Almost Cornet: choke shielding question

gurevise · « **on:** 30 Dec 2003, 02:19 am »

Guys,
I have implemented CLC power supply filter in my Cornet.
Do you know if I need to shield wires running to and from choke ?
Here is a picture of the board with choke mounted next to it.
Wires run about 4 inches.

[img]http://home.att.net/~gurevise/public/choke_wires.jpg[/tag]

Thanks
Sergey

gurevise · « **Reply #1 on:** 30 Dec 2003, 02:31 am »

Guys,
What do I do wrong here that image does not appear in my post ?
I see that BBCode is enabled and I enclose link between tags:
[img] link [/tag]
Help !!!!

Sergey

Marbles · « **Reply #2 on:** 30 Dec 2003, 02:36 am »

Quote from: gurevise

Guys,
I have implemented CLC power supply filter in my Cornet.
Do you know if I need to shield wires running to and from choke ?
Here is a picture of the board with choke mounted next to it.
Wires run about 4 inches.

Thanks
Sergey

Segey, where you had[/tag] it should have been [/img]

gurevise · « **Reply #3 on:** 30 Dec 2003, 02:57 am »

Thank you Marbles,

So, back to my original question:
Do I need to shield wires going to and from choke ?

Thanks
Sergey

mgalusha · « **Reply #4 on:** 30 Dec 2003, 03:38 am »

Sergey,

Since the current flowing through the choke and it's wires is DC, shielding shouldn't be needed. At least in my mind.

mike g

hagtech · « **Reply #5 on:** 30 Dec 2003, 05:08 am »

I don't think you'll need shielding. Just tie wrap the leads together.

The issue will be stray magnetic flux. The location is good (away from front end), but orientation might be an issue. This choke construction has strong fields out the top and bottom, nulls on sides. As mounted, the spray is headed out towards the input tube. Fortunately, you have distance working to your advantage and will probably be ok.

I always measure transformers and chokes for their external stray fields. You can always find a cancellation null. I did that for the power transformer. It's null is straight along the line of tubes, which is exactly why they are inline.

For measuring, I use a many-turn RF coil connected to a Tek 7A14 current probe amplifier. Ok, so you don't have one of these, but you could still probably connect the output to any scope input or even a DVM. It measures the 60Hz and 120Hz fields.

jh

gurevise · « **Reply #6 on:** 30 Dec 2003, 02:57 pm »

Thank you for very, very informative info.

Jim,
If I were to make RF coil probe to test magnetic field, I'm sure it would prove your statement about magnetic field orientation. But, it would not help me with what level of magnetic field is acceptable and what not, as this DIY measurement tool would be very inaccurate.
So, I'm thinking of two "real life" test scenarios.
First one is to short RCA inputs with 1k (for MM cart) resistor and see the noise/signal level at the outputs. This would measure how much of a signal is induced from power supply internally.
The second one is to use 3 feet phono cable, terminated again with 1k resistor (to simulate cartridge) connected to the inputs. Again, measure output signal. This, hopefully, would tell me if I get electromagnetic interaction from power supply (choke and transformer) to the input cable.

Any comments on these two test ideas?

Thanks
Sergey

hagtech · « **Reply #7 on:** 30 Dec 2003, 06:50 pm »

Yes, that's how we measure SNR. Short the inputs. It's easy and lets you measure added noise (noise factor for your RF junkies).

jh