Vallon VMH3CS Mine Detector

[Ferric Toes]

A couple of hours out this morning. I am not overly happy with the 30cm coil perhaps a bit to sensitive for gold hunting....With it ground-balanced, the only way its use-able is with the sensitivity down to 8. Higher than that and it squeaks on just about everything and would sound off if I lifted the coil off the ground.....I buried my 1.8g nugget down about 6 inches and the 30cm coil set at 8 sensitivity could not find it....Regular coil did
Managed to find a 2.2g bullet lead at around 5 inches, made a lovely sound with the 30cm coil. The regular coil picked up a small 0.3g piece of some sort of aluminium thing at about 2 inches easily and a 1.5g bullet lead that it absolutely screech on that was just under the surface.
Going out again tomorrow, so will see what happens....If I am finding lead and aluminium, gold cant be far behind ha ha

Maybe the 30cm coil is better for searching the beach where you don't need the mineralised setting, except on black volcanic sand of course.

I lent Daverave a Vallon for beach testing and he has also my 28cm homemade coil to compare with the stock coil. Results so far have been good -

QUOTE
a very small thin 22 ct gold ring....6"
titanium/silver wedding band ring.... 12"
silver wedding band ring....10"

So far havent found any gold as yet but a very deep bullet and some tiny small round pieces of copper about 4mm diameter which were again deep and the vallon gave
excellent sensitivity on these...with excellent stability and good pin pointing....larger coil seems very good.

He, or I, will post more results as they come in. I am also in the process of making a 15" coil for testing, but I have no areas of high mineralisation here except for a small car park laid with fired brick. However, that would be far weaker than the ground in Australia.

Eric.

[6666]

A couple of hours out this morning. I am not overly happy with the 30cm coil perhaps a bit to sensitive for gold hunting....With it ground-balanced, the only way its use-able is with the sensitivity down to 8. Higher than that and it squeaks on just about everything and would sound off if I lifted the coil off the ground.....I buried my 1.8g nugget down about 6 inches and the 30cm coil set at 8 sensitivity could not find it....Regular coil did
Managed to find a 2.2g bullet lead at around 5 inches, made a lovely sound with the 30cm coil. The regular coil picked up a small 0.3g piece of some sort of aluminium thing at about 2 inches easily and a 1.5g bullet lead that it absolutely screech on that was just under the surface.
Going out again tomorrow, so will see what happens....If I am finding lead and aluminium, gold cant be far behind ha ha

Keep at it

[kingswood]

A couple of hours out this morning. I am not overly happy with the 30cm coil perhaps a bit to sensitive for gold hunting....With it ground-balanced, the only way its use-able is with the sensitivity down to 8. Higher than that and it squeaks on just about everything and would sound off if I lifted the coil off the ground.....I buried my 1.8g nugget down about 6 inches and the 30cm coil set at 8 sensitivity could not find it....Regular coil did
Managed to find a 2.2g bullet lead at around 5 inches, made a lovely sound with the 30cm coil. The regular coil picked up a small 0.3g piece of some sort of aluminium thing at about 2 inches easily and a 1.5g bullet lead that it absolutely screech on that was just under the surface.
Going out again tomorrow, so will see what happens....If I am finding lead and aluminium, gold cant be far behind ha ha

[kingswood]

schematic of the Tx??

About 12 pages back I think

[localbug]

Any image of the board or schematic of the Tx??

[kingswood]

One new feature that does not seem to be documented, is to press 'pinpoint' while searching in the compensation mode and to hold it down. The dynamic mode is switched off but the signal appears sharper than in the dynamic mode and no apparent loss in range, ground compensation is not affected, and there is no screeching when the coin is removed. Could this make a good searching mode? Perhaps some tests could be done by our friends in Australia, or other highly mineralised areas, to see if there are any downsides to this.Eric.

I will have a look at this next weekend. I have tried the pinpoint button only a couple of times previously....When I released the button, got lots of screeching.....It seemed pretty accurate at finding roughly where the signal was

[Ferric Toes]

Ground Compensation.

Reading through the different manuals of the VMH3CS, for 2007, 2010 and 2016, the methods for ground compensation are a bit confusing. I think we can discount this section in the 2016 manual as the majority of used detectors that are on the UK market at present seem to be dated 2006 - 2010. Vallon state that the software settings can be different depending on what market they are selling into. Some features, therefore, that are mentioned in the various manuals may not be accessible, or may be slightly different in their setting up procedure.

According to the 2007 manual the 'mineral' setting of the control switch "activates a standard program for mineralised soils". Switching to that mode automatically gives basic soil compensation, but which may need a little tweaking "to adjust to a fine adaptation directly at site", as the manual says. This involves keeping C pressed and after the beep, moving the coil up and down over the soil for maybe a minute or so, until a continous tone is heard. Release C and there will be a short beep to show that the setting is stored. I found that this worked well on a tray of Australian ironstone gravel and a large lump of ironstone which in normal mode sounds like a piece of metal.

When in ground compensation mode the SAT or dynamic mode is much slower than in the normal mode. The signal from a coin above the coil will slowly die away, but when you remove the coin there is then a loud screech from the detector which can immediately be silenced by pressing C, or, it will die back to nothing on its own, if left to do so.

One new feature that does not seem to be documented, is to press 'pinpoint' while searching in the compensation mode and to hold it down. The dynamic mode is switched off but the signal appears sharper than in the dynamic mode and no apparent loss in range, ground compensation is not affected, and there is no screeching when the coin is removed. Could this make a good searching mode? Perhaps some tests could be done by our friends in Australia, or other highly mineralised areas, to see if there are any downsides to this.

