Which oscilloscope probes for testing audio amp speaker outputs

[exe]

However, it is very bad at determining sound level.

Earplugs .

[Ground_Loop]

You need to get a couple of these:


A 10X probe should  be fine.  For many scopes, the attenuator will get down to 50V/div with a 10X probe.  If the output is too high you may need to adjust the trace vertical position to see the clipping point.  Also, there really isn't any diagnostic benefit to "seeing" where your amp clips.  Further, at the clipping point you are running a very high DC current through the output transistors and they will heat up fast.  Be very careful.

[TimFox]

After taking all the safety precautions suggested above, if you really want to see the clipping in action you could use a higher resistance load (16 to 25 ohms, maybe) so that you do not run excessive current at high output.  Vacuum-tube amps were unhappy with high load resistance, due to the output transformer and resulting high voltage swing on the primary, but transistor amps are less sensitive to that.

[vk6zgo]

Back in the days of tube audio amplifiers, we tested them for output power by replacing the speaker with a resistive load
This load was made up of a higher value resistor & a lower value one "in series".

In use, we measured across the lower valued resistor, to minimise any loading upon the value of the overall resistance of the load.
We usually used an analog VOM to read the RMS voltage to determine the power output, which had a much lower input impedance than things like DMMs, VTVMs & Oscilloscopes.

Because we were reading a fraction of the voltage across the total load, we had to use a "correction factor".
This was easily determined, as we knew the ratio of the lower resistance to the overall resistance (plain old voltage divider theory).

With the calculated total voltage, we used "V^2/R" to calculate the power output.

We did hang an oscilloscope across the same points on the load, to determine the clipping point.
Another thing we did was, using a Noise & Distortion meter bridged across the same points measure those parameters at more normal operation levels.

The VOM, like a DMM, didn't have one lead grounded, neither did the N & D set, but a 'scope or VTVM did.
Tube amplifiers used output transformers, the speaker terminals were not connected to ground, so there was no problem.
Even with the early solid state amps, where the output had one side grounded, as long as you checked that, you were "good to go".

Amplifiers with bridged output stages are another story---- connect either speaker output terminal to ground, & you can damage your amplifier.

There are two workarounds:-
(1)The "proper" way--------buy a differential probe.
These are not as horrendously expensive as they once were, but the cost is not inconsiderable, either.

(2) Using two channels of your 'scope, hang the probes off both ends of your load resistor, (with both ground clips to a convenient ground) & using, for instance, the "channel 1 plus channel 2" setting of your 'scope, you  can see the voltage across the load resistor.

This is commonly known as the "pseudo-differential" connection, & is usually frowned on by the purists in this forum , but for tests of the level you are attempting, will give satisfactory results.

[gfmucci]

Most differential probes appear to be high voltage probes, like this Micsig...
https://www.amazon.com/Micsig-DP10013-Differential-Attenuation-Tektronix/dp/B074K4XPW3/ref=mp_s_a_1_1_sspa?dchild=1&keywords=differential+oscilloscope+probes&qid=1591971403&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExN0k4NTFTMVdHQTZaJmVuY3J5cHRlZElkPUExMDE5MjY5MlpQNVVYSEdYS1JZTiZlbmNyeXB0ZWRBZElkPUEwMTEwODgyM1E0Sk9GWllONUZJWCZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Is this the type you would use?  This particular one is a 50x/500x as I mentioned near the beginning of the thread.

[Vovk_Z]

A bit strange topic. TS doesn't know how to use an oscilloscope and even how to calculate a voltage, but he wants to check clipping?
Hm.

[EPAIII]

The idea of attaching the ground clip of a probe to a point in a circuit that you are not DEAD CERTAIN is actually grounded is, to my way of thinking, just asking for trouble. That ground lead on the probe really is connected to the AC power's safety ground in most scopes I have ever used. It is a hard ground. And if it is attached to a point in the circuit which is not at ground potential, then CURRENT will probably flow. And it will be flowing through a very low resistance to that real ground. I SMELL SMOKE!

Most professional equipment and many high end consumer circuits will have ground test points scattered around the PC boards for just this purpose. When higher frequency signals (MHz and higher) are involved, using these ground test points is the only way to see an nu-distorted signal on the scope's display.

What I do is attach the ground clip of the probe to a KNOWN ground point in the circuit that is as close to the signal I am going to look at as possible. That is the ONLY point to ever attach it to. Actually, with audio frequencies which are fairly low, most of the time you can leave it unattached and just let that AC safety ground connection through the scope's power cord provide the return path for the signal. But connecting it to a ground point in the circuit is a better habit to be in.

Then you can use the probe (10X or 1X) to look at each side of the load, one at a time. If you do not get a clear picture of what is happening that way, then use TWO channels/probes, one on each side of the load and set the scope to A-B mode to see the difference signal. I have used this technique (two probes and A-B mode) many times to see what a balanced (+/-) signal actually looks like.

Virtually every scope has at least two channels and an input switch that allows you to combine them with a sum or a difference circuit.

[magic]

Just FYI, this thread is 2 years old and has been necro'd by a spammer.