Testing Audio Voltage on an Oscilloscope

This video will show you how to use an oscilloscope to test the voltage of an audio signal, with a focus on arcade board safety. In the past few years, so much equipment has been destroyed by superguns without audio protection and this video will show you how to prevent that from happening in your setup!

[RetroTechUSA]

Great video. I had no idea that audio voltage could possibly damage equipment, but makes sense. Thanks

[yoshiyukiblade]

Thank you both for the brief overview on the technical audio details. I was thinking about dabbling with audio stuff some day and I was going over some schematics and doing early research. I was lost because there was no specific info on specs like I'd normally see with video (75 ohm source/load termination resistance, 700 mVpp under load, etc.). So I guess we just need to make sure the peak voltages stay within the linear region of the amplifier under a high impedance load like 100 kohms while staying in the neighborhood of a few volts peak-to-peak.


On a side note, it's been a little over a year since I got a scope thanks to your technical videos, and I've been trapped down the rabbit hole ever since. I hope you're happy :P

[chrisjenkins]

For the Y combiner question, there has to be a change in impedances for the voltage levels to not change. With fixed impedances, superposition principle says that signals can constructively add up to 2x your voltage. To properly Y-combine, a series resistance change would help the effective voltage divide each output sees. The circuit has to be properly constructed so that each output can not see the other output as a load, which could cause the signal to clip (low output impedance sees low input impedance). Of course, there is the nuance of whether your source is a voltage source or current source, but the latter is true in this case.

[yoshiyukiblade]

(EDIT: I re-tested a few things and got different results compared to what I wrote initially, so I'm rewriting this post with updated results)

I've been learning about audio stuff lately, and I did some basic studying on how the peak voltages relate to sound levels in OBS, a program that most of us are probably familiar with. I used a signal generator to put a sine wave into my capture setup, and I found that the 0 dB point (full scale) corresponds roughly to 2.5 Vpp at around 10 KHz. This is with the Line-In volume at 100% in Windows. The SNES can output up to 3 Vpp, so it can actually clip in a few situations (causing pops). Lowering the Line-In volume prevents clipping (note: this is *not* the volume slider in OBS, which adjusts volume after clipping has occurred). I think I will aim for 3 Vpp output the next time I mess with audio circuits.

[mluna]

Loved the video. I wish you talked about the signal coupling though.

[dlang]

Great informational video! Also, anyone else spot the dreamcast with the HDR cable coming out of it? Ste was sending us a message... the unicorn is real... 😁

[RdCrestdBreegull]

So then combining the left and right RCA audio channels from typical retro video game consoles like the SNES/N64/etc with a Y cable and plugging it into the mono input of a TV/monitor that only has a mono RCA input is completely safe? (combining a stereo audio signal with a Y-adapter so that you get the full audio when your TV only has a mono input)

[michalkracik]

I am trying to troubleshoot audio distortion issues so I'd like to listen to the output as well as measuring it. Instead of the 100kohm resistor, can I use RCA Y splitter, connect first output directly to oscilloscope without a probe (1Mohm), and second output to actual load (mixer input and speakers, 10kohm)?

[elgansito]

Is this information useful for people that are just using a Sega Genesis with ossc? Are usually watch a lot of your content but I have no idea what you’re talking about in this video lol

[FirstLast-czlz]

Do HAS versions earlier than 4.0 include protection?

[cheater]

You forgot to mention dc vs ac coupling and 10x vs 1x probe settings, both of which will make the measurement bad.

[danijelkanuric]

I think i blowup my probe with friking music for oscillscope..