MOS1 630 enhancement

[John Vanderlee]

1.5 years ago we installed a MOS1 630 in a church. We mounted 4 speakers in a good location and the church was happy.
Now the organist wants a more "immediate" sound so he can hear it better. We gave him four small speakers to parallel with the others and place them in his sound field.
He said they were too soft. So he got a powered stereo mixer and "Y'd" the inputs from the S100 inputs into 4 channels of the mixer. According to him now that really kills the sound overall. Is there some major impedance mismatch? It's more than hour from here and I'd like to be armed with more knowledge than I have now.
Any ideas are welcome!
John

[myorgan]

John,

To the best of my knowledge, the S-100 is a "stepping" amplifier. As connections are added, the amplifier divides the signal between them. It's probably best they unhook the Y splitters because it may cause damage. At least until you can visit the installation.

Michael

[Admin]

Yes, an impedance mismatch. MOS-1 organs require a high-impedence amplifier input. The amplifier input is in effect in parallel with the LDR of the expression circuit, shunting the signal to ground. By placing another amplifier in the circuit, you've in effect shorted out the LDR so the resulting signal will be reduced to less than that of the closed expression pedal and the expression will be inoperative or greatly limited.

The input impedance of most audio gear is less than that required for the MOS-1 circuitry and placing a lower impedance amplifier in parallel with the signal further exacerbates the problem. The simplest solution would be to feed the speaker output of the S-100 through a suitable resistor to the mixer input. The value of the resistor needs to be such that it reduces the maximum voltage level at the speaker terminals to the nominal input level required by the mixer. You could start by a selecting a resistor that's 10x value of mixer's input impedance.

[John Vanderlee]

Makes absolute sense. Explains all the problems! How about this: Mixers have hi gain inputs, what about placing a suitable resistor in series with the mixer hi gain input. Isn't what H-labs does with their adapters?