LOOKING FOR GOLDSCAN 4 Schematic.

[Reg]

Jose,

I am not quite sure what you are saying is the problem. So, I am not sure how to answer you.

When you increase the frequency of the pulses, you also increase the frequency of samples. Since the sample and hold amplifiers are full sample and hold, you end up with more samples over the same time. This should give you a sharper and smoother signal with the possibility of a little less noise. On the down side, the pulse width has decreased if the way you increased the pulse rate was to change the timing capacitor on the 555 timer.

Double the pulse rate and you should see a very distinct drop in pulse width. So, you might check this and see if increasing the pulse width helps. You could see a pulse width drop to 100 usec or so when it was originally somewhere between 230us and 250us or so.

Now, did you turn the sensitivity down to see if that helps?

BTW a longer pulse width works better when trying to detect silver and copper objects as well as larger deeper objects. So, depending upon what you are trying to find, should determine what you set the pulse width at. Keep in mind, increasing the pulse width and/or the frequency will have an effect on the battery life.

Reg

[Jose]

Thanks Reg
I'll try to explain better.
You say the rate increase, "should give a clearer signal and smooth with the possibility of a little less noise."
In fact the opposite is true in my GS4, when the frequency increases, the signal is more rough or cracked (less smooth and more sharp), for audio referred.
I think this is due to the integrator, and detector generally, is designed to give maximum response to the original frequency (450-550 Hz).
Put another way, the sound becomes choppy, moving abruptly from silence to a higher pitch, when doubling the original frequency.
Sorry my bad English
Jose

[Reg]

Jose,

I think I understand now. If this threshold signal is changing dramatically thus causing the signal to sound rough and raspy even with no object being detected then what is most likely happening is there is some external electrical signal that is combining with your pulse rate and creating a very noisy threshold. This is extremely common on a PI because of the broadband preamp design.

The reason the frequency control is built into the detector to try to eliminate what you mentioned. If the threshold and signals are noisy and rough even when the detector isn't detecting anything, then as I said, it usually means the detector is picking up external EMI (electronic noise) that is mixing with the frequency setting you have set at that time. If this is the case, the the proper procedure is to slowly adjust the frequency control until you find a spot on the control where things smooth out. This has to be adjusted slowly to give the detector time to respond.

Normally, there is at least one or more settings of the frequency control that will smooth things out. Try adjusting this control and see if it eliminates the problem. If it doesn't you may have to move the frequency a little one way or the other to find a range where this doesn't happen.

The integrators are there to give you a normally smooth signal but can't eliminate noise. On some PI's, a lot more filtering is used but what happens then is the sharp choppy signal becomes a loud warble that is almost as annoying. Slowing down the integrators doesn't really fix the problem but it does sort of appear to help. Unfortunately, slowing the integrators will also cause the detector to require very slow sweep or small targets will simply be ignored.

The key integrator capacitors in this detector are in the sample hold circuits and are C22, 23, 23 and 25. You will notice all are the same value, 330nf. What isn't obvious is these capacitors are usually matched to 1% so the timing circuits are identical. This keeps the signals all balanced.

Other capacitors in circuits past the integrators do the same basic thing but are not as effective.

Again, any jittery or raspy type signal is normally caused by this EMI problem. Changing the pulse rate shouldn't cause the signal to suddenly become rough and raspy if everything is working properly.

BTW, did you move the frequency to try it or because it was causing an annoying hum when using headphones? There is no need to move the frequency if there is no objectionable hum. A slower frequency like what this detector is designed for does reduce the current draw, so batteries last longer.

How did you change the pulse frequency?

