Power flow to Class D guitar amplifier

[eem2am]

Hello,

I wonder does any reader own a ~300-400W guitar amplifier.?
(-or in fact any power level, big or small)

I am sure the readership including myself would be delighted if the following test could be done............

1.....Turn the amp up to maximum.

2.....Give a sudden , single axe-like strum to an A chord, (held down at the tuners end of the fret board...ie the opposite end to the guitar body)

3.....Show the current draw to the amp throughout this effort
-i.e. by scoping the voltage across a series current sense resistor.

4. Also, for good measure, show the output rail voltage of the PSU during this too....just to check that your vout stays up for the load transient.


Does any reader know what the waveforms would look like?.....say from a +-50V class D power supply?
(or in fact any PSU?)


Now if this could be repeated exactly the same , but this time strumming , "axe-like" at as high strumming frequency as you possibly can.....


......and once again, show the current and voltage of the PSU output to the Class D amp throughout this.

Does any reader have waveforms for anything like this?.......or can guess what they may look like?

[nigelwright7557]

I would expect the supply to sag a little but not huge amounts or there is a design fault.

[eem2am]

thanks .......though its the waveform showing the instantaneous current values, over time that is the key one here.......for example , at the instant of the strum, is there a huge sudden current draw to the class D amplififer, and then when the strum has been done, and the strings are jangling out.....what is the current like then?......is it much less or the same current being drawn as for the instant of the strum itself.

In other words, whats the difference in instantaneous power draw for the strum_contact and the post-strum jangling-out of the strings?

and is it possible, by any guitar players means, to actually play a guitar in such a way that it made the Class D amplifier draw its peak, maximum power continuously...for several minutes?

[nigelwright7557]

The current will be taken at the same frequency(s) as the strum.

There will be a big surge as the strum is hit and it will die off as the strum fades away.

Class d amps can take current oddly as half bridge can send power back into the supplies and get bus pumping especially on low frequencies.

[AP2]

Hi,
This is a burst 80 & 240Hz on power amp.
voltage rail (70V @ idle)
at 512w(4R) drop 2,7V...you can use this performance for ref.

Regards

[runebivrin]

I'd just like to point out that guitar amps are rarely any beefier than 100W. And the audience would often be happier if the guitar player understood the value of a 15W amp...

[AP2]

Originally Posted by runebivrin

I'd just like to point out that guitar amps are rarely any beefier than 100W. And the audience would often be happier if the guitar player understood the value of a 15W amp...

Hi,
I full agree with you.
And add.. is very joke if any Guitar-man want D class amp.
This is one case that not have sense ,show a super measure on amplifier.
simple you see a 1Khz fft @100w on..super amplifier d class and in a-b class mosfet amp.

Regards

[eem2am]

Thanks AP2, but i thought they had DSP on Class D to filter out the unwanted harmonics?

By The Way, Runebivrin......thankyou for stating that and bringing up an EXTREMELY interesting point....................i am not being funny when i say this, but rather value your and other people's comments....

You say "100W amplifier"


...but the term "100W Amplifier" is absolutely and utterly meaningless.



Does "100W" refer to the peak power or the average power?

..it makes a huge difference.

When a Class D FET turns on, the instantaneous power can be very high.......but the average power drawn is nowhere near as high as this.

Similarly, a sudden strum on a guitar causes a high peak power, and much bigger than the average power

So in audio it is always needed to know the Peak and/or average power........becuase a 100w peak amplififer is a world apart from a 100w average amplifier.

[runebivrin]

What you have on a class-D amp is a fully analog low-pass filter on the output to get rid of high frequency artifacts. DSP has nothing to do with that.

You can use a DSP to tailor the behaviour of the amp as a whole to more closely resemble a classic tube amplifier, complete with a (from a hifi point of view) crappy speaker.

But class D for guitars only offers tangible benefits for a battery powered application due to the higher efficiency. For bass it's a different story. A 500 watt bass amp isn't anything unusual, and it can be needed.