Eric.

[kingswood]

Not easy to put in simple terms but it's units are henries, millihenries, and microhenries. Named after Joseph Henry.

Inductance, or self induction, is the property of an electric current by virtue of which it tends to resist any change in its rate of flow. It is sometimes spoken of as magnetic inertia and is analogous to the mechanical inertia of matter. Self induction is due to the action of the current upon itself during variations in strength. It becomes especially marked in a coil of wire in which the adjacent turns act inductively upon each other upon the principle of mutual induction arising between two adjacent circuits (the individual turns of wire). Self induction manifests itself by giving momentum to the current so that it cannot be instantly stopped when the circuit is broken, the result being a bright spark at the moment of breaking the circuit. When the circuit is closed there is no spark because at the instant of closing the circuit the current is at rest and on account of the self induction, the current cannot rise to its full value (until some time has elapsed).

The above is taken from Hawkins Electrical Guide No.1 1917 and I used this because more modern books tend to gloss over a word description of what is happening. In a PI detector coil the current rises relatively slowly to its final value and on the switch of we get a high voltage spike, all due to this property called inductance. We do not get a spark as the book states because the high voltage is clipped or otherwise controlled so this does not happen.

Hope this helps,

Eric.

Thanks Eric....I am slowly learning
No background at all in this type of stuff and up until a few months ago would never have given it a second thought!...Now my mind is constantly filled with coil inductances, time constraints, pulse rates, pulse lengths and delay times ha ha !! Okay, back to more reading!

[Ferric Toes]

I have a question!...lots of google and I am still lost
So the Vallon coil inductance is 1.5mH....What does "inductance" really mean? Sorry, I have tried and tried and think I may well have ended up more confused than when I started !!
Does inductance effect depth??

Not easy to put in simple terms but it's units are henries, millihenries, and microhenries. Named after Joseph Henry.

Inductance, or self induction, is the property of an electric current by virtue of which it tends to resist any change in its rate of flow. It is sometimes spoken of as magnetic inertia and is analogous to the mechanical inertia of matter. Self induction is due to the action of the current upon itself during variations in strength. It becomes especially marked in a coil of wire in which the adjacent turns act inductively upon each other upon the principle of mutual induction arising between two adjacent circuits (the individual turns of wire). Self induction manifests itself by giving momentum to the current so that it cannot be instantly stopped when the circuit is broken, the result being a bright spark at the moment of breaking the circuit. When the circuit is closed there is no spark because at the instant of closing the circuit the current is at rest and on account of the self induction, the current cannot rise to its full value (until some time has elapsed).

The above is taken from Hawkins Electrical Guide No.1 1917 and I used this because more modern books tend to gloss over a word description of what is happening. In a PI detector coil the current rises relatively slowly to its final value and on the switch of we get a high voltage spike, all due to this property called inductance. We do not get a spark as the book states because the high voltage is clipped or otherwise controlled so this does not happen.

Hope this helps,

Eric.

[kingswood]

I have a question!...lots of google and I am still lost
So the Vallon coil inductance is 1.5mH....What does "inductance" really mean? Sorry, I have tried and tried and think I may well have ended up more confused than when I started !!
Does inductance effect depth??

[kingswood]

Looks great Eric. Top work!
I like the stand too.

[Altra]

Hi Altra,
Yes, in the Vallon connector there is wire that links pins B and F. This mutes the internal speaker. According to the manual, F is ground and C is live to the piezo phone. In my commercial connector the link from ground to B is provided by the switch on the small box housing the transformer. You can do it with three wires in the cable.

Eric.

Thanks for the information.

Mark

[Ferric Toes]

That looks great Eric. On my unit I didn't want to source a connector, so I used the factory audio cable/connector. What I noticed is the external speaker is muted when the connector is plugged even with nothing connected to the two wires. In other words using the factory headphone cable and connector, you can't have the option of toggling between speaker and headphone as you have done. I suspect there is a load resistor or some kind of jumper potted in the connector? When I get time I'll pull mine apart and take some ohm readings.

Hi Altra,
Yes, in the Vallon connector there is wire that links pins B and F. This mutes the internal speaker. According to the manual, F is ground and C is live to the piezo phone. In my commercial connector the link from ground to B is provided by the switch on the small box housing the transformer. You can do it with three wires in the cable.

Eric.

[Altra]

That looks great Eric. On my unit I didn't want to source a connector, so I used the factory audio cable/connector. What I noticed is the external speaker is muted when the connector is plugged even with nothing connected to the two wires. In other words using the factory headphone cable and connector, you can't have the option of toggling between speaker and headphone as you have done. I suspect there is a load resistor or some kind of jumper potted in the connector? When I get time I'll pull mine apart and take some ohm readings.

[Ferric Toes]

Latest Audio Converter

Here is the latest version of the audio converter for standard moving coil headphones. A switch has been added so that the internal speaker can be used instead of phones if quiet conditions allow. i.e switch toggle pointing away from phones socket is internal speaker only: switch toggle pointing to phones socket is for phones only and speaker is muted.

A 100nf capacitor has been also added in series with the transformer primary to eliminate the 'thump' on each audio pulse when the detector is self testing and also on the 1 second 'confidence pulse'. This is necessary because the moving coil headphones have a much extended low frequency response than piezo ones. With the phones set to stereo and connected in series at the socket (common ground not used), either volume control can be used to reduce the sound level, which is more than adequate when turned right up.

Eric.