It also helps to drink a lot !
Tom-W4BQF
> 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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