Symmetrical Clipping

[vdi_nenna]

Ok...

What is an accurate way to test for symmetrical clipping in an amp? How is it executed? What equipment is needed?
If it's not too complicated, can step-by-step be provided?

Thanks!

 

[FYC]

The only equipment that you can rely on is a CRO, without this you will not be able to do it accurately.

 

[vdi_nenna]

What's a CRO? Cathcode-Ray Osilliscope? Never heard of a CRO.

If I get a CRO, what do I do with it? Set it to monitor the output for the onset of distortion in the + and - halves of a waveform?

thanks

 

[promitheus]

Yeah that´s what a CRO is. You monitor the output and with a test tone from either a generator or a test cd you try to bias the amp so when clipping it clips even (the same ) on top and bottom of the wave form. It not a cheap set up But it´s the only that does the job. It would be easier if you could use someone elses. Like from a Lab or a friend .

 

[FYC]

Yes, CRO is oscilloscope.

If you got one, then you should hook up a signal generator to the input of your amp. (or if you have a test CD with tone signals). Hook up your CRO to the output of the amp. Slowly turn up the signal, you should start to see the waveform on the CRO grow larger and larger but keeping a good sine waveform.. At some point, you should start to see the top of the sine waveform flatten out, the amp is clipping. At such stage, turn your bias adjustment VR until you see that the flatten portion of your sine wave is symmetrical on the top and bottom. You are done.

 

[vdi_nenna]

Got it. Thanks.

 

[Freddie]

I've made a test cd, a year ago or so..
So If you have a CD-burner you can easily do one yourself.

I used Cool-Edit I think, It could generate perfect sinewaves. I downloaded a shareware version on the net.

 

[pixie]

Not to be pedantic, but...

How I would do this more accurately is stretch the time/div out as far as you can and still see the top of the wave. Then measure the clip's length. Then switch your trigger from + to - and measure the bottom.

That should eliminate some of the guessing.

pixie

 

[FYC]

My experience is that stretching too much on time scale will flatten the sine waveform so that it is not so easy to tell where it start to clip. Keeping 2 full cycle on the CRO screen to me give the best picture.

This tuning is not intended to be mV type of work, so extreme accuracy is not the prime concern.

 

[promitheus]

use triangle wave

If you have a triangle wave on your tone generator it would be more helpfull. At 1 KHz and with a triangle wave you can see clipping right away. When you see both parts of the wave start to clip at the same time then your adjustment is correct.

 

[Julianhull51]

A few years ago when I first started I just bought a cheap oscilloscope off Amazon for about £30. Downloaded a 1khz sine wave to my phone and used the phone as the signal generator. I think someone else has said that a triangle wave is probably more accurate for symmetrical clipping. Do you have pots for adjustment. What amp is it?