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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th March 2013, 05:09 AM   #141
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Yea, I think my definition of "good source" is far looser than you guys..

I have a modded x-fi, which I consider "GOOD" source

I don't really plan to get anything above this.. as I feel diminishing returns on audio equipment especially the "unmeasurable" kind is tough to swallow.

I mean, new CPU, benchmarks higher.. new audio equipment, yea, sounds m0ar warm... $800 please... thankyou, here you go, come back next year when we release m0ar warmness
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Old 12th March 2013, 09:33 AM   #142
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Quote:
Originally Posted by tp4tissue View Post
well... the 2.2uf caps are in "what little" schematic we "do" have...

But yea, if you bypass and have a really good source.. I think just direct shoot would be "fine.." although you'd still at least need those 0.01uf in the loop for noise control going over "distance"
I cannot see C20 and C21 in the schematic in post #1.
In post #104 I see C20 and C21 still in place.
Post #3 reports: "The first mod I did was to replace C20 & C21 with film caps." but in post #7 they seem to have been removed.
Finally in post #93 (see pic) most of the components have been removed...

Sorry but I'm a little bit confused...
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Old 12th March 2013, 06:04 PM   #143
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Quote:
Originally Posted by Fukinagashi View Post
I cannot see C20 and C21 in the schematic in post #1.
In post #104 I see C20 and C21 still in place.
Post #3 reports: "The first mod I did was to replace C20 & C21 with film caps." but in post #7 they seem to have been removed.
Finally in post #93 (see pic) most of the components have been removed...

Sorry but I'm a little bit confused...
Fukinagashi

I believe what they mean when they say you don't need C20 C21, it's assuming you have short travel between your source and the amp where there isn't much noise being picked up.

However, the issue is.. Many times, either the SOURCE has some noise, or the length of wire isn't optimal, this is where the 2.2uf Caps will come in handy, and from my experiments "perhaps, also keep the opamps", as I've found that opamps smooths out the sound of poor sources like my iphone.

Edit:

When i say keep the opamps, i mean keep opamps in the loop, I DON'T mean keep the ORIGINAL Opamps which sound like total crap

Last edited by tp4tissue; 12th March 2013 at 06:18 PM.
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Old 12th March 2013, 06:25 PM   #144
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Quote:
Originally Posted by Fukinagashi View Post
I cannot see C20 and C21 in the schematic in post #1.
In post #104 I see C20 and C21 still in place.
Post #3 reports: "The first mod I did was to replace C20 & C21 with film caps." but in post #7 they seem to have been removed.
Finally in post #93 (see pic) most of the components have been removed...

Sorry but I'm a little bit confused...
C20 and C21 are on the output of the schematic in post #1, before the TA2020 (connected to the right most wire and not shown).

In post #7, they are there, you can barely see one of them. They are now film caps, not big electrolytics, as I posted in post #3. In the photo in post #93, they are the big white caps, no longer on the board. Post #93 is just for illustration purposed.
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Last edited by Redshift187; 12th March 2013 at 06:33 PM.
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Old 12th March 2013, 06:26 PM   #145
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Originally Posted by tp4tissue View Post
I believe what they mean when they say you don't need C20 C21, it's assuming you have short travel between your source and the amp where there isn't much noise being picked up.
No. C20 and C21 have nothing to do with noise. They are to block DC from the source. If you don't know for absolute sure that your source has no DC, you MUST have capacitors there. Otherwise you risk both the amp and your speakers.
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Old 12th March 2013, 08:37 PM   #146
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Originally Posted by Redshift187 View Post
No. C20 and C21 have nothing to do with noise. They are to block DC from the source. If you don't know for absolute sure that your source has no DC, you MUST have capacitors there. Otherwise you risk both the amp and your speakers.
Would you really plug in something that has DC?

Which piece of audio equipment doesn't have decoupling caps at the output stage??
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Old 12th March 2013, 08:43 PM   #147
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Well for one, the Raspberry Pi has significant DC on the output for a few seconds after starting and stopping media.

Are you willing to risk your amp and speakers on an assumption?
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Old 13th March 2013, 12:53 AM   #148
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Originally Posted by Redshift187 View Post
Well for one, the Raspberry Pi has significant DC on the output for a few seconds after starting and stopping media.

Are you willing to risk your amp and speakers on an assumption?
raspberry Pi is not audio equipment
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Old 13th March 2013, 07:16 AM   #149
4sfed5 is offline 4sfed5  New Zealand
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well i just ordered one from ebay for my office.
I am going to make a stand for my LCD monitor that will house 2 6"x4" car audio speakers on each side and the lepai in the middle. i will power it from a spare PC ATX power supply so i can use the 12V to power the Lepai and the 5 volt will power some dummy USB ports to charge my phones.Source will be my phone or my laptop 3.5mm output jacks.

Do the new boards need modding for reliability?
Do you have to remove the zener?
i am assuming i wont need to fit a bigger Power cap as the PC atx power supply should have more than enough capacity?
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Old 13th March 2013, 08:52 AM   #150
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Quote:
Originally Posted by Redshift187 View Post
No. C20 and C21 have nothing to do with noise. They are to block DC from the source. If you don't know for absolute sure that your source has no DC, you MUST have capacitors there. Otherwise you risk both the amp and your speakers.
I've recently tried to use my tube pre-amp with the Lepai and results are very promising: the Lepai itself is not same level if used with a good pre.
Now I'm planning to use it as a final stage.
In the pre output stage (in series with the signal) I have a couple of big paper-in-oil 2uF capacitor. Could I use them instead of C20 and C21?

Last edited by Fukinagashi; 13th March 2013 at 09:20 AM.
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