[BC] Black Box circuits

[Dana Puopolo]

I built a bunch of similar clippers back in 1980-90. They had two schottky
diodes (at the time Radio Shack actually sold HP Schottky diodes for 79 cents
each!). A 5K trimpot fed the diodes (wiper connected to the diodes). This
sourced the diodes at a fairly high impedance, resulting in a softer clip. To
raise the output level up, I used  a single opamp (first a TLO-71, later an
AD-712. There was an output trim control that was in the feedback loop of the
op amp. The prototype used two 9 volt batteries for power. Later ones ran off
a 12 volt AC wall wart (with two half wave rectifiers to make the + and -
voltages).

This clipper kicked ass - especially if you put a Sta Max or MSI (hard)
clipper after it.  

About 1-2 db of soft into about 1/2 db of hard clipping really did the trick!


Grady built a similar type of clipper except he drove the diodes from the nose
of two opamps and varied their bias via the opamps to get the desired clipping
depth. It was a really sharp clip!

-D





------ Original Message ------
Received: Thu, 06 Jul 2006 07:39:17 PM EDT
From: "Thomas G. Osenkowsky" <tosenkowsky at prodigy.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Subject: Re: [BC] Black Box circuits

My "Black Box" was literally black. It was a passive baseband
clipper. Two Zener diodes (RCA SK Series) very low voltage.
The Zeners were across the Composite Input BNC jack. The
hot side was connected to the high side of a 5k trimpot with the
wiper feeding the BNC Output jack. There was a SPST switch
in series with the Zener diodes.

You adjusted the Composite Output of your processor for
105%, 110%, 115% whatever amount of composite clipping
you wanted with the switch Off. Turn the switch On, placing the
diodes in line and adjust the 5k pot for 100% peaks. You had to
readjust the Pilot Level and possibly the Composite Level on the
exciter.

I used this at KC-101 when we signed on in summer, 1979. We
(legally) blew everyone off the dial. I used a modified Crown
crossover, three modified DBX 160's and a modified Harris
MSP-90 FM limiter. Not really fair since no one else was using a
composite clipper and this was before the FCC forbid pilot modulation
by the composite clipper.

I sold one to a NJ FM for $100! They had coverage into the NYC
market.

Tom Osenkowsky, CPBE

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