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Old 21st August 2009, 08:54 AM   #1
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Default how to effectively ground or not?

hi guys

i have a beautiful sansui aux-901 amp, i installed an iec socket to allow for the tci mains cable to clean up the electrical feed to the amp. i found it did wonders but decided later to ground the amp as well as it had none. here is where the pear shapes appear! the sound with any unit was very good but stick a pc on there and there was a constant hum that caused me migranes.

now on removeing the earth 4 years later i have found that silence is golden. i also found that same night a very scary i dont know what to call it but occurance? when turning the volume up to check the hum had gone the speakers would move in! and out with the increase or decrease of the volume. its stopped now as i never turn of the amp but run denson demagnetiser through it every couple of months and the sound is great again.

first of are all amps not 3 core?

when not then how is it that grounding is then done to improve the sound?

what do you think the speakers moveing was about???

is it a fault?

if i am to have the amp serviced what are all the things i should ask for as in things that are the most important to sound: capaciters, resitors and so on??? also i live in chiswick london so anyone know of a great service agent?

god bless raju
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Old 21st August 2009, 11:02 AM   #2
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Originally Posted by praer4life View Post
i found it did wonders but decided later to ground the amp as well as it had none.
You should always leave equipment in the state it was delivered. Don't disconnect Earth, if there is one, and done connect Earth, if there is not supposed to be one.

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Originally Posted by praer4life View Post
its stopped now as i never turn of the amp but run denson demagnetiser through it every couple of months


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Originally Posted by praer4life View Post
first of are all amps not 3 core?
If you mean earthed, no they are not. Most commercial amplifiers for home use are Class II, which means they have no direct connection to Earth.

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Originally Posted by praer4life View Post
when not then how is it that grounding is then done to improve the sound?
It is not grounding that improves the sound. It is correct grounding that may improve the sound. Incorrect grounding can e. g. lead to hum, as you already have experienced.

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what do you think the speakers moveing was about???

is it a fault?
Yes. The speakers move according to the DC offset, which changes with the potentiometer position. If it is big enough to lead to a visible membrane movement, you should have it checked. Sansuis sometimes come with a selector for AC-coupled or DC-coupled operation. If yours has that option, set it to AC-coupled to rule out that the DC comes from the source.
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Old 21st August 2009, 11:12 AM   #3
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I had similar problems with my pc and gainclone. The problem is that both are earthed, and both are also connected to ground via the signal cables. What happens is you have a loop formed by the power cables (though the wall socket) and the interconnect cable between the pc and the amp. Small currents circulate around and around this loop causing hum.

I built an earth loop breaker as per Rod Elliots article here --> http://sound.westhost.com/earthing.htm completely cleared up the problem. no audible hum even with ear against the speaker cones.

Tony.
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Old 21st August 2009, 11:25 AM   #4
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thank you guys just the last part then

if i am to have the amp serviced what are all the things i should ask for as in things that are the most important to sound: capaciters, resitors and so on??? also i live in chiswick london so anyone know of a great service agent?

god bless raju
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Old 21st August 2009, 11:26 AM   #5
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oh guys one more thing the back of the unit has a switch that is 220/ 240 which one hsall i leave it on? 220 as it is now?
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Old 21st August 2009, 11:46 AM   #6
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Quote:
Originally Posted by pacificblue View Post
Incorrect grounding can e. g. lead to hum, as you already have experienced.
The problem is that correct grounding can lead to hum. Disconnecting the shields at one end is a band aid that usually works. But that causes signal return currents to flow through the earth ground instead of its intended path. Earth loop breakers (diodes in the ground leg) are another band aid that normally works, but technically they're not legal. If the only problem you have is a cable TV feed causing trouble, consider yourself lucky because those isolators are a no-compromise solution.
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Old 21st August 2009, 04:24 PM   #7
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Default service knowledge nothing to do with tvs

the question at hand thank you guys just the last part then

if i am to have the amp serviced what are all the things i should ask for as in things that are the most important to sound: capaciters, resitors and so on??? also i live in chiswick london so anyone know of a great service agent?
and also should a switch for the amp be set at 220 or 240.

god bless raju
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Old 21st August 2009, 08:38 PM   #8
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I have found this with my amplifiers that I build myself.

If I have a floating source like an MP3 player i need to connect the earth to zero volts.
If the source has an earth I need to disconnect the earth from zero volts.
Its probably worth putting in a switch for both options.
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