Relative Power = 20 Log10( Voltage_Ratio ) dB
so the attenuation of a 220 ohms tap series with 2 2.2 K ohm resistors is:
20 Log10( 220 / (220 + 2200 + 2200) ) = 20 Log10( 1/21) dB = -26 dB
this assumes that the page port output has fairly low impedance (is
not loaded by the attenuator), and the microphone input has fairly
high impedance (does not load the attenuator), and the microphone
input to the amplifier is isolated. If one side of the microphone
input to the amplifier is essentially ground, one resistor does
essentially nothing and the attenuation will be
20 Log10( 220 / (220 + 2200) ) = 20 Log10( 1/11) dB = -21 dB
I estimated Log10 in my head. A calculator will give more accurate numbers.
BTW: I assume that the first poster already made certain that the
music-on-hold source is connected to something (radio) or grounded,
and that the system is not set up to send the music-on-hold source to
the amplifier when no paging is occuring.
Paul Gusciora
San Rafael, CA
(Chemical Engineer, Control Systems person, and amateur radio wannabe)
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED], [EMAIL PROTECTED]
Subject: Re: KX-T: Humming sound on KX-TA624
From: chris Snyder <[EMAIL PROTECTED]>
Date: Wed, 3 Jul 2002 08:11:43 -0400
I would highly recomend not going into a mike input of an amp with out an
input attenuator, microphones typicaly put out a -60 db signal and page
ports put out 0 db or greater so you end up with a terrably destorted
audio as well as possably picking up all sorts of electrical noise.
An attenuator I have used sucessfully is made from three resistors, one
220-270 ohms acrost the mike input then a 2.2k ohms from each mike
terminal ( pins 2 and 3 on an XLR jack) to the page port.
On Tue, 2 Jul 2002 22:26:16 EDT [EMAIL PROTECTED] writes:
> you may have a ground loop. try putting either .01 mfd capacitors in
> series
> with the output and input, or a 600-600 ohm matching transformer for
>
> isolation. Depending on how the circuit board is laid out inside
> the TA624,
> you may be picking up hum from a power supply, or transformer. Be
> sure to
> use good shielded wire, West Penn 292, or equivalent, or good rca
> type phono
> coax cable. Be sure your impedence between the TA624 and the input
> of the
> paging amp is the same, or the input on the amp is Hi Z 10K-50K. If
> you are
> going into a mic input, which is typically 150 ohms, you are loading
> down the
> TA624, and that can generate noise and hum. Always go from a lower
> impedence
> to a higher one, never the reverse.
>
> So endeth the lesson.
>
> Steve L. Martin
> <A HREF="http://www.geocities.com/surfsidesound/";>Surf Side Sound,
> Inc.</A>
Chris Snyder
Advantage Telcom
Cosby, Tn.
Sevier County's oldest interconnect.
_________________________________________________________________
KX-T Mailing list --- http://kxthelp.com/
Subscription changes: http://kxthelp.com/mailman/listinfo/kxt
