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

[merlin el mago]

Have you read the datasheet? Carefully search for the word shown here in green . . . . .

http://www.diyaudio.com/forums/atta...mer-snubber-using-quasimodo-test-jig-what.png


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Oh my good, have I to change or can I leave it?

 

[merlin el mago]

In place of NTD4906N I used IRLB8748 that is pin compatible, I desoldered the mosfet and measured and it's OK.

 

[merlin el mago]

Replaced the timer & the FET.

 

[merlin el mago]

Changed LED for a new (no blinking) 1.9VDC 20mA, now red LED lits always

Voltage across resistor 12.85VDC
Voltage across LED 1.9VDC

Time to measure again the transformer?

 

[merlin el mago]

Left to right side: InfinityRs, 100Rs, 500Rs, 250Rs & 100Rs

 

[trobbins]

Primary 50R + 250R

Thanks Merlin. It was worth checking the influence of the nominal impedance of the mains connection that would normally be loading the primary winding in an actual application.

Would you be able to measure the primary winding DC resistance, so as to 'round out' the comparison between shorted versus nominal primary impedance.

Ta, Tim

 

[merlin el mago]

164 ohms

 

[merlin el mago]

Changed LED for a new (no blinking) 1.9VDC 20mA, now red LED lits always

Voltage across resistor 12.85VDC
Voltage across LED 1.9VDC

Time to measure again the transformer?

Are OK the measurements done with 15VDC?

 

[merlin el mago]

Left to right side: InfinityRs, 100Rs, 500Rs, 250Rs & 100Rs

100Rs is the optimum value for snubber?

 

[merlin el mago]

I suggest you snap a series of scope photos at different measured values of Rs, just like the color overlay plots in post #1 of this thread. This will help you find the Rs which just barely flattens out the first waveform "trough" like the red trace (see yellow arrow).

From your first photo, it seems that Lsec might be in the neighborhood of 1200 uH, so zeta=1 critical damping would be expected to occur somewhere in the vicinity Rs = 170 ohms or thereabouts. Assuming your Cx really was 10nF, and so forth.

Cx is really 10nF, I measured with two different LCR meters, after the last photos still you consider the Rs value in the vicinity of 170 ohms? attached pic scope set 5V/cm 10uS with Rs 170 ohms

 

[AndrewT]

pic5 of post405 shows one cycle after the return to zero.
pic4 of post405 shows three cycles after the return to zero.
post 410 shows two cycles after the return to zero.
The damping in these three are different.

Which is the best for least effect downstream?

 

[merlin el mago]

I guess pic5

 

[merlin el mago]

First cycle is near 5V, could I lower the Rs value or is enough with 100R?

 

[AndrewT]

I agree, but let's hear from some others.
Maybe even less than 100r.

Have you scope pics of lower resistances?

 

[merlin el mago]

Yes 81 ohms, amplitude 5V/cm

 

[merlin el mago]

41 ohms amplitude 2V/cm, can't go lower than 1V because appear a new horizontal line in the middle of the screen.

 

[AndrewT]

82r and 41r do not show the ringing when C alone is used.
It appears that 82r is good for damping.

I'm not sure what the long tail with the 41r is telling us.

 

[jameshillj]

I suggest you setup your supply with an active sound system and have a LISTEN and then decide what's most appropriate for your supply(s)

I've found that even with comprehensive power supply filtering (C-Multipliers, Shunt Regs, etc) it's 'not always best' (sorry for the vague terms) to critically dampen the secondary windings, despite the obvious engineering -

There's a point where the amp/preamp, etc seems to lose dynamics when over- dampening the secondaries sometimes - not sure if same effect on class AB circuits and probably also varies with our different hearing abilities too

 

[merlin el mago]

I listened with 47R, I hear the highs and lows more nitids no lose of dynamics. The tx is connected to Salas Reflektor-D powering Buffalo III DAC.

 

[AndrewT]

the ability to replay dynamics is totally dependant on current supply.
That current comes from the local decoupling and the last smoothing capacitor stage.
The current to the load does NOT come from the transformer, thus the current supply is NOT affected by the snubber used on the transformer secondary.

BUT
ringing of the supply will affect the amplifier and this can leak to the load. This can sometimes be audible. Some listeners hear the "extra detail" of the HF components of the ringing and declare "much better".
Ears tells lies, sometimes !