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Old 3rd June 2004, 09:34 PM   #1
TNT is offline TNT  Sweden
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Default Class D preamp ??

Hi!

Firstly, I post in analogue because I think that class D is analogue rather than digital.
Anyways, I have grown very fond of my ice-power based power amplifier and wonder if it would be possible to implement a preamp based on class d as a gain stage?

The amount of voltage fed to the ice-power modules does not influence the gain, but what does? Does different implementations behave differently in this respect ?

I would like to avoid passive potentiometers if possible..

Any thoughts about this? Is it feasable?

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Old 3rd June 2004, 09:51 PM   #2
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Default Re: Class D preamp ??

Quote:
Originally posted by TNT
Anyways, I have grown very fond of my ice-power based power amplifier and wonder if it would be possible to implement a preamp based on class d as a gain stage?
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.
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Old 3rd June 2004, 09:54 PM   #3
dhaen is offline dhaen  Europe
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Quote:
I post in analogue because I think that class D is analogue rather than digital.
What better justification for a class D forum?
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Old 3rd June 2004, 10:00 PM   #4
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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.
Well, I think that they sound extremly good as a power amp (i.e. nothing) which would also be a nice attribute of a pre-amp - no?

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Old 4th June 2004, 04:21 AM   #5
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Class D pre-amp?

Ridiculous.
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Old 4th June 2004, 06:18 AM   #6
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Hi,

if you want to try it just for the sake of it, I think CD4000 series of CMOS logic devices with +/- 8V power supply would be your best choice.

Best regards,

Jaka Racman
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Old 4th June 2004, 11:53 PM   #7
TNT is offline TNT  Sweden
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Quote:
Originally posted by Bill Fitzpatrick
Class D pre-amp?

Ridiculous.

Good - I like feedback !

Would You possible be just a bit more specific regarding why You think it is Ridiculous ?

Best Regards .....
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Old 5th June 2004, 01:34 AM   #8
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Because it's pointless. One can make a case for a class D power amp in terms of cost and weight savings. No case can be made for a pre-amp because they are flea-power to begin with.

But, if you can make a case I'm all ears.

On another note, It's a shame I have to make this reply in a different browser but it seems that DIY has become dysfunctional. I'm going to be complaining about this in every post I make until it's fixed.
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Old 5th June 2004, 08:04 AM   #9
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OK!

So how is the gain set in a class d amp ?


is it in the switching bridge thingy or in the conventional driver stage ?

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Old 5th June 2004, 08:23 AM   #10
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Hi,

class D gain stages usually have fixed gain. In self oscillating designs power supply rejection is pretty good, so you would need to atenuate the input like in classic preamp (pot in feedback path is nogo in class D). Carrier based modulation class D designs without feedback have zero power supply rejection, so power supply modulation could be used to some extent. But do not expect more than 20dB gain control in that case. I remember also that there are PWM based analog multiplier designs, but right now I can not think of implementation.

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Jaka Racman
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