[Amps] The Pin One Problem

[Carl]

You stated in that memo (Id steer away from "tutorial as K9YC has a lock on 
that term) that :

" or any indication of inadequate shielding. It rather is caused by AC 
currents that flow on the outer surface of the interconnecting cable 
shields."

How can that be since copper has a skin depth of 8.6mm at 60 Hz which is 
many, many times thicker than the typical shield wire mesh used in audio and 
other consumer cables? Tin plating is invisible at 60Hz.

Hum on those systems is not common mode related but a simple case of a 
difference in potential between various pieces of equipment. This has been 
known since broadcasting began and the first PA system.

As far as your later statement about using vintage mikes, I own several 
D-104's (unamplified) and other mikes that can be switched or mixed using 
standard surplus BC equipment on vintage AM ham gear. There is no hum with 
proper grounding techniques even with several audio pieces daisy chained.

The D-104 is capable of over 2V output and "wants" a 5-20M grid termination 
for full available bandwidth.This is not a Pug n Play mike for a SS SSB rig. 
If some were to use a matching transformer with a Station Pro consider the 
degradation with a low quality transformer if driving a tube transmitter. On 
most tube type or SS SSB audio is bad already so restricted bandwidth of the 
D-104 may be tolerable if there is a way to limit the driving voltage.

I cant find any data on the Heil XT-1 and suspect it is not a good choice 
for the D-104 if broadcast audio is desired. Restricting the mike 
response/bandwith is not the way to do it since it also modifies the 
pattern, do the shaping in the transmitters audio chain for the desired 
transmitted bandwidth. I prefer 7-8 KHz total on AM and have tailored the 
equipment to that.

BTW, Heil does sell a dynamic element for the D-104 which will then 
interface with a wide range of vintage and newer gear.

Vintage dynamic mikes are fine with 50K.

Carl





----- Original Message ----- 
From: "Jim Garland" <4cx250b at miamioh.edu>
To: <jim at audiosystemsgroup.com>; <amps at contesting.com>
Sent: Thursday, June 06, 2013 1:49 PM
Subject: Re: [Amps] The Pin One Problem


>I realize we're straying rather far afield from amplifier topics, so pse
> overlook my wading into the discussion. The proliferation of outboard 
> audio
> devices for transceivers, and the desire to mix and match vintage mics and
> rigs with modern ones, has caused hum pickup problems to plague many hams. 
> I
> discovered this fact to my dismay with my StationPro station controllers.
> Most StationPro builders had no problems, but probably five percent 
> reported
> audible hum when routing their microphones through the StationPro.
> Fortunately, these problems were nearly always easily cured, but the "fix"
> usually required the builder to understand the possible origins of hum in
> their microphone audio circuits. Hum is not ordinarily, as many suppose,
> induced "pickup" from nearby fluorescent lights, transformers or whatever.
>
> I ended up writing a brief tutorial on the subject, which can be found 
> here.
> http://www.w8zr.net/stationpro/images/download%20files/Microphone%20Hum.pdf
> This will be old hat to most of you, but might be useful those who don't
> know what the "pin 1" problem refers to.
> 73,
> Jim W8ZR
>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Brown
>> Sent: Thursday, June 06, 2013 11:29 AM
>> To: amps at contesting.com
>> Subject: [Amps] The Pin One Problem
>>
>> On 6/6/2013 10:05 AM, Peter Voelpel wrote:
>>
>> > The pin 1 problem generally is not a problem with the gear but with the
> external wiring
>>
>> Actually, it is a problem built into equipment by a
>> designer/manufacturer who fails to terminate a cable shield for external
>> wiring to the shielding enclosure, but instead to interior wiring
>> (usually a circuit trace). The most common way this happens is that
>> connectors are mounted to the circuit board, not to the shielding
>> enclosure. This manufacturing defect is nearly universal in consumer
>> electronics of all sorts, in nearly all ham gear (except antenna
>> connectors), in most semi-pro audio and video gear.  I still see Pin One
>> Problems on the exhibit floor of audio and video trade shows.
>>
>> The Pin One Problem is addressed by AES48, which can be downloaded from
>> www.aes.org.  There is a fee for the download for non-members. There is
>> also considerable detail at k9yc.com/publish.htm
>>
>> Fundamentally, The Pin One Problem couples common mode current into
>> equipment, where it is then detected and added to the signal.
>> Corresponding suppression for unshielded wiring should typically include
>> chokes on the conductors and bypass or feedthrough capacitors to the
>> chassis.
>>
>> 73, Jim K9YC
>>
>>
>>
>>
>>
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