MXL 770 Omni/Cardioid Switch Mod
When using a dual diaphram capsule to replace a single diaphram capsule, the simplest thing to do is to either tie the two capsule leads together to create an omni mic, or leave the back diaphram disconnected to create a cardioid mic. However, a simple switch is all that is required to turn this mod into an mic that can easily be both. The trickiest part of this mod is how to mount the switch. Although there are a number of ways to mount a switch to be externally accessable, another easier method is to mount the Omni/Cardiod switch inside the body - no body modifications required. This is what we opted to do with this pair of MXL 770s.
We mounted a small toggle switch down near the base, using heat melt glue. The switch is tiny, so the heat melt glue seemed like it would be plenty strong enough. Below we see the mounted switch. The white wire comes from the back diaphram, and the black wire runs to the same point on the circuit board that the front capsule wire connects to.
The advantage to mounting the switch near the base is that, you only need to unscrew the bottom ring of the body to access the switch - the body sleeve itself does not need to be removed, so there is less chance of damaging or contaminating anything on the circuit boards. The disadvantage is that the capsule leads are longer and thus potentially more prone to picking up stray noise. As of this writing, we haven't had a chance to really test these mics much. So far, however, this doesn't seem to be a problem, but keep it in mind.
Below is a close up of the switch, with the body sleeve in place. You can see we have marked the switch functions with a marker.
Before modding this pair of 770s with this switch setup, we modded one 770 for Omni/Cardioid switching by using the existing Hi-Pass filter switch for the Omin/Cardioid function switching by cutting some traces on the circuit board, and removing the Hi-Pass filter components. We think adding the third switch is a cleaner approach, however.