Kingston

Hello,

I have a tube preamp with a mains switch on the front panel. Without going further into details, the situation is such that the switch resides very close to wiring that is VERY subject to the 220/240VAC signal, DI input and interstage gain pot for example. The switch obviously has the mains signal going to and forth the switch, thus doubling the problem. No matter how I move the wire around, I measure about +40dB of added 50hz mains hum (FFT display). If I move the wire (with switch) completely away from the troubled spot the hum completely disappears, no longer measurable.

1. The easiest solution would be to move the switch to the back of the panel. But the souffle is already eaten, the hole is drilled. And I do prefer the switch on the front side.

For academic reasons lets look for alternatives:

2. obvious solution to the problem is shielding the wire. I managed to remove about 30dB of the hum by shielding with this heavy duty transformer sheet I have. I fashioned it so that it completely covers the wire and the switch. Unfortunately this also creates weird occasional clicks in the signal. Not loud, but I can't ignore these either.

What is the best way to shield mains wires? Clearly I didn't do it correctly. What is the best shielding material for this?

3. The last brute force solution I thought of is remote relay based switch. I guess I could create a special 12VDC signal for the relays which would have no effect of the front panel wiring. This means constant standby current draw of course, which is not not ideal.

Tips and tricks appreciated. Any easy "slap-on" solutions?

Thanks,
Mike
« Last Edit: April 06, 2010, 07:41:50 AM by Kingston »


tv

Couldn't you just add a vertical piece of aluminium that would make a small "compartment" in the case for the power-line wires? Or at least test the idea with f.e. an unetched piece of FR2 (pcb-material).

If you sprinkle when you tinkle, please be neat and wipe the seat.

Kingston

The switch is somewhat in the middle of the front panel, and there's no room for a case-wide compartment. But I have seen aluminum pipes (square or circular) that would possibly fit there. I guess I could create a duct for the wire/switch this way.

tv

Yeah that would be awsome ... "The Kingston Duct" !

On the second thought, an "U"-profile would be even better in case of maintenance, but I think (if you are pedantic enough) that a "square pipe" with a cut in one of the sides (the top side) would be Just Fine for repairs etc....

or something like this:


from here:
http://www.elecdirect.com/search.aspx?q=Wire%20Duct

If Style-over-substance required, I think that some black anodized wire-mesh duct could look absolutelly stuningly badass..
« Last Edit: April 06, 2010, 12:48:55 PM by tv »
If you sprinkle when you tinkle, please be neat and wipe the seat.

mad.ax

And what about a mechanical remote?
You keep the switch in the back of the case where it does no harm, and you use some aluminium tubing in order to actuate it...
Obviously this would be easy with a rotary or push/push type switch... but would not work with a toggle...

Axel

Kingston

I think (if you are pedantic enough) that a "square pipe" with a cut in one of the sides (the top side) would be Just Fine for repairs etc.

I found this pipe from a store nearby. Still have to work that metal to test it. I really hate metal work. wish it wasn't such a big part of DIY.

And what about a mechanical remote?
You keep the switch in the back of the case where it does no harm, and you use some aluminium tubing in order to actuate it...
Obviously this would be easy with a rotary or push/push type switch... but would not work with a toggle...

I have no room for anything but a small toggle, so this is out of the question. Certainly food for thought for future projects. I have seen all kinds of odd looking pot extenders in audiophile builds. Now I know some of the reasons why they do that.

tv

Quote
I really hate metal work.



-------------------------------------------
Edit: re- actuating the on/off switch. Personally "I" wouldn't ever think of inserting "some thing" to the power-switch. Other controls, yes (unless this could be avoided "by design"). IMHO a power switch should stay as un-cluttered as possible, leads to it should be well shielded but accessable - in case of "emergency", I wouldn't want anything to go between ...


« Last Edit: April 07, 2010, 07:53:30 AM by tv »
If you sprinkle when you tinkle, please be neat and wipe the seat.

leadbreath

i hope im not talking out my arse here but have u tried using the nuetral instead of live for the switch??
f**k marlbro's and weed ill stick to smoking germanium and silicon

JamesW

Mike

Are the mains Twisted? Protect the small signal from the DI input with shield.
Subject to change with out notice

Tips and tricks appreciated. Any easy "slap-on" solutions?

