Valve Mic Cable for G7?

[marktokach]

Ok I will just hook the spiral shield to pin 1 and see what happens. Sure wish I could get someone to chime in here though. I know it seems obvious but I have never wired a tube mic cable and searched and did not find any info for sure. Guess it is to obvious for a response. :-\

 

[mad.ax]

>Marktokach
I am not familiar with the Mogami cable so I checked the specs here: http://www.mogamicable.com/Bulk/micr_cables/tubemic_cab/tubemicc.html
No wonder why I prefer Gotham GAC7, it has 7 conductors, where the Mogami has only 6!

Now, how do you wire a 6 conductors cable to a 7 pin connector is not really "obvious" since there are a lot of possibilities!
You may get more answers by telling us what mic you are building according to wich schematic?

The shielding spiral is suposed to be connected to ground in order to have a shielding effect, but it is not a good practise to carry current trough it.
Assuming you are building a tube mic, you need 2 conductors for audio, 2 for heater, one for B+, one for ground, and eventualy one for the capsule bias voltage if you have a remote patern selector.
You may also need to remotely switch a relay for instance...
So if you need a remote selector, I guess the obvious solution with the Mogami cable is to use the same wire for ground and heater 0 Volt. Take the big green one. That would leave the red one for B+ and the purple for remote...

Axel

 

[marktokach]

Well yes that does sound better to have all 7! I am building a G7 mic, that is why I posted in this thread, according to the Gyraf audio website. Pins 7 and 6 are heaters, 5 and 2 patterns, 3 and 4 audio. That leaves pin 1 which is ground which I guess I have to hook to the shield. Thanks for you response. Now I am thinking I should have got the Gotham. I got this because supposedly it's the best.

 

[mad.ax]

Sorry! I didn't pay enough attention to the thread tittle....
Well, since Jakob recommends the Mogami cable on his website, I guess there's no problem using it with wiring the HV and heater grounds together.
Then just forget about the remaining pin...

Axel

 

[marktokach]

Thank you very much! I appreciate it and all that is done on the site by everyone.

 

[zayance]

Hi there, just a stupid question, what will be a good length for the 7cond. Cable?

 

[Rob Flinn]

I normally work on 4-5 metres, figuring that the PSU can be relatively close to the mic.

 

[zayance]

Thanks Rob!

 

[marktokach]

Just to be sure, I wire the HV and heater grounds together? Using mogami tube mic cable.

 

[david-p]

For my U47 clone, using Skylar's EQU47 body and the excellent Binder connectors, I chose Gotham cable.  It is less flexible than I recall the original U47 cable was, and doesnt coil as well.  I find a lot of cables move about inside the insulation when you coil them these days.

I have connected the shield, which is double and wound left- and right-handed to the connector body, as the Binder makes an excellent connection to chassis.  Then the two fat wires are used for the 500 mA heater of my EF14 and the rest are all the same size; so 2 for +/- audio, two for HT +/- and one for the polarizing voltage.  I have connected HT- to pin 7 as it mates first, and use that as the general 0v connection, also strapping it to chassis near the connector entry.

I havent finished building, so if I run into any problems with this configuration, I will post changes here.

David

 

[dandeurloo]

Stupid question.  Does mic cable make that big of a difference?  Like would a better 7 pin cable help compared to the standard Chinese cables that come with 460's and ll those?

 

[marktokach]

I am using amphenol connectors, I have all hooked up except pin 1 which I believe is the 0V GRND for the tube heater. Am I supposed to connect it to one of the other pins which all have wires on them already? The shield is connected to connector with a metal strap and 2 screws. Do I take a wire from it to pin 1? Almost done!

 

[Blue Jinn]

Marktokach: I don't think this is obvious at all. take a look at the file in the your other PSU thread. I haven't built a G7 (yet) but if I'm understanding what I've read in the other threads, you need 7 wire cable not 6 (not including the shield), because the heater and B+ have separate grounds until they meet within the mic body. Jakob mentioned that somewhere in one of the G7 threads.

I don't understand this enough to know if it would make a difference to join the grounds at the PSU.

The shield cable should be connected to the chassis at the PSU end XLR and unconnected at the mic end. Check out this thread too:

http://www.groupdiy.com/index.php?topic=36857.0

 

[marktokach]

Yes Blue Jinn, I know what you mean. Here is a link to Mogami tube mic cable.

http://www.mogamicable.com/category/bulk/microphone/tube/

I am wondering if what mad.ax meant was to jumper pin 1 to pin 7 inside the 7pin connector?

 

[Blue Jinn]

Yes Blue Jinn, I know what you mean. Here is a link to Mogami tube mic cable.

http://www.mogamicable.com/category/bulk/microphone/tube/

I am wondering if what mad.ax meant was to jumper pin 1 to pin 7 inside the 7pin connector?

I don't think so, I think he meant to wire it like the link to Emperor Tomato Ketchups grounding scheme, with one XLR pin not used. (H+ B+ Ground, Signal + Signal - Pattern = six)  FWIW, BigUgly's Royer circuit (which uses the G7 polarization scheme) has a shared B+/Heater ground  BTW Redco sells 7 conductor cable:

http://www.redco.com/shopexd.asp?id=706

 

[mikeyB]

Hi Rob - used the canford mogami - quality is good - shame i skimped on the xlrs - used cheap no brand from cpc - N-or-man Col-li-e-r- along with a few cracks, pops and bangs! - n-ee-d i s-ay m-ore!

 

[marktokach]

I got mine from Redco. I know they have gotham, I got this because it was supposed to be the best. 7 conductors would have taken the guess work out of it though. Someone will post the answer soon. It's the last step before I plug it in.

 

[marktokach]

After reading some other posts around, some people have grounded their mics to psu chassis and some not. I have my IEC ground hooked to center 1 on end of psu pbc and xlr 3 pin, and xlr 7 pin and that's all. Is that right? Just a little worried about plugging this thing in and putting my lips on it lol!

 

[marktokach]

This is how I have it hooked up so far;

7 pin xlr PSU connections
pin 1 Ground from IEC , pcb pin 1, and 3 pin xlr
pin 2 +160 v

pin 3 audio+
pin 4 audio-

pin 5 pattern

pin 6 +6.3
pin 7 0v

Mic cable connector connections
pin 1 not used
pin 2 +160

pin 3 audio +
pin 4 audio -

pin 5 pattern

pin 6 +6.3
pin 7 0V

Mic 7 pin connections
pin 1 ground
pin 2 +160

pin 3 audio+
pin4 audio -

pin 5 pattern

pin 6 +6.3v
pin 7 0v

I believe I should connect pin 1 and pin 7 inside mic body before tube somewhere and connect to chassis.

 

[zebra50]

Hi Mark,

I just answered your PM about this, but it's worth having it here to share with others.

If you look closely, the G7 PCB actually connects the heater and audio 'zeros' (pins 1 and 7) inside the mic. It should be connected to ground, and the shield inside the mic.

Normally audio ground will be connected to the PSU chassis at one point only (although even this can be a contentious issue!). 

The IEC ground MUST be firmly connected to the chassis!

Stewart