My experience was that the BBD was getting too much signal and that was causing the BBD to distort.
I replaced R15 with a trimpot to find out at what value the signal was loud enough and clean enough. Then I removed the trimpot and measured the value at wich the trimpot was set and used that value for the resistor at R15. So yes you can substitute R15 with a different value, but you have to find out what works for you. I ended up with 56k. So my suggestion is to socket R15.
Marc
Marc,
Thanks fore re-posting the info here. This is extremely helpful.
My pleasure. I know all about the importance of finding the right info ;)