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Author Topic: Bandwidth of Power Amp  (Read 1888 times)

Loudthud

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Bandwidth of Power Amp
« on: March 15, 2012, 06:27:45 PM »
I'm prototyping a solid state power amp. It's class A, sort of a JLH meets Nelson Pass thing. It runs without any compensation although there is a slight oscillation. I added a couple of caps and that killed the oscillation and cleaned up the square wave response. The -3dB bandwidth is still over 500kHz. So I put the typical RC on the input, knocked the bandwidth down to 40kHz. I could go lower, just change one capacitor. I like the single PNP transistor input borrowed from JLH. When you overdrive it, you get a 40/60 square wave.

My question is, how much bandwidth should a power amp have? I know it's important that when you are overdriving it, the slopes should get steeper the harder you drive it. The amp sounds ok to me so far, even without the bandwidth limit.

joecool85

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Re: Bandwidth of Power Amp
« Reply #1 on: March 16, 2012, 10:12:46 AM »
The human ear can't hear above 20khz anyway, so I'd knock it down to around there.  While you're at it, most folks can't hear below 20hz either, might as well knock that out as well.
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phatt

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Re: Bandwidth of Power Amp
« Reply #2 on: April 11, 2012, 07:55:10 AM »
Hi loudthud,
 FWIW,

I'll assume you are trying to recreate the valvey thing?
If so then Search out the response curves of famous valve gear and you will be quite shocked when you find just how limited the bandwidth is on old marshalls some of which now fetch big $$$$.

I'd remove a few zeros and then work out how to loose -30 Db above 4kHz and loose around -60Db below 100 Hz then you will be close. winky.

Those old amps where magic because they where so bad,,, LOL,, problem is even the worst SS Amp designs are way too good for recreating that response curve.

Maybe a poorly designed OT hung on the out put might help,,, Oh yeah don't forget that half the distortion is likely starting in the PI section as well.
Yep a hard one to answer in one sentence. head scratch.
Have you noticed KMG's great work with fets? that may interest You.
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