Re: Quad FM3 no stereo
The bias emitter follower takes its voltage from an internal rail, derived from a zener and feeding a darlington pair. There is no value on the zener. However, since the minimum rail voltage is 8V, a reasonable guess is that the zener is ~6V. Which would set the internal rail at ~7.5V
The net effect is that the base of the input transistor is at 5.8V, regardless of the supply voltage to the chip.
So synchrodyne is right - there should be a mono output regardless of whether there is enough signal strength to allow stereo decoding.
The datasheet says that the maximum supply voltage for the decoder is 14V - which is what Quad used! That is sailing rather close to the wind. Particularly since there is a +/-5% tolerance on the zener from which the +/- 14V rails are derived.
The IF chip CA3089 is fine - the maximum voltage is 16V
Craig
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