Looking for exciter schematics

[Paddock, Toby]

I have a Rocktron exciter/imager and was wondering HOW it works.  
The manual seems to be a little light on the details.  
I can sort of understand the _phase_ mode, but am missing something with
the _frequency_ mode.
US patents 4647876 and 4696044 are listed, but look like just the noise
reduction part.

The following is from the instruction manual:


EXCITER/IMAGER/HUSH II
INSTRUCTION MANUAL

 OPERATION
Each channel of the RX20 is divided into four sections: Process,
Frequency/Phase, Mix, and Hush II.  
Let's look at each section individually.

PROCESS
The Process Module is basically a gain control feeding the dynamic
filter/excitercircuit.  
Two things happen as we increase the level of Process: 
1) the Dynamic Filter is opened more resulting in processing of a wider
bandwidth of program; i.e. the more the process, the higher the
frequency allowed to pass to the Exciter. 
2) the higher the level going to the detection circuit is set.  
The Led readout can be used to determine the extent of the bandwidth
being enhanced.  
The more Leds that are lit, the higher the frequencies that are being
excited.  
Try setting the Process control so the first three Leds are lit most of
the time and the fourth one (red) comes on only in load passages.  
This is one of a multitude of settings possible, but is a good starting
point.

FREQUENCY/PHASE
Two modes of operation are selectable in this module.  Frequency and
Phase.  

In Frequency mode we dial in the desired cut off point of the signal
feeding the Exciter circuit.  
With the control completely counter clockwise the lowest frequency sent
to the Exciter will be 50OHz (fig. 1).  
As we turn the control clockwise we raise the cut off frequency to as
high as 5kHz.  
In any event the only thing we are changing is the lower limit of
bandwidth, and the Exciter is always receiving frequencies up to 2OkHz.

   (fig 1:  a generic high pass filter graph with 2 cutoff frequencies
and an arrow pointing up in freq)

In Phase mode (button pushed in), there is a notch created in the filter
which we can move between 50OHz (knob turned to right) and 4kHz (konb
turned to left) or a frequency in between (fig. 2). 
The depth of this notch is directly related to the level at the input to
the dynamic filter circuit.
As the level increases the notch depth increase and the enhancement of
frequencies above the notch point are accentuated.

   (fig 2:  a generic notch filter graph with notch at 4k and an arrow
pointing down in freq)

MIX
The Mix Module simply controls the ratio of enhanced signal to that of
the uneffected signal.
As we turn the Mix control clockwise we increase the amount of enhanced
signal sent to the summing amp.  
With the Mix control turned completely clockwise, we will have the
highest level of enhancement at the output of the RX20.

HUSH II
The Hush II Module is the single ended noise reduction circuit in the
RX20.  
Before exploring the controls, we need a basic understanding of how this
Module works.
The circuit is comprised of two parts: the Expander and the Dynamically
Controlled Low Pass Filter.

(and so on about noise reduction...)


Hoping this finds you,
Toby Paddock
- -- -  - -- -  - -- -  - -- -  - -- -
http://www.seanet.com/~tpaddock
Pronteon Approved, 98% content-free