OT: Diode Question

[Alan]

I'm pleased it's sorted. What you described was a classic situation of 
that type. So easy for some to spot, but totally perplexing for anybody 
who hasn't seen it before.

Disconnecting pin 1 at one end of the lead is all you need to do. It's 
best to make sure the other end is connected though, but with a lead 
just a foot long, nothing too bad is likely to happen anyway. Grounding 
is far less critical with balanced audio.

Under the circumstances you describe, it's unlikely that you'll get any 
advantage from using a DC-Dc converter or a transformer. The ground 
lift should be fine.

You'll also need to ensure that you don't get accidental shorts if a 
grounded metal part of the receiver were to touch a metal part of the 
camcorder. Usually there's enough plastic parts to make that unlikely.

Alan



On Friday, May 27, 2005, at 22:12 Europe/London, Eric Galli wrote:

> You figured it out! If I unplug the XLR audio cable from the camera to 
> the receiver, the light and receiver turn off. It appears that the 
> wireless receiver tied the (-neg) power and  the XLR ground (pin 1) 
> together. What I did was a full ground lift and disconnected pin 1. It 
> now seems to be working properly. This is (was) a balanced audio 
> connection. What negative effect will this have on audio quality? It 
> is a very short cable, only 12 inches. I don't think such a short 
> cable will pick up any interference.
>
> I did a quick search on DC-DC converters and found a lot of different 
> types. I really need to keep this small and light. Cheap would be a 
> real bonus too.
>
> Thanks so much!
>
> -E-
>
> On May 27, 2005, at 3:04 AM, Alan Taylor wrote:
>
>> DC equipment uses just a supply rail and Ov. Looking at it from the 
>> point of view of the battery, one will be the positive and the other 
>> the negative. There isn't a specific ground connection.
>>
>> Could it be that you're in a situation where the camera might be 
>> regarding the negative line as ground, while the radio mic is 
>> regarding the positive as ground, or the other way round ?
>>
>> In such a situation, the ground connection from the audio output of 
>> the radio Rx will be shorting the power supply when it's all 
>> connected together.
>>
>> One way of checking would be to unplug the radio Rx audio connection  
>> from the camera, but leave the power connection made. If the Rx 
>> initially works and then goes wrong when you connect the audio, you 
>> have your answer.
>>
>> If that's the problem, possible cures might be either a DC-DC 
>> converter to float or invert the polarity of the power to the RX, or 
>> to use a small audio transformer to float and isolate the audio 
>> connection between the Rx and the camera.
>>
>> Alan
>>
>>
>> On Friday, May 27, 2005, at 01:37 Europe/London, Eric Galli wrote:
>>
>>
>>> Maybe one of you engineering types can help me out.
>>> My video camera has an accessory port to supply power to external 
>>> devices such as a light. I tapped into the power cable and added a 
>>> power tap for a wireless microphone receiver. The camera also has 
>>> the ability to toggle the power to this power port based on if the 
>>> camera is recording or not. It all works until I actually plug in 
>>> the power cable for the wireless receiver box. I think there is some 
>>> current leaking back to the camera or some noise, confusing the 
>>> circuit that controls the accessory power state. So my question is, 
>>> could I put a diode in line to try and isolate the wireless receiver 
>>> power from the camera power circuit.
>>>
>>> -E-
>>>
>>>
>>
>>
>