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I have already posted something but it got blocked because the spam filter thought it was spam (it was that long sorry) so here is the very expurgated version.
Take a 10nF disc ceramic capacitor and connect it from one side of the motor power supply (either side will do) to the earth terminal on your amplifier. This cures the problem completely- I have just tried it.
It must have a voltage rating in excess of 15V and it must be a disc ceramic component (low series inductance). This takes the awful electrical racket to earth once and for all.
Take a 10nF disc ceramic capacitor and connect it from one side of the motor power supply (either side will do) to the earth terminal on your amplifier. This cures the problem completely- I have just tried it.
It must have a voltage rating in excess of 15V and it must be a disc ceramic component (low series inductance). This takes the awful electrical racket to earth once and for all.
Hi
Here we have capacitive coupling between the supply and the sensitive input stage of a phono amplifier. Only a few micro volts would be sufficient to cause a problem that would be noticeable. After all full output is achieved with an input of only 5mV rms!
This will work on any turntable. I have completed the modification and there is no hum even with the volume control turned fully up.
I agree that a Rega would be much better but I couldn't find one locally. I work in electronics so resolved to find a solution and hopefully this will help others who are lumbered with one of these things
The problem is twofold. First there is inadequate screening within the turntable. Around the cartridge connections this is unavoidable with any turntable so it is vital that the cartridge lives in an electrically quiet environment. Using a switch mode power supply connected to the mains is a disaster waiting to happen. The power lead is screened but the radiation is from the negative and positive supply lines ie the screen itself acts as a transmitting aerial.
I cut open the plastic insulation near the power connector plug, eased the outer screen wire (negative supply) away from the inner wire, tinned a small area of the screening wire and soldered one side of a 40nF (0.04uF) disc ceramic capacitor to that. I soldered a wire to the other side of the capacitor and connected this to the earth terminal on the turntable. I covered the whole thing in heatshrink sleeving to add strength. Result no hum whatsoever! The low reactance of the capacitor allows the transients and high frequency harmonics to pass gratifyingly to earth where they are buried forever-and good riddance. Use a disc ceramic because these are ideal for decoupling noisy supplies by virtue of their low series inductance. The hum is not just good old 50Hz although the fundamental is certainly 50Hz. You can hear that there are higher frequencies involved because the hum has a rasping buzzy nature,m not just a smooth sinewave type hum. This can only come from the cheap and nasty power supplies used by these cheapskate manufacturers.
Here we have capacitive coupling between the supply and the sensitive input stage of a phono amplifier. Only a few micro volts would be sufficient to cause a problem that would be noticeable. After all full output is achieved with an input of only 5mV rms!
This will work on any turntable. I have completed the modification and there is no hum even with the volume control turned fully up.
I agree that a Rega would be much better but I couldn't find one locally. I work in electronics so resolved to find a solution and hopefully this will help others who are lumbered with one of these things
The problem is twofold. First there is inadequate screening within the turntable. Around the cartridge connections this is unavoidable with any turntable so it is vital that the cartridge lives in an electrically quiet environment. Using a switch mode power supply connected to the mains is a disaster waiting to happen. The power lead is screened but the radiation is from the negative and positive supply lines ie the screen itself acts as a transmitting aerial.
I cut open the plastic insulation near the power connector plug, eased the outer screen wire (negative supply) away from the inner wire, tinned a small area of the screening wire and soldered one side of a 40nF (0.04uF) disc ceramic capacitor to that. I soldered a wire to the other side of the capacitor and connected this to the earth terminal on the turntable. I covered the whole thing in heatshrink sleeving to add strength. Result no hum whatsoever! The low reactance of the capacitor allows the transients and high frequency harmonics to pass gratifyingly to earth where they are buried forever-and good riddance. Use a disc ceramic because these are ideal for decoupling noisy supplies by virtue of their low series inductance. The hum is not just good old 50Hz although the fundamental is certainly 50Hz. You can hear that there are higher frequencies involved because the hum has a rasping buzzy nature,m not just a smooth sinewave type hum. This can only come from the cheap and nasty power supplies used by these cheapskate manufacturers.
If it's the one I'm thinking of, that was just to stop rumble from the motor, on account of the fact it's decoupled from the chassis with an elastic band like something John Noakes might have built on Blue Peter.BigH said:
Yup, that's the one. (Although all motors are decoupled using a suspension belt - that kit adds sorbothane dampers between the motor and the chassis).
The electrical hum above half volume issue described, that is present on a small amount of Debut Carbons (compared to volume sold), and was addressed by Pro-Ject in manufacturing well over a year ago now.
As I mentioned elsewhere, these units should be returned to the dealer where they can be sent back to the local service center to be resolved.
PS - Nice work Tannoyed !
The electrical hum above half volume issue described, that is present on a small amount of Debut Carbons (compared to volume sold), and was addressed by Pro-Ject in manufacturing well over a year ago now.
As I mentioned elsewhere, these units should be returned to the dealer where they can be sent back to the local service center to be resolved.
PS - Nice work Tannoyed !
I had this problem years ago on an old Thorens turntable, and found disconecting the earth lead (green) from the mains plug cured the problem. However, i'm no electrician so I would seek advice on safety issues.
Hello, can you show a photo how you did that.
"I cut open the plastic insulation near the power connector plug, eased the outer screen wire (negative supply) away from the inner wire, tinned a small area of the screening wire and soldered one side of a 40nF (0.04uF) disc ceramic capacitor to that. I soldered a wire to the other side of the capacitor and connected this to the earth terminal on the turntable. I covered the whole thing in heatshrink sleeving to add strength"
"I cut open the plastic insulation near the power connector plug, eased the outer screen wire (negative supply) away from the inner wire, tinned a small area of the screening wire and soldered one side of a 40nF (0.04uF) disc ceramic capacitor to that. I soldered a wire to the other side of the capacitor and connected this to the earth terminal on the turntable. I covered the whole thing in heatshrink sleeving to add strength"
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