Aleph 2 problem!Help...

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nar

nar

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Joined 2002
#1
I have just finished 2 Aleph 2 s. Tested separately,both of them worked well , without been connected to the ZLS balanced mode.

I did the set up , powered on the left block ...the toroid was buzzing very loud,and some smoke became to get out of the amp.

I put it off immediately.The smoke was discrete,and
.was not coming from the power mosfets
. The inductor of the Pi filter for V+ was burning,litterally.The one on V- was cold.
Before,I had a problem with one mos of the 240s Aleph current source.I forgot to connect its Source to the dedicated 1 ohm 5W resistor.First I tried to solder it back,but when powering up the resistor became a nice power bulb ,orange like.So I thought the mos died,and replaced the mos and its resistor.Test was ok then.
. The offset at speaker terminals was very high when problem occured, 0,5V at least.
.The ground of each amp is tied to earth via chassis through a 5W 4,7 ohms power resistor.That one too was burning my fingers !

So , my conclusions for the moment are

. I have a problem elsewhere in the current source than the CCS s 240s , maybe the MPSA18
.The current source may be oscillating ,who knows ....strange...the one on the other block does not !
.or the 240s of the CCS have a problem. I don't have time to check voltages before smokes arrives!And I don't want to break everything....

Has someone an idea of what happens to me ???

Please guys,help !!!

Regards
 
#2
I checked the resistance of the inductors.Clearly the V+ inductor has fried in 10 secs time ,it has now no DC resistance compared to the V- one :cannotbe:

I am perplex :scratch:

The other block runs perfectly :devilr:

I am getting mad:headshot:


Anael
 
#4
MPSA 18s are connected same way on the 2 blocks,and it is the good way ,BTW :bawling:

The initial current draw is less than 4 A my 4 A 250V fuse doesn't blow up :nod:

Total bank capacitors is 182.000uF

Bridges,47.000 , 22.000/inductor/22.000 for each rail :clown:

I wonder why the current is so exessive at start through ground to earth by 4,7 ohms 5W series

:devilr: :devily: Who has any explanations ? 😕

Regards
 
#5
BTW.If that can help,I use air core inductors.Can't understand why the V+ one fried dissipation on it is 2,52V at idle for the amp.The idle bias for me is 2,4 A approx , not the 3 A expected on the Passlabs schematic.

Problem not solved ! Please some help ! :bigeyes:

Regards

anael
 
#6
Sorry to read your misfortune.

Did you try disconnecting the amp from the supply?
Check the supply thoroughly. Namely the rectifier bridge(s).
Could it be half of these died on startup? A diode test using a simple meter should give you a good idea.

If the supply is OK. Check the zener and fet in frontend.
Test all output fets.

btw use a variac when testing please.

Take your time to check everything and I am sure you will find the solution

Regards
 
#9
R 52 /R 53 in Aleph 60 ? Snubers?

This morning I re-measured the 2 inductors in the Pi filter section.

The V+ one hasn't fried!It has same DC resistance than V- one,namely 1 ohm.

I am lost.Must have been very tired last night....

On the other block ( the one 's running perfectly :devily: :headshot: I measure on both inductors a 2,52 V value , which shows the permanent draw of the amp.Little reduced bias compared to Aleph 2 schematics,but anyway.

What I am about to do :

Disconnect PSU from amp and make it run separately,at a 100mA test resistor on both sides V; and V-

Check tensions are equal

I can't get a variac today , Sunday damn every shop is closed !

Re run the amp is everything OK on PSU alone ,but use some extra parts found in the Aleph 60 , namely R 0 , R 52 and R 53
I think the initial current draw is too important for the inductors,so R52/53 might help ! And If I had a ground loop?R0 would be useful :cannotbe:

What is the purpose of R 52 53 in Aleph 60 ? Anybody can tell ?

THANX :devilr: !!!!!!
 
#10
I re-ran the problematic block this morning alone,i.e connected to nothing no pre no load

It runs OK !!!!:nod: :nod: :nod: :nod:

So I guess pb comes when linked to other equipmnent.

I guess it is a juicy ground/earth loop ....

So I decided to isolate circuit ground from PSU ground by 2X 1,8 ohms/5W series

As my ZLS runs with no earth linked to pre-ground,I guess I have a problem when splitting this gnd not earth referenced to 2 mono blocks.

In the mono blocks I have

Earth directly tied to chassis

PSU gnd linked to chassis gnd via 4,7 ohms/5 W series

Circuit gnd was linked directly to PSU gnd

I will add in each block a 3,8 ohms/10W to isolate circuit ground from PSU ground , As shown in Aleph 60

Hope it would work !!!!

More clear for anyone about ground/earth loops ??
 
#11
:devilr: :devilr:

GOT RID OF THE PROBLEMS ! ! ! ! ! !

nar-> :headshot: <- problem

This was a bad bad bad ground/earth loop.

If i would have used thermistors it would have never shown out.
But I only had resistors to do it.

So the solution was :

The ZLS has only one PSU , i.e. both channels have same ground but no earth connection audio ground is no common with chassis

On each mono block,earth is diectly linked to chassis

PSU ground is linked to chassis via 4,7 ohms / 5W cement resistor

The circuit ground is isolated of PSU ground through 3,6 ohms / 10 W resistor ( in fact 2 1,8 ohms 5W in series )

That way problem vanished as soon as I did the mods on each block 😉

The Aleph 2 is an impressive natural sounding amp.

I settled R 21 to 825 ohms Edwin 😉

Everything is prefect 😎 I have to wait for burn in time + 50 hours typically

Thanks to everyone in the forum for tech support :devily:

I will post pics soon .

Regards
 
#15
Yes Edwin but what do you think of my 825 R value for R 21 😉

Makes me remember of the old Aleph X thread ....:devily:
Click to expand...


You can measure if your ACS is running 50% by throwing a 1khz 9V RMS sin wave into your Aleph.

Now measure the AC voltage over a negative side of a bias resistor and over the parallel output resistors. From this you can calculate the amount of amperes running.

Divide both number and you should get 0.50 ! There are some other threads about how to do this in detail.

I am running now on about 900 ohm (measured in circuit so it is not totally precise) .

Edwin
 
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