I'm sure glad I'm a CW man!
73, Mike N4NT
----- Original Message -----
From: "Robert & Linda McGraw K4TAX" <RMcGraw@Blomand.Net>
To: <tentec@contesting.com>
Sent: Thursday, June 24, 2004 9:26 PM
Subject: Re: [TenTec] Heil ProSet adapter with Orion -- hum
> Actually no. The input stage toady is typically a differential device
> having a non-inverting and an inverting input. The output of that stage
is
> coupled back to the inverting input via a R network including a bias R to
> reduce or establish the input stage gain. This then causes the two
inputs
> to be of different Z and thus unbalanced yet above ground. The audio
ground
> is used the carry the difference in current which is a result of the
> different loads presented to the + and - because of difference in Z of the
> two inputs. In a true balanced configuration, no audio ground is needed
as
> there is no difference in I and R load between the two audio lines.
Another
> way of looking at it is the 230 volt power distribution with our homes.
The
> neutral is only there to handle the difference in current between L1 and
L2.
> Considering non inductive loads, if the current on L1 is 10 amps and the
> current on L2 is 8 amps the neutral current should be 2 amps.
>
> In our classic differential device, if a voltage of equal magnitude is
being
> induced from the outside world into audio + and audio - lines and these
> connected to the non-inverting input and the inverting input the resultant
> output is zero while a differential voltage from the mike produces an
output
> equal to the input voltage plus the gain of the stage. In one companies
> mike cable they use a single conductor shielded cable. If the audio
signal
> line (center conductor) is connected to the non-inverting input and the
> shield to the inverting input then any noise on the shield is amplified
and
> thus appears at the output of the device.
>
> Traditionally the XLR connector has been used for both balanced and
> unbalanced service in professional and broadcast audio for years. It has
3
> pins which have been designated as audio + audio - and ground. But what
> about shield? In a balanced audio system, no ground is needed. However,
> shield is provided and is connected according to IEC standards to pin #1
> with pin #2 being audio high or + and pin #3 being audio low or -. Where
I
> find most problems arise is that shield is connected to pin 1 on both
ends,
> thus when connected between two pieces of equipment and may present a
> condition that allows current to flow on the shield conductor. Now we all
> know the laws of physics with regard to current flow and magnetism, the
> right rule of thumb and such. The point is that under these conditions
the
> shield can not effective perform as intended purpose with no current flow
> and its intended purpose is thus largely negated.
>
> Enter 3 conductor shielded configuration. In this configuration, we
provide
> conductors for audio +, audio -, ground and shield. In using XLR
connectors
> there is a 4th connection which picks up the shell of the connector. Its
> intended purpose is to provide continuity of shield without providing a
> current carrying path. I was startled to see a line of plastic/non
> conductive connectors introduced some years ago. At one installation that
I
> serviced they created havoc.
>
> Now enter the unbalanced mike. With the above holding true, the unbalance
> should occur or be created at one end of the cable only, thus typically
the
> input. The accepted rule is to treat it as balanced all the way to the
> load, in this case, the active input device.
>
> I stated earlier here on the reflector that all of my audio lines are 3
> conductor shielded. Oh yes I may have 2 of the wires and a shield
connected
> together on the RCA plug that goes into the radio with one wire to the
> center pin. That is the point that it gets unbalanced. If the
source/mike,
> is unbalanced then so be it. The wiring is standard and works in all
> configurations, balanced, unbalanced, balanced to ground or unbalanced to
> ground. of course in a balanced or unbalanced to ground condition an RCA
> connector is not suitable for the terminus.
>
> Perhaps this helps answer some of the concerns of those surrounding
balanced
> vs. unbalance conditions. I wish we only had a way to present drawing
here
> as it would make the picture very clear without the extensive verbiage.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "George Skoubis" <george.skoubis@verizon.net>
> To: <tentec@contesting.com>
> Sent: Wednesday, June 23, 2004 11:33 PM
> Subject: RE: [TenTec] Heil ProSet adapter with Orion -- hum
>
>
> > Bob,
> >
> > Is the audio ground only present when using a balanced mike? With an
> > XLR connector?
> >
> > On a Heil headset I can only envision +, -, and shield.
> >
> > I'm not trying to be a smart alec with this question, just wondering
> > where the audio ground is found on a headset.
> >
> > Thanks,
> >
> > George / KF9YR
> >
> > -----Original Message-----
> > From: tentec-bounces@contesting.com
> > [mailto:tentec-bounces@contesting.com] On Behalf Of Robert & Linda
> > McGraw K4TAX
> > Sent: Wednesday, June 23, 2004 10:55 PM
> > To: tentec@contesting.com
> > Subject: Re: [TenTec] Heil ProSet adapter with Orion -- hum
> >
> > I shouldn't bring this up again for someone will blame it on the "Pin 1
> > problem". The fact is there's typically 4 connections for microphone
> > audio.
> > There is the Audio Hi or +, Audio Lo or -, Audio Ground, and Audio
> > Shield.
> > That's 4! The big problem lies in the misunderstanding that Audio Lo,
> > Audio
> > Ground, and Audio Shield can be the same or connected together. They
> > can't
> > and shouldn't. Shield is shield and ground is ground. They aren't the
> > same
> > as ground may be a current carrying conductor and shield should not be a
> > current carrying conductor.
> >
> > In all of my mike lines there are 3 conductors which are surrounded by
> > one
> > shield. None of these are used for DC or PTT. They are all for proper
> > audio
> > connections.
> >
> > 73
> > Bob, K4TAX
> >
> >
> >
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