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Class D Switching Power Amplifiers and Power D/A conversion

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Old 6th December 2005, 09:19 PM   #101
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[QUOHow about those caps across the output terminals?? Is it recommended to replace those?? If yes, then with what?? Again, my apologies if I missed a post answering this question...TE]

I replaced them with 0.1uf M Cap poly's and removed the on board C19 & C20. It seems to really open up the detail. It is early days with this last mod and things may change, it sounds good at the moment.
PS make sure you twist the speaker cables from the board to the terminals..


Barry..
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Old 6th December 2005, 10:16 PM   #102
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C19/C20 are the Differential Output Capacitors. They are meant to drain off some of the RF.
Tripath calls for 0.01uF. That should have an impedance of about 800 ohms at 20kHz and 16 ohms at 1MHz. Some Tripath based boards use much larger caps. I don't know what the Sonic uses.

The terminal output caps could make a difference, as they are larger. A lot of people have reported better results without the caps across the speaker terminals, or the use of better caps.

The output filters of Class-D amps is wide open to research!
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Old 6th December 2005, 10:26 PM   #103
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Quote:
Originally posted by panomaniac
R01/R02 set the input impedance.

In the post above by BWRX, he most have been thinking about R4/R5.
You are quite right. Thanks for the correction.
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Old 6th December 2005, 11:57 PM   #104
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Default Thanks again!

Thanks all for the tips! I have a real good idea of my final mods list now, and will start the ordering process in the next week-ish. I even have an idea of what I want to do for a re-box, but I'll keep that card close to my chest, in case it doesnt work out... it'll be neat if it does.

Pano - Thanks for the tip on the power supply. I have a BK Precision 1686 bench supply that should do the trick for now. I checked out wluk and will be ordering a half dozen from him.

I also added the .15 uF output caps to the parts list (Digikey number P3876-ND).
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Old 7th December 2005, 08:31 AM   #105
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A picture of my finished T Amp
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Old 7th December 2005, 08:33 AM   #106
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And the messy guts..
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Old 7th December 2005, 11:40 AM   #107
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Quote:
Originally posted by audio1st
A picture of my finished T Amp
Sweeeet! You've out done my old Mauna Kea amp. What a great design - Bravo!
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Old 7th December 2005, 07:42 PM   #108
DcibeL is offline DcibeL  Canada
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Quote:
Originally posted by panomaniac
R01/R02 set the input impedance. They simply tie the input to ground via 10K ohms. This is a bit low for normal purposes. 50-100K would be better for most sources. 10K was proabably choosen to give a good load for the headphone output of portable CD/MP3 players.

So you can remove them if you are using a 100k or 50K volume control, or replace them with those values if you are not. You can place them anywhere upstream of the input cap, and after your input connectors.
I think for the time being I'll be using the stock volume control still (50k pot I believe) so I'll just take R01 and R02 out. Thanks.
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Old 22nd December 2005, 03:42 PM   #109
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Hello to everyone, i am new to the forum (but have been reading quite a bit lately). What a great forum and also a great community! Keep up the good work!
I also have a little (easy) question regarding my t-amp. I just want to replace the input caps to foil types with 2.2uF. Since they are *big* i was wondering if i could just unsolder the input cap of each channel, bypass it with wire, and then wire the new cap between the pot and the board. Basically this would leave the input circut intact, but the decoupling cap would be right "after" the pot in the schematics. (A bit like the "stealth-mod" from Panomaniac but easier)
Thanks a lot!
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Old 22nd December 2005, 05:52 PM   #110
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Default Input cap question

nilsomat,
That is the way I did it. I feel it is best as the film caps are supported by the pot on one end and the larger connector pad on the other. However for this to work you must remove r01 and r02 other wise the amp will not turn on.
Roger
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