low,
your output mosfets will be off and you will see zero voltage across R18.

 

[Kingsportal]

You can measure the voltage across R7 at the holes on each side of the R7 pot.

That voltage is important and should be in the 4 to 5 volt range. If it's too low,

your output mosfets will be off and you will see zero voltage across R18.

R7 is reading 0 volts

 

[Dennis Hui]

Can you try turning R7 and see if you can get a voltage there?

 

[Kingsportal]

Can you try turning R7 and see if you can get a voltage there?

I turned it about 15 times clockwise and nothing

 

[Kingsportal]

I turned it about 15 times clockwise and nothing

The amp is ice cold from my air conditioning.
The heat sinks are not warm at all.

 

[Dennis Hui]

What about turning in the other direction?

 

[Kingsportal]

What about turning in the other direction?

No reading when turned either direction about 50 times. I can hear sort of a click when potentiometer is maxed in both directions

 

[poseidonsvoice]

Dennis has asked the relevant questions. My question is what JFETS do you have installed in Q1A and Q1B? They both should be 2SJ74’s or equivalents. I can’t see it since you have some heat shrink on them. If you don’t have a voltage at R7, my suspicion lies in the JFETS as Dennis had said, you need 4-5V at the gates of the MOSFETS to turn them “on” so they can be biased.

Please confirm what Q2, Q3, and Q4 are as well.

Your N channel MOSFETS appear to be correct in the pictures (IRFP 240).

Best,
Anand.

 

[Kingsportal]

Dennis has asked the relevant questions. My question is what JFETS do you have installed in Q1A and Q1B? They both should be 2SJ74’s or equivalents. I can’t see it since you have some heat shrink on them. If you don’t have a voltage at R7, my suspicion lies in the JFETS as Dennis had said, you need 4-5V at the gates of the MOSFETS to turn them “on” so they can be biased.

Please confirm what Q2, Q3, and Q4 are as well.

Your N channel MOSFETS appear to be correct in the pictures (IRFP 240).

Best,
Anand.

Hello and thank you for helping.

Q1a and Q1b are Linear systems quad matched jfet LSJ74.

(Aleph J Transistor kit)

Q2. ZTX 550.
Q3. ZTX 450
Q4. ZTX 450

The flat side of j fet faces CBE printed on the board on q2 q3 and q4. I hope they are correct.

What does 24v at the rails mean?

I am getting 24 volts when I check the euro blocks on the power supply board.

My antek 500VA 18V Transformer
does not have a ground cable. It has 2 pair of mains and 2 pair of secondary cables.
Could this be a problem?



Thanks again
Keith
View attachment 954297 View attachment 954300

I am also getting 20 volts at the speaker terminals.

View attachment 954301

 

[Monk55]

Jfets should both be lsj74....if the flat side of the ztx is facing you the leg on right is C.

 

[Kingsportal]

Jfets should both be lsj74....if the flat side of the ztx is facing you the leg on right is C.

Thats what I did. Just like these in the build guide.



View attachment 954303

I was able to get this shot of q1a View attachment 954304

Ok picture of q1b looks different

View attachment 954306

 

[Kingsportal]

Dennis has asked the relevant questions. My question is what JFETS do you have installed in Q1A and Q1B? They both should be 2SJ74’s or equivalents. I can’t see it since you have some heat shrink on them. If you don’t have a voltage at R7, my suspicion lies in the JFETS as Dennis had said, you need 4-5V at the gates of the MOSFETS to turn them “on” so they can be biased.

Please confirm what Q2, Q3, and Q4 are as well.

Your N channel MOSFETS appear to be correct in the pictures (IRFP 240).

Best,
Anand.

It looks like I have Q1A as LSJ74
and Q2B as LSK 170.

Is this my issue?

View attachment 954310 View attachment 954311