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Class D Switching Power Amplifiers and Power D/A conversion

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Old 5th July 2010, 03:44 PM   #401
Pano is offline Pano  United States
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Quote:
Originally Posted by sendler View Post
shorting the dc probably won't damage the dac especially since it is only loaded by 50k but it might sound better with a cap to block the load.
I was thinking about this and at first thought for sure he needed a cap. But running the DAC into a 50K pot the DC load is only going to be about 0.05mA. Not likely to hurt it, you're right. Tho just to keep things in balance, maybe a 50K resistor to ground on the unused leg of the DAC? The data sheet does not seem to say what the max DC load is.

Generally these are meant to run into a lower impedance load. The Cirrus engineer I spoke to said they spec them at a 1K load. He would not tell me how they perform on other loads. I have not found higher impedances to be a problem.

Since your amp has DC blocking caps after the pot, you are not worried there.
The only thing I'd worry about is the amp switching noise getting back up into the DAC. You might want to put a little cap (0.01-0.1uF) across the inputs to drain off some of that noise.

Sure is a simple way to go!
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Old 5th July 2010, 03:56 PM   #402
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Be careful, I just worry about the DC output of DAC will lead to a DC output of amplifier.
So, the cancellation of the input caps will be a risk to try.
Don't worry about the noise you mentioned, it will not happen I think. May be considering more about the ground will be more important.
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Old 5th July 2010, 04:03 PM   #403
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For someone who want to have a try, I myself advise to adjust the DC of amp again before connect to the speaker. And good luck for your DIY.
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Old 5th July 2010, 04:24 PM   #404
DJK265 is offline DJK265  United States
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Originally Posted by hifimediy View Post
Hi Dan.
I think 30V is ok for v2.0. If you don't need much output power, you can choose around 24V power supply. And thanks for your advice.

hifimediy
Thanks for the response, I'll start with 27v and adjust accordingly and measure the DC offset as well.
Dan
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Old 5th July 2010, 10:43 PM   #405
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Originally Posted by AP2 View Post
if you have an oscilloscope, you can make a simple measure.
put CH1 at Vcc, ch2 at output of amp on load. Amplifier drives with burst signal 60Hz or 100Hz 33mS duration and see voltage decrease on oscilloscope.
sadly no. Just a digi-multimeter. I really cannot imagine that a voltage decrease should happen and if itīs really the case - it must be responsible for the tight dry and quick bass I am listening out of the speakers. I love voltage decreases

So I have to believe that you are right because I am a greenhorn in this area. Maybe someone else with more technical understatement could throw in his/her opinion ??
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Old 6th July 2010, 10:11 AM   #406
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Originally Posted by sendler View Post
shorting the dc probably won't damage the dac especially since it is only loaded by 50k but it might sound better with a cap to block the load. Try another of the same cap you are using for the amp. Any value between 1uf and 3uf usually works well and gives enough extension in the bass.
I added a cap between the cs4397 and the tk2050 amp, and the sound is so good! Everybody should try this!!
What is the downsides, why doesn't commercial DAC do this?
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Old 6th July 2010, 12:00 PM   #407
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Originally Posted by Nick122147 View Post
I added a cap between the cs4397 and the tk2050 amp, and the sound is so good! Everybody should try this!!
What is the downsides, why doesn't commercial DAC do this?
Running a dac chip directly out from the pins doesn't make sense to an engineer and they only want to do what makes sense even after we tell them something else sounds better.
.
AK4395/4396 ultrasonic noise spectrum graphic
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AK4395 vs. AK4396 listening comparisons
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Old 6th July 2010, 02:32 PM   #408
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Right, it's not good "engineering practice". In the real world, you never know what people will connect to your design, so you have to be careful. The most important thing is that is works. And with a wide range of equipment. You don't have that restriction, you know what you are using.

I've tried the cap only and like it. But to my ear the transformer output sounds better. A matter of taste, really. Scott likes the cap coupling better.

Don't worry about added DC offset in this configuration. Your amp has DC blocking caps at the inputs, so the DC from the DAC will not pass thru. No worries.
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Old 6th July 2010, 04:57 PM   #409
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sadly no. Just a digi-multimeter. I really cannot imagine that a voltage decrease should happen and if itīs really the case - it must be responsible for the tight dry and quick bass I am listening out of the speakers. I love voltage decreases

So I have to believe that you are right because I am a greenhorn in this area. Maybe someone else with more technical understatement could throw in his/her opinion ??
SMPS are usually capable to mantain a very well constant regulated voltage till their current limit.
If you notice a voltage drop on a regulated smps this means that the smps is underpowered for the application (you need more watts).

A *very little* voltage drop (about 0.01 V @ 7A for a 200W AT smps) is caused by the voltage drop on the output cables (more is the current consumption, more is the voltage drop on cables), this voltage drop generates a little accuracy error on the feedback circuit.
If you take the feedback signal downstream the output cables you will not have this irrilevant voltage drop.

That's my experience. I love smps.
Maybe they could produce some noise on the output, but if the board is well filtered (capacitors...) you will not hear nothing bad.

*Theoretically* a linear amplifier should sound better than a class T, but practice teaches us that's not always true.
Quite the same for linear power supply vs. switching power supply.
My 2 cents
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Old 6th July 2010, 05:07 PM   #410
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[IMG]Click the image to open in full size.[/IMG]
Where can we find more information about the T3 board?

Thanks,
Robert
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