A long time ago I had a similar problem with very expensive custom made instrument. The manufacturer recommended removing the mains switch and wiring but I didn't like the idea.

My solution was a battery operated bistable relay and (on)-off-(on) toggle switch in the front panel. A 9V battery lasts forever since the relay consumes power only when it is changing.


Kingston

i hope im not talking out my arse here but have u tried using the nuetral instead of live for the switch??

I always wire both wires to mains and use DPDT switches since there is no real "neutral" available. The mains VAC ground contains all noise and crap you can imagine so it might not work and will still contaminate the high impedance wires.

But certainly worth the experiment. Thanks for the tip.

Are the mains Twisted? Protect the small signal from the DI input with shield.

Yes of course they're twisted. Hey I even twist DC wires (but for convenience reasons).

My solution was a battery operated bistable relay and (on)-off-(on) toggle switch in the front panel. A 9V battery lasts forever since the relay consumes power only when it is changing.

If all else fails, this seems like the way to go. Thanks for the tip.

zebra50

This is probably a bit naughty, but I once solved a similar problem using a length of canare starquad cable from the inlet to the switch at the front - 4 wires shielded gives you there and back again. You'd need to check the current rating for your application, or just suck it and see if it's a DIY build.
Ribbon microphone services
http://www.xaudia.com
Microphone blog

Kingston

i hope im not talking out my arse here but have u tried using the nuetral instead of live for the switch??

I always wire both wires to mains and use DPDT switches since there is no real "neutral" available. The mains VAC ground contains all noise and crap you can imagine so it might not work and will still contaminate the high impedance wires.

But certainly worth the experiment. Thanks for the tip.

I just did this and it worked. I took just the "live neutral" ground to the front panel, and 220VAC went straight to transformer. Hum gone. Thanks leadbreath.

I have not done this in the past "for safety reasons". But now that I think about it, I can't see any way this could turn sour.

Could there be any problems with this type of wiring?

Could there be any problems with this type of wiring?

In most countries power plugs are not polarised. And the noise level in the "neutral" wire depends on the electric installations of the building. (Plus the safety issues already mentioned.)

Kingston

I think I will leave this particular amp be for now. I measured about 0.1VAC of crap between safety ground and live ground. As far as I know in europe we live "polarised".

If anyone knows, I would like to know what exact safety issues there might arise with wiring like this.

I still will keep wiring dual switches for my future projects.

As far as I know this type of unpolarised plug is used in most European countries (except UK and maybe some others):



Dual switching is recommended (if not mandatory) because you can't be sure which pin is live and which is neutral.

Fuse in both wires is always a good idea (and especially if you are using a single pole switch).

Kingston

Dual switching is recommended (if not mandatory) because you can't be sure which pin is live and which is neutral.

Doh! What a stupid mistake, should have thought it further. Yes of course dual switches are mandatory.

And it makes this "neutral wire" hack pointless. if I plug it in "mirrored" the neutral wire (no longer neutral) going to front panel leaks VAC to high impedance circuits, again.

minus 10 points to Kingston, and go sit in the corner!  >:(

tmuikku

Dual switching is recommended (if not mandatory) because you can't be sure which pin is live and which is neutral.
minus 10 points to Kingston, and go sit in the corner!  >:(

hehe :) Seems like old hi-fi "myth" could apply in this case: If there is hum try to rotate mains plug

leadbreath

hi guys

kingston, im glad to hear i could b of assistance? though reading thru this post im not really sure if i did or not. ???

ive seen the 2-pin outlets on mainland europe, but arent these meant tp be for "class 2" appliances ie: made with only plastic? if u use any metal appliance arent u meant to use the 3-pin one with the earth available? id be a bit wary installing any audio(especially metal enclosed) gear into a 2-pin outlet as effectivley u dont have atrue earth???

just my 2 cents

mick
f**k marlbro's and weed ill stick to smoking germanium and silicon

tv

http://en.wikipedia.org/wiki/Schuko
http://en.wikipedia.org/wiki/Europlug

Got to be Schuko.

Wise men say, only fools rush in.
If you sprinkle when you tinkle, please be neat and wipe the seat.


 

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