The SPP and the Freq control

[Reg]

I had a rather unique question asked by a forum member who asked a question regarding the frequency control on the SPP. The question asked was; would anything be hurt if the freq control was removed so they could use the hole in the box plus use the connector and wiring now on the freq control for the addition of a conductivity switch? This would allow the switch to be placed in the hole the freq pot is in now and use the freq pot wiring to connect to the conductivity switch to the proper pcb connection.

Well, the simple answer is no, nothing should be hurt if you remove the freq control completely. In fact, that is exactly what is done by the factory so you do not have a delay control. Better yet, you can unplug the frequency control wiring from the pc board and plug it into the delay pcb connector and now have a delay control instead of a freq control. Yes, the pot value and connections are the same.

There is a problem though when eliminating the freq control and that is, the freq control does something useful in many places where there is a lot of emi noise. Adjusting the frequency control in areas with high EMI does reduce EMI noise and reducing the noise, will increase depth. It is difficult to hear the noise but it can be done.

Out in the field where there is little noise, then eliminating the freq control won't hurt a thing.

So, for you who don't want to add another hole in the box, this is a solution. I don't recommend it for those who might be using the SPP in EMI areas, but in isolated locations, it should be fine.

One more note, the wires to the various controls and pcb connectors are small and delicate. Be careful because after repeated bending they will break. Worse yet, tugging on them can cause real damage not only to the connector but also to the pc board if the connector is pulled away from the board. When in doubt, disconnect the various connections when separating the housings. The pcb is marked well so you can easily put things back where necessary when done.

Reg

 

[ronniecruisin]

Hi Reg. From what you are saying, it sounds like the extra control points as the TDI SL has do exist on the SPP board as we all suspected. Soooooo if one were to order as a spare part say the pot and loom setup for the ground balance on the SPP it could be plugged straight in to the delay plug on the board giving us that ability without sacrificing our frequency pot. Have to put another hole in somewhere for it of course. Bung in the conductivity switch the same way and we almost have the same setup to the TDI SL......Yes????? Some have already done the switch and as we now know....it works. Is the GB pot the same as the Freq. one???? Regards...Ronnie.

 

[dazza513]

All this is starting to sound very interesting

 

[Reg]

Hi Ronnie,

The operator adjustable GB pot is NOT the same as the Freq pot. The GB pot is a 10K pot and is part of a feedback ckt on the GB amplifier. Internally, there is another small pot that is used to calibrate the GB pot. This internal pot might be tried to see if it helps with the GB on DD coils. Right now, I don't know if it would help or not but it should extend the range of the GB pot. BTW, this internal GB pot is the only internal pot on the pc board. So, one might mark its present setting and then adjust it to see if it helps with the GB of DD coils.

The Freq pot and the delay control are the same setup, 100k pots. Both of these pots go to inputs in the microprocessor and are nothing like the GB pot. So, if a person wanted to try to add a delay control, then you would have to order a spare freq pot.

Now, I have not actually tried connecting the Freq pot into the delay pcb connection on the SPP, but as far as I know, there were no changes to the software on the SPP. So, I would think it should work.

Keep in mind there are two sizes of pcb connectors, a three wire and a two wire. Order a Freq pot and wire assy and this should be able to work on the delay. Also, the three wire connector and wiring used on the freq control should work on the Conductivity switch.

Reg

 

[ronniecruisin]

Thanks Reg. That would certainly make it very easy as the tiny connectors are very hard to get here, not to mention how fiddly they are to work with. Thanks for your input. You are a credit to the forum, and I'm sure others would feel the same way....Regards ....Ronnie.

 

[dazza513]

I was standing on a hill right next to a mobile phone tower and the spp was in the car, hmm so I got it out and switched it on... ok nice and smooth, ground balanced nicely on hot'ish ground and no warble or hiccups either hmm...

I grabed a tiny bit of junk I'd found the day before and waved it over the coil with the detector coil down on the ground and nothing??? hmm got another small piece out of my pocket (slightly bigger) and it just found it, I moved the freq pot a quarter turn and tried again and the signal was way stronger...

has anyone else tried this? the spp had dumbed down to stay quiet but I had no real way of finding the best freq setting as the noise reduction hid the emi so good! gain was at 7 and there was no hint of any emi warble or chatter even when I maxed the gain.

any ideas ?

 

[Roscoe]

Dazza i have had the exact same thing happen to me, the noise reduction circuit is so good it just about makes the frequency control virtually obsolete unless its a more predictable EMI source, such as an electric fence or some thing similar which has a constant pulse and stays within a certain frequency band.

 

[Reg]

Well fellas,

Looks like a boo bood when I said you could install a delay control and it would work. That appears to be WRONG!!!!! According to the tech at Whites he said he had to reprogram the SL to get a delay control to work.

Sooooo, don't try to add a delay control, it won't work.

Sorry for the bad information.

On a different note, Roscoe noticed that emi can reduce the depth capabilities if the freq control is not set at the best setting. As Roscoe said, it is difficult to know when the freq pot is set at the setting where the noise is the least.

I turn the threshold down to just barely hearing anything at all and listen for the threshold to rise or fall slightly. Even at this setting it is difficult.

Reg

 

[dazza513]

It would be great if you could "switch off" the noise reduction and tune the frequency while you can really hear all the extra noise then switch the noise reduction back on and be confident your at the best frequency

 

[Reg]

It is possible to do this, but working on the SM board is extremely touchy and frustrating. The less done the better.

The best way to set the freq control is to turn the threshold to right at no signal and then listen for slight increases. Adjust for minimum signal. Increase the threshold just a tiny bit and repeat.

Reg

 

[Reg]

I have a question and that is, what if you could manually set this noise reduction level or at least made it a little less active? This would mean you would get some noise in extremely bad locations.

Reg

 

[old hand]

Extra noise of any kind puts the operator at a disadvantage as deep target may be missed by the smallest audio noise .Deep targets may just be a faint break in the threshold not a audible signal regards john

 

[dazza513]

I have a question and that is, what if you could manually set this noise reduction level or at least made it a little less active? This would mean you would get some noise in extremely bad locations.

Reg

Reg

I found that whilst on the hill beside the mobile phone tower the spp had lost some sencitivity to small targets but was able to keep a steady threashold and didn't seem to hiccup there even with the gain at 8. To have the ability to raise or lower the amount of blanking would be fun to try but you could find yourself just replicating what the spp does allready?

If my spp had a "noise cancel pot" to adjust in the field I would definitely want to see what it does!

Regards Daryl

 

[Roscoe]

Oldhand, that's true mate but you have to remember the SPP is slightly less sensitive then the TDI Pro because of the noise filters and i would say that the Tdi pro is less sensitive to other PI detectors out there because it has more filtering then them. Its a double edged sword, more noise more sensitivity, less noise less sensitivity. I would say if you mainly operate near power lines etc. then leave the machine as is, but if you mainly operate the machine out away from these influences then reducing these filters would give you an advantage over the current configuration in hearing faint targets.

 

[old hand]

Roscoe I am only saying what we have found after using ML detectors PI since the 2000 and 2100 days run noisy and you will loose targets .Well if the SPP is less sensitive you need everything in your favour and I don't think noise helps any way I am just concentrating on getting the hiccup fixed at the moment regards john

 

[Roscoe]

You are dead on there Oldhand a smooth threshold is always the better way to go.