[BC] Re:111C repeat coils

[Mike McCarthy]

The 4008 was never designed for audiophile applications.  Somewhere I have 
the schematic for that board and it's not brain surgery.  I think the total 
dynamic range on the card is maybe 90 dB if set to lowest gain.  When you 
max out the gain, you are lucky to have 70dB dynamic range (noise floor to 
clipping).  But since tariff for a 15Khz circuit is only 68dB, (22dBrn), 
that's all they were designed for.

I have in the past tried pre-equalizing some circuits at the sending end 
where there is no practical limitation other than the hardware before the 
111C and have been able to get away from needing so much/any EQ at the 
other end. Just a simple gain block--20dB +/- is enough.  In one case, I 
was able to one man EQ a pair of circuits by simply sending the audio 
directly through the FM composite input and using the modulation monitor at 
the studio to set the amount of equalization.  Of course, I modeled the 
chain before hand using the digital path (which the dry pairs backed-up).

I then passively summed the two at the TX end in order to check phase and 
level match by driving the send end with inverted audio.  That worked 
remarkably well for years until the station moved and dry pairs to the TX 
were no longer an option.

MM

At 11:59 PM 4/6/2007 -0400, Xmitters at aol.com wrote

>In a message dated 4/6/07 11:39:29 AM Central Daylight Time,
>broadcast-request at radiolists.net writes:
>
><< The telco 111-C "repeat coils" are available on the surplus market. 
>They are
>  probably the finest audio-frequency transformers --ever. They have four 
> shield
>ed coils and the core is a toriod made of mu-metal strip. Very impressive 
>for s
>omething designed in the 1920s. The companion shunt equalizers are also 
>availab
>le although I don't remember the number. They consist of a tapped inductor 
>and
>tapped series resistors. Basically, you shunt-out >>
>
>OK, here is a dumb question. If telco copper loops are still around and 111C
>and equalizers are not considered Old Fart Engineering (see  my previous
>post/coinage of term) then why are there not companies still making the 
>111C?
>As
>ROTL, et. al.  pointed out, Jenesn makes some nice transformers. It appears
>that the choice is either Jensen or surplus 111C. To me,  it is odd if 
>equalize
>d
>copper is still not antique technology today, that 111C type performance 
>could
>not be had without resorting to the surplus market. Seems like you could
>outfit a specialty plant in China with some knowledgeable technicians, and 
>you
>could turn out high quality affordable product. A new 111C made in the states
>would likely cost $500.00 I would guess. Just wondering.
>
>The last I looked, the companion repeat coil card for the other end of a Tel
>Labs 4008 equalized circuit, was a bit anemic at the low end as well as 
>anemic
>in the head room department.
>
>I'm sure that there are others out there besides me, that have restrictions
>about buying used stuff. What I do is, if used product is the only 
>alternative,
>
>I pay for it myself, then donate it to the station. I can only do that if the
>item costs but a few bucks.
>
>
>Jeff Glass
>Northern Illinois University
>
>Dell CPi-D266 Win98SE AOL 5.0
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