Jolida JD-9 Upgrade

First thing is if you've been running the same tubes for 20 years then they probably need replacement. There are lots of options for 12AX7s - I really liked the Sovtek 12AX7LPS. Low noise, readily available, sound great.

I did all my own upgrades on my JD-9, and they're easy to do. It's possible your output caps have deteriorated in 20 years, but they don't get stressed much in the JD-9 so they're likely fine. I replaced my OEM caps with Jupiter Beeswax and it made a noticeable improvement. Again, there are many choices.

Opamps might fail but don't wear out. I originally installed the Burr-Brown (OPA627) op amps and they were better than the OEM but not dramatically. The big change came when I bought 6 Burson V5i on sale; they were majorly better.

If you can solder, you can easily DIY all these changes. Good luck!

@armstrod Burson V5i sounds interesting.  Does the JD-9 take single or dual version?  Thanks

All triode tube units will present a capacitance at the input, if the gain stage is a simple common cathode topology. This is due to capacitance between the anode and grid, primarily, and to a lesser capacitance between the grid and cathode. This is called Miller capacitance. The 12AX7 has very high miller capacitance owing to its high gain factor. So add 50 to 100pF to whatever you think is cable capacitance. A cascode at the input avoids miller capacitance, but usually you won’t have a 12AX7 in a cascode. Transistors and op amps exhibit a similar phenomenon.

Thanks for the advice.  The tubes get replaced regularly.  I'll look into the caps and opamps.

@jrcotner,

The correct V5i for the JD-9 in all positions is the Single x 2.