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Old 7th March 2008, 06:04 AM   #1
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Default Digital amp

I am just wondering if digital amp like the Lyndorf TDA2200 available in DIY?

I understand that Class D still have analog input and therefore required DA conversion. Would be nice if the DAC can be skipped and the digital output is directly connected to the amp!
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Old 7th March 2008, 07:08 AM   #2
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Why would you wish to do this?

A digital-input amplifier is basically a power DAC. Given the current state of technology it provides higher performance and lower cost if you implement the DAC as a low-voltage device, and then feed the analog signal to a class-D amplifier. This allows to to use a simple technique like 'UCD' which provides a proper NFB loop around the whole of the analog amplifier section. If you look at the few digital-input amplifier designs that enclose the amplifier in an NFB loop, you will find that they are dreadfully complex. (Look at the latest TI or Zetex designs for example). It seems a bizarre example of progress if you need a full DSP to do something that a UCD amplifier does with two resistors and two capacitors!
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Old 7th March 2008, 07:44 AM   #3
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I thought this arrangement may avoid DA-AD conversion and possible make the chain simpler with better sound....

Seems to be the repond form those using TDA2200
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Old 7th March 2008, 05:55 PM   #4
jkeny is offline jkeny  Ireland
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I agree ackcheng - pure digital amp = fewer places to degrade the sound & introduce jitter, so its easier to focus on optimising the amp circuit rather than the whole chain of DAC + PS supply-> analog amp + PS supply

This is my reasoning for the Panasonic class D amp thread Panasonic class D amps
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Old 9th March 2008, 07:23 AM   #5
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1. the volume control is the problem,
you can control it digi-> dsp->digital-input amplifier .
and use the dsp to control the volume.
this will make the noise floor very high when it was running at a low power output .

someone(perhaps sharp) control the power supply voltage to control the volume , strange way, but low noise.

2. the thd from the current (output) will be very high,
this is same like open loop vs close loop style,
some one like open loop even bad performance,
but most of open loop class-d amp have no very good performance at this time.

funny

rg
fumac
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Old 9th March 2008, 12:59 PM   #6
jkeny is offline jkeny  Ireland
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Quote:
1. the volume control is the problem,
Yes Texas Instruments have published a vol control circuit using variable PS here: http://www.google.com/url?sa=t&ct=re...sFSU8nUNYasMVg
and Panasonic use this in their SA-XR* pure digital no feedback amps

Quote:
2. the thd from the current (output) will be very high,
again TI have achieved low open loop THD and Panasonic have implemented this in their amp range. Agreed the PS quality is the critical factor in achieving low THD - a good, stiff, low impedance, regulated PS is hard to do
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Old 9th March 2008, 01:31 PM   #7
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Quote:
Originally posted by jkeny



again TI have achieved low open loop THD and Panasonic have implemented this in their amp range. Agreed the PS quality is the critical factor in achieving low THD - a good, stiff, low impedance, regulated PS is hard to do

sorry can you show me this ?

thank you

fumac
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Old 9th March 2008, 02:40 PM   #8
jkeny is offline jkeny  Ireland
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Here you go - low but not very low thd in open loop - http://www.diyaudio.com/forums/showt...328#post915328

My readings have led me to believe that an amp should be designed with the lowest open loop thd before neg feedback is applied, rather than relying on neg feedback to cure all ills.
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Old 12th March 2008, 02:00 AM   #9
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anybody can share some information how to design a "good" PSU for class D amp? I am working with a power supply company here in China to design a PSU for class D. Anybody interested to join this project?
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Old 14th March 2008, 10:56 PM   #10
jkeny is offline jkeny  Ireland
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Sorry,
I noticed the link I gave above doesn't work - here's the correct one: http://focus.ti.com/analog/docs/tech...ctName=slea028
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