My Aleph 5 isn't working

[DJG]

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]

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]

Hello, MikeW!

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

thx,
DJG

 

[MikeW]

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

 

[DJG]

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]

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]

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]

What 10 ohm resistor?

 

[trigon]

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]

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

 

[ststone]

Thank you Nelson, It takes many talents to guide an international group of people. Language, Insight in other cultures, Tolerance, Geduld (Patience).

Chapeau, Shalom and Seasonal Greetings

 

[DJG]

Yes it is 1 Ohm resistor. I have measured all the resistors(1 Ohm) and they all have 0.2V.
Is the problem on the MPSA 18 - because I have BC550 instead?

thx,
DJG

 

[grataku]

Junior,
I just wanted to let you know that your posts stick out as being out of contest, long, and waaaayyyy to numerous. You succeded in getting my attention. And I have the distictive feeling I met you before on this forum under another member name. You are annoying me in exactly the same way.
Oh, and copying picture I post to your avatar is cheesy.

 

[ststone]

The last thing I wanted to is to upset you, because its all about you, again sorry and seasonal greetings.

(change an A to an E and add a T)

 

[DJG]

Any thoughts on my problem?

 

[grataku]

you should definitely get that fixed!

Sorry Dude I have no idea of what you mean by clicking, how much input you are feeding, try to be a little more specific.

 

[DJG]

Well, i can't give you any specific values of the input signal, but from experiences I would say that the maximum output signal is about 15W befor clipping. Does that help?

 

[dodonoid]

Hi DJG,

look at the transistors (BC-s) if they are connected correctly (I mean the pinout of the transistor can differ from the ZTX). If it is ok, then recheck the resistors in the current source, and the mosfet's source resistor to which you connected the emiter and base of the upper tranny.

Another thing can cause a similar problem: didn't you connected ALL of the source resistor in paralell??? On the scematic is only specified X3 (or anything...), and may happen, that you connected the transistor's base and emitter to ALL of the source resistors...

Good luck & regards,
Miki.

 

[dodonoid]

It's me again...

The MPSA18 has E-B-C (if you look at the "face" of the transistor), the BC550 has C-B-E....

The ratings for the two transistors are very close (altrough it's not so important...), so in my oppinion BC550 is good for Alephs

Miki.

 

[MikeW]

Do all your transistor get warm after the amp has been on for a few minutes? They should be. Do you have a scope to look at the output? Are your rail voltages stable?