Reg

[Jose]

Thanks Reg, for your extensive reply
You describe exactly how does my MD because of EMI. Even with the slow adjustment often eliminates much of the noise and in the countryside away from power lines is much more stable.
Now I understand better what is happening and the cause may be the changes that I made in order to obtain maximum profit while maintaining low consumption.
Let me mention a few changes to better understand what is happening.
Replace the 555 in a 7660, source in synchronism with the pulses TX, to reduce noise originated.
The front stage using an NE5532, the scheme is equal to that used in the hammer. Improved gain with less noise.
Canceled the TX resistor R78, of 2.2 ohms; Use a makeshift coil 30 cm., 380 uH and ohm 2; Original frequency Variable 450-550 Hz, pulse width 100 useg.
The resistor R27 2.2 k was modified slightly for maximum profit.
Use a capsule speaker 600 ohm telephone connected directly to negative 14.4 volts instead of L4, to eliminate disturbances in the 12 volt line.
The source also modified, copied GS5 scheme published in the forum, regulated 10 volts negative and a current limiter for TX.
I do not use "Reset" to use R49 and R50 1Mohm. "Hold" is an internal control for adjustments.
With these modes, the detector is sensitive, low power (140 Ma), fast response to small objects, but somewhat noisy in the "Off" mode, in other modes is quiet and stable.
I tried to take it to the MD about 1000 Hz but these problems occur aforementioned.
As you mention, and I think the EMI, noise noise generated itself, may be the cause, I'll have to review the case made, especially in TX and RX, if want to increase the frequency.
Regards
Jose

[Reg]

Jose,

You can expect more noise when using a large coil. Fortunately, your 30cm coil (almost 12") isn't that large. The larger the coil, the more noise because a coil acts like an antenna and the bigger the antenna, the more noise it can pick up. Mono coils also are noisier than DD coils.

What are you using for shielding on the coil?

R 27 is a 2.2K which is also a large noise generator. Reduce this to 1K and the noise will be reduced noticeably. That is one reason a 1K is used in the Hammerhead. I need to try lower values but I will have to parallel one of the 1n4148 diodes first to compensate for the increase in current.

I am puzzled as to why the OFF mode is noisier? I noticed that with one of my modified units also. In theory, the off mode should be quieter. So, I need to look into what is happening there especially if it is noisier than the ALL mode. In the OFF mode all signals will sound off like a low conductor so it should be quieter.

One thing you might try is to turn the GB to maximum and see if the noise level is closer to that of the OFF mode. If it is, then it makes sense to a point. When the GB is set somewhere between the two, the summation of the gold channel and the iron channel signal is reduced in value for two reasons. One reason is there is a resistance between the different opamp's output and the summing point and the second is the cancellation action between the two.

If you want to make a spare coil winding that can be used for testing, you might make one similar to the one you are using but twist it into a figure 8. This figure 8 shape should cancel noise if the halves are equal. This type of coil can be used for testing even in doors to reduce the noise. The alternative is to build a small coil maybe a 5" coil. The figure 8 coil should be quieter, though.

I am wondering about something that might be causing the noise but I need to check into it first. If sel 1 or sel 2 are quieter than the off mode then I need to look into that also. I no longer have the sel 2 feature but can test the sel 1.

You need the reset function to adjust or align the different pots used to set the outputs to zero. At least, that is the best way.

Now, the adjustment of RV 4 is more critical than people realize and may be part of the problem causing the noise. The closer it is to turning on the better. In other words, if the output of U12b is 0.000v then you can set RV4 for 1mv or even less. I am not happy with the design of this circuit and may change it in the future.

Reg

[Jose]

