As mentioned previously, I'd also change to Fast ON. Gain amplifies the audio response from what the coil senses in the ground, much like a volume control changes the audio level on your radio. But when you have static on a radio station, turning down the volume won't make the static go away. Similarly, lowering the Gain will not make your problem go away. I'd suggest your problem more likely comes from your Sensitivity settings when using the larger coil. Larger coils are more succeptible to changes in ground conditions because they have to analyze more soil at any one time. More soil usually results in more magnetic interference. More magnetic interference usually results in instable Sensitivity levels. By setting your Sensitivity manually, you've taken away one of the most effective functionalities of the E-TRAC. The ability to self-adjust Sensitivity levels "on the fly".
Auto Sensitivity has 3 channels operating at three different levels. Those levels are determined in software, based on the conditions of the ground. If one channel becomes irratic due to magnetic interference, the E-TRAC changes the level of that channel. I land hunt in the Midwest and don't use manual Sensitity. My highest Auto Sensitivity levels are usually in the mid-upper 20's. I use Auto +3 in less trashy places and drop down to Auto in areas with lots of targets. My reasoning is because when I'm using +3 in the Auto mode, the E-TRAC provides that +3 "boost" to the levels of all three channels. But even then, all three channels are still operating independently of each other and the levels are based on ground conditions. In manual mode, all 3 channels are set at the same level. If the E-TRAC software determines that ground conditions would be better served by operating at a different level, it can't switch to a channel with a different level because you've locked all three of them in to the same level, manually.
Auto Sensitivity is a great concept. I don't completely understand how the technology works. But I figure if the Minelab engineers are sharp enough to design a detector that ignores the effects of mineralization (allowing the user to not worry about maintaining a proper ground balance), then they surely designed Auto Sensitivity with our best interests in mind as well. Allowing me to tweak Auto Sensitivity + or - (with 3 variables either way) allows me the flexibility to accomodate the conditions of the ground and still utilize the technology behind it. If I were using a larger than stock coil and encountered your situation, I'd definitely be using Auto Sensitivity. If it still chattered, I'd try putting a negative offset in the Auto Sensitivity before I lowered the Gain. JMHO HH Randy
