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

Jump to Latest
#2,623
Thanks Mark. So the switches parallel the resistors per that chart and the resulting frequencies are displayed.

I assume there is a reason that you can vary the frequency; namely that the snubber resistance value will change. If that is correct how do you determine what frequency is optimal for determining the snubber resistance value for a particular transformer?

I'm a mere implementor, not an electrical engineer. But I'm interested in how these things work.

Thanks for creating Quasimodo,

John
 
#2,625
Wow Mark, you thought of everything! I'm using a new Hantek inexpensive digital scope so the frequency shouldn't be an issue. But some of the guys in audio do prefer the analog CRT based scopes, so putting in the frequency selector was a good call.

I know you must get tired answering the same questions over and over. I did try to do a search. I do apologize for the bother.

John
 
#2,626
My first project e2e. Measured Rs for Hammond 1182M15 as 16.9Ohms in independent parallel mode.

1744600958348.png


1744601013044.png

1744601038453.png
 
#2,628
P2 and P6 connect to 9v power supply. The jig is drawing 20 mili amps of current.

For reference I have a benchtop power supply (see the red and black banana plugs attached to it. they directly connect to the quasimodo board on the right hand side.)
1744609204509.png
 
Last edited:
#2,631
Re-thinking powering the Quasimodo board. Mark's white paper says to power the board with a +15V. The Siglent supply in the picture above is using +/-9 V. Without seeing this I would have set it for +15V and used the red terminal and the green ground terminal on the power supply.

What is it that I don't understand about powering the Quasimodo?

Confused again....
 
#2,632
From @mvaldes to me

To operate the Quasimodo you need to:
1.- connect a power source to Vin e Gnd (2.6 to 18Vdc) (two Vdc connector are there just for redundancy)
2.- connect the secondary of transformer to P7
3.- connect the scope probe to p4 / P5
3.- short the primary of trasformer
4.- insert the Cx, Cs and Rs components in their respective socket (use the value suggested by Mark)

5.- turn on the Quasimodo power and look the result on the scope screen
6.- adjust the Rs trimmer until you get the correct dumped figure on the scope
7.- take out Rs trimmer form his socket and misure it with a multimeter. This will be the Rs value

at this point you have the correct Rs, Cx and Cs value to correctly dumping that specific transformer
Click to expand...
 
  • Like
Reactions: jminassi
#2,638
Ok guys, I followed Neo's script above except that I powered the Quasimodo board with +/-12 DC volts using my bench power supply. The first photo is the scope reading without the trimpot installed (infinite resistance) per Mark's suggestion. Then I installed the trimpot and adjusted it until the line was flat. Measuring the resistance necessary to accomplish this I get 13.3 ohms.

The transformer is a Toroidy 500 VA with dual 50 V secondaries.

Let me know is this looks reasonable. Also, what causes suck out in the middle of the trace in the second photo?

Many thanks for your help with this (especially Mark and Neo),

John
 

Attachments

  • IMG_0134.jpeg
    IMG_0134.jpeg
    833.9 KB · Views: 35
  • IMG_0133.jpeg
    IMG_0133.jpeg
    836.6 KB · Views: 31
#2,640
Hi guys. It’s my first post on this forum.
I am always grateful for evey useful information.

English is not my tongue, please pardon me if there are strange words..


I built a tube guitar amp a while ago.

It had faint buzz on high frequency.
I couldn't figure out what was causing it, but I thought it was probably a transformer problem.

Today, I installed CRC snubber and..
surprisingly, the buzz is gone!

..However, I realized I had a mistake.
I installed it just like this;

IMG_5365.jpeg


I should installed them on each winding, not just like this.. right?

However there is no issue so far, fortunately. and It’s obviously effective and working well, since the buzz is gone.
The amp is functioning normally.

This is high voltage circuit(340v-0-340v), I have no spare HV capacitor right now. (I used 1KV MKPs)
I’ll order the components later and fix this..


If it is done this way, what potential problems can be expected?

EDIT : I’v read a thread after I posted this.
dwjames

Thread 'how to apply transformer snubber to a centre tapped secondary and 2 diode full wave?'

Hi guys,
what's the recommended method for adding a snubber across the secondary of a transformer if it's centre tapped and being used with a 2 diode full wave rectification?
Do you only need a single snubber across the 2 outer wires, ignoring the centre tap or is it better to have 2 lots of snubbers going to the centre tap like this?
A5CWBif.gif

I did a bit of searching around but couldn't find a definitive answer.
thanks,
James

according to this, I’ll be fine.. I used SiC diodes, so the diode snubbing is not my concern.

Another question remains, rating of the snubber.

the snubber seeing pretty large voltage now : 680v~700v AC. the capacitors rated 1kV. I don’t know well about peak voltage(?) in snubbering, I wonder 1kV would be suffice.
 
Last edited:
You must log in or register to reply here.
Top Bottom