adding phantom to a 1272 with only a single 3.3K? JLM?

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J

JRE Productions

Well-known member
Joined
Dec 10, 2004
Messages
255
Location
Chicago, IL USA
Looking at several of JLM's schematics he lists a single 3.3K resistor connected to the center tap of the two primary coils on the neve 1272. Does this seem right, or am I missing something? Is he using the coils as part of the resistance?

http://www.jlmaudio.com/JLM1272hotrodmod.pdf

Thanks

Joe
 
Just save a resistor and matching time and layout in chassis is easier due to one less part.

Does same thing as two 6.8 K's in parallel.

Transformer ct use for phatom has been discussed, jury still out.
 
However, a short on either end of the winding to ground (happens more often than one might think; for instance, ratty mic cables that decide to come apart and short) may cause some problems.
Click to expand...

I also wouldn´t do it, but the short possibility is not a valid reason. If you feed the 48v throght two 6k8 resistors, and one of the sides gets shorted, you will still have the same problem of current flowing throught the transformer...

Or am I getting confused here?
 
where the heck you beeN?

KAyaking the Amazon?

If he keeps the CT grounded and resistor shorts out, all the current goes thru that resistor and to ground, dc inbalance and probably a fried transformer, no 48 due to short.

But if no CT ground, 6.8 K shorts, power just goes thru there and down the cord to the mic, no harm done.
 
Any noise generated in the resistor (generating noise is their secondary function :evil: ) is canceled in the transformer since it's common-mode, whereas when using two resistors, the noise adds. And noise is proportional to R (as well as temperature).
 

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