[Boatanchors] SSB Generation - Phasing VS Filter Opinion Sought

[Robert Nickels]

Having been a SWL and first licensed in 1965 I remember that well, 
because AM was still commonly heard and the HT-37 was the SSB 
transmitter that sounded most AM-like.    If we look at the schematic 
(found on BAMA)  the audio section is not unlike most AM transmitters of 
that era (before hammy mods to replace all the coupling caps with .1uF 
for the "broadcast quality sound").   I haven't swept one but I'd guess 
the audio bandpass will be pretty flat up to 3 kHz which will preserve 
the highs needed for good intelligibility.    It's considered good 
practice in a phasing rig to include a lowpass filter before the phase 
shift network to prevent splatter and the HT-37 has a simple pi section 
filter using a pair of .1uF caps and a 50mH inductor.   I put them in 
Elsie and the response is flat to 3kHz and down 6dB at 10khz:

https://i.imgur.com/2TX3UIS.png

This audio bandpass means that pretty much all speech-range frequencies 
that get to the mic jack will be reproduced and not clipped by the skirt 
of a filter.    And since audio response is a function of the design,  
the "sound" of a phasing rig will not change much over time, whereas 
carrier oscillator crystals to drift and shift frequency with age, and 
either aren't properly aligned or end up drifting out of range of the 
alignment trimmers or the filter crystals themselves shift frequency 
which results in some filter rigs sounding bad (the "soup can" filters 
in the early Drake transceivers are notorious for this).

It would be easy to use an external audio processor to change the sound 
of a phasing rig, but I prefer to plug in a big honking chrome dynamic 
mic and let people remark on the audio quality.

73 Bob W9RAN