Cable type vs noise pickup
- Thread starter jwhmca
- Start date
Help Support GroupDIY Audio Forum:
If balanced twisted pair is always nice in noise performance, but higher capacitance and in some applications may won't be the better choice... Ive seen 4 twisted wires (I have a pair of those for my monitors) and opposite pair used as same conductor in order to get closer electrical space of both conductors and get a better noise rejection (at the input stage) but again higher capacitance...
I'd like to know the aplication and the space where we are talking about... Air is always a good noise screen if you put enogh of it between the source and the receptor.
JS
I'd like to know the aplication and the space where we are talking about... Air is always a good noise screen if you put enogh of it between the source and the receptor.
JS
Well, It's the output of a little 8 channel mixer, internal, to the I.O. PCB. But the cable runs right over the mains transformer and can't really be moved very far from it without a major pain. It used to be a flat cable. I replaced it with a twisted set of leads, about 12
If the ribbon has pairs adjacent twisted pair won't help much.
If the noise is from the transformer, it is the magnetic field probably making the hum so run the cable farther from the transformer, even if it must be longer.
Alternatively you could shield the cable, perhaps wrap a couple of layers of mu-metal foil around it?
The only other thing I can suggest is that often transformers radiate asymetrically, so simply moving the cable to different positions relative to the transformer may make a difference. (this is why folks rotate toroidal transformers to minimize hum).
If the noise is from the transformer, it is the magnetic field probably making the hum so run the cable farther from the transformer, even if it must be longer.
Alternatively you could shield the cable, perhaps wrap a couple of layers of mu-metal foil around it?
The only other thing I can suggest is that often transformers radiate asymetrically, so simply moving the cable to different positions relative to the transformer may make a difference. (this is why folks rotate toroidal transformers to minimize hum).
You can sheild your transformer with cupper tape around it (any EI or toroidal)
You also should try moving it aroun at least to be sure that the noise came from here.
Low Z output shouldn't be sensitive to noise... if output op amp has a couple of resistor for decoupling the output replace them with OLI as jensen's (33 or 39Ω 1W carbon resistor and 40 turn of wire around it, must be carbon 1W because of diameter, around 5mm I guess)
JS
You also should try moving it aroun at least to be sure that the noise came from here.
Low Z output shouldn't be sensitive to noise... if output op amp has a couple of resistor for decoupling the output replace them with OLI as jensen's (33 or 39Ω 1W carbon resistor and 40 turn of wire around it, must be carbon 1W because of diameter, around 5mm I guess)
JS
It depends on the circuit... Single conductor, worst is loose wire, best shielded with grounded shield.jwhmca said:
For balanced pair or signal with ground, twisted pair offers some first order cancellation of noise pickup.
In general if dealing with hum pick-up by sensitive circuits the answer is neither (use shielded cable). For general purpose low impedance audio twisted pair is pretty effective (like POTS phone lines).
JR
PS Adding copper foil around a transformer, is called a shorting turn because it in effect shorts out the magnetic field. That shorting turn is often grounded.
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