DD coils and the SPP

[Roscoe]

Interesting Old hand, If these DD coils require a Ground balance of 10 then whats the effect of that finding gold. I looked a Reg's chart and going by the chart (If i read right) a GB of 10 would knock out a lot of Gold signals? That's ground balancing right in the heart of Very Low Inductors like gold?

What did the Mono's GB at Old hand?

 

[old hand]

I just had a look and its on 7.5 with a 14x7 nf coil .I have not seen the chart you are talking about I ground balance till the threshold it smooth moving the coil up and down only about 3 inches.

 

[Reg]

Don't interpret my chart incorrectly. The chart is only a relative idea of what to expect and by that I mean if you are hunting low conductor objects, increasing the GB can reduce the depth of detection. Many low conductor objects never balance out throughout the GB range available. If you look at my chart, you will see a typical low conductor still generates a high tone at a setting of 10.

The chart is simply to show what happens to target responses and what happens to those responses as the GB is changed. So, in simple terms, low conductor signals will lose depth when the GB is increased but high conductors will gain depth. In many cases, the depth difference over the GB range may be minimal. In fact, gold could be close to 1/4 oz before it is knocked out if the gold is pure and if the gold is not pure then it may never have much of an effect by increasing the GB.

As an example, I have a couple of half oz nuggets that are still a very strong low tone at maximum GB. Steve Hershbach stated that most gold found at one location in Alaska generated a low tone even if the gold was several oz's. So, just what happens can vary dramatically.

Reg

 

[Reg]

I like the term "Hiccup" for a sound that can be made by the TDI series. Usually, it is on the SL models but can happen on both.

The design of the TDI series is such that a hiccup type signal can occur. The design of the TDI is strange since it shuts off half of the signal generated. So, unlike the ML that has a wee-woo or a woo-wee, the TDI only has a wee or a woo. The other half of the signal is eliminated.

There is a capacitor on the SL or SPP that can be shorted out that will help with reducing or eliminating this signal and others. Actually, this cap isn't needed but is still there in the design. When Eric was designing the GS 5 he ran into a problem of a slight drift in the threshold and added the cap thinking the drift came from some of the op amp circuitry. That wasn't the case since the drift came from his transistor audio portion. However, the cap was left.

Now, this cap can cause another strange response some of you will experience and that is on some weak signals, the threshold may not return to normal right away but sort of moan or linger for a few seconds. Usually, a quick bob of the coil will reset this signal. None of the quirks cause any problems outside of being annoying.

Actually, the cap could be shorted out since it doesn't do anything of value. For those interested, the cap is C42 located close to U12A. This is located in the lower left portion of the pc board if looking at the board with the front end towards the top.

Reg

 

[Roscoe]

Thanks Reg, for the clarification. I have been doing some testing on various coins, gold rings, nuggets etc, with different GB positions. I have noticed as It is very interesting how one can manipulate the Gb setting to give different tones and responses with this machine. I did also notice as you stated that most Low conductors stayed through out the GB range.

Old Hand. 7.5-8.0 is where my SPP ground balances at the moment in my soil at home. Your GB methods Fine Old hand its just a quirk with the model as Reg explains.

 

[old hand]

I will get out some time today and just re check my DD gb on 10x5,14x9,11 round and 16 round xp will post them when I have done it that hiccup shore is annoying have to come back checking the spotS . I did notice yesterday with 12 whites 10x5nf,8 m/l and 14x7nf I had no hiccups but I still think its the ground balance I have ordered a 10 pot that will just sit on top of the original one thanks john

 

[Roscoe]

I hope it works Oldhand, but i don't think it will. I think that its the ground balance system trying to soak up the ground signal but it can't. The only thing i found was if you reduce gain then it goes away. It reminds me of a VLF detector in this regard, low gain the detector balances out with no sound raising and lowering the coil. Push the gain to high and you get a slight sound going up and down even though its at its best balance point. I do agree it would make ground balance point more easier to achieve, but i doubt it will eliminate the hiccup sound? like i said i hope it does thought.

Head off tomorrow morning for a weeks break will take SPP on the beach on & off over the course of the week.

 

[ronniecruisin]

Hi. Reg. That hiccup sound is certainly annoying. I'm not an electronics wiz, but would like to do what you say with that cap if that solves the problem. What exactly do you do to short it out.??? And to Stalker. The batteries were fully charged. I think the problem is that the GB control does not go round far enough. Normally the control is like three quarters of the travel to start the deeper sound...soooo I believe if it could go say to twelve it would fix the problem. There is nothing wrong with the coil. As I said, wave a target across it above ground and it performs perfectly. Tis only when placed near the ground it plays up. Regards....Ronnie

 

[KarlS]

Ronnie, I believe you had your SPP open. Did not you accidently plugged your ground balance plug into delay socket? I did and for while I was stumped why I can't ground balance . The symptoms were similar to yours.
Karl

 

[ronniecruisin]

Hi. Karl. Had it open but didn't touch anything. Haven't done the conductivity thing yet. Monos still work fine. Only issue is the DD.

