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Old 26th June 2006, 03:42 AM   #1
lgreen is offline lgreen  United States
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Default Power Supply Question- Single lead to Caps

Here is a question that has been bugging me. You want to beef up your power supply, so you put some caps in parallel to the main filter caps

However you only put in a single line to the capacitors from the bridge, in other words you CUT THE LINES at point "CUT" indicated in the picture.

Would this be a problem, it seems that there may be conflict with current going into the lower cap bank and the need for current to come out of the cap bank, as current can only flow in one direction at a time. If the load needs current when the caps are charging the caps will not be able to provide it because current can only go one way-- and its flowing in. Or will current stop going in and come out naturally???

As you can see I am confused on this.
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Old 26th June 2006, 07:00 AM   #2
AndrewT is online now AndrewT  Scotland
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Hi Lgreen,
have a look at Choco's PDF,
http://www.diyaudio.com/forums/attac...amp=1151245617
It shows
Quote:
Tight coupling of transformer to rectifier to first stage smoothing.
Link PSU common to star ground.
Bring clean and dirty grounds to star ground.
Keep decoupling and speaker return separate from clean ground.
Your additional caps should be tightly coupled to the rectifier, not hung way towards the amp.

It's all in the interests of keeping the high value peak charging currents away from the amplifier.
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Old 26th June 2006, 07:07 AM   #3
lgreen is offline lgreen  United States
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Default Huh?

I don't think Iget it. I realize caps should be close to diodes and away from amp, and all that star groundng makes my head hurt.

I have some room to add a bank of caps far away from each (like 3 inches), figure it cannot hurt or if it does I can remove the extra caps.

The issue is whether I can just use 3 wires or whether I need 5 or 6 wires to/from the cap bank.
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Old 26th June 2006, 07:30 AM   #4
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Default Re: Power Supply Question- Single lead to Caps

Quote:
Originally posted by lgreen
If the load needs current when the caps are charging the caps will not be able to provide it because current can only go one way-- and its flowing in. Or will current stop going in and come out naturally???

As you can see I am confused on this.

Say what you will but reading and understanding some basic electronics/physics books is a must. No amount of forum browsing can substitute this.

3 wires will do you fine.
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Old 26th June 2006, 01:40 PM   #5
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Quote:
The issue is whether I can just use 3 wires or whether I need 5 or 6 wires to/from the cap bank.
You just need the 3 wires.

You are getting confused about where the currents flow and how. If the caps are connected with thick wires it doesn't matter so much what route the current takes EXCEPT at high frequencies.

All wires have inductance. You need to read up about the effects of inductance at high frequencies. This will answer questions like whether the caps should be close to the rect or close to the amplifiers or both or neither. It is generally best to make the wires between the sets of caps as short as possible, and to put them in a chain: rectifier to 1st cap, 1st cap to 2nd cap, 2nd cap to amplifier, repeat for the opposite rail.

My immediate question for you is why you want to add more caps? Eg: adding more caps without changing anything else is no guarantee of making the circuit sound more powerful - it may degrade the sound. You must also check that the rectifier has enough current rating to charge the extra caps.
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Old 26th June 2006, 02:00 PM   #6
AndrewT is online now AndrewT  Scotland
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Hi Trader
Quote:
it doesn't matter so much what route the current takes EXCEPT at high frequencies.
I don't agree.

The charging pulses to the second set of caps must also be kept in the tight loop around the rectifier & transformer.

Do not connect the extra caps further down stream where the charging voltage drop will contaminate the lower current wires to and from the amp power circuits.

Lgreen,
have you had a look at Choco's sketch? It is very simple to follow.
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Old 26th June 2006, 03:19 PM   #7
lgreen is offline lgreen  United States
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Default hmmm....

OK, to explain it one more time. I have a working power supply and-

- I want to add capacitance.
- I don't have any room in the case except to put them on the top cover. Like This.
- So I connected them up like shown in the diagram and if you really want to see the whole thing, its here.
- the stuff on the bottom of the diagram are the rooftop caps, connected as shown

OK or not?
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