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Old 25th April 2007, 11:18 AM   #1
geminni is offline geminni  Yugoslavia
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Angry 4 Amplifiers on 1 PS? Ground problem

I have made 4 amplifiers for 2 way active sistem and put it in one case. I have one transformer, rectifier and enough Caps. I have a problem with ground hum.

When i powered it on, there was pritty loud buzz from every channel, some louder then other. So i disconected two aplifiers. After trying everything, allmost black magic , two channels got quiet, not total but just barely can be hear buzz. Then i conected other two channels and now they hum and buzz like in fist place, but first two channels stayed ok.
Is there any proper way for this situation? 4 amplifier moduls on one PS?

This is not the first time i bulit 4 amps in one case but this time i have only one power source. Two other projects were fine, with no hum, buzz, or something like that. One had separate transformers, second had one tranformer but 2x2 windings so there is allso two rectifiers and caps for them.
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Old 25th April 2007, 10:20 PM   #2
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A detailed photo of your current wiring would be helpful.Recheck all of your ground solder connections as well as your input shield solder connections.Do all of your speaker returns/grounds go to the same common star ground(they should).

Dave
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Old 26th April 2007, 06:34 AM   #3
OzMike is offline OzMike  Australia
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Having multiple amplifiers running from one supply can cause a ground loop when they are connected to external equipment as the commons are joined.

Mike
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Old 26th April 2007, 08:06 AM   #4
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Default star ground ...and more

star ground will solve most of your problems .....meaning :

ground point somewhere inside the amp should include
a) ground comes directly from trafo
b) ground cable or two from star point to capacitors
c) finally 4 ground cables from star point to each amplifier board

( keep in mind that electrically if you take one cable starting from ground and to first amp then the second and goes on its exectly the same ::::: you also this way provide ground on amp boards ....but for audio THIS IS NOT WORKING .....ground loops are created this way and pick up lots of noises )

all cables should be individual and seperate ....AND I MEAN ALL !!!

PLEASE NOTICE !!!!

a) this star point should NOT include or in any way connected with the box case ......
B) the same apply for the boards none of the boards should be grounded in the box ( often screws we use to attach board or hetasink to the the box provide ground to the circuit even if this is coming from a leaking isolation .....
or IC circuit that it is attached to heatsink and then heatsink to box ground ....)

the two most importand is this with ic ...and after all that things.... the only thing you should check is if any of your rca plugs of your inputs is coming in contact with the box cause it should not !!!!

of course you dont forget that the box itshelf should be also grounded with the ground cable provided from ac supply cables

finally to my amps speaker ground cable i take from amplifier board and not from star point ground ( others prefer the oposite ....to take also from star point )

good luck
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Old 26th April 2007, 08:38 AM   #5
geminni is offline geminni  Yugoslavia
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This is how i have made conections. Strage, but every other method made one or more chanell to buzz! Signal ground is connected to all four amplifiers and gnd from suply is not. One wire from center (star) of suply is conected to center gnd to active crossovers suply. And it works

Gnd for sepakers are separate and come from center of suply.

I wonder is this safe for amplifier?
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File Type: jpg ground my way.jpg (44.4 KB, 179 views)
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Old 26th April 2007, 09:27 AM   #6
Junior is offline Junior  Singapore
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Hi,
I had made 4 preamplifiers (instead of 4 amplfiers - as in your case) with one single PSU. The problem I encouter is that if I were to wire up 2 (not 3) Preamplifier to the PSU, no hum or hissing sound - evrything work just fine. But, if I were to connect 3 Preamplfier to the only PSU, no hum or hiss but the music just go distorted after a few minutes of playing.

Sad to say I did not know what had happened but I got away with the problem by using 3 ways 3 poles switches to selectively select powering up the Preamplifier I wanted to use. One thing to note is that to use those switch that break before make.... hope it helps...


cheers
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Old 26th April 2007, 10:16 AM   #7
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the star connection should appear at one of the caps.

Gajanan Phadte
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Old 26th April 2007, 10:56 AM   #8
geminni is offline geminni  Yugoslavia
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Junior, maybe your premaplifiers have oscilations! In my case, for the same 4 channel amplfier, first 2 amps were fine but second 2 were making distorted sond. When i disconect one of them (3-rd of 4-th channle) everything wass ok, no distortion. The poblem was small 22 picofarad cap paralel with negative feedback resistor. Without it it worked fine.
The first and second amp had zobel so thats why they didn't make distorted sound I put zobel on all four amps and pull out small 22 pic cap.

I just remembered that i had similar ground issue with Quad 405, only stereo not 4 like this one. Input rca-s are on wooden back pannel. Signal goes to the pot and after that directly to amp boards. The buzzing was eliminated with left amplifiers PSU ground disconected! With it it has buzz.
Right channel has PSU ground, with amps have signal ground conected.

I had luck with project similar to the first one, 4x40wats with active crossover. One transofrmer, two separet windigs (2x2) with separate rectifier and caps. It worked at first! There was no need for reviering ground at any point. No buzz, no hiss... I thinks that it some black magic

I am only woried for the original problem, will that make any harm to amplifier? like on picture i posted earlier.
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Old 26th April 2007, 03:27 PM   #9
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Default it could be

something wrong with electronic xover ....disconnect that to see what changes ....also possible that red lead ground starpoint to xover is the problem ....

post pictures it will help more ....detailed ones also
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Old 26th April 2007, 03:30 PM   #10
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Default now that i see better

the red lead that connects the 2 grounds is not needed remove it ( since you have sepearte psu for x over )

also did you check all the rest i told you grounds isolation and bla bla .....???
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