I to built this preamp many years ago, but was never happy with the mm phono stage which suffers from hiss (but no earth hum audible). The line stage is spot on though. Would a change of the transistors on the phono stage cure the problem, or is it likely to be something more serious? I have not used same wiring layout as in the mag, but have kept wiring as short as possible.
A friend also built one and I can confirm the oscillation as the volume control approaches zero. The cure (for me) IIRC was 6K8 resistors in series with the wipers of the pot.
This is a very classical problem which often happens when there is no resistor in series with the base of the input transistor of an amplifying circuit. The value may be much less than 6k8 Ohm which will introduce some noise and distorsion, 100 to 300 Ohm is usually adequate.
This is a very classical problem which often happens when there is no resistor in series with the base of the input transistor of an amplifying circuit. The value may be much less than 6k8 Ohm which will introduce some noise and distorsion, 100 to 300 Ohm is usually adequate.
Indeed yes. Usually a negative resistance at the cause of it....
It did require 6k8 as the minimum value to totally cure it in this case though!
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