Problem with Kwak Clock power supply

[Bricolo]

Hi,


I made some measurements on my KC-7, and saw something strange when I looked at the PS rails.

On the attached picture, you can see how the voltage is at the comparator's supply pins.
The upper curve is the positive supply, the lower curve is the negative supply.

There are 20mV peaks every 100ns, this corresponds to the clock period.

The strange thing is that there's garbage on the positive supply, but the negative one is clean.


When I look how the voltage is at the regulator's output (before the chokes), it's clean on both rails.

Another thing is that the clock draws 14mA on the positive supply, and 6mA on the negative one.
Elso said once that the clock draws 7mA. I don't know if it's 7mA on both, or total. But 14mA is clearly too much.

The multiturn pot's whiper is at 0.64V



Does anyone have an idea why I have this "noise" on the comparator's positive supply?

[Elso Kwak]

Hi Bricolo,
Do you have a 0.1 µF decoupling cap directly at pin 1 (+supply) of the comparator?
Do you have a decent clock output?
You did use chokes in the powersupply line? I only advice small ferrite beads.........

[hjelm]

Is it the KC7 and if so are you measuring after L1 or L2?
Edit: sorry you do not need to answer. I saw now that you measure at the comparator.

[peranders]

It's important _how_ you measure. Keep the ground cable very close to the comparator. You can also try to twist the ground cable around the probe in order to make the antenna smaller, less loop area.

How about decoupling very close to the comparator? 10 nF ceramic cap? C4, C15, 100 nF (unknown cap) is maybe not sufficient? BTW, is it the model 7?

[Andypairo]

As soon as I get home I'll measure my supplies to see if it is "normal" or not.

Cheers

Andrea

[Bricolo]

Elso:
yes, there's a 0.1uF ceramic cap just aside each supply leg of the comparator
the clock output looks OK, you've seen pictures of it on another thread
of course it's ferrite beads, I wrote the wrong word.

Hjelm:
yes, directly on the comparator.

Peranders:
this is how the grounding on my probe is done (like the one on the left)

BTW, since the negative rail is clean, I don't think the problem is in the measurement stuff.

Andypairo:
Thank you.
If you can measure the current drawn from each polarity it would be nice too.

[Bricolo]

Here's the ferrite bead datasheet.
I'm using the BL02RN2-R62

[Elso Kwak]

Originally posted by Bricolo
Here's the ferrite bead datasheet.
I'm using the BL02RN2-R62

Hi Bricolo,
I am terrible sorry but you got the wrong bead or the right bead at the wrong place. You can use your beads BL02... but before the regulator.
You can use Farnell part# 3234861 just before the comparator.

[Bricolo]

what's wrong with mines?

[Elso Kwak]

Hi,
I am probably using these:

www.elfa.se
Stock number: 58-727-26
Product name: Ferrite bead FB-73-101
Manufacturer: Amidon http://www.amidoncorp.com/aai_ferrit...ldingbeads.htm
Type designation: FB-73-101
Edit:
Actually it is this one:
Ferritebead for HF decoupling. Maker Philips. Outside diameter 3,7mm. Length 3,5mm. Has one hole of 1,2mm diameter.
Sorry no datasheet.