The service manual is just a joy isn't it?
Considering that it is also the owners manual, yes!
For the uninitiated, the "Stereo Mode Controls" are not entirely self-explanatory to some so an explanation is needed.
Although, I believe most folks would grasp it once they played with it.
Also not entirely comprehensible to some is:
Bass Mode
This switch controls the turnover frequency of the bass control.
Lifted, the "shelving" position, the bass control has somewhat less effect than more common bass controls. It affects the lower frequencies without altering the lower midrange as much as ordinary bass controls.
The lower setting controls only the deepest bass. Its effect is even more subtle than the upper position.
Lifted is subtle & lower is even more subtle. Not at all like 'normal' BASS tone controls.
High Filter
Use this filter to remove noise from scratchy records or AM radio.
This is a 12 dB/octave low-pass filter at 8 kHz. It is only active with the tone controls active.
I never use this filter. It's too sharp and at too low a frequency for use with better recordings.
Any time the tone controls are active and this filter isn't selected, a 40 kHz filter is selected instead.
And there are these few rather entertaining things (I especially like why you would want to use the 'MUTE' feature)
MAIN 2 Output
There are places on the circuit board for our technician to replace jumpers with a resistive pad for the MAIN 2 output, if needed to optimize the gain structure for your power amplifier.
Mute Switch
Be sure to hit this when you put in your headphones. The output to your power amplifiers does not mute automatically.
Laboratory Trick
If using the Holman Preamplifier in a laboratory, it might be handy to have a licensed technician readjust the the volume control knob so that unity gain is straight-up.
Quadraphonic Synthesis
With two Holman Preamplifiers, you can synthesis and control four output channels from just two input channels.
Apply all your inputs to the first Holman Preamplifier. Use it for all your tone controls, filters and source and tape selections. Leave its Stereo Mode in Stereo.
Connect the first Holman Preamplifier's MAIN 1 output to one power amplifier and your two front speakers.
Connect the first Holman Preamplifier's MAIN 2 output to any line-level input of the second Holman Preamplifier.
Connect the second Holman Preamplifier's MAIN 1 output to the power amplifier for your two rear speakers.
Rotate the second Holman Preamplifier's stereo mode control to L-R, and start by setting it to about unity gain or a bit less, and keep its tone controls flat. The tone and filter settings of the first Holman Preamplifier are fed automatically to the second Holman Preamplifier.
Set balance on the first preamp. Set front-rear balance on the Volume control of the second preamp.
Leave the power switch of the second preamp ON, and plug its power cord into a switched outlet of the first Holman Preamplifier. Now the power is controlled by the first Holman Preamplifier, too.