I am using the same dual motor turntable for almost 8 years now. In the past, I use a Kotseu Rosewood cartridge until a few years ago, I switched to VDH Colibri. After changing, I can denote low frequency noise from the speaker whenever I turned on the motor. Although the noise is very low and it reduces when the cartridge move away from the edge of LP towards the center, I feel it is annoying.
Recently, people told me I can shield motor RFI (I don't know if it is RFI or not) by wrapping the motor assembly with mu-metal. I purchased a small roll of mu metal foil (with adhesive back) and covered the motor assembly, noise level further reduced but not eliminated.
Is the noise RFI?
Is mu-metal foil capable to shield off RFI?
Is there different kind of mu-metal foil that some can provide better shielding? What brand is it?
One last question, why I can't denote the noise from Kotseu and can hear it when I changed to VDH?
Recently, people told me I can shield motor RFI (I don't know if it is RFI or not) by wrapping the motor assembly with mu-metal. I purchased a small roll of mu metal foil (with adhesive back) and covered the motor assembly, noise level further reduced but not eliminated.
Is the noise RFI?
Is mu-metal foil capable to shield off RFI?
Is there different kind of mu-metal foil that some can provide better shielding? What brand is it?
One last question, why I can't denote the noise from Kotseu and can hear it when I changed to VDH?
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It's probably mostly magnetic and induced into the pick up coils in your cartridge, it could have a lot to do with the internal design of the cartridge and placement of the coils. Stronger magnets, smaller coils = less hum susceptibility, orientation and compactness play a role, some cartridges may deliberately or inadvertently provide some resistance to magnetic fields in certain planes.
You could try adding some more tape, and perhaps covering areas you had not previously. Watch out for motor overheating if you block ventilation holes in the motor (if they even exist.
Some cartridges may also have higher dcr which could make unshielded pick up wiring more susceptible to electrostatic coupling. Grounding the motor casing could help here.
I have also had MC cartridges that were susceptible to hum pick up and others that were not.
You could try adding some more tape, and perhaps covering areas you had not previously. Watch out for motor overheating if you block ventilation holes in the motor (if they even exist.
Some cartridges may also have higher dcr which could make unshielded pick up wiring more susceptible to electrostatic coupling. Grounding the motor casing could help here.
I have also had MC cartridges that were susceptible to hum pick up and others that were not.
Perhaps You hear some sort of rumble (vibration) and not hum ...check also the arm shielding. Try shielding the cartridge shell itself with the tape in order to determine if it is magnetic coupling of some sort. Move the arm above the disc with the hand isolated if You must touch the metal. Be Careful to not damage the stylus.
When I moved the tonearm away from the motor, the noise reduced. I also tried to take away all silicon bands so the turntable is not spinning. The noise is there when I switch on the motor, even if I lifted the motor above the table. In these respects, I believe it is hum.
There are a number of different brands of mu-metal in the market. I tried one with little achievement but I can't try all of them in the market. Is there anyone tried with good success to reduce noise from motor? Actually, do I need RFI shielding or electromagnetic shielding?
There are a number of different brands of mu-metal in the market. I tried one with little achievement but I can't try all of them in the market. Is there anyone tried with good success to reduce noise from motor? Actually, do I need RFI shielding or electromagnetic shielding?
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If it is low frequency then it isn't RF so more likely magnetic field.
Is the turntable base earthed ?
Is the turntable base earthed ?
The turntable is sitting on a piece of marble, then on a peace of heavy metal called ISOPLANE not earthed, then sit on a HiFi Rack not earthed.
I saw the description of mu-metal foil saying they can shield RF and magnetic field but when I tested them right now, the mu-metal foil with adhesive back is not able to stop the magnetic field from my screw driver to an iron washer on the other side. The mu-metal sheet that I purchased from Percy is actually being attracted to the screw driver.
In these respects, can I say they are not able to shield magnetic fields?
Should I look for other alternatives?
Any suggestions?
I saw the description of mu-metal foil saying they can shield RF and magnetic field but when I tested them right now, the mu-metal foil with adhesive back is not able to stop the magnetic field from my screw driver to an iron washer on the other side. The mu-metal sheet that I purchased from Percy is actually being attracted to the screw driver.
In these respects, can I say they are not able to shield magnetic fields?
Should I look for other alternatives?
Any suggestions?
Mu metal is simply high mu metal. It is not a magic shield. It diverts the magnetic field so that the field preferentially goes through the mu metal. Used wrongly it could increase magnetic coupling - just like an ungrounded electric field 'shield' can make things worse.
It easily saturates, so generally it is best to put it at the 'receiver' end of the magnetic problem where fields are weaker
As soon as you bend it, it loses mu so is less effective.
It easily saturates, so generally it is best to put it at the 'receiver' end of the magnetic problem where fields are weaker
As soon as you bend it, it loses mu so is less effective.
I have found some of the materials these guys sell to be highly useful:
LESSEMF
In particular Giron which can be bent without degrading its performance and can be used to make boxes, etc. It's fairly effective.
The site is shall we say "interesting".... The products however work extremely well and are quite popular in engineering labs around here.
LESSEMF
In particular Giron which can be bent without degrading its performance and can be used to make boxes, etc. It's fairly effective.
The site is shall we say "interesting".... The products however work extremely well and are quite popular in engineering labs around here.
Mu-metal diverts *varying* magnetic fields.
It won't block steady fields like a magnet.
Magnetic fields like to go around magnetic shielding. You need to form a nearly closed box to reduce that hum.
It won't block steady fields like a magnet.
Magnetic fields like to go around magnetic shielding. You need to form a nearly closed box to reduce that hum.
Noted with thanks on all the input. I think I will try Giron but it takes time to send from USA to Hong Kong. Can only wait.
Actually, the mu-metal foil I am using has reduced the hum to a great extend. Right now, I have to turn on the volume to 2 o'clock that the hum is becoming not acceptable while I am listening comfortably at 10 o'clock position. At 10 o'clock, I can only hear the hum 6 inches from the speaker that I can accept.
Actually, the mu-metal foil I am using has reduced the hum to a great extend. Right now, I have to turn on the volume to 2 o'clock that the hum is becoming not acceptable while I am listening comfortably at 10 o'clock position. At 10 o'clock, I can only hear the hum 6 inches from the speaker that I can accept.
Either I have just learnt something I didn't know, or you have got it wrong. I thought mu metal is simply an alloy with very high mu, so thin sheets of it can do the same job as thick sheets of soft iron.PRR said:
Not sure I understand exactly what "noise" is perceived here, is it like white/pink/brown noise or some other type of HF noise, or did you mean low frequency mains hum, or both?
You say the noise appears when switching on the motor, besides potential mains frequency hum perhaps there's a lot of HF garbage on your mains supply, you could try a mains filter too.
You say the noise appears when switching on the motor, besides potential mains frequency hum perhaps there's a lot of HF garbage on your mains supply, you could try a mains filter too.
When you remove the belts, You are actually "undamping" motor shaft vibrations. Do You hear a brrrr ? ... What happens if you stop the shaft by hand ?
Instead of buying other materials to try, I opened the motor assembly today and use the mu-metal foil that I purchased earlier to cover the motor top and side. After putting everything back, the hum is better again. I think I can live with it since at listening level, I can hardly denote the hum anymore.
At the bottom of the motor, it labels SMR 300-100, Made in Czech Republic. Is it a good motor? Is there any better replacement?
An externally hosted image should be here but it was not working when we last tested it.
At the bottom of the motor, it labels SMR 300-100, Made in Czech Republic. Is it a good motor? Is there any better replacement?
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