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tdi sl or pro or tdi
Posted by: stateguyt
Date: December 10, 2017 01:47PM
is there a big difference in these machines
when i see a used tdi or pro for sale they sell rather quickly
unlike the sl it might not sell at all
Why do people want the tdi and pro series
i want the better one for the beaches

Re: tdi sl or pro or tdi
Posted by: stephenscool
Date: December 10, 2017 11:10PM
I've only had the sl. Some advantage are.. light weight, smooth threshold, easy to travel with, warranty. Need to buy an after market battery or make 1.

Re: tdi sl or pro or tdi
Posted by: Reg
Date: December 12, 2017 03:44PM
I have written more than enough to make a small book on the differences of the TDI versions on this forum, so I won't go into any real detail this time but will address your basic questions.

"is there a big difference in these machines"------The simple answer is no, they are extremely similar in design and gain.

Why do people want the tdi and pro series"--------Simple, people think they go much deeper. The truth is a TDI and the SL vary in depth by maybe an inch or so and this is mainly because of a difference in battery voltage and/or coil.

The TDI and the Pro version primarily because of the filtering difference. Change the filter values in the TDI to those found in the Pro and you have a "poor man's Pro".

Change the filters in the SL, plus use a 4 cell Li-ion battery and it can also become a poor man's Pro.


Edited 2 time(s). Last edit at 12/12/2017 03:46PM by Reg.

Re: tdi sl or pro or tdi
Posted by: sonnar28
Date: December 12, 2017 04:39PM
Hi Reg,

Thank you very much!

I thought that is what you had written in the past, but I did not want to post without reflection.

Is the SAT the same on the TDI and the TDI Pro? The TDI Pro seems capable of a faster sweep speed.


Re: tdi sl or pro or tdi
Posted by: Jim Robertson
Date: December 12, 2017 04:50PM
Hey Charles
I think on any PI machine you can swing to fast. That is even true on the GPX's. And that is very true in hot ground. I have found the slower you go the deeper the target you will find. Jim

Re: tdi sl or pro or tdi
Posted by: stateguyt
Date: December 12, 2017 06:34PM
Thanks everyone

Re: tdi sl or pro or tdi
Posted by: Mega
Date: December 12, 2017 08:16PM
I was lucky too purchase the last TDI Pro into the UK,but i would have no problems with using the 'sl' version,but what i would change if i bought a sl was change the rod assembly,i am not a fan of 'S' shaped shafts,but its a relatively easy changing it over using either Whites or aftermarket shaft components.Of course this is just a personal thing and nothing too do with performance.

The way that i currently have my TDI Pro setup is using the Coiltek 14x9 Mono which i love as it does give me better ground coverage,slight depth advantage but the biggest thing i like about it is how light this coil is,its foam filled rather than say resin based,but of course the only down side of having a coil foam filled is that if you use it for surf detecting then it would want to float like a fishing float which is not good,but as i rarely do beach detecting then this is not a issue for me.

As i am mainly after silver hammered and small gold coinage then i mainly run the machine in low conductivity as this i find this the best settings for my sites that i detect on,this will eliminate most small nails and the like but sounds out when the coil goes after my chosen targets.Of course if i am also going in for the kill on a scattered hoard site then i would run it in straight PI mode with either the Coiltek coil or even my Minelab Commander 15x12 mono Coil,slightly heavier but does give me even better depth.

Re: tdi sl or pro or tdi
Posted by: Reg
Date: December 12, 2017 09:01PM
Yes, the SAT speed is identical on the TDI, the Pro, and the SL. The only difference is in the stage just before the SAT and it is in this previous stage that there is too much filtering. This excessive filtering conflicts with later filtering which causes a depth loss if the coil is swept too fast. This previous stage is what I call the integration stage and it is the stage that adds all the sample signals together to form the target response. The TDI uses .22uf capacitors and the Pro uses .10uf capacitors. Change the TDI caps to .10uf types and you convert a TDI to a poor man's Pro.

The only other differences between the TDI and the Pro are the Pro has a vernier GB control and the volume control moved from the motherboard to an external adjustment. In other words, the TDI has an internal volume control while this control is removed off the motherboard and added as an external adjustment on the Pro. Those people who had their TDI's modified previously had the option to have the caps changed on the TDI to the values in the Pro, thus if they had this mod done, they already have a pseudo Pro, or what I call the poor man's Pro. Outside of the three mentioned differences, the TDI and the Pro are identical, component wise. THERE ARE NO OTHER MAGICAL DIFFERENCES BETWEEN THE TDI AND THE PRO.


Re: tdi sl or pro or tdi
Posted by: markg
Date: December 26, 2017 07:36AM
Thanks reg. It's there a picture anywhere indicating the location of the caps that need replacing

Re: tdi sl or pro or tdi
Posted by: hecbom
Date: January 09, 2018 12:09PM
Are these caps surface mounted? I don't currently own a TDI SL but plan on getting one soon, ( I have built my own PI based on the Mini Pulse Plus) and works great.


Re: tdi sl or pro or tdi
Posted by: Reg
Date: January 10, 2018 08:35AM
The caps that need to be replaced are C20 and C21 and are not surface mount. Remember to use a quality cap rated at 50v such as a panasonic or rubicon stacked metal film polyester type. The technique used by Paul when replacing caps on the TDI was to cut the caps leads with a 1/4 inch left and bend them over then cut the leads of the replacement caps, bend them into an ell shape and solder them to the cutoff leads of the original caps legs. This was done to keep from removing the pc board and because the boards are multi-layered.

The caps being removed are .47uf and will be replaced with .22uf types.

The caps are located about midway down the left side of the motherboard reasonably close to the left side. In the pic, they are the first 2 orange caps along the left side with arrows pointing to them. The pc board is well marked.

If you are unsure of your soldering ability, please find someone qualified to do this.


Edited 1 time(s). Last edit at 01/10/2018 08:38AM by Reg.

Re: tdi sl or pro or tdi
Posted by: AlexP
Date: January 14, 2018 02:06PM
Hi Reg. I am going to try this mod on my standard TDI (not Pro). What is the outcome of the mod expected to be - a bit more depth (an inch or so)? Will it have any negative effects?

So the capacitors to be replaced are C20 and C21 and the replacement capacitors need to be .22uf (or .10uf - as per your previous post) and rated at 50v?

I am not into electronics, but already did one mod a few years ago after reading another post of yours. Changed the pre-amp which resulted in the detector being more stable. I can max the gain out and the detector runs stable. The threshold is very smooth, but there is a slight buzz when using certain coils at high gain.

Re: tdi sl or pro or tdi
Posted by: Reg
Date: January 14, 2018 10:57PM

Please read my posts carefully!!!!!! C29 and C21 are part numbers for the smaller SL and not for a big box TDI. On the TDI the part numbers are C59 and C60. Do not mix the SL posts with the TDi POSTS!!!!!!!.

This mod will allow for a faster sweep and maybe a little depth increase


Re: tdi sl or pro or tdi
Posted by: AlexP
Date: January 15, 2018 09:07AM
Thanks Reg. So on a standard TDI it is C59 and C60 that need to be replaced with .10uf capacitors. I will give it a try.

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