OK, got round this morning to trying out the circuit you advised. You did not specify which was the Pos line so I took a guess and it didn't work. tried it again with the 100k on its own just cut into the positive line. This worked but not quite well enough so I added another 100k and that worked out just about right. So now I have (in effect) a 200k resistor in the line and that has brought the level down to one that is controllable with the volume contol. Thanks.
Have now got a break in activities while I go to hospital for an operation, then I can get back to experimenting with the reverb.
Catch you later,
Deigh