One of us is a recovering electronics engineer so we're familiar with the phenomenon John is describing (commonly known as heterodyning). We also liked what Kaleea had to say about other strings vibrating.

So, we did some more thorough testing. Both tuners appear to work perfectly on the autoharp using their internal microphones and they agree with each other (more or less). When the Matrix pickup is plugged in to the Seiko tuner it also works well and agrees. When the pickup is plugged in to the Korg, it works and agrees on 22 of the strings but reads consistently sharp on 15 of the 37 strings (that's right, 37 - this is a Dolgeville Model 73 built in 1898!). Most of the errors are concentrated in the region where the tuning pins change direction, that is, near the top of the lowest octave. We tried very carefully damping each and every string simultaneously except the one being tuned and there was no difference.

We conclude that both tuners and the pickup are working fine but, for some reason, the Matrix pickup is not compatible with the Korg tuner. So, we ordered a new pickup made by Korg, Model CM-100 which, they claim, is designed to work with the CA-30. It looks very similar to the Matrix pickup but we think it has wider "jaws". We should have it in a few days and we'll let ya'll know what happens.

Bev and Jerry