Thanks for your helpful replies. We have obtained a manual for the 630T. It is very comprehensive. Using it, we have discovered that the trouble is in the "manual preamp 2" section of the preamplifier. I was in error in the previous post. The distortion occurs in all ten voices using this preamplifier. [mainly flutes] It is quite noticeable and needs to be corrected. All three preamplifiers are on the same circuit board, which is going to be a "bear" to replace. Many wires. If you know of a good source for replacement parts for this instrument, please let me know. Thanks. Rick Powers _EpOrganist@xxxxxxxx (mailto:EpOrganist@xxxxxxx)