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Old 24th June 2008, 12:39 PM   #1
kjb is offline kjb  Sweden
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Default 4 ch esp p3a psu Buzz

Hi!
I have constructed 4 ch esp p3a using dual rectifiers and separate filter capacitor banks for each p3a board. Each board are two channels.

I'm getting buzz when connecting inputs to more than one p3a board at the same time. I guess there is some gnd loop in my system.
This only happens when I use one transformer to both ps-units and p3a boards. look at the image provided. If I'll use two transformers (one for each psu) then there is no problem at all.

If i connect both star grounds with each other (both to chassi) there a little less buzz but still to much.

how can I resolve this issue? mount a 1 ohm resistor in series of gnd and one of the p3a? will it help?
Thanks /Joel
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Old 24th June 2008, 09:22 PM   #2
jaycee is offline jaycee  United Kingdom
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Dont connect the signal grounds to the P3A boards - connect them to the star ground, with a 1-10R resistor.

Personally I wouldn't use the seperate supplies, I don't think it's worth the hassle.
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Old 25th June 2008, 08:43 AM   #3
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Default MAKE SURE .....

that you input leads are not connected to each other (regarding groung) and also that the set of input leads is not connected to the sassi in any possible way ( regarding ground )

meaning that the rca you use for inputs are not to be connected to eachother and also have no conection to sassi ground ....

in a few words use isolated input connectors
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Old 25th June 2008, 09:46 AM   #4
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Default wiring in red

must be totally removed ....this is most of the trouble i think ....
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Old 25th June 2008, 10:05 AM   #5
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The red wires are OK and provide safety earth route and RFI shielding, I would not remove them.

Are you using insulated input and output sockets, i.e. insulated from the case?

Also, if you connect a fully floating source such as a battery powered CD player, do you still get the buzz?
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Old 25th June 2008, 10:06 AM   #6
AndrewT is online now AndrewT  Scotland
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Hi,
you have at least two solutions.
Try both to hear which sounds better.

Cheap & easy:-
Connect all the PSU zero volts together.
Connect all the input signal returns (RCA terminal grounds) together.
Connect all the speaker returns together.
Now connect all three of these at one big star ground.
Use a disconnecting network to connect this star ground to mains Safety Earth.

Separate channels:-
Connect each channel up separately.
Connect speaker return + RCA return + PSU zero volt+ power decoupling together and use a disconnecting network to link to the mains Safety Earth.
Connect each channel similarly each with their own disconnecting network.
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Old 25th June 2008, 10:12 AM   #7
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Default have you ever seen

Quote:
Originally posted by richie00boy
The red wires are OK and provide safety earth route and RFI shielding, I would not remove them.

Are you using insulated input and output sockets, i.e. insulated from the case?

Also, if you connect a fully floating source such as a battery powered CD player, do you still get the buzz?
any comercial amplifier with this topology ?????

well not really ...if there is topology like that together with it you will find a ground lif switch ....
if not then sassi gorund has nothing to do with audio grounds ....

this is a mistake
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Old 4th August 2008, 12:53 PM   #8
kjb is offline kjb  Sweden
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Tanks guys for great answers. Sorry for not answering myself but I'll been on a long vacation and my amp project has been on ice for a while.
I'll try these solutions out when I got some time over.

Right now I'm building a pair of speakers (Lynn Ohlsen:s ME2). The elements has bees lying on a shelf for several years now so I thought I'll free up some shelf-space and get me a pair of bedroom speakers at the same time. Why cant I'll just finish my previous projects before starting new ones?

I'll get back when I have tried these solutions. Maybe just adding a transformer will be easiest if noting else works.
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