Really, the snubber circuits are not going to make one iota of difference to the audio performance...
but I´m a bit confused as the recommended values for snubbers are 47nF - 1uF and 4,7Ohm - 47Ohm...
I don´t agree. Slo diodes may increase switching noise.Regular diodes are slow and that reduces switching noise
Audio electronics design is full of superstition and speculation. There might be some voodoo involved. I just use a scope or spectrum analyzer and measure things.
The snubber values depend on the transformer's power, voltage and construction (toroid vs EI).
I think the DIY-Audio Heaven values are out to lunch by a factor of 10. 1uF is just silly huge and 4.7 ohms is low unless a SMPS. 10-100nF and 10-1,000ohms I've used, at 1/4W for under ~40V and 1-3W for high voltages 85-600VAC. I gave values for EI transformer typical for a DAC or headphone amp. The switching spikes are high peak value but low energy so MOX or carbon comp are fine.
I find any capacitor directly across the transformer secondary or across the rectifier diodes shifts the ringing down to the 100's kHz. I'd removed the four caps to do the tests.
Rectifier switching RFI is significant when scaled up for audio power amplifiers. Big diodes, 500-2000VA power transformers - then the RFI is stronger. Prove it with an EMI probe or AM radio on the line cord or near the amplifier's wiring, or a look-see with a scope.
So I add snubbers for low level audio and metrology circuits, just to keep RFI to a minimum, as good practice.
A mains filter would interact such a tiny amount with a secondary snubber, it's not a factor. Leave it in.
The bigger noise compared to metal film resistors here is of no interest. Any other noise around this resistor is magnitudes higher.some say carbon will do better here. Why?
Hi,
The bigger noise compared to metal film resistors here is of no interest. Any other noise around this resistor is magnitudes higher.
But carbon resistors have better pulse rating compared to metal film resistors.
Consider: a 10 Ohms snubber resistor needs to widhtstand full sine peak voltage across it for a short time.
At 230V RMS the peak voltage is about 325V. connected to an uncharged capacitor ... this means there will be about 32A of short peak current flow causing about 10,000W of short peak power.
With a 100nF capacitor this current drops to about one third of current each microsecond (tau= R x C) .. causing the power to be reduced to about 1/10 each microsecond.
10,000W --> after 1 us --> 1,350W --> after 1 us --> 180W --> after 1 us --> 24W --> after 1 us --> 3.3W --> after 1 us --> 0.45W
Note: These are theoretical values for zero line impedance.
Klaus
All we can do is guess.Do you think this will be correct?
Are Carbon the same as Carbon composite and/or Carbon dioxide?
There is nothing like a carbon dioxide resistor. Two common types are composite and film.
For low values (say less than 1M) you can usually ignore the thermal noise. There are other types of noises that are dependent on the manufacturing process. Usually film resistors have lower noise.
There are metal film resistors that may have still lower noise figures but your application does not need it.
For your application, a 10 Ohm resistor (say about 2W; even 1W will do) may be sufficient.
You see that the resistor type is not at all critical. It will dissipate less than 0.5W in the normal operation.
is film a subcategory to composition or are there three different kind of Carbons?
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