Thanks for listening Reg
I'm using Scotch tape No. 24 as shielding. Larger coils as 40 X 40 cm. is almost impossible to use in the place where I live, but works acceptably well the field, I have to do more tests.
I do not know if I'm confused, but in the "OFF" mode, which is the No. 1 channel works only gold, the sensitivity is maximum and is noisier, in this way, not work the potentiometer GND.
In other modes, "2 ALL METAL", "3 SELECT 1 and 4 SELECT 2", is set GND. The sensitivity decreases in these modes, and also reduces noise, as it moves forward with this control, to its maximum value.
I think I expressed myself badly, in the previous post, I apologize, so I have a key "RESET" on the PCB, for the corresponding settings of the presets.
Regarding setting RV4, I found it worked better if you set the output voltage U12B slightly negative, take the value of 5 millivolts negative to give a small safety margin. RV4 then adjusted until the gain decreases sharply, then back off this control until it regains the gain, then advanced a fraction that is multiturn this control, this is done with the internal RESET disabled.
I do not know if this procedure is correct, but it is what works best in my GS4. And it not seems to affect sensitivity.
Another change you make is to replace R51 220 K for a 22 K, the improvement is remarkable, this idea suggested to me by a colleague who saw the forum in a similar scheme.
I am experimenting with a difference of 35 useg. in both channels by changing R15, in principle appears to increase the sensitivity at the position 2, 3, and 4. Although I do not know if I'm missing something.
I have yet to try a DD coil and Figure 8 as you suggest.
Jose

[Reg]

Jose,

It sounds like you have a pretty good idea of how the GS 4works and what to try next. Varying the time between samples (R15) will display a few different things such as where the iron is eliminated. Advancing the time requires more iron signal for proper ground balance at the minimum delay and because of this may cause a slight increase in noise but not as bad as no GB or full GB.

The R51 and C34 combination adds a small delay turning on and turning off the FET's that are there to eliminate the opposite half of the signal. In this case, a negative signal is normal and when the signal out of U12b goes positive, the FET's are turned on determined by the RV4 setting. If this stage is inhibited by activating the Hold switch, the audio heard would be a wee/woo if the threshold is high enough. This is the more common signal one hears on other PI's. Also, when the capacitor C29 or C28 are discharging, there is a time when no target could be heard. So, by quickly discharging the caps mentioned, the detector can quickly respond to different targets very close to each other.

Changing R51 to a lower value reduces the several millisecond delay mentioned above but it is still there. This delay does cause problems.

Changing the subject, maximum noise on this detector should happen at the None setting or when the GB control is at maximum. At any other setting of the GB there is a signal loss which should result in a reduced noise but also a reduced gain.

Because this is a full sample and hold design, you might want to try shorter sample time. This might reduce the noise also. I think the sample time is set by C19 and R19 and R20, but I don't remember for sure. You should be able to go down to a very short sample time of less than 5 usec with little obvious difference except for possible noise. Be careful, the value of R 19 and R20 shouldn't be less than 5K according to the specs on the 4538's.

How are you current limiting the transmit? That was originally tried on the GS 5 but abandoned later. Maximum depth will occur when the target is fully saturated and this happens at a larger tx current with pulse length designed for the metals you desire to find. Coin size objects do reasonably well with 100 usec but larger silver and copper objects or very large iron objects should show an improvement in depth with a longer pulse on time.

Now, with that said, using a larger coil also increases the depth potential providing noise doesn't become a problem and the target signal on a target at depth provides a response deeper than half the diameter of the coil. This means if you can detect a target much deeper than 15 cm, then that target can be detected deeper with a larger coil. Just how much deeper can be sort of determined by using a graph made by Eric Foster many years ago. I have attached that chart.

Reg

[Reg]

For those of you who may be confused with the chart, here is what Eric posted back in 2002 when he posted the chart on how to use the chart.

