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Old 9th September 2004, 12:56 AM   #11
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Default Re: Re: Class D preamp ??

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Originally posted by peranders

Before you go any further: What are the advantages of class D in a pre amp? I wish that you try to answer this first.
It seems that altering things in the time domain seems easyer than changing the level/svinging voltage. Could this be the reason for class d amps sounding so "free" ?




Anyone have a genious idee about controlling the level without an traditional autenator?

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Old 9th September 2004, 10:13 AM   #12
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Hi,

I think class d amps sound so "free" due to the AD conversion being ideally 100% linear, kind of like an ideal class A. I guess that's kind of what you said.

Since you can't control the amplitude of it with traditional means, I think realistically the best bet would be a very good class A pre amp stage. Since it's very low power.. it really shouldn't be a problem.

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Old 9th September 2004, 10:49 AM   #13
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A class-D pre-amp is a bit of a case of additional circuitry and complexity for the sake of it, but one advantage can be use of a single pot to adjust level. Check out John Linsley Hood's attenuator and compressor in Electronics World a few years ago.
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Old 9th September 2004, 12:26 PM   #14
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Old 9th September 2004, 08:44 PM   #15
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Quote:
Originally posted by richie00boy
A class-D pre-amp is a bit of a case of additional circuitry and complexity for the sake of it, but one advantage can be use of a single pot to adjust level. Check out John Linsley Hood's attenuator and compressor in Electronics World a few years ago.
I was thinking if a d stage could replace the ordinary output buffer maybe. If that could be combined with some very smart attenuator, "somehow" within the bridge, I would like to try it. Normal input circuits could be used. My knowledge in "d" is really shallow so ....

Are Elektor articles available on the web? I never subscribed to that mag.


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Old 9th September 2004, 09:16 PM   #16
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A class-D pre will definitely be a lot more complex than a class-A or B one. I think JLH used an output buffer to ensure the PWM filter was loaded correctly, so the benefit you are hoping to achieve wouldn't be done.

EW (not Elektor ) articles are not available very easily other than looking up the article on softcopy and then ordering the back issue from EW.

I may have the mag somewhere and I have just purchased a scanner though... However, I don't recall the article having a board layout. Maybe not a good first design project.
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Old 9th September 2004, 09:49 PM   #17
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Aha - I hoped that it would be quite insensitive to it's load. Is this due to the typical high impedance of the input for a typical power amp?

I'm shure I could do anything with some scematics but it would maybe be a good read (if I can grasp it contents).

Please - You must be dying to try that scanner

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Old 10th September 2004, 07:12 AM   #18
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Maybe I misunderstood, but I got the impression you were trying to eliminate the typical output (op-amp) buffer. If I have remembered correctly, the JLH design does *not* do this, as a buffer is placed after the PWM stage to ensure it's loaded correctly. Thus the power amp input impedance is of little consequence.
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Old 10th September 2004, 07:33 AM   #19
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TNT,

Didn't you use ICEpower?

As far as I know the ICEpowers run at +12VDC / -12VDC for the Opamps, perhaps you can upgrade the opamp in the inputsection of the ICEpower to an AD8620 or OPA2134.

Perhaps this will make the sound of your setup much better?

As thinking of a Class-D preamp...........

I would definatly go for a passive preamp and increase the input impedance of your amplifier, or a very nice discrete Class-A preamp.


Cheers,

Jan-Peter
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Old 10th September 2004, 04:28 PM   #20
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Unfortunately I do not have the magazine here to scan as I left it at my parents house. The issue required is April 1995.
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