How do you measure ripple on the B+?

porkchop61 · 3rd October 2005, 04:29 PM

Ok, so I'm still learning this electronics stuff.
How do you measure ripple on the DC power supply?
This is high voltage, so I assume you can't just connect your probe from the scope to the DC, right? Are there high-voltage probes for doing this type of measurement?
I'm not sure my Tektronix 585a would like this much voltage

Thanks.
Glenn

EC8010 · 3rd October 2005, 04:42 PM

Very carefully.

You first check the voltage rating of your probe. It's probably only 250V. At that point, you reach for your high voltage (2.5kV) probe and you switch the oscilloscope to AC coupling and measure away.

Of course, you might not have a high voltage probe. At that point, it gets rather more exciting. With the amplifier turned off, you solder one end of a 100nF 1kV capacitor to your 400V HT and the other end you take via a 1M resistor to 0V. You then power up and connect your probe across the 1M resistor and look at the hum. Alternatively, you take the signal across that 1M resistor to another audio amplifier and listen to the hum.

You all of this very carefully...

dhaen · 3rd October 2005, 05:43 PM

Quote:

Originally posted by EC8010
Very carefully.

SNIP.. You then power up and connect your probe across the 1M resistor and look at the hum. SNIP..

Note the order...
1 Power up
2 Connect probe (carefully)

porkchop61 · 3rd October 2005, 06:07 PM

Quote:

Originally posted by EC8010
Very carefully.

You first check the voltage rating of your probe. It's probably only 250V. At that point, you reach for your high voltage (2.5kV) probe and you switch the oscilloscope to AC coupling and measure away.

Of course, you might not have a high voltage probe. At that point, it gets rather more exciting. With the amplifier turned off, you solder one end of a 100nF 1kV capacitor to your 400V HT and the other end you take via a 1M resistor to 0V. You then power up and connect your probe across the 1M resistor and look at the hum. Alternatively, you take the signal across that 1M resistor to another audio amplifier and listen to the hum.

You all of this very carefully...

Thank you for that information.
Of course I don't own a high voltage probe

, that's mostly why I asked the question. I assume you mean to connect the other end of the 1M resistor to ground when you say 0V, right?
Thanks again, I'll give it a try!
Glenn

EC8010 · 3rd October 2005, 07:12 PM

Yes, ground = 0V.

Regarding order, it depends. An amplifier with silicon rectifiers can bump its HT around rather abruptly at switch-on, so I prefer to connect the probe when everything has settled down. You might not be so confident in your handling of a probe near high voltages and prefer to connect up, then power up. If you do, I suggest that you set your oscilloscope to 50V/div before switching power to the amplifier. In fact, I'd say as a general thing that it's a good idea to do that when poking around HT. Once everything is stable, increase the sensitivity of the oscilloscope. That way, you're less likely to blow up the oscilloscope's input stage (they tolerate overload, but maybe not all that much).

cerrem · 3rd October 2005, 11:29 PM

The quick and dirty way is just to use your DVM...set it for AC voltage and put it on the DC high-voltage rail.... This will give you a rough idea of the RMS ripple...which you can "very roughly" deduce the peak ripple.... The ripple will be 100Hz or 120Hz depending on where you are located.... The waveform is not always a true 50% duty cycle...due to the size of the input cap as well as the current demand ...this will alter the conduction angle the diodes are turning on ...So sometime it's better to see it on the scope...

Chris

Enzo · 4th October 2005, 02:52 AM

I'm with Cerrem on this, just use your meter. This is not a laboratory measurement, you just want to know how much ripple you have. This is close enough. If you view it on your scope, you can determine the amplitude of the ripple, but trying to come up with a reasonable equivalent voltage from the sawtooth waveform will be problematical. SO just trust your meter.

jan.didden · 4th October 2005, 06:22 AM

Quote:

Originally posted by Enzo
I'm with Cerrem on this, just use your meter. This is not a laboratory measurement, you just want to know how much ripple you have. This is close enough. If you view it on your scope, you can determine the amplitude of the ripple, but trying to come up with a reasonable equivalent voltage from the sawtooth waveform will be problematical. SO just trust your meter.

... if you are SURE that meter can withstand the high DC on it's AC scale. There will be a blocking cap in the AC meter line. What is that cap's spec? 250V? 450V? Do you know, or you want to gamble?

Jan Didden

dhaen · 4th October 2005, 08:08 AM

A meter will only give an approximate RMS value of ripple. They're designed to measure sine wave.
Of course it's fine for comparitive measurements.

Best also use it with EC8010's CR network.

Enzo · 4th October 2005, 11:51 PM

If the input of my meter is rated to 600VAC or 1000VAC, then it shouldn't care if part of that is DC.

3rd October 2005, 04:29 PM	#1
porkchop61 diyAudio Member Join Date: Aug 2004 Location: Mansfield, Connecticut	How do you measure ripple on the B+? Ok, so I'm still learning this electronics stuff. How do you measure ripple on the DC power supply? This is high voltage, so I assume you can't just connect your probe from the scope to the DC, right? Are there high-voltage probes for doing this type of measurement? I'm not sure my Tektronix 585a would like this much voltage Thanks. Glenn

3rd October 2005, 04:42 PM	#2
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	Very carefully. You first check the voltage rating of your probe. It's probably only 250V. At that point, you reach for your high voltage (2.5kV) probe and you switch the oscilloscope to AC coupling and measure away. Of course, you might not have a high voltage probe. At that point, it gets rather more exciting. With the amplifier turned off, you solder one end of a 100nF 1kV capacitor to your 400V HT and the other end you take via a 1M resistor to 0V. You then power up and connect your probe across the 1M resistor and look at the hum. Alternatively, you take the signal across that 1M resistor to another audio amplifier and listen to the hum. You all of this very carefully... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

3rd October 2005, 07:12 PM	#5
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	Yes, ground = 0V. Regarding order, it depends. An amplifier with silicon rectifiers can bump its HT around rather abruptly at switch-on, so I prefer to connect the probe when everything has settled down. You might not be so confident in your handling of a probe near high voltages and prefer to connect up, then power up. If you do, I suggest that you set your oscilloscope to 50V/div before switching power to the amplifier. In fact, I'd say as a general thing that it's a good idea to do that when poking around HT. Once everything is stable, increase the sensitivity of the oscilloscope. That way, you're less likely to blow up the oscilloscope's input stage (they tolerate overload, but maybe not all that much). __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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3rd October 2005, 11:29 PM	#6
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	The quick and dirty way is just to use your DVM...set it for AC voltage and put it on the DC high-voltage rail.... This will give you a rough idea of the RMS ripple...which you can "very roughly" deduce the peak ripple.... The ripple will be 100Hz or 120Hz depending on where you are located.... The waveform is not always a true 50% duty cycle...due to the size of the input cap as well as the current demand ...this will alter the conduction angle the diodes are turning on ...So sometime it's better to see it on the scope... Chris

4th October 2005, 02:52 AM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	I'm with Cerrem on this, just use your meter. This is not a laboratory measurement, you just want to know how much ripple you have. This is close enough. If you view it on your scope, you can determine the amplitude of the ripple, but trying to come up with a reasonable equivalent voltage from the sawtooth waveform will be problematical. SO just trust your meter.

4th October 2005, 08:08 AM	#9
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	A meter will only give an approximate RMS value of ripple. They're designed to measure sine wave. Of course it's fine for comparitive measurements. Best also use it with EC8010's CR network.

4th October 2005, 11:51 PM	#10
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	If the input of my meter is rated to 600VAC or 1000VAC, then it shouldn't care if part of that is DC.

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