[AMRadio] F/S Volumax

Geoff/W5OMR ars.w5omr at gmail.com
Fri Nov 30 20:17:06 EST 2007

Bob Peters wrote:
> It is the VOLUMAX 4300 And I have the manual with it.
> Anyway offers???

Here's what I found on the Volumax 4300...

in 1970, CBS Laboratories produced a revolutionary product.  The Volumax 
4300.  The first analog signal processor for maximum loudness.  It 
contains two circuits.  A special compressor, and a peak limiter.  This 
device is connected after the main slow acting compressor.  The special 
compressor is a FAST acting compressor.  Unlike the main compressor, 
this one has a medium-fast attack time, around 8.5 msec, and a 
relatively fast release time, around 260 msec.  Percussive sounds faster 
than 8 msec do not trigger the compressor and go straight through with 
their original volume level.  The syllabic sounds are compressed and the 
gain is re-adjusted very quickly due to the 260 msec.  This only works 
well if the average signal input is relatively constant - the job of the 
main slow acting compressor.  The two compressors work together in 
preventing gain pumping, and allow percussive sounds to sound loud 
because they don't reduce the gain of the second compressor (ie. their 
attack time is not altered), yet the syllabic variations are highly 
compressed and are brought up to maximum gain quickly, making the signal 
sound very loud, with a further increase of 6 dB or 4x power compared to 
not using it.


Thus the second circuit in the Volumax 4300 is an unsymmetrical clipping 
circuit which takes care of the negative peaks, fixing them at the -100% 
modulation level.  The 6dB improvement from this device alone is all 
totally useable since at no time will the transmitter be overmodulated 
in the negative direction, neither will it be undermodulated, as the 
average signal will always be close to the clipping level.  Every top 40 
radio station wanted one of these.  One does not really hear any 
distortion because the energy in the clipped peaks is very low - and 
what is left can fully modulate the transmitter toward -100%  almost 

On the other side of the coin, there are these comments...

>/ >I have at one site a Volumax 4300.  It's a single channel 1U AM processor.
>/ I believe that model had the clipper diodes BEFORE the output
/>/ transformer. Self induced tilt and overshoot!
Yeah, its peak control wasn't that great.  But it did work ok for limiting a 

Mind you, these reports are from 'professional broadcasters'.

Amateur signals aren't nearly as 'broad' as broadcast professional 
stations.  Typically, an Amateur AM signal is 6kc wide.  Broadcast 
stations have a 10kc channel spacing.

Isn't there something in the Rules and regs about emission bandwidth?

Hmmm...  seems the only thing I can find, is:

(1) No angle-modulated emission may have a modulation index greater than 
1 at the highest modulation frequency.

(2) No non-phone emission shall exceed the bandwidth of a communications 
quality phone emission of the same modulation type. The total bandwidth 
of an independent sideband emission (having B as the first symbol), or a 
multiplexed image and phone emission, shall not exceed that of a 
communications quality A3E emission.

however, Part 97 doesn't not define what the width of a 'quality A3E 
emission' is.

I -did- find, however, what appears to be a reply to a petitioner.../*

10.* Regarding Petitioner's request that amateur stations transmitting 
emission type A3E not be authorized to occupy more than 5.6 KHz 
bandwidth on amateur frequencies below 28.8 MHz, _we agree with 
commenters who note Petitioners have not demonstrated there to be a 
particular problem with stations that transmit AM emissions. Moreover, 
the Commission has previously declined to restrict bandwidth for AM 
because to do so would be inconsistent with the basic purpose of amateur 
service and our desire to offer amateur operators the opportunity to 
experiment with various types.

It appears that currently, an AM transmitter can have a width of <6kc.

I feel, as Amatuers, we should probably limit ourselves to something 
around the 6kc area, just to be 'neighborly' to our near-frequency 
neighbors, as to reduce the amount of bickering and bitching on the 
band, which would lead to a much more enjoyable environment to all hams, 
regardless of what mode we are on.


Driving your AM Rig without a scope, 
is like driving your car at night, without headlights. (K4KYV)

73 = Best Regards,

More information about the AMRadio mailing list

This page last updated 16 Dec 2017.