"Here are the curves I have used for many years. As Robert said, the range reaches a maximum when it is equal to the radius of the coil. Coils larger or smaller than this optimum will result in less range. To show how this works, along the bottom axis you see coil diameter, which is obviously 2 x the radius. So for an 11in coil, if we go up the vertical scale to A, we have 5.5in. Also note the diagonal line and the series of ever increasing semicircles. Everything to the left of this line shows increasing detection range up to the maximum where it intersects the line, then decreasing range to the right, where the semicircles are shown dashed.
If a certain metal object is just detected at 5.5in with the 11in coil, then going larger in coil size will cause a reduction (going down the dashed side), and going smaller in coil size will have a similar effect. Initially, it won’t be much, i.e. going from 11in to 8in will only make 0.5in difference but below 4in diameter, the range will drop rapidly.
Now, suppose with the 11in coil, you can detect an object at about 12.5in (B on the vertical scale. This indicates that the coil is not an optimum size for that particular object. If we carry on up the curve (direction of arrow) we can see that by using a 20in coil, we could gain another 2.5in (C). The curve peaks at 15in with a 30in coil. But the extra inch gained hardly makes such an unwieldy coil worth while.
Other factors come into play of course. The curves assume that the number of turns and the coil current is the same in all cases; which it isn’t necessarily. For the same inductance value, a smaller coil has more turns, which counteracts to some degree the loss in range. Also a smaller coil will pick up less electromagnetic noise, earth’s field noise and ground effect, which make for a smoother threshold.
The end result is, that with a small nugget that can be detected at between 5 and 7in with the 11in coil, so that it is on the top part of the curve, an 8in coil may well give a similar range. That is not to say that smaller coils do not have other advantages. Small coils and probes are very useful in rocky areas or searching in undergrowth. They have less drag too for water hunting, and less pickup from mineralised soil or conductive sea water plus better signal separation on close or multiple objects.
One other point regarding PI, is that the small object sensitivity is largely determined by the sample pulse delay. If an object is so small, or thin, or made of high grade stainless steel, such that all the signal has decayed before sampling takes place, it would not matter how small a coil you made, it would never be picked up.
Bed time problem for the depth junkies – If the Aquastar with a 10in coil can pick up a ring at 20in, what is the optimum size coil for maximum range, and what range could theoretically be achieved? That’s the depth at which a mere pulltab could trigger suicidal inclinations [IMG]file:///C:\DOCUME~1\Reg\LOCALS~1\Temp\msohtml1\01\clip_ima ge001.gif[/IMG]
Eric. "

Keep in mind this chart only gives an approximation and doesn't take into account noise problems or other anomalies. It does give a general idea of what one can expect if they build a larger coil and just what size might be the ideal size if you know what you are trying to find and have one of that object you can test.

Now in the case in the explanation by Eric shows that if you can detect an object at 12 1/2" with a 11" coil, you gain about 2 1/2 inches in depth by almost doubling the coil size and less than 4" if you triple the coil size.

So, this sort of shows there are depth gains but not as dramatic as one might think.

Reg

[Jose]

Thanks Reg, for the comments and illustrations.
I am using the current limiter based on LM337. Not sure if the R-value of 2.2 ohms, is suitable, do not increase this value, to keep low, the voltage difference between the input and the output of the regulator.
The pulse width corresponding to the sample, in my GS4, is somewhat less than 20 useg.
I will follow your advice and then comment on the results.
Jose

[ABDW9]

Hello everyone
I have a problem in the absence of the element (j113) What do I have to do
Is there a replacement?
Thank you

[Reg]

Jose,

I made an error when I said you may not see much of a depth loss if you shorten the sample width. To be honest, I was thinking of a different design where multiple things change when the sample width is altered. As for the GS 4, I haven't done any calculating so I can't say for sure just what will happen but I suspect there will a be a depth loss. I just don't know how much.

To be honest, I did do some experimenting with a somewhat similar design but at the time, I changed both the sample width and the frequency of samples so I really don't remember just what happens or by how much things change by only changing the sample width.

One person who has done a lot of designing of PI's recommended a very short sample time, so part of my recommendation came from his advice.

Sorry if I confused you.

Changing the subject again, what do you plan on hunting for with your GS 4? I am also curious as to where you are located if you don't mind saying.

Changing the subject again, the DD coil does a little better on really small targets but won't have the depth potential of a similar size mono coil. I haven't tried a balanced Concentric coil yet and that is on my agenda to build. Dave Emery's explanation is quite thorough for those who haven't read it. There is a copy of his explanation on how to build this type coil on the Geotech project page. Now there is a discussion about various coils on another thread on this forum. For those interested, it is in the coils forum under advanced PI coils.

