Simple, no-math transformer snubber using Quasimodo test-jig

Another Quasimodo lives!

I built it up last night, but only getting to use it tonight. After figuring out how t trigger the scope properly etc, I think I have stable waveforms. I connected up a random 12v transformer and was able to adjust the pot to get pretty close to the pictures in the manual that @Mark Johnson kindly provided - not quite as clean, but not bad. I also tried a much heftier 40V transformer and that was cleaner looking. Finally I pulled out my Aleph J, big 20V transformer and hooked it up. The results are below.

A: This first one is essentially undamped - I think the pot was up around 500R or so.
IMG_20220511_200452-01.jpeg

B: If I'm right, this one is I think the goldilocks spot - just damped, maybe a tad underdamped:

IMG_20220511_200506-01.jpeg

C: And this one I think is over damped.

IMG_20220511_200517-01.jpeg

I hope I have that right - If I do then I'm well on my way.

On all 3 of the transformers I measured with standard capacitors as per the manual, the resistor reading is quite low - from 15R to 30R. Is this normal? Should I change the capacitor values to achieve a higher resistance?

Fran
 
Hi all...

Lately i build a FFT measurement setup for testing my amplifier's. Link!
But this lead me to some issue's i see in some of my amps.
Attached picture here is a somewhat cheap LM4780 Cloneamp. (Schematic + FFT shoot)
(Feed with Victors 1KHz osc. at 1.055v ---> CloneAmp. ---> 8ohm-load ---> Soundcard)

I belive it's mostly 100Hz rectifier "noise" bleeding through the PSU (50Hz mains here in Denmark)
I'am in doubt if the Quasimodo snubber will help curing this? Or if the ringing it would cure are somewhat another issue
- I see it could be obvious but i can't really find anywhere showing this.

(For sure i'am up for building it, could be i cannot resist nomatter what)

Jesper.
 

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I did some more intensive reading now.
Looking closely at the note - i clearly see the point in doing this that transformer won't "ring/vibrate" any longer ::

Ring.png


But still cannot find any info why this can cure 100/120Hz noise. (Other than affecting diode turn-off somehow ???)
I found somewhere where it was discussed, but didn't gave me any clear answer also :)

Jesper.
 
HI...

I think the ringing on the Figure 10 are somewhere around 10KHz, eventhrough i'am not sure i did the math correctly.
The diodes are switching off somewhere between 100ns and 500ns depending on type.

This is somehow bleeding into the amplifier, and can be measured with RTA/FFT around 100Hz/120Hz depending on the mains freq.
That's only what i think, still i cannot seem to find the info about it clear (Also i'am non native English, which makes it harder to understand)

But i think i'am going to build it anyway, would just be very nice to have some kind of explanation that is :)

Jesper.