Litz wire and Tube Mic PSU

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guavatone

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Joined
May 21, 2005
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1,608
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Very strange.  I bought Studio Projects 7 pin XLR cable that has litz wire.  This Litz wire has a resistance or 1.2 Ohms. So it is dropping 0.6 Volts on the Heaters for a MK7 Supply.  I got it because it was an amazing deal. 

Any ideas?

Here is the product

http://www.bhphotovideo.com/c/product/429151-REG/Studio_Projects_SPC_207X_SPC_207X_Litz_Solid_Core.html


 
Interesting... I didn't know about this cable. And there's little info about it except the usual marketing BS. Any chance you take some picture of the conductors so we could see the structure?

Did you measure 1.2 Ohms on each of the wires? Or just on the one carrying the heater supply?
The problem with litz wire is that it's a pita to solder. Each conductor is made of a lot of small separately insulated wires. The insulation is provided by enamel. So you need heat and aggressive flux to get rid of the enamel when you tin the conductor. If not done properly you can end up with only a few wires making proper contact, the others remaining insulated, hence the higher resistance...

Google Litz wire to learn more about its principle and construction, and resolder the offending wire properly, it should solve your issue.

Litz wire has better conductivity at high frequency (>1MHz) therefore it is loved by audiophiles, but the fact remains that for DC operation it is inferior to conventional wire. So I guess for a tube mic cable, it would be better to have Litz wire just for the audio signal, and regular copper for the rest...

Axel
 
keep the voltage drop, the tubes will last longer.

bought a huge hammond pwr xfmr and the thing spits out 6.7 volts heater voltage no matter how many tubes i wire into it.

somebody missed a turn,

gave up, so i just let them burn at 6.7.


why are you using mic cable for a pwr supply?

go to kragen auto and get some 16 ga.

 
One cable passes power and signal nice and clean. 

Was that 1.2 measured pin to pin or solder to solder?  It could be bad termination.  Or a cheapo 26ga wire has 1 ohm resistance per 12 feet so a 15 footer gets you there. 

I had a similar sitch with a pair of test leads.  I was testing rebuilt Studer A800 power supplies under load with four different meters and the negative 15VDC outs were always 3V lower.  I noticed that the test leads were warm and found that these POS leads were dropping 1.5V each about 15% of the output.

Anyways, you can't go wrong with GAC.
Mike
 
I just used some gotham tube cable on a KM54 rebuild. Mic was given to me for free sans PSU and cable. Used the gotham as part of the refurb and I could not be happier
 

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