HAL - SCM & XAP Mixers



I've been using an open-air mike system based on Jim Lipsit's design for some time.

My only mods to this were:
Using a common ground for all inputs and outputs, omitting the low voltage power supply.
The logic outputs from the SCM810 are in effect switches to ground, which the Ocelot/SECU inputs are designed to work with - just don't forget the 1K resistor from each input to ground.

And, using an isolating transformer between the mixer output and the PC line input, to eliminate ground noise. This is simply a transformer removed from a scrap PC modem card. One winding connects directly across the mixer output, the other winding has one end to the line-in ground and the other to both left & right inputs in tandem.


I'm presently working on replacing the Shure mixer with a XAP800 DSP-Based mixer, which has echo cancelling and more advanced configuration control.

This is in an early stage, I need to do more wiring yet to route audio (from sources to be 'cancelled') back to the mixer location.

For anyone else experimenting with this changeover, rather than re-do the existing Shure control wiring I've made a short adapter cable to convert the Shure single control connector to suit the two connectors on the XAP800. My initial pinout for this is:

Shure PinSignalXAP Plug & Pin
Mixer Outputs - Gate Open signals (Note 1)
1Mike 1 Gate OpenA 17
15Mike 2 Gate OpenA 18
4Mike 3 Gate OpenA 19
18Mike 4 Gate OpenA 20
7Mike 5 Gate OpenA 21
21Mike 6 Gate OpenA 22
10Mike 7 Gate OpenA 23
24Mike 8 Gate OpenA 24
Mixer Inputs - Mike Mutes (Note 2)
2Mike 1 MuteA 1
16Mike 2 MuteA 3
5Mike 3 MuteA 5
19Mike 4 MuteA 7
8Mike 5 MuteA 9
22Mike 6 MuteA 11
11Mike 7 MuteA 13
25Mike 8 MuteA 15
Mixer Inputs - Mike Overrides (Note 3)
14Mike 1 OverrideB 1
3Mike 2 OverrideB 3
17Mike 3 OverrideB 5
16Mike 4 OverrideB 7
20Mike 5 OverrideB 9
9Mike 6 OverrideB 11
23Mike 7 OverrideB 13
12Mike 8 OverrideB 15
Signal Ground
13GroundA 25 + B 25

Note 1: The XAP Gate Outputs appear to be identical in function to those of the Shure SCM.

Note 2: I don't use the Mute signals yet. These inputs on the XAP are programmable, if mutes are required it should be possible to configure them for this function.

Note 3: The XAP does not have the 'force open' override of the SCM. The inputs I've given for the XAP are actually Preset Selects, which allow routing configurations to be selected in real time. I'm simply leaving the 'B' connector out until I am ready to make use of this capability.
If you need the 'force open' facility, it should be possible to work around this in the external logic by muting all other channels when one becomes active - if there are no other inputs, it won't switch away from the active channel.


If you need any more info on this, you can contact me via the HAL Forums (username rajenkins). Or, as a last resort, email me

Copyright Robert Jenkins 2007 - 2010
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