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Old 17th April 2013, 02:03 PM   #2381
hajj is offline hajj  Lebanon
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Richard,
Thanks for chiming in.
Next stop, PS build.
Regards
Nick
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Old 19th April 2013, 07:04 AM   #2382
hajj is offline hajj  Lebanon
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Ok, got the PS part wired up as per Wirehead's and Richard's intruction (single bridge, center tap as common ground)
Got all the connections to the VSPS 300 boards (populated with kit parts from RJM) through a 1 meter long umbilical.
Checked voltages at pins 4 and 7 for positive and negative voltages, all good.
Mounted IC1 (OPA27) on the boards
Connected the outputs to the amp, (no turntable hooked up yet)
Turn on the amp, and......
HUMMMMMMM!!!
A nice, steady, powerful, 50hz hum

Troubleshooting time:

-Checked all solder joints, cabling, nothing to declare.
-Tried moving the PS around, rearranging cables, the hum is unaffected.
-When I touch the input wires running from the RCA connectors to the boards, the hum increases, this happens for both channels when I touch their respective input wires.
-Input wires are around 10 cm long and shielded.
-Power wires are twisted positive and negative with a third loose wire for ground.
-Comm ground on board is not connected to anything yet, (everything is mounted on wood boards for testing)

***One important thing to note is that over here in Lebanon, there is no earth connection in our power outlets, it's a simple L,N outlet.

Does anyone have any idea where to start from?

Thanks

Nick
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Old 19th April 2013, 07:56 AM   #2383
rjm is offline rjm  Japan
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Short the inputs, repeat.
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Old 19th April 2013, 12:49 PM   #2384
Bibio is offline Bibio  Scotland
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Quote:
Originally Posted by hajj View Post
-Input wires are around 10 cm long and shielded.
-Power wires are twisted positive and negative with a third loose wire for ground.
-Comm ground on board is not connected to anything yet, (everything is mounted on wood boards for testing)

***One important thing to note is that over here in Lebanon, there is no earth connection in our power outlets, it's a simple L,N outlet.

Does anyone have any idea where to start from?

Thanks

Nick
input wires - is the shield connected at both ends?
power wires - loose ground wire? explain a bit more
comm ground - i thought that this has to be connected to the phono ground connectors or the casework.

if there is no earth wire in Lebanon then i would presume you don't connect the earth wire to the chassis.

earth and ground should not be connected to the same case and only earth to the power supply case if separate and if same case then no earth, since you don't have an earth in Lebanon then you cant earth the case and i would use 2 core rather than 3 for power.
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Old 19th April 2013, 01:00 PM   #2385
hajj is offline hajj  Lebanon
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Quote:
Originally Posted by Bibio View Post
input wires - is the shield connected at both ends?
No, not connected to anything, btw, the wires in question are from the RCA post to the boards.

Quote:
Originally Posted by Bibio View Post
power wires - loose ground wire? explain a bit more
loose as in not twisted with the positive and negative wires

Quote:
Originally Posted by Bibio View Post
comm ground - i thought that this has to be connected to the phono ground connectors or the casework.
For the time-being, no case and no turntable connected.

Quote:
Originally Posted by Bibio View Post
if there is no earth wire in Lebanon then i would presume you don't connect the earth wire to the chassis.

earth and ground should not be connected to the same case and only earth to the power supply case if separate and if same case then no earth, since you don't have an earth in Lebanon then you cant earth the case
Thanks for the tip

Quote:
Originally Posted by Bibio View Post
i would use 2 core rather than 3 for power.
Can you explain a bit more please

I'll short the inputs and report back too.

Thanks

Nick
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Old 19th April 2013, 01:23 PM   #2386
AndrewT is offline AndrewT  Scotland
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Where you have no Protective Earth you are in effect building ClassII equipment.

I recommend that everything is insulated so that one can never accidentally touch a part that has become Live due to a wiring breakage/fault.
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Old 19th April 2013, 01:33 PM   #2387
Bibio is offline Bibio  Scotland
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if you only have live and neutral in Lebanon coming from the mains then there should not be an earth wire so you would use 2 core mains cable from household mains to the power supply. do not use the comm to 'earth' the supply case.

the comm should be connected to the turntable ground and phono amp case but since there is no turntable connected and no metalwork then it should not be connected as far as i know.

as far as i know shielded cable has to be terminated at one end only, but i could be wrong.
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Old 19th April 2013, 05:56 PM   #2388
hajj is offline hajj  Lebanon
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So,
Shorted the inputs, hum is nearly gone, just a tiny bit remains and I have to stick my ear to the speakers to hear it, or turn the amp volume higher than I usually need to.
Next step?
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Old 19th April 2013, 06:17 PM   #2389
Dimitris
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check your turntable's grounding
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Old 20th April 2013, 05:36 AM   #2390
rjm is offline rjm  Japan
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Quote:
Originally Posted by hajj View Post
So,
Shorted the inputs, hum is nearly gone, just a tiny bit remains and I have to stick my ear to the speakers to hear it, or turn the amp volume higher than I usually need to.
Next step?
Put it in a metal case, and connect it up. You should be good to go.

Phono preamps, even MM stages like the VSPS, must be fully shielded to operate hum free. You cannot expect them to have a quiet output when open on the workbench.
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