Jolida JD-9 Upgrade

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.

@armstrod just replaced my JD-9 Burr-Brown 637 OPA’s with a set of 6 Burson Single V5i’s.  Definite all around improvement. Well worth the $115 at Parts Connexion.  Appreciate the suggestion in the thread.