Clipping Indicator?

[tadawson]

The preamp/power amp clipping question depends on how the preamp is coupled to the power amp. If it is DC coupled, then year, same destructive waveform out. If it is more typically coupled via a cap or high pass filter, it may still sound bad, but would me much less destructive since the filter will "soften" the square waves to something will much less DC. Power amp hard clipping? Pretty much DC all the way at the peaks . . .

- Tim

 

[steveksux]

The preamp/power amp clipping question depends on how the preamp is coupled to the power amp. If it is DC coupled, then year, same destructive waveform out. If it is more typically couples via a cap or high pass filter, it may still sound bad, but would me much less destructive since the filter will "soften" the square waves to something will much less DC. Power amp hard clipping? Pretty much DC all the way at the peaks . . .

- Tim

Actually any caps in the sig path in the power amp would also block DC, trim the edges of real square waves from the preamp also.

Randy

 

[Mark Reccord]

The preamp/power amp clipping question depends on how the preamp is coupled to the power amp. If it is DC coupled, then year, same destructive waveform out. If it is more typically couples via a cap or high pass filter, it may still sound bad, but would me much less destructive since the filter will "soften" the square waves to something will much less DC. Power amp hard clipping? Pretty much DC all the way at the peaks . . .

- Tim

I'm not sure where you're getting that a highpass filter will 'soften' a square wave. Unless you're at a frequency where the crest of the wave is actually longer in duration than the time constant of the filter a high pass filter will pass a square wave intact. This isn't real likely considering that most amp stage coupling is a 1st order HPF with a corner frequency well below the audio band (typically 3 or 4 Hz). If, by some chance, you do get to a frequency that low, the filter won't soften the waveform, it will actually sharpen the leading edge of the wave, because the pseudo-DC at crest will actually drop exponentially with time (think of the step response of a first order network).

It is also not correct to think of square waves as having a DC component. They don't. Add up the area under the curve for one cycle of a square wave for proof...

They do, however, have equivalent heating power to DC, but in the case of a speaker, they won't heat it like DC would because the alternation will still result in cone movement and the cooling effects associated with that, whereas the cone won't move with true DC.

Of course, you'll never see true square waves from a real amplifier...

 

[tadawson]

Actually any caps in the sig path in the power amp would also block DC, trim the edges of real square waves from the preamp also.

Randy

True, but ever since the advent of the Crown DC300 years ago, a lot of power amps have been DC coupled, and WILL pass the DC. (As an interesting anecdote, in college, a guy I know needed to speed control a tape deck motor, so he got out a D cell, potentiometer, and a DC300, and it worked just fine . . . . . . ). Most likely not the case in instrument amps, and lot of bass amps have high pass filters as well, to protect against over excursion, etc., which would also tend to strip off the DC from the preamp output as well.

- Tim

 

[Jerrold Tiers]

That's not to mention that if you have any EQ off flat, and the EQ is after the clipped stage, the wave may look NOTHING like a square wave.

A high pass filter takes a square wave and tends to turn it into a sawtooth, straight fronts and a slope down after that. Generally, that is for a filter set higher than 1/10 or 1/5 of the frequency.

Soundwise, that tends to change the timbre to take out fundamental and leave all the harmonics. Not always what you want.....

Conversely, the output transformer of a tube amp will, depending on frequency, take off higher harmonics, leaving the fundamental and the more musically related harmonics. Same with any high cut EQ after the clipping.

Naturally, though, if you clip at 50 Hz, the transformer isn't going to filter very much...... Unless you are in a Soft Machine tribute band, that isn't likely to be what you wanted.....

 

[Bob Lee (QSC)]

DC coupled power amps were a fad in the late 70s, and a bit into the 80s, but it has passed. There may be a few out there still being made by obscure companies who think it's a good idea.