Strange voltage curves

Hello,

I have a working Aleph 4, however when I look with a scoop on the traces of the + and - voltages of left and right channel I get very strange views... Only the first trace looks like I would expect. both channels are wired the same. They are all very different. Timebase and amplify are all the same for all pictures!

I have 0.22uf 250V around the rectifier bridge and across the + 0 - side of the elco's. You can see this on a picture below.

channel 1 +
[IMGDEAD]http://www.xs4all.nl/~edwind/b.jpg[/IMGDEAD]

channel 1 -
[IMGDEAD]http://www.xs4all.nl/~edwind/a.jpg[/IMGDEAD]

channel 2 +
[IMGDEAD]http://www.xs4all.nl/~edwind/c.jpg[/IMGDEAD]

channel 2 -
[IMGDEAD]http://www.xs4all.nl/~edwind/d.jpg[/IMGDEAD]

Help what can it be!

Edwin
 
Capacitor

Are those Phillip 26000uF/75V capacitors with the 3 connectors? I hope they are not the cause of the "problem" because I just bought a bunch of them.
By the way, if they are 26,000uF each, why do you need some many per channel? You just want to do way overkill since it's DIY?
 
Re: Capacitor

fcel said:
Are those Phillip 26000uF/75V capacitors with the 3 connectors? I hope they are not the cause of the "problem" because I just bought a bunch of them.
By the way, if they are 26,000uF each, why do you need some many per channel? You just want to do way overkill since it's DIY?

For the record; these are pictures of the power supply + and - rails... not of the output or input of the amplifier.

The channel 1 has the least hum.

They are 63V 22000uf BC components (philps) with 2 times M5 screw on connectors.

Yes, DIY overkill! To lower the ripple of the powersupply, however something does not work!

Edwin
 
fcel said:
1. Does the transformer has shielding?
2. Did you try installing the transformers side by side instead of on top of each other?

The transformers do not have shielding. They are 1000VA 40-0-40 transformers.

I mounted them on top of each because of easy fixing. I did not try to move them around, as they are bolted on to the wood, and soldered with thick wires (do not bend easy). Can this be a part of the problem? I looked once in a Plinius amp and they do the same trick.

Edwin
 
Edwin a couple of quick questions.

1. What do you have as a load for the amp while testing?

2. Do you have the bias set for both channels?

3. Is there any DC ofset at the output?

Just looking at the scope traces it looks like channel 2 has a higher bias current setting than channel 1. It also looks like there may be a - offset in both channels (more current from the - supply that the + supply).

The only other thing I can think of that would cause a wave form like this is that some of the power supply caps may have a bad connection of are defective.

Hope this helps.
BZ
 
The only other thing I can think of that would cause a wave form like this is that some of the power supply caps may have a bad connection of are defective.

Hope this helps.
BZ [/B]

Looks like you are my hero! I just removed all elco's from one channel and retighten them again, without the washer between the elco poles and the copper plates. I have a ~~~~ kind of washer one the other side to tighten the screw.

On channel 1 I now have both the same picture on the scoop!

Ok, now the other side!!! Let you know within the hour :)))

Edwin
 
Edwin Dorre said:


Looks like you are my hero! I just removed all elco's from one channel and retighten them again, without the washer between the elco poles and the copper plates. I have a ~~~~ kind of washer one the other side to tighten the screw.

On channel 1 I now have both the same picture on the scoop!

Ok, now the other side!!! Let you know within the hour :)))

Edwin

Thanks!!!!

My problem is FIXED!!! I used ~~~~~ type washers which were not very conductive between the copper of the PCB and the elco!!! Stupid stupid stupid...

Washer moved to other side of the PCB, so the elco's touch the copper directly, and ... beautifull curves like the first of the pictures!!!

Edwin
 
Yes Edwin,it works.What you see on the oscilloscope is just the residual noise on the voltage rails.

Don't know if it is right,but you should try a Pi filter to remove little bit more hum.Try something like 22.000uF parallel/choke 4.7mH series/22.000 parallel for every rail.Just put it after the main PSU capacitors,and before the main board connections.For the chokes air core type with 1.4mm dia. should be fine(they heat a little,but warm,not hot.)like the big speaker types for crossover networks.

Changes sound in the medium range.In fact,more inductance,the medium gets more accurate,sweet and less"bad sense wild".

Try it...