TDI coil question.

[dfbowers]

So.. I picked up a TDI Sl new in box through a trade. It came with the standard 12” & 7” dual field coils. During power up it may take 1/2 second or so after turn on before it’s ready to go.. I wanted to make a few mono coils of my own for the TDI.. which work just fine.. but I noticed during power up that the audio goes out to lunch for a while and just screams with my home built mono coils but they finally settle down after 10 seconds or so.
I also purchased a “Black Mamba”coil designed for the Minelab GPX series. It works just fine as well with the TDI but it too has the long transition time during the power up cycle but much longer.. It takes a good 10 seconds or so for the audio to settle down but eventually works great.
Anyone have any idea on why the stock coils power up so fast?
Thx.

[6666]

About 6 seconds with a nugget finder 14x7 coil

[dfbowers]

About 6 seconds with a nugget finder 14x7 coil

Thx..
I noticed that turning up the delay shortens the transition somewhat. Not the 1/2 second that I see with the dual field coils though..

[6666]

I will try and find the stock coil, which measures about 450uH and try it, not sure where I have stored it

[dfbowers]

I will try and find the stock coil, which measures about 450uH and try it, not sure where I have stored it

Both my dual field stock coils measure 364uH. Black Mamba measures 317uH.

[godigit1]

Both 12 dual field coils I have are 370 and 367uH. On the Mpp they damp at 660 ohms.

Try a coil that damps in that value or close as the Tdi is pretty forgiving.

[6666]

Ok, I re measured my stock coil it is 335uH, must of got confused with another coil, sorry about that, wrong lead in box of coils, any how it does seem a fraction quicker to start up,
I have the Australian PRO tdi

[godigit1]

You guys got me curious as I had not noticed any delay on start up.
I have a 2013 model TDI pro
I tested a few coils
Minelab 11DD
Jimmy sierra folded mono
coilteck Joey
stock 12 dual field.

All the coils fired right up no delay on my machine.
Maybe the newer models have some sort of soft start ??
Its been a long time but I tested 3dss coils in the 300 to 350us range on my TDI with good results.

[dfbowers]

With the stock coils maybe 1/2 second low tone on start up . Any other coil the machine just gives a growling low tone like you are holding it over a high conductive target. This is a fairly new TDI SL model.

[Carl-NC]

It's a coil decay speed issue. When you turn the unit on with no target presented the output of both demod channels is a DC level that depends on exactly where the coil has decayed to at the sample points. If, for example, you have an incredibly fast coil then both demods should be at 0V. But due to the finite decay, they are not at 0V, and it's the purpose the SAT circuit to remove this residual DC.

When you first power on, the SAT caps aren't charged up yet and the DC levels get passed on to the subtraction/gain circuit which then has another high pass filter that's even slower than the SAT circuit. This is the one that causes audio overload. The SAT circuits charge up pretty quickly but the speed at which the post-gain HPF settles depends on how far the gain stage is driven into overload. A well-behaved coil will cause less imbalance that allows the HPF to settle faster, and a slower coil will cause more imbalance that takes longer to settle.

[godigit1]

Thanks Carl,
Thinking that because I had my coils off the rod and close to metal when I turned on that maybe it fired up faster than normal due to a target being presented at the time of turn on.

Ill try again with stationary coils and see what happens.

[godigit1]

Dfbowers and 6666,

Do either of your coils make humming sounds on your TDI's.

Strange that my dual fields make noise on the Tdi but not on a Mpp Or HH or Barracuda.

[6666]

Dfbowers and 6666,

Do either of your coils make humming sounds on your TDI's.

Strange that my dual fields make noise on the Tdi but not on a Mpp Or HH or Barracuda.

No humming on my TDI coils, I have heard that before on other projects I've made

[Carl-NC]

The humming is due to the wires literally vibrating.