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Old 27th February 2003, 08:27 AM   #1
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Default help me modify my phono amp.(Please)

I've been thinking of modifing my Sonneteer phono stage.Housed in a full sixe case there is a transformer at one end and the circuitry in the other.
I was thinking of either removing the transformer or the circuitry and putting them in a seperate box.
If say i put the circuitry in a seperate box is plastic best?
Could I build a sheild of copper linked to the ground?Do I ground the cartridge on the power supply box or the circuit with a wire leading to the power supply ground?
As you can see I am a novice at this but it doesnt look too hard , just cut the wires from the transformers make a plug join the wires via the plug to the circuit board and place it in a different box.
But is there more too this and is it worthwile?
I see that most high end phono stages have a seperate box for power supply to keep it far away from the circuits so is this a good route?
Also i often pick up radio broadcasts on the MC input will moving the circuit from the power supply solve this?
Any other suggestions?
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Old 27th February 2003, 09:22 AM   #2
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If you don't have any problems with hum, don't remove the transformer.

AM radio problems: Remove the pickup and shorten the input.

Do you still hear the radio?
No, the pickup and the cable is involved.
Yes, the has problems. The first thing I can think of of is unsufficient decoupling av the power supply voltage, either too little, bad caps or wrong placement. The amp may be shielded more.

You may need a mains filter.

Since you use MC you could app up to 1-10 nF as input load. You could also add inductors but this is the last thing I would do becauce I hade to break signal paths and/or power wires.

Is the amp CE approved?
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Old 27th February 2003, 06:46 PM   #3
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As peranders said, if no hum, keep it that way.

Also check the cables and connectors. Maybe there is a loose ground connection. Try a different cable, with a good shield. Try adding a seperate ground connection between the TT and the preamp. Check the cartridge. Some have a ground connection between one of the 4 pins and the arm. Try gounding or not the cartridge.

As you may guess, endless thing to try.
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Old 27th February 2003, 07:39 PM   #4
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Default Ground

I have a ground connector on my pre amp .When you say try a seperate connector on your pre amp do I connect to both phono amp and pre amp or just pre amp?
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Old 28th February 2003, 11:25 AM   #5
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With preamp I mean the amp where you plug-in the TT, so it would be the riaa stage. I your case the phono amp.

If you have a separate ground connection on it, try connecting a thick (0.75mm^2 or so) from the chassis of your TT to that ground post on the phono amp.
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Old 28th February 2003, 12:01 PM   #6
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Hi sleepy,
I once modified my Mark Levinson JC1 AC moving coil cartridge preamplifier by installation of a few turns of wire on a ferrite bead and a small silver mica cap to ground after that in the signal iput leads.
The mysterious voices in the background were gone and sound improved too!
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