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Old 19th May 2008, 03:29 PM   #1
eketehe is offline eketehe  Indonesia
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Question need help psu design 2.1

Dear All,
I'm about to rebuilt my 2.1, and an improvement on PSU.
These are things i already have :

10A E1 trafo 24 - 0 - 24 VAC
8 x 3300uF/50V
8 x 4700uF/35V elcaps. both 3300/4700 have a same size.

The amps will runs on +/- 30VDC,

the stereo will be lm3886 or lm1875,both with 2x1000uF each as switch caps on PCB.
the subwoofer amp will be 150W BJT ETI, or SC or bridged tda7294 100W.

I'm planing to use that single big trafo for all amps power.
I haven't deal with alot of caps in PSU, and never know before if we can using a double diode bridge in single CT trafo or not.
and herewith i attach some drawing,

I need any idea or input to maximize this PSU, if this will be an overkill to use all caps, i'm ok to use only some of them.

My 1st prior is the stereo perfomance, subwoofer will be the 2nd.
Hope the high power needs of subwoofer not bothering the stereo's.

There are some questions :
Which kind of PSu design belows is the best for this 2.1?
Which subwoofer amp will suitable?
in case a single 10A trafo, which have better capacitance, 2 x 27.000uf or those small caps?
snuberized or not?

Any suggestions, inputs or anwers will highly appreciated,
Brgds
Eka
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Old 19th May 2008, 03:30 PM   #2
eketehe is offline eketehe  Indonesia
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no.2
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Old 19th May 2008, 03:31 PM   #3
eketehe is offline eketehe  Indonesia
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no.3
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Old 19th May 2008, 03:32 PM   #4
eketehe is offline eketehe  Indonesia
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no. 4.

Thks,
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Old 19th May 2008, 03:38 PM   #5
AndrewT is offline AndrewT  Scotland
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hi,
The single rectifier is supplying all the capacitors in parallel. It makes virtually no difference whether they are grouped as you have shown for each channel, or all grouped together feeding all the channels in parallel.

The second shows two rectifiers.
This time the bass PSU is partially separated from the other pair of channels, but note that the power ground is common with the centre tap, i.e. all channels share the same dirty ground.
Again the two upper frequency PSUs are effectively in parallel.

The only thing separating the PSUs is a tiny inductance in the wires feeding the groups.

Take care with this common ground arrangement to avoid hum & buzz in your amplifiers.
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Old 25th May 2008, 12:54 PM   #6
eketehe is offline eketehe  Indonesia
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Hi Mr Andrew,
It is hard to have clear of humm and buzz with double diode bridge ( sorry for the wrong diode pics),
Single diode bridge will be the choosen.

I'm curious about what inside the CT trafos.
so i break one of small E1 CT, and as predicted, there are 2 in 1 0 leads, then 1 separate the CT leads.

I imagine that soon i will have PSU like shown at chipamp.com ( LM3886 )
anybody have try this?
is this not recommended for any reasons?
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Old 25th May 2008, 01:59 PM   #7
glennb is offline glennb  Australia
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Quote:
Originally posted by eketehe
no.3
The diode bridges are not drawn correctly. Two diodes are supposed to point to the +ve rail, and the other two diodes point away from the -ve rail. You've drawn them going around in a circle, point-to-tail, which is wrong.
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Old 25th May 2008, 08:18 PM   #8
eketehe is offline eketehe  Indonesia
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Yes glen, thks
no1-4 shows wrong diode bridge pics
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Old 25th May 2008, 08:22 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi Ek,
the example showing 12-32 is using 20Vac as the transformer output.
This wastes VA that cannot be used.
You end up with 20/32*VA as the maximum output from the transformer.
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Old 26th May 2008, 03:50 PM   #10
eketehe is offline eketehe  Indonesia
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Quote:
Originally posted by AndrewT
Hi Ek,
the example showing 12-32 is using 20Vac as the transformer output.
This wastes VA that cannot be used.
You end up with 20/32*VA as the maximum output from the transformer.

OK Thanks Mr Andrew,
I'll skip that one.
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