There are two design differences between the TDI and the SL. First one is the noise reduction circuitry. Can this one cause a reduction in depth? Maybe, if it causes one to ignore setting the frequency control to minimize noise, then it can be possible it could result in a depth reduction. However, this also holds true for the TDI for the same reason.
Now, the other difference is the battery voltage. Clearly, the SL does not have quite the voltage the TDI has. How much this impacts the depth capability is really difficult to say. What can make any difference more noticeable would be or could be more noticeable is when the voltage between the two becomes quite pronounced.
What this means is use a new battery in the TDI and a well worn down one in the SL and the voltage difference can be quite a bit. A fresh TDI battery is over 15V and a worn down battery on the SL can be almost 8.5V before the low battery alarm goes off. This means the voltage difference can be as much as 40% to maybe 45% or so. This difference in voltage applied to the transmit coil can and will cause an obvious depth loss. How much of a depth loss? Again, that is hard to say, but I would place range of depth loss at maybe less than 5% to 10% when both have fresh batteries to possibly as much as 30% on certain targets because of a dramatic voltage difference between the two detectors.
Factor in the clarity of the SL compared to the TDI and that depth difference might be reduced, especially when the SL has fresh batteries. Again, a lot depends upon the operator and how noise affects their ability to recognize very weak targets when the background is noisy.
So, to answer your question, there should be some difference in depth capabilities between the two, but just how much depends a lot upon the user. One that keeps the batteries fresh on the SL will come much closer to having their SL approach the depth of a TDI than an operator that tries to squeeze as much out of a charge as possible.
Use the Li Ion third party battery pack such as that made by RNB for the SL and the voltage difference will be more constant, and as a general rule, will be less than using the rechargeable NiMh's, which start out quite a bit lower. This is the method I prefer.
A more expensive way to sort of boost the SL would be to use the Energizer Lithium iron disulfide batteries that are not rechargeable, but they are a little higher voltage than standard Alkaline's in the SL so the voltage difference is less. Also, they don't discharge as fast.
So, the answer lies with the operator and his practices as much as anything.
As for me, I prefer the SL and use the RNB battery system. What little I lose in depth, I make up with convenience and reduced weight. BTW, I have both detectors and I now cheat when using my TDI. I use a special home made 4 cell battery pack which is lighter than the standard 8 battery pack. My continuous run time before having to change batteries is far less, but the weight reduction makes it worth while.
Now, what we need is an adapter that would allow the use of the higher (4 cell) voltage battery pack to be used on the SL.
Reg
