^ Exactly. The neat part for me using a scope (again, I'm a visual guy) will be to observe the output signal staying "clean" / non-deformed during the "Klunk" and even after the transition. Then, once I start to reach max power at output, I can see the output signal begin to clip. This is probably standard measurement for those "in the know", but I've never actually thought about it until you posted it.
I know it happens... I can sorta visualize it happening... I even think I understand why/how it happens; but I love the idea of watching it. It took ZM showing me a simple circuit simulation with the waveforms for current and voltage to understand the relationships in a push-pull output stage. I struggled with it mightily until I saw that one little animation. Then... KLUNK! I got it.
IAIMH,
If you don't mind, please post scope photos when you get around to it.
I have one channel of an AMB B22 headphone amp and it is biased (150-160mA) in class A, although not heavy duty like our behemoth amplifiers. I am planning on doing exactly what Dennis has mentioned to see the effect myself. But it might be the weekend before I get to it!
Best,
Anand.
Happy to do it. It's highly likely you'll get to it before I manage. If you do... I'll show you mine... if ...
Cheers,
Patrick
When I want to look at current across an output power resistor I just float the ground of the scope. You do have to take care what you touch while doing it...
So given that many of us don’t have isolation transformers and that our desktop scope’s negative probe is connected to AC ground, would it be a safer option for one to insert a battery-powered (therefore completely isolated) DMM in AC A mode in series with the dummy load resistor for the purpose of measuring output current? With an AC sine wave signal, the DMM should give you a reading in RMS, which must be multiplied by 1.4142 to give the peak current.
Would another option be to use a battery operated scope? Like what VZ Audio sells here?
Best,
Anand.
Would another option be to use a battery operated scope? Like what VZ Audio sells here?
Best,
Anand.
while scope (probe) is connected to circuit which is safety grounded, you can put (safety gnd) cheater plug on its mains plug
Yeah you can get too used to battery scopes. I used the named scope above for 5 years in industrial environment. Had to work in different area of plant one day on a drive. Hooked up standard scope and blew the drive bc ground clip was at ground. Whoops forgot about that. Had to explain that to Plant Manager.
A bit OT, but I've finally got the extra probes, and I ordered some beefier load resistors. Probably ~7 to 10 days for arrival. Also, as luck would have it, a local member had some test gear that I picked up last week. Still learning the ins and outs, but I now have a distortion analyzer, a few extra scopes, and some other goodies.
FWIW - There seem to be a lot of great opinions / used options / implementations for high-wattage dummy-load/power resistors. I had looked for some of the Vishay/Dale that seem to be commonly used, but prices for new pieces were higher than I was willing to pay, and their availability on the used market (along with my patience) was waning. I chose to go with chassis mount, low-inductance, 250W, 8-ohm from Ohmite out of TX. Arcol Part NHS250 8R F. Digikey has a direct order qty through Ohmite. It seems like it's essentially a 3 for 1, but the min order qty is 3 pieces. Just passing info along for anyone interested. It's the best price I could find by a large margin for that type of part (new), but I didn't scour the world.
FWIW - There seem to be a lot of great opinions / used options / implementations for high-wattage dummy-load/power resistors. I had looked for some of the Vishay/Dale that seem to be commonly used, but prices for new pieces were higher than I was willing to pay, and their availability on the used market (along with my patience) was waning. I chose to go with chassis mount, low-inductance, 250W, 8-ohm from Ohmite out of TX. Arcol Part NHS250 8R F. Digikey has a direct order qty through Ohmite. It seems like it's essentially a 3 for 1, but the min order qty is 3 pieces. Just passing info along for anyone interested. It's the best price I could find by a large margin for that type of part (new), but I didn't scour the world.
If you have a 2 channel scope that can invert one channel and sum the 2 channels (+A -B), it is possible to measure across a component that does not have one side of that component grounded. You are essentially putting the scope in differential mode. Just make sure both channels are set to the same Volts/division.
^ An exceptional tip! Thank you. I'd have never considered that. Within the last hour, I've watched this for what must be the 5th time. I still admit to lacking some fundamentals and being a big ol' fraidy-cat. 😀 Easing from the kiddie pool into the shallow end. Feels warm.
Edited to add - I think I've seen him do something similar to what you describe when he was doing a video on how to measure power supply ripple. Hmmmmm. Another video to rewatch.
Edited to add - I think I've seen him do something similar to what you describe when he was doing a video on how to measure power supply ripple. Hmmmmm. Another video to rewatch.