Aleph 5 problem

[pmchoong]

Hi all. I m in the midst of testing my Aleph 5 mono with Mark Finnis's pcb. When connect to the speaker (one channel) nothing seems to happen. When I switch off the amp, the LED stays illuminate for 20 minutes before finally dim. I matched the N fets according to a diagram by Kristijan. They are value at 3.03 to 3.20V. Is this possible? I used a 19V to a 150ohm resistor. The power from the PSU is measured at 37.75V. The speaker terminal measured at 0.07V. What is the problem??

Thanks in advance.

[kilowattski]

The LED stays on pretty long because you probably have some monster power supply caps and no sort of bleeder resistor for the caps to bleed off the charge.

[Jaac]

Seems like there runs no current at all trough your FETs. You can check if there runs current. You can measure the voltage over R11 it must be around 4 Volts. You can also see if the voltages are the same of each channel.

[Rodeodave]

Pictures are always welcome. Helps a lot sometimes.
In fact, by looking at the pics I posted in the Mini A thread, rtirion spotted the wrongly inserted Zener diodes my circuit. The Zener has to be orientated correctly to make the currentsource work.
So be sure to post pictures and check the orientation of the Zeners in the current source.

[pmchoong]

Right, I have some zeners reverse and the transistors are BC550, which has the CBE on the reverse as oppose to MPSA18. I have rectified these but problem persists. When I switch on the amp, the speaker moved forward and the lights are not on now. I have attached some pics. Thanks guys, i appreciated your help.

[pmchoong]

another picture

[Rodeodave]

The cone moves out and stays there? Or does it move back again? And the lights are not on? If the lights are not on something might draw a whole lot of current and will cause the supply-voltage to drop. Not a good thing. In that case you should also hear a buzz from the transformer as the core saturates.
I hope you have some cheap test speakers...

We now need some numbers. Do you have the aleph 5 service manual? On page 6 there's the schematic with some voltages.
Please measure the DC voltage of the following points (take a look at the schematic):

- Voltage across the Zener and the source-resistor in the CCS

- Voltage across all the BC550s from collector to emitter

- Voltage across the output-FETs' source resistors and the FETs themselves (from drain to source)

- Voltage across the FETs of the CSS and the differential pair (also from drain to source)

- Voltage from drain of the IRF9610 in the CCS to ground

- Also please measure the supply voltages in reference to ground and the output-offset.


This should give some clues.

[pmchoong]

zener (Z5) at Q3 - IRF9160 measured at 8.89
Z2 measured at 0.10
Z1 measured at 0.13
Z3 at 0.43
Z4 at10.26

Q5 - BC550 between C and E measured at 0.56
Q6 - BC550 between C nad E at 0.0

R11 measured at 5.29
R14 measured 0.0

Q1 - IRF9610 between G and S measured 0.5
Q2 - IRF9610 between G and S measured 0.53

All output resistors measured at 0.0

[pmchoong]

How do I measure the gnd and the output offset? Is it between the star gnd and the output at the speaker terminal?

[Manu]

Originally posted by pmchoong
How do I measure the gnd and the output offset? Is it between the star gnd and the output at the speaker terminal?

Yes, DC offset : measure DC value just between your 2 output terminal + and - (star grd).
Manu