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Old 12th September 2006, 03:03 AM   #1
henkel is offline henkel  Malaysia
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Default Tranny Qs?

Hi!

When wiring transformer power to balanced(XLR) audio board with on board regulators, I am experiencing hum when tapped from a single tranformer. An advise that I got was to run another transformer or to make a transformer with individual taps to the balanced audio boards.

Questions is why would there be hum if the transformer tap is shared?

Can anyone help enlighten me?

Thanks for reading.
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Old 12th September 2006, 03:53 AM   #2
singa is offline singa  Singapore
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Hi,
It's hard to help when the information available is minimal. Hum usually results when there is improper ground termination or adding other equipment which cause ground loops.Here are additional information which you need to supply in order to get help.
1. What is it you are connecting?Actual setup?
2. When do you hear hum?Loud/soft hum?
3. Cables checked for good termination? No frayed ground wire touching signal lines like balance cable.Broken or about to break cables/connectors?

Photos would be helpful.
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Old 12th September 2006, 07:33 AM   #3
henkel is offline henkel  Malaysia
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Singa,

Thanks for the reply, here is more details of what I've done.

I am building a pre-amp using the V-3310 volume kit (Balanced) from http://eshop.diyclub.biz/. I also bought the 50VAC R-core tranny said to be design matched for the V-3310 with 2x12V and 2x9V tabs. The V-3310 only needs 2x12V and 1x9V tab per board.

If you could see from the photos provided in the webpage, the V-3310 balanced has 2 boards and will require double the taps(as in 4x12V and 2x9V tabs) that one 50VAC R-core can provide. Hence I had to parallel the tabs at the R-core to wire up a pair of V-3310 for balanced.

The hum is rather high pitch.(slighty louder on the left chanel)
Cables are well terminated.(checked many times by my self and another friend)

I hope you can understand what I am trying to convey thru writing.

Please let me know what you think?
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Old 12th September 2006, 09:12 AM   #4
singa is offline singa  Singapore
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Hi,
As far as I can see from the photo of V3310 kit,it comprises of a signal board and a display board with a remote.Since it's a small picture I can't tell whether it takes so many AC inputs as you describe.There are simply too little input holes for the stated number of AC voltages.Since it has balanced outputs,I assume your power amp can accept balanced inputs?

Since this is a tested commercial kit it should work without problems if you followed the instructions to connect?Can you tell me how you connected the signal pcb giving position relative to the photo?It would help me a lot.To me I think the pcb only need a 12-0-12Vac as common input and the various regulators will do their job.Is this the case?What does the instruction sheet say?
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Old 12th September 2006, 04:58 PM   #5
henkel is offline henkel  Malaysia
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singa,

Yes, my power amp accepts XLR inputs, and my CDP also out puts in XLR. That's why I want to build this pre as balanced.

The boards take 2x12V(+/-) and 1x9V each.

One of the problems is that the instructions are poorly written in english, due to chinese text translation. that makes it very hard to comprehend.

Anyway, I think I may have found the problem, the input board is too near the display board. I found out by accident when I mutethe pr-amp, the display goes blinking and the hum blinks along with it!.

I'll try to build a sheild in the case work to separate the two boards tomorow. Let's see how it goes. Thanks.
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