Using a distortion meter or oscilloscope to see distortion?

P

photographer86

Audioholic
Has anyone used a meter made to see distortion for setting amp gains or a oscilloscope to see the ac wave of a 40hz to say maybe 1k hz single to see really how far they can turn up a amp or stereo before it clips or distortion starts?

I was thinking, disconnect your speakers and play a 40hz tone from your AVR. Then using a proper meter or if a tool is made turn on your system volume reading its ac output, measuring with a oscilloscope until you see a clean sine way of given hz goes to a square wave. Then at which you would have a max volume setting you could set too with out sending a dististored signal to your speakers from amp. After that set the volume to the level found just below distortion and run your RCA cables to a subwoofer. Then read the output of amplifer in subwoofer, adjust gain of sub dial until meter read distortion. Gain set properly and knowing you're getting max output from amp without distortion and would never blow a sub ever again. The reason I thought of this was cause we set gain on a subwoofer it's in prime location after doing subwoofer crawl to read 75db spl at listening postion. But we may have to turn up gain to far and it could be adding distortion. I don't own a type of meter above but I am gonna research one. Wondering if anyone has went this far or thought of this. Thanks.
 
slipperybidness

slipperybidness

Audioholic Spartan
Done it as part of my electronics courses. An O-scope is very handy to be sure you have gotten the correct gain structure on a DIY amp. Then, you can see how much overhead you have before clipping. An O-scope would also show you any crossover distortion for a class AB topology.

I tried to do some THD+N measurements as part of the same project. But, I had borrowed a distortion analyzer from a friend, and didn't realize that it didn't have a built in low distortion oscilator, so what I ended up measuring was the THD+N from the function generator, as the amp being measured was certainly a couple orders magnitude better than the function generator.
 
lovinthehd

lovinthehd

Audioholic Slumlord
How many subs are blown due to gain structure settings, tho? Might want to expand on the crawl/setting 75dB/then turning up gain thing.
 
P

photographer86

Audioholic
Thanks sliperybidness and Lovinthehd. I guess I am looking at it as a base line. Know there would never be any clipping period and gains would be set properly still. So you would still after setting gain with a meter, then you would set to 75db and sub crawl.

However its true that most with sub crawl and 75db level matching probably isnt clipping the signal. But it's just a comfort thing I guess for me. Thought it was interesting and knowing your not stressing your amplifer. Just a extra step of course. Probably not many subs blown level matching for sure. But really gives you that knowing you're not clipping, distorting. Just thought I would ask and see what people have done.
 
M Code

M Code

Audioholic General
The only way to measure distortion is with an Audio Precision system..
Preferably the APX-555...
Using a distortion analyzer will give U a reading but typically the distortion from the analyzer could be higher than the component being measured. Using a scope will show U when an amplifier is clipping...
All major audio brands, tech centers, magazine labs use AP systems.

Just my $0.02... ;)
 
S

Speedskater

Senior Audioholic
an O-scope won't see distortion until it get into the 3 to 5 percent range.
While an Audio Precision system (in the $25,000 range) is the best way, there are other free or inexpensive ways to do it.
 
P

photographer86

Audioholic
So if I am viewing a audio signal on a $200 scope and wave goes from nice and smooth up and downs to start to become square..... you're saying that is 3 to 5 % then?
 
slipperybidness

slipperybidness

Audioholic Spartan
an O-scope won't see distortion until it get into the 3 to 5 percent range.
While an Audio Precision system (in the $25,000 range) is the best way, there are other free or inexpensive ways to do it.
An O-scope would also show you any crossover distortion for a class AB topology.
 
slipperybidness

slipperybidness

Audioholic Spartan
So if I am viewing a audio signal on a $200 scope and wave goes from nice and smooth up and downs to start to become square..... you're saying that is 3 to 5 % then?
Likely more than that!

A "sine wave going square" is clipping, and that is serious distortion! That is best avoided.
 

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