I just looked up the circuit of the JD9. It appears to be a solid state phono stage connected to a tube line stage packaged as one phono preamp. If the solid state phono stage has enough gain already then a 12AX7 in SRPP line stage will have way too much gain. And if you switch to 12AU7, which is a better tube for line signal, and still have too much gain then the whole tube line stage is redundant. It's really a solid stage device trying to use tube to "flavor" the sound and there's nothing wrong with that but they should wire the tube as a cathode follower, which has no gain. In full signal it can reach 80dB of gain! That's one hot preamp!
If you are handy with a soldering iron, you can bypass the line stage entirely and get a purer signal but you will lose the tube flavor. The difference between the high and low output is just a resistor voltage divider at the output, one resistor in series and one resistor to ground, essentially a fixed volume control. Changing the value of the resistors will provide you different gain but will change the output impedance. I don't understand why they didn't just add a volume control in front of the tube stage is beyond me. Or you can just change one input resistor and it will get to where you want. Look at the schematic and change resistor R01 to, say, 220k, and you will get half of the gain. Just try till you get the gain right for your system. Or simply add a pot in there. Add another input and a selector and, voila, then you have a full function preamp! One with solid state phono stage and a tube line stage.
Good luck.
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If you are handy with a soldering iron, you can bypass the line stage entirely and get a purer signal but you will lose the tube flavor. The difference between the high and low output is just a resistor voltage divider at the output, one resistor in series and one resistor to ground, essentially a fixed volume control. Changing the value of the resistors will provide you different gain but will change the output impedance. I don't understand why they didn't just add a volume control in front of the tube stage is beyond me. Or you can just change one input resistor and it will get to where you want. Look at the schematic and change resistor R01 to, say, 220k, and you will get half of the gain. Just try till you get the gain right for your system. Or simply add a pot in there. Add another input and a selector and, voila, then you have a full function preamp! One with solid state phono stage and a tube line stage.
Good luck.
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