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Pangloss
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Groove Tubes Valve Mic - Cable Type?
      #382217 - 17/11/06 09:01 PM
Hello everyone,

I recently bought a Groove Tubes Model 1B valve mic from ebay, which I was happy about as I have wanted one for a long time now. The thing is though that it didn't come with the mic-to-power suppply lead as I expected and I am beginning to resign myself to having to buy one.

I don't really want to pay over 45 quid for a cable so I want to make one up.

It is a male-to-female, 7-pin Neutrik XLR-type lead, of which 6 contacts are used (I presume 2 for the valve power, 2 for the phantom power and 2 for the signal - if this is wrong someone please correct me).

If this is the case, what type of cable will be the correct type to use?

Should the signal strands be shielded as they are running along side power strands (albeit DC)? Or is it OK to use all unshielded strands?

I have looked at Maplin and Studiospares catalogues and I haven't seen anything which jumps out at me.

Any help or advice appreciated.

Alec


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Steve Hill
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Re: Groove Tubes Valve Mic - Cable Type? new [Re: Pangloss]
      #382285 - 18/11/06 12:14 AM
Probably not premium quality cable but would this one get you going?

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Hugh RobjohnsAdministrator
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Re: Groove Tubes Valve Mic - Cable Type? new [Re: Pangloss]
      #382302 - 18/11/06 02:23 AM
Quote Pangloss:

It is a male-to-female, 7-pin Neutrik XLR-type lead, of which 6 contacts are used (I presume 2 for the valve power, 2 for the phantom power and 2 for the signal - if this is wrong someone please correct me).




There won't be any phantom power for a start. Two wires will certainly be for the balanced mic output signal, and they need to be a twisted pair, possibly with a separate overall screen. A third connection will be for that audio earth.

Then there will probably be two more for the valve heater. That makes five so far. And one more for the anode voltage (probably using the audio earth for the return).

However, there are variations on the theme, so you really do need to make sure you know what is on what wire and what the cable construction is if you want the mic to recah the published specs.

Also, bear in mind that the anode voltage could be a hundred volts or more, so the soldering needs to be neat and reliable, and the pions need to be sleeved properly.

Quote:

Should the signal strands be shielded as they are running along side power strands (albeit DC)? Or is it OK to use all unshielded strands?




Individual wires can be unshielded because the power rails are usually all DC (although the heaters could be 50Hz AC). There will certainly be an overall screen though. Some cables shield the aduio pair separately.

hugh

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Steve Hill
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Re: Groove Tubes Valve Mic - Cable Type? new [Re: Pangloss]
      #382338 - 18/11/06 09:25 AM
Hugh - before the original poster seizes on my suggestion to get a cheapo Thomann cable as a stopgap, do you know if there is any official convention (AES?) about pin wiring these 7 pin cables? So (assuming all use Neutrik plugs) are the cables interchangeable between say an AKG Solidtube, a Neumann M147, a Groove Tubes, a T-bone etc?

In short, is there any chance of an inconsistency which could result in say the valve heater power going to the mic capsule with unfortunate results? A brief google search drew a blank. And this thread got me thinking that it might not be a bad plan to have one or two spare 7-pin cables in the studio....

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Pangloss
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Loc: London
Re: Groove Tubes Valve Mic - Cable Type? new [Re: Pangloss]
      #382348 - 18/11/06 10:03 AM
Thanks Hugh, thanks Steve,

Yes I suppose what I was really asking is whether or not there is a convention for this kind of thing. Given the way that even with 3-pin XLRs many people can't agree on which is hot or cold or whether to include the shield in the signal path etc. I just thought it safer not to make any assumption for 7-pin XLRs.

However, the Thomann cable at that price looks more tempting than getting the soldering iron out. Thanks for the link Steve. It will be very handy if that is suitable in my case.

Thanks Hugh for the info - yes I forgot about valve heaters. Which voltage is used to provide the potential to the capsule? Is that the anode voltage you mentioned?

Sorry to sound thick - I've never taken one of these apart before.


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