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TDI with Noise Reduction Mod


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A couple of recent posts referred to the whites TDI – so I thought I'd pass along the following.

Last week I purchased a secondhand TDI from a guy who had sent it in to have Reg Sniff's noise reduction mod done - along with replacement of the op-amp.

I had a TDI previously and the difference between that one and this one is like night and day. My old one had a warbly threshold that drove me nuts and made it very difficult to use the sensitivity higher than about 2/3 of full. My house is EMI hell, the neighborhood has underground utility service and the transformers sit on the ground. Even mildmannered VLF's like Whites Classics go nuts here at full sensitivity.

This TDI has a silky smooth threshold with just an occasional blip at full sensitivity (12). It also air tests 17" on a nickle with the standard 12" DP coil! That's 4" more than I ever got with my old TDI here at the house with the same coil.

I have been playing with the silver coin hunter trick with the high conductor mode selected and the GB offset to kill all ferrous. It really works - with the GB on 4, I hear no iron - and a quarter that I buried down 8" about 5 years ago gets a good signal with 2-3" air gap even using a 10" elliptical Coiltec mono.

Now I need to find a dead Bigfoot coil and build a mono PI "Bigfoot".



The mods were $125. Reg could probably furnish current details.

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Hi Rick,

Glad you like the mods.  They really do help for those who have never heard of them.  Besides more depth because of the reduced noise, they set the base for a new DOD coil that will really help the TDI.  Right now, the coil is in the development stage.  My prototype shows you won't need any GB in many places so you can turn the GB off and gain that extra depth.  The down side of the coil is the signal strength is not that loud so a good set of headphones is required for maximum depth.  The big advantage is the super quiet threshold.  It is so quiet, I am thinking of cranking up the gain to add even more depth. 

Now, as for your wanting a dead Bigfoot coil for the housing, you can buy 3 different sizes of rectangulart coil housings just up the road from where you live in AZ.  Bill Hays makes three sizes of rectangular housings and he is in Prescott Valley.  The three sizes are a 12" by 3 1/2", a 15" by 3 1/2" and an 18" by 5 1/2".  He sells the larger one for $16.50 and less for the other two.  Shipping is extra.  His phone number is 1-928-772-2624 for those interested.  He may not answer because he gets so many solicitor calls, so leave a message and he will get back to you.

Building a mono bigfoot is easy.  Just shield it right and it should work fine.  If you want to get a little fancier, you can build a big foot ground and noise cancelling version.  This one requires a rectangular mono tx and a figure 8 RX winding.  This design should be extremely quiet and require little to no GB signal.  Only half of the coil will create a signal on the TDI, though. 

So, there are new things in the works for the old tired TDI.

Reg

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So, what will the TDi enhancements cost us Reg? I have an original TDi myself.

Ps, can you hardwire a 4 inch Tesoro coil to a Tesoro Compadre and shorten the cable to like 18 inch? I believe the coil has a 5 pin connector. Not sure if this coil is Compadre compatible? I had it on a Tesoro Umax machine long ago. Trying to make a discriminating pinpointer detector like Steve did with his Fisher GB2?

Thanks.

-Tom V.

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Ivanwho,

I don't do the mods myself.  My hands don't work that well any more so I have a friend do them.  He does the work and keeps all the money since the mod is somewhat labor intensive and does require a pcb trace mod. 

A full TDI mod costs about $125 (return shipping included with $500 insurance) and that includes replacing the preamp with a much better IC, the addition of a small pc board to reduce the noise, a filter change so the regular TDI is upgraded to the filtering of the Pro for a faster response.  The mod also includes calibration of certain stages to 1 millivolt to assure the mod works as designed.  This TDI pro filter mod makes the regular TDI like the Pro but without the extra GB pot and volume control.  The volume control was added to help reduce the noise problem, but with the noise reduction mod, is not needed for that purpose any more.

One additional mod is to short out a capacitor which eliminates a third filter that is not needed and can cause weak signal problems.  This mod does increase the gain which in turn increases the noise level.  Fortunately, reducing the gain using the gain control about 20% or so makes it back to normal.  You do gain a little depth but more noise with this mod.  One advantage of this mod is weak signals become more reliable. 

Reg

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Reg,

I am interested in the SL simply due to weight-----

I have seen Diggerbob with them and they seem like they have a good solid threshold--

What are the pros and cons of them?---- I am in NorCal and fighting some steep slopes and lots of trash...

Can they benefit from any mods?

Thx and I didn't mean to hijack the thread Rick-----

(If there is some place I can do more research on them please let me know and I will do my reading before asking anything else....)

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Vanursepaul,

The SL has noise reduction circuitry to reduce the noise but it has its own quirks.  Fortunately, they do not cause much of a problem here in the US.  However, any SL going to OZ should be modified to eliminate the "hiccup" that happens over there because of the SL noise reduction design. 

It is my understanding that SL's made after November of last year have this hiccup mod, but I can't say that for sure.   I have no communication link with White's any more. 

Reg

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vanursepaul,

There are things that can be done to the SL to improve it and I am pretty sure Digger Bob has them done to his units.  The reason I say this is because I modified a SPP and that unit was sent to Digger Bob for him to evaluate.  Bob has some of the worse ground in his back yard that approaches that found in OZ.  What he found was the modified SPP ran smoother and was easier to ground balance.  He probably knows if all newer SL's are modified or not.  

Now, there is a guy making 4 Li Ion cell batteries for the SL that increase the gain so it is much closer to the TDI.

My buddy can make mods to the SL also and one of those mods is to change the filters so it is more like the Pro.  This makes the detector a little more responsive to small gold. 

Reg

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