Still some problems with Crescendo. Oscillation or what?

[Eccu]

Hello...

I have changed those zeners but I have still some buzzing or humming.


1st picture is measured after main capacitors plus line (wire).
Ripple is quite normal I guess so... or is it? About 300mV Peak-To-Peak.
X-axis: 100mV/div and Y-axis: 2ms/div

[Eccu]

But this second picture is quite odd....
This is measured from output when input was short circuit.
Little test speaker was connected to output.
X-axis: 50mV/div and Y-axis: 2ms/div


Where those (100Hz) peaks come from?


(pictures quality is not so good because those was taken using mobile.... as you can see that from reflection )

[joensd]

The 300mV ripple seems OK to me.
How is your set up bias current at the moment?

The 100Hz peaks gotta come from the power supply but shouldn´t be nowhere near that big.
Maybe your power supply is too near to the audio circuitry in places?
Make a permament connection from output to oscilloscope and try to move cables around a bit and see if the picture changes.

[Eccu]

Hi Joensd....

Yes, I must try that "cable moving thing".


Do you have one or two rectifiers in your power supply?
And where you have set your star point?
And could you send me some pictures of your power supply schematic?

[Upupa Epops]

Hi Eccu, your problem is probably in wrong grounding of input part . Can you show how is it made? Ground of input part you must connect right to the middle of power supply main capacitors.

[joensd]

I´m using one rectifier in the PS as described in the article.
I had to move the transformer in all of my amps to minimize PS hum.
Do you use the boards from Elektor?
If so you could connect your speaker ground directly to star ground and not via the PCB. (I still haven´t done it but this should improve it as well)
As Upupa mentioned it could be input grounding as well.
I cheated a little on that one and connected the audio input ground via 10Ohms resistor to amp ground.

Cheers
Jens

[Eccu]

hello...

Upupa Epops:
You mean ground from wall socket. I dont have connected that to main capacitors center piece. Its only connected to chassis.
So this might be reason.... lets try this next.


Hi Joensd.
I use diy PCB boards.... similar layout as Elektor have.
You said that you have connect that audio input ground to amp ground via 10ohm. Is that amp ground same point as star point?
So you have disconnect that audio input ground from amplifier board (that jumper wire)???? Or how?

[joensd]

Usually you connect the signal input ground directly to the designated point on the PCB so to main ground.
I just put a 10Ohms in series so it is "separated" a little more and more immune to ground noise.

[joensd]

Forgot to say you should properly earth your chassis first before trying anything else. Maybe this gets rid of all hum.
There are many solutions : resistor, NTC, bridge rectifier or combination of all of them.
Look HERE for some information.
The ZenV4 for example uses bridge rectifier, Aleph3 just NTC.

Cheers
Jens

[Eccu]

I have connect socket earth directly to chassis. Is this wrong and should I connect socket earth first to star point and take there some wire to chassis or what?

Damn, I have some fever now. I must go to bed now.
I try fix my Crescendo on next weekend once more.