I have spent quite a while puzzling over hum pick-up when listening to turntable.
Initially blamed turntable grounding.
After reading a post suggesting to check nearby equipment as a source of the hum I investigated.
Turns out my telephone base (landline with removable handset) was the source. Rotating the base in 3 axes causes the hum to come and go.
Moving my hand near the base likewise - moving a few cm goes from loud to silent. Moving base to opposite side of room made no difference.
Short of moving the base to another room, any suggestions? Base is powered by wall SMPS so not transformer hum. Unplugging base from power and the hum totally disappears.
Initially blamed turntable grounding.
After reading a post suggesting to check nearby equipment as a source of the hum I investigated.
Turns out my telephone base (landline with removable handset) was the source. Rotating the base in 3 axes causes the hum to come and go.
Moving my hand near the base likewise - moving a few cm goes from loud to silent. Moving base to opposite side of room made no difference.
Short of moving the base to another room, any suggestions? Base is powered by wall SMPS so not transformer hum. Unplugging base from power and the hum totally disappears.
That´s annoying.
*Just in case* noise is some SMPS emission, test your phone base powered from a conventional supply.
If it comes from the base, you will unfortunately have to move it farther away or maybe you can make some shield (kitchen aluminum paper glued to some wood and grounded).
Here experiment beats calculation so .... hands on and try different ideas 😉
You might also try to shield the turntable itself, or at least its arm or pickup.
*Just in case* noise is some SMPS emission, test your phone base powered from a conventional supply.
If it comes from the base, you will unfortunately have to move it farther away or maybe you can make some shield (kitchen aluminum paper glued to some wood and grounded).
Here experiment beats calculation so .... hands on and try different ideas 😉
You might also try to shield the turntable itself, or at least its arm or pickup.
Maybe your phono input needs an RF filter. Alternatively, can you try a different PSU for the phone base?
I'll experiment some more when I get the time.
Worst case I'll run an extension upstairs and swap the master/slave bases.
The slave base doesn't seem to interfere.
Worst case I'll run an extension upstairs and swap the master/slave bases.
The slave base doesn't seem to interfere.
Can't you put far away both telephone base and turntable? It seems to be the easiest way to avoid interference. EMI decreases with the distance squared.
There was recently a similar discussion on a Dutch forum. Apparently DECT telephones and base stations emit bursts that repeat at a frequency that sounds like hum. The RF signal can get picked up by wiring and demodulated by any even-order non-linearity.
You can try shielding the phono amplifier and putting a ferrite ring around the incoming cable, as a common mode choke. The trick is to find a ferrite ring that works at DECT frequencies.
You can try shielding the phono amplifier and putting a ferrite ring around the incoming cable, as a common mode choke. The trick is to find a ferrite ring that works at DECT frequencies.
I can get the interference when putting the base at the opposite end of the room 4 to 5 meters away. I have a 'scope. This could be my first real use of it - viewing the signal from the phono output. See the shape and frequency. Probably this weekend I'll take a look.
Funnily enough it's a Philips base.
Funnily enough it's a Philips base.
I had a Philips DVD player which interfered with nearby AM receivers. It was worse when switched 'off' (but still plugged in to the mains). I took it back to the shop, described the symptoms and got a refund. I noticed that the shop assistant wrote "faulty" on the form as the reason for return. I bought a Sony and that was a lot better. Both items were made in China so I can only assume that Sony insist on better EMC performance than Philips.
IMO, the former set was not faulty. As part of "green technologies", recent devices must comply certain norms respect to stand by leak. Many modern switchers (An IC containing all parts including power, like TOPxxx devices and many other that uses external MOSFET's to the part), when light or no load, enters in a low frequency or burst mode in which the supply normally starts up, refresh output caps charge, saturates the opamp and then goes off some time depending on the load state of the device. This way, although noise generated is most important, power wasted in loading resistor(s) in the SMPS itself is reduced. As in a relaxation oscillator, low frequency oscillation will depend on mains voltage, hysteresis of the IC itself, load state and main (sensed) voltage output capacitor value.
Also, a PFC is included that pre-regulates the supply to the power main converter, normally synchronized with mains switcher, but not always. This is made for the following reasons:
1) PFC drains AC sine wave currents, as they only have small 1µF RF bypass capacitor following bridge rectifier.
2) They are designed to support 110 or 220V operation without manual or automatic switching (The BW of the PFC supports the full AC range).
3) It crudely pre-regulates the DC bus for the main regulator, and at roughly constant voltage, usually higher than the higher peak AC voltage expected, and between 380 and 400VDC)
Most manufacturers use PFC in off state when the device is in stand by and starts it when the set is fully powered on (Plasmas, LED, etc), but not all do those.
Also, a PFC is included that pre-regulates the supply to the power main converter, normally synchronized with mains switcher, but not always. This is made for the following reasons:
1) PFC drains AC sine wave currents, as they only have small 1µF RF bypass capacitor following bridge rectifier.
2) They are designed to support 110 or 220V operation without manual or automatic switching (The BW of the PFC supports the full AC range).
3) It crudely pre-regulates the DC bus for the main regulator, and at roughly constant voltage, usually higher than the higher peak AC voltage expected, and between 380 and 400VDC)
Most manufacturers use PFC in off state when the device is in stand by and starts it when the set is fully powered on (Plasmas, LED, etc), but not all do those.
If it radiates then it is faulty - unless it is supposed to be an RF transmitter, which a DVD player is not.
Moved some stuff & found a telephone socket I'd forgotten about.
So master base upstairs, slave base downstairs.
Interference gone. Heatwave now so blow measuring!
So master base upstairs, slave base downstairs.
Interference gone. Heatwave now so blow measuring!
Yes, I used "faulty" to include faulty design and deliberate omission of components to save money in the factory. In that sense the report written down when I returned it to the shop was accurate, although not very helpful. Perhaps I should have insisted that they wrote down "poor EMC performance".
All devices which handles signal in part are radiated. As an example, see the labels under your keyboard.
Yes, I know that any situation where charge is accelerated will cause radiation. However, good EMC design means that this will be small. In audio equipment there is no reason why it should not be very small, and even in a cordless phone the radiation should be limited almost entirely to the intended communication between the base and the handheld unit. A phone base which interferes with a phono preamp means at least one of them is faulty or poorly designed.
I agree, but sometimes it's impossible. For example, did you see what happens when a cell phone in near an audio system?
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