Author Topic: Stereophonic 3 channel document uploaded  (Read 63 times)

Motorola Minion

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Stereophonic 3 channel document uploaded
« on: September 21, 2017, 09:41:47 AM »
An article from a 1960 magazine "PF reporter" on how the various manufacturers achieve the phantom 3rd channel. Since Magnavox did not participate in this development, it is in downloads of other manufacturers.
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Dave

jeffs01879

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Re: Stereophonic 3 channel document uploaded
« Reply #1 on: October 09, 2017, 05:13:32 PM »
Interesting article.  I have a Motorola SP-30 phonograph from around 1961 that has the three channel setup.  The left and right signals are sent through a high pass filter to single ended left and right outputs, and the signals are also summed and put through a low pass filter and sent to a push-pull center channel.  In addition, the phonograph incorporates the Vibrasonic reverb system, which taps the speaker outputs of the left and right channels, sums them and feeds them through a reverb tank.  Then the signal from the reverb unit is amplified and added into the center channel after the low pass filter.

The unit uses a 6BM8 each for the left and right channels, a pair of 6BM8s for the center channel, a 12AX7 for the input amplifier, another 12AX7 for the reverb amplifier, and a 6CA4 rectifier.

Makes for an interesting sound.

Jeff