 

[KarlS]

Well, then I don't know. I can GB with 2 DDs and 1 mono coils without problem in my back yard and in 2 different parks locations.
Tomorrow I'm going to my sister's property for few days. There are some diggings there, so I will test different coils. Although there is not much chance to find gold with detector, only gold found there was fine aluvial.
I will look on this cap mod when I get back.
Karl

 

[old hand]

Re test DD coils with a gain of 8 for all test, on different ground from yesterday at my test patch ,all targets are the same date and it starts at 6 inch s and goes to 21 inch s they have been in the ground for about 6 years. The nf 10X5 GB was 8.5 could only pick up the 6 inch target, next the 14x9 nf GB was 9 could pick up the 9 inch target but would not dig it terrible signal, M/L 11 round GB at 9 the 6 inch target only with the 16 nf xp GB8 6 inch target only, tried it on xp mode with the same result .I found the DD coil are more forgiving as fare as ground noise that I would expect , I had to moving the GB control 1 to 2 spots before the DD s started to hiccup as mono s can do. After this I think I will be staying with mono coils on the spp regards john

 

[Reg]

Hi Ronnie,

The hiccup is more complicated than the cap I mentioned. Adding a small wire across the cap can help. Nothing complicated is needed. Just take a small wire and solder it on both sides of the cap. This eliminates the high pass filter that does nothing. Now, jumping the cap may not eliminate the hiccup since it is far more complicated than the cap. In fact, lots of parts are involved including the circuitry that eliminates the half of the signal plus the special noise reduction circuitry.

Sometimes, you can add another jumper but use a switch and jumper part of the noise reduction to reduce the hiccup. The best way is to get the GB set as best as possible. If th GB is off then the hiccup can be worse.

Now, I mentioned a second jumper that would jumper a diode on the pc board. Shorting this diode reduces the noise reduction slightly but can reduce the hiccup and gain a very slight amount of depth since the noise reduction does reduce the depth slightly.

On my unit, I added another switch to be used to short the diode, so I can switch the mod in or out. This mod can be temperamental in the fact that if dual field coils are used, you may create another problem. At least the tech at Whites had problem with this. I could never duplicate his condition he claimed he got. A friend who is duplicating my efforts couldn't create the problem either.

If you listen to the SPP very carefully, you will hear targets get weaker but never fade out softly like they do on the TDI. Instead, they fade down to a weak level and then simply disappear suddenly. This is caused by the noise reduction circuitry blanking the noise. Unfortunately, any very weak signal down in the noise is also blanked. Thus, the TDI will allow you to hear the weak signals in the noise but the SPP and SL won't.

I personally feel a switch should be used so switching back to normal can be done if something strange should result because of ground conditions. The diode jumped sort of puts the detector back to non GB mode when at threshold. Thus, the depth increase.

Reg

 

[Reg]

When using a DD coil make sure to use a very slow sweep speed. Practice and you will see what I mean why it is important. Also, round DD coils work better since they do a better job of reducing ground signals. The natural action of a DD coil is to reduce the ground effects by cancelling some of the ground signal. Pass a target beneath the coil and you will hear different signals as the object is passed from one side to the other. From the edge to the inner crossover zone, the signal will reverse or get quiet. This area will try to cancel the ground signal somewhat.

Something else happens and that is small iron which is a high tone will become a low tone if the iron object is close enough when under the overlap zone. This can cause small iron junk to stutter or even disappear if very close to the coil when you are operating in the low conductor mode.

Reg

 

[ronniecruisin]

Hi Reg.My understanding of electronics is very limited, and from what you are saying, re. the hiccup probably wont disappear completely, it's sounds like it's not worth messing with. What I do find amazing however is that it exists in a product designed and built supposedly by techs that know their stuff. Surely this is a glitch that should have been designed out of the thing. It seems to happen most of the time so is obviously a problem with the design of these machines. Also of note is that the sweet spot to achieve ground balance is IMHO quite difficult to balance. Moving the control a hair sends the machine high or low and the perfect spot for good GB is quite often difficult. ie. The perfect window is very tight indeed. Once you do get it right it works ok, but the nearly constant hiccuping is very annoying. Ronnie.

 

[KarlS]

Hi Reg.My understanding of electronics is very limited, and from what you are saying, re. the hiccup probably wont disappear completely, it's sounds like it's not worth messing with. What I do find amazing however is that it exists in a product designed and built supposedly by techs that know their stuff. Surely this is a glitch that should have been designed out of the thing. It seems to happen most of the time so is obviously a problem with the design of these machines. Also of note is that the sweet spot to achieve ground balance is IMHO quite difficult to balance. Moving the control a hair sends the machine high or low and the perfect spot for good GB is quite often difficult. ie. The perfect window is very tight indeed. Once you do get it right it works ok, but the nearly constant hiccuping is very annoying. Ronnie.

There is easy solution to add fine adjustment to GB, but unfortunately it will void warranty. By adding another potentiometers in series with GB pot you will be able to fine tune your setting. If you use pot that is 10% of value of main pot, you would get fine adjustment approximately of one number of main GB pot dial.
Karl

 

[ronniecruisin]

Now, That sounds like a good plan Karl. If it does the job you say it will, I for one would not give two hoots about voiding warranty! Makes you wonder why whites didn't put in the fine control. It is a very annoying problem that as you say could very easily have been fixed. My problem is ...I don't know how to do what you are saying. Can you provide me with the info on the part I need, and maybe a simple drawing showing how to do??? Regards....Ronnie.

 

[KarlS]

Ronnie , I'm going away for few days. When I get back I will open SPP and find out what value of pot they are using and look up suitable fine adjustment pot.
Karl

 

[ronniecruisin]

Thanks Karl. Have a good time away...Regards...Ronnie.

 

[old hand]

hi I have one of these on order should have it early next month

once I have I will see what it does to the ground balance regards john