At 01:14 PM 2009-04-10, Scott Fraser wrote:
>Hi Richard:
>I knew somebody would probably have an update for this. My learning
>experience with this arrangement (Mics > Neumann Phantom power supply
> > ReVox A77 unbalanced mic preamps,) took place about 30 years ago
>while setting up to record Vietnamese Buddhist Monks chanting in their
>monastery. No go until I procured a set of Shure balanced low Z to
>unbalanced high Z transformers, to go between the power supply & the
>ReVox inputs. I assume the XLR-TRS adaptors I tried first tied pins 1
>& 3 together, thus bringing the Phantom voltage to ground & the
>session to a temporary halt. With capacitors are you blocking the 48
>volts on the output side of the Phantom PSU?
Hi, Scott,
That is exactly what you're doing--keeping the mic pin 2 and pin 3 at
+48 V, while removing the DC and grounding the audio for pin 3 and
passing the audio from pin 2 to the preamp with no DC. You're lucky
you didn't take out the preamp with the 48V going into it! Of course,
limiting the current to 10 mA makes it safer.
On a related note, this article in my blog could be called fun with capacitors!
http://richardhess.com/notes/2009/03/07/phantom-powering-of-early-sennheiser-mics/
Your capacitors would be turned around--the above circuits use
phantom from the mixer.
Assuming you have P48 on pins 2 and 3, put the negative side of the
cap to the unbalanced input, grounding the cap on pin 3 and connect
the negative side of the cap on pin 2 to the hot. Tun a 10K from the
neg of the pin 2 cap to ground. Use at least 100 uF 63 V caps.
Cheers,
Richard
Richard L. Hess
Aurora, Ontario, Canada http://www.richardhess.com/
Detailed contact information: http://www.richardhess.com/tape/contact.htm
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