Let's suppose you have a diode bridge in your amplifier's power supply. What are the symptoms that call for a snubber? I mean if you consider the amplifier a black box (you have no access to the internals), what signal degradation or unwanted signal do you see at its output?
In general, how do you tell whether a precisely selected series RC parallel to each diode is necessary or just a C of 10nF value is sufficient?
In general, how do you tell whether a precisely selected series RC parallel to each diode is necessary or just a C of 10nF value is sufficient?
An answer to this was given on DIY Audio-
Purpose of output "snubber" on diyaudio p/s board? - diyAudio
You will see any differences more easily with a high speed square wave inputted with an oscilloscope connected at the output rather than a sine wave (leading edges for example ) any misshape /bursts of oscillation etc.
Purpose of output "snubber" on diyaudio p/s board? - diyAudio
You will see any differences more easily with a high speed square wave inputted with an oscilloscope connected at the output rather than a sine wave (leading edges for example ) any misshape /bursts of oscillation etc.
In general, we always need a snubber (across transformer secondary windings). This lowers a noise floor of a system. And we may need snubbers (or C) across diodes if we supply high-frequency circuits (>=1 MHz).
You typically know when you do EMC testing. Further, when you look at voltages around in your circuit and realize that various (unwanted) inductances cause ringing voltages that may stress some components. You need an oscilloscope for such a check.
Whenever you test a power supply circuit, in particular an SMPS, you should test with an oscilloscope that all voltage shapes look "nice and clean". With experience you start knowing where are the most likely problems.
Whenever you test a power supply circuit, in particular an SMPS, you should test with an oscilloscope that all voltage shapes look "nice and clean". With experience you start knowing where are the most likely problems.
Audibly, when one hears hum or rattles at a frequency twice the power line frequency, it indicates a snubber or at least a disk cap across the output of the rectifier bridge should have been used. Diode shutoff artifacts tend to be at higher frequencies due to the vertical edge, but happen at twice line frequency. Successful amps I have bought have gotten away with only the cap without the series resistor.
In theory you are less likely to need them if you use slower diodes and/or soft-recovery diodes, its the commutation abruptness that generates artifacts than might need snubbing.
For mains rectification I'd say avoid fast rectifiers, those are for SMPS's.
For mains rectification I'd say avoid fast rectifiers, those are for SMPS's.
I’m not sure if there is much science to the method but I probe the final capacitor of the power supply with a short ground wire on the ‘scope probe.
I load the power supply to the highest expected current draw as I find that the ringing becomes more pronounced with a load and is sometimes not apparent with no load at all.
The ringing shows up in the ripple waveform and some fiddling with the triggering level on the ‘scope centres it so that you can expand the time base and get a look at it.
After reading the “Quasimodo snubber jig” thread I just use a 10nF and 100nF cap with a temporary variable resistor directly on the power supply PCB itself and turn the pot whilst watching the ringing and null it out. I then desolder and measure the potentiometer and replace with a fixed resistor of that value.
Has it helped in the sound of the various line level stuff I have added snubbers to since reading that thread?
It’s hard to say, they don’t seem to make much difference with elaborately filtered power supplies and discrete preamps but perhaps I can hear some improvement on OP amp based stuff. I may be imagining it or wanting to hear an improvement but it seems to make a crossover I have sound... smoother? Less harsh, something like that, easier to listen to perhaps.
I load the power supply to the highest expected current draw as I find that the ringing becomes more pronounced with a load and is sometimes not apparent with no load at all.
The ringing shows up in the ripple waveform and some fiddling with the triggering level on the ‘scope centres it so that you can expand the time base and get a look at it.
After reading the “Quasimodo snubber jig” thread I just use a 10nF and 100nF cap with a temporary variable resistor directly on the power supply PCB itself and turn the pot whilst watching the ringing and null it out. I then desolder and measure the potentiometer and replace with a fixed resistor of that value.
Has it helped in the sound of the various line level stuff I have added snubbers to since reading that thread?
It’s hard to say, they don’t seem to make much difference with elaborately filtered power supplies and discrete preamps but perhaps I can hear some improvement on OP amp based stuff. I may be imagining it or wanting to hear an improvement but it seems to make a crossover I have sound... smoother? Less harsh, something like that, easier to listen to perhaps.
When you connect your speaker output terminals to a soundcard/laptop that is mains isolated and runs a spectrum analyser and you see no mains related frequencies in the noise floor for both no signal, and full rated output of a tone. If you see something then it is your amp, and looking at the bridge rectifier and what is placed across the diodes will be the least of your concerns, as there are other major issues you should be attending to first imho.
from here:
snubbering | DIY-Audio-Heaven
"In general it is better to use a 220nF and 10Ω resistor than not use anything at all."
snubbering | DIY-Audio-Heaven
"In general it is better to use a 220nF and 10Ω resistor than not use anything at all."