[Amps] The Pin One Problem

Fri Jun 7 15:15:55 EDT 2013

I am quite familiar with the issue and while Dr. Garland may call
it a "ground loop", the problem with The W8ZR Station Pro is the
same old problem in interfacing with improperly designed amateur
equipment.

If you bother to look at the schematics for nearly every Yaesu, Icom
or Kenwood transceiver, you will find that the "mic return" connects
to the emitter (discrete transistor preamp) or non-inverting input
(op amp amplifier) of the microphone preamp or amplifier and that
point is connected to the transceiver chassis via an RF choke for
DC.

When the mic return is not *tightly bonded* to the chassis, it causes
currents on the return to find their way to the chassis through the RF
choke and in doing so produces a voltage in series with the mic audio
(I^2*Z).  It is not rocket science and not "new."  It is amazingly poor
design - one "designer" coping from another - nobody knowing what they
are doing and why.  A lot like the blind copying of "floating" grids
in common grid triode amplifiers.

Quite simply, when a transceiver and an audio processing accessory
- whether it be W8ZR's Station Pro or a microHAM microKEYER II -
are connected to a common power supply (at the power supply), some
fraction of the current drawn by the transceiver will return to the
power supply via the connections (PTT return, Computer control return,
mic shield, FSK return, Key return, headphone return, etc.) between
the transceiver and accessory device.  Unless *all* of those returns
- *including the mic return* - are terminated to the transceiver
chassis that current will appear across the RF choke (remember the
current varies at at an RF rate) which will act like an old fashioned
choke modulator.

It doesn't take much current through that RF choke to generate enough
modulation to be a problem.  Typical audio levels for a microphone
vary from around 5 mV for a dynamic (Kenwood, Yaesu) mic to around
25 mV for an electret (Icom) element.

There are a large number of "band aids" for the design problem in the
amateur transceiver mic inputs.  *ALL* of them work by reducing the
current in the returns between the transceiver mic amp and the
accessory.  They are as varied as the designer - including reducing
the resistance in the power supply jack on the rig (multiple pins
in parallel), increasing the gauge of the power cord, bonding the
respective chassis together with wide strap, providing power to the
accessory from an *isolated* power supply or from an aux port on the
rig, etc.  However, none of them really fix the design flaw in the
transceiver which would generally be as simple as connecting the
mic return directly to the chassis at the mic jack and connecting
a jumper across the offending RF choke.

The amateur manufacturers (except Elecraft, in part) have not learned
what Muncie showed decades ago in professional audio equipment.

73,

    ... Joe, W4TV

On 6/7/2013 11:38 AM, Carl wrote:
> It is obvious that you have drifted off the subject which related to the
> Station Pro which Jim thouroughly explained the ground loop issue.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Joe Subich, W4TV" <lists at subich.com>
> To: <amps at contesting.com>
> Sent: Friday, June 07, 2013 11:12 AM
> Subject: Re: [Amps] The Pin One Problem
>
>
>>
>> The problem is that it is not a "Ground loop" - there is no issue
>> with multiple grounding if the inputs to the device are designed
>> properly.  It occurs only when the signal return is not correctly
>> connected to the shielded enclosure or bypassed - that also impacts
>> things like VHF/UHF stability, etc.
>>
>> If you continue to call it a "ground loop" it is obvious that you
>> do not understand the nature of the problem.  "Pin 1" problem is
>> as good a term as any since the mechanism for this issue in audio
>> was first identified in professional equipment using XLR connectors
>> and the understanding extended to audio equipment with other
>> connectors (including consumer/prosumer equipment with RCA I/O).
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>>
>> On 6/7/2013 10:58 AM, Carl wrote:
>>> That would be too easy since ground loops go almost back to prehistory
>>> when many discovered the same thing independently at almos the same
>>> time.
>>>
>>> OTOH, before the Brown Theorem it was always called ground loops,
>>> especially in the pro audio industry.
>>>
>>> Carl
>>> KM1H
>>>
>>>
>>> ----- Original Message ----- From: "Alex Eban" <alexeban at gmail.com>
>>> To: "'Ian White'" <gm3sek at ifwtech.co.uk>; <amps at contesting.com>
>>> Sent: Friday, June 07, 2013 5:11 AM
>>> Subject: Re: [Amps] The Pin One Problem
>>>
>>>
>>>> What about plain old ground loops, numerology set aside?
>>>> Alex 4Z5KS
>>>>
>>>> -----Original Message-----
>>>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Ian White
>>>> Sent: Friday, June 07, 2013 9:52 AM
>>>> To: amps at contesting.com
>>>> Subject: Re: [Amps] The Pin One Problem
>>>>
>>>> K9YC wrote:
>>>>
>>>>> When you invent, create, or discover something, you get to name it.
>>>>
>>>> Would that would be "Brown's Law"?  I'm sorry, Jim, but it just
>>>> ain't so.
>>>>
>>>> We all understand your personal respect for Neil Muncie, but there are
>>>> other
>>>> overriding priorities such as respect for truth and accuracy.
>>>>
>>>> It is only justifiable to call this "the Pin 1 problem" where that name
>>>> accurately applies: specifically to Pin 1 of an XLR connector in the
>>>> pro
>>>> audio industry. But this problem extends far beyond the area where
>>>> it was
>>>> originally identified by Neil Muncie. It is no disrespect to insist
>>>> that the
>>>> more generic problem needs a better name.
>>>>
>>>> Calling it the "Pin 1" problem in situations where it simply isn't
>>>> pin 1,
>>>> and even where there isn't a connector at all, is a deliberate
>>>> falsehood
>>>> which misdirects and confuses people. It can only be understood by
>>>> someone
>>>> who is already initiated into the secret. At so many different levels,
>>>> that
>>>> is simply A Wrong Thing To Do.
>>>>
>>>> We badly need a short GENERIC name that accurately indicates the
>>>> nature of
>>>> the problem. That won't be easy to find, but it is something we can
>>>> work on.
>>>> Calling it the "Pin 1 problem" simply isn't good enough.
>>>>
>>>>
>>>> 73 from Ian GM3SEK
>>>>
>>>>
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>>>>
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>>>>
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>>>
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