Reg

[Reg]

ABDW9,

The J113 shouldn't be that hard to find. Where are you located? Do you have access to ebay because they have some for sale on ebay.

As for a replacement, I am sure there are cross reference books that provide some cross reference number. Right now I don't have access to one.

Now, the J113 is a N channel Jfet. So what you will need is a N jfet. Next you need to look at the specifications of this part and try to find one that has similar specs. Things like cutoff voltage and current at 0voltage on the gate are important.

I suspect some of the jfets used on other PI's or for similar purpose of a switch like the TIS 75 or the 2n5485 would most likely work. However, I didn't check the pin configuration so make sure you do that. In other words, if the board is made to use the J113, make sure you place the gate, drain and source leads where they belong.

To be honest, I am not one that is any where close to being a Jfet expert. So, I am hoping others more knowledgeable will jump in with other or better recommendations.

One more note, these Jfets used are usually matched so at least use the same N jfet and not mix and match different fet numbers.

Reg

[Orbit]

replica j113 also 2n4393 !

[Jose]

Reg, I made some experiences with Delta Pulse, decreasing the width of the sample in the range of 25 to 50 useg. The result was that the gain decreased.
I do not remember where I read in the forum, some fast driving small objects, such as gold, can be lost if the sample is wide, so do not rule out perform the experiments.
I did some DD coils for DP, but did not walk in my GS4, apparently caused by noise in the PCB mass points, not enough experience.
I think the GS4, can be used to detect gold nuggets, in places where the soil is highly mineralized and other PI would not work, with the limitations that are known,
I live in a village in the province of Chaco, Argentina to 10 km of the river Paraguay, forest predominates here and the plain, the sea is more than 1000 km. The soil does not have many minerals, and no gold nuggets around here. however I performed detectors for hobby and my first MD, was the "sandcastle".
There are places near where I live, where there was the triple alliance battles in the last century (Brazil, Argentina, Paraguay, and Bolivia) and many stories of buried treasure, but I do not do any research until now, is a project that is pending.
Conducted tests in some natural spas around here, to find common use coins or other items of little value, so my experience as a hunter, is poor.
I'm passionate about Pulse MD as TDI, but I know him only by youtuve pictures and videos.
I love watching my GS4, that will not stop ringing in the back of my house by the trash, calms when adjusted to remove a nail.
Cordial greetings
Jose

[ABDW9]

ABDW9,

The J113 shouldn't be that hard to find. Where are you located? Do you have access to ebay because they have some for sale on ebay.

As for a replacement, I am sure there are cross reference books that provide some cross reference number. Right now I don't have access to one.

Now, the J113 is a N channel Jfet. So what you will need is a N jfet. Next you need to look at the specifications of this part and try to find one that has similar specs. Things like cutoff voltage and current at 0voltage on the gate are important.

I suspect some of the jfets used on other PI's or for similar purpose of a switch like the TIS 75 or the 2n5485 would most likely work. However, I didn't check the pin configuration so make sure you do that. In other words, if the board is made to use the J113, make sure you place the gate, drain and source leads where they belong.

To be honest, I am not one that is any where close to being a Jfet expert. So, I am hoping others more knowledgeable will jump in with other or better recommendations.

One more note, these Jfets used are usually matched so at least use the same N jfet and not mix and match different fet numbers.

Reg

replica j113 also 2n4393 !

Thank you my brother shaking
Ask your thorough explanation
Thank you for your interest
I I live in Sudan and we have many sites to buy electronic parts, but unfortunately I did not find this element j113 I do not know why not be present to have, although I got on all the elements of the device
For long positions this painted this component of many sites, but of no avail was not sure if they had Ohtamo my application or is this sites and fake sites only ... I do not know!!!


You mentioned that Bomkanni use is similar in function to the power cuts and the current 0voltage important gateway.
Does this will do the job in the GS4 enough that does not impede or no affect on the device?
Like my use of similar 2N4393



And thank you very much
You all due respect salute you.