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

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#2,181
Figure 13 on page 11 of the Quasimodo design note will help. Thick black lines indicate "shorting bars", i.e., transformer terminals that need to be shorted together during Quasimodo testing.


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#2,183
Beginners beggings

Hello!
Finall, I got here:
Use my Quasimodo.
Never having played with this kind of stuff (scope, 😱), I don‘t know what to ask to get to useful results.

I already hooked everything up, and all seems to be running as expected:
Tranny connected, Q powered with a 9V battery, scope connected, when turning the trimpot the curve (which looks quite like those in Marks doc!) moves and flattens until a certain point when it ( the curve on the scope‘s screen) kind a runs away before it is fully flattened after that first spike.

If you read until here you‘ll understand I don‘t quite understand all this…

So if you could point me to a manual/handholder so that I could get along, this would be great…

Thanks a bunch!
David
 
#2,184
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#2,185
Thank you, Mark.
From these suggestions, I conclude I'm supposed to know what I'm doing, am I not? :rofl:

I'm going through that stuff right now and will dig further. I may be able to figure out how to apply it on Q, if not, I might use a click or two. ("Tri Ethyl Borane", you know 😉 ) (But since I'm one of those who often miss a corner...)

...
d🙂
 
#2,188
I think I am quite close to a valid result on a toroid.

I have
Cx 10nF
Cs 150nf
Rs 46R

A variation with Rs = 36R seems to be good too. Not sure where the sweet spot is? Practice!

The curves are below.
(Screenshot-export not yet figured out, but I'm closing in)

IMG_1835.jpg
IMG_1836.jpg
 
#2,190
@myleftear - neither of those are correct. Be sure you look at page 1 and download the notes from Mark and read them. The top picture is underdamped, the bottom picture is overdamped from what I am seeing.
Are you using a potentiometer to find the sweet spot?
 
#2,192
Hi myleftear,

.. but your second 'scope pic is pretty close. 😀

I'd say you're doing pretty good for just 'getting the hang of' an excellent new 'scope!

Was the 2nd trace the 36 or the 46 ohm resistance? If it was the 36, then 46 ohms is probably just about right.

Cheers
 
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#2,193
6L6 said:
This is the shape you should adjust for…


Smiley face optional, but it certainly does not hurt…. 😀 😀 😀
Click to expand...


RickRay said:
@myleftear - neither of those are correct. Be sure you look at page 1 and download the notes from Mark and read them. The top picture is underdamped, the bottom picture is overdamped from what I am seeing.
Are you using a potentiometer to find the sweet spot?
Click to expand...


Thanks to everyone helping me!

Rick, the underdamped one is actually undamped (trimmer removed).
With the overdamped one I wasn‘t sure about where to stop. I of course read the manual (omitting the „f“ in the acronym)

I use a Quasimodo V4 with everything on it, thus it is a 1K trimpot.

But I obviously didn’t catch the sweet spot‘s signs. Is it more like „make the curve look like this“ or rather „make the curve not go into a „flat-but-still-present-negative-curve“?

Will read rhe manual again as soon as I made the dishes 🙂

…

Jim, I don‘t know how to adjust the jig + oscillator to get a smiley onto the screen :rofl: no seriously, what’s the 6000 saying to me? (Can’t relate)
 
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#2,194
Rick PA Stadel said:
Was the 2nd trace the 36 or the 46 ohm resistance? If it was the 36, then 46 ohms is probably just about right.

Cheers
Click to expand...

Thanks Rick 😀

It was 46 R.
I had a 36 R result too, and although it was very close to the 46 R variant, it seemed better to me. but didn’t pictured it. And it wasn’t the shape Jim advised me…

Nevermind, it‘s just plain fun, and I have my toe in the scope-water (learning, woohoo [emoji322]!)
 
#2,196
IIRC (a big 'if'), *optimum damping* is when the area under the curve below '0', and the area under the curve above '0', are equal. But I could be wrong (considering my lack of success in college calculus 😱)!

And try not to get frustrated by those trimpots with a little too much 'slop' in the mechanism.

Regards
 
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#2,200
I'll try really hard not to fill this great thread with my blabber, but that is really difficult—MJ's eloquence, and ironic ways of saying ... well ... something like "no", or "please, think/read". Even or especially when I am the prey (victim, target), makes me smile from ear to ear.

BTW, as I understand the Introduction, we're supposed to get to ζ > 1 (overdamp the beast and thus go further than critically damp it), I still can't quite relate the "optimal" curve as the "target" and not just the "starting point"? Or not? Do we aim ζ ≥ 1 ?

I don't don't believe you, I just don't understand it (the lumpity bumpity thing).
 
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