First' it's a long time since I did audio but the phantom power was applied
to both cores of a microphone (balanced pair) to power the mic. This was
injected through a pair of 47K resistors

Second standard audio level a pair of pots to a point of common coupling.
Simplest

Better a virtual earth mixer one TL071 and three resistors all 47k will do
fine. Bipolar +/- 9v and earth the non inverting input. Feed back resistor
from output to inverting input. The other two resistors to the two (pot
wipers) signals.=20

Steve


-----Original Message-----
From: piclist-bounces@MIT.EDU [mailto:piclist-bounces@MIT.EDU] On Behalf Of
Alexander Winnig
Sent: 11 October 2012 17:27
To: piclist@MIT.EDU
Subject: [EE] Two questions regarding telephones and mixing audio signals

Hello.

First: Which voltage level should not be exceeded between both=20
microphone cables(Signal and Mass) *between *a telephone handset and=20
it's telephone?

Second: I have two AC signal sources with a maximum voltage of 1.2 Volts=20
each. Which circuitry is the one with the least amount of components=20
that combines them in an adjustable way without distorting them or=20
diminishing the overal volume?

Best

Alex

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