Vallon VMH3CS Mine Detector

[Altair]

Hi Carolina,
could you explain more about vacuum test you made to ensure water proof of unit?
I wonder how I can have confidence to submerge my unit!

[Carolina]

The test on the full submerging of the VALLON lasted 4 hours 10 minutes without any problems in waist to chest deep water.
I retrieved a number of targets including coins, jewelry, and trash. I have had no luck posting a picture though but will try again.
I have not noticed any tone difference between gold, silver, nickel and trash. The only tone difference I hear is in the depth of the signals and the double blip from shallow targets. This could be me though.

[garyq]

Interesting Kingswood as Aluminium can be a close substitute to Gold.

[kingswood]

The Vallon screams when detecting Aluminium!! The sound (to me) seems a bit different to metal or lead....Aluminium sounds "cleaner"...more of a fuller screech....If that makes any sense

[Mdtoday]

Hi Carolina,

Excellent, they are certainly well made machines, good hunting��

Brian

[Carolina]

Brian: The vacuum test was done prior to servicing the machine. My first VALLON was submerged for a brief amount of time to satisfy my curiosity. They both have had firmware updates but only the second went thru the vacuum test and then received new gaskets, o rings, dehydration capsule, arm rest strap and a test of the new firmware. This machine will be my extended submersion machine four hours or so. The first VALLON will be my wash and damp sand machine although I feel extended submersion would be fine. VALLON tells me that ALL VALLONS are made to be submerged so the service member could swim with it. Also they are used to clear irrigation ditches in chest deep water. I was told that only the water pressure actuating the tactile switches limits the VALLON to the six foot depth. I might add a vacuum test of the coil was also preformed. I plan a spin this weekend for a extended submersion and will report back.

[Mdtoday]

Did you have to do anything to the unit Carolina?

Brian

[Carolina]

Vallon #2 back home. Ready for full submersion. Held vacuum .500mbar twice the time limit within .003mbar. Should have no issues at six feet

[Altra]

Thanks for posting the photos. The more I think about this circuit the less I believe it will work with a vco as an input. It is probably just a self powered gated oscillator. Which would work good on coin machines like Tesoros or a Garrett Ace250. Better to follow Eric's original idea of using a divider. Maybe a cmos flip flop to divide the audio by two and if possible power it by the signal?

[Qiaozhi]

Here's some photos from my archive:

[Mdtoday]

A long time ago. There were frequency changing headphones marketed as "Rat Phones". When the inventor went out of business he posted the schematic. It uses a cmos 555 timer and is self powered by the audio signal. I never built it but this may be perfect for the Vallon.

[ATTACH]39859[/ATTACH]

It will be interesting to try. I built a similar circuit using just the VCO portion of a CMOS 4046 PLL with a low pass filter from audio signal input to VCO input and it worked OK except for 2 things, it inverted the frequency response and also produced an elongated tone of the confidence beep to a point where it was way too distracting. I set it aside to look at again at some stage.
Maybe this little circuit will work better, hope so.

Brian

[Carolina]

Hi Altra:

I have never seen the tone shifting phones and am not aware of their production. ( Does not mean they weren't only I have never seen ) and yes the interchangeable cable was the ( trade mark ) as the rat tail appearance coined the name. If anyone finds
those 600 ohm kobetone speakers please let me know.

[Altra]

Hi Carolina,

He used to post on this forum, don't remember his forum name. Another innovation on the Rat Phones was the interchangeable cable. Which is what usually fails in headphones.

After posting the above schematic, I recalled that the tone shifting headphones are different than what you have and may have been an experiment which were never marketed? Those 600ohm speakers are rare these days.

[Carolina]

Altra: His name is Rick Viola and the old Rat Phones were some of the best I ever had. They used a 600 ohm Kobetone speaker
that is no longer produced. I bought 6 pairs from mouser several years back and use them in phones today. Their tone is much more mellow and not so harsh and tinny as the benders. I'm sure Eric will come up with a solution to his problem, but for me, the kobetones alone, and the VALLON volume control still allow me to hear the deeper signals as well as alert me to it being a deep signal
and doesn't blow my head off on the shallow ones. I believe it is the Grey Ghost that have a limiter transformer and of course Minelab
has over come this problem with volume, tone and gain control.

[Ferric Toes]

A long time ago. There were frequency changing headphones marketed as "Rat Phones". When the inventor went out of business he posted the schematic. It uses a cmos 555 timer and is self powered by the audio signal. I never built it but this may be perfect for the Vallon.

[ATTACH]39859[/ATTACH]

Thanks for that: it looks very interesting and easy to knock up and try.

Looking at the output of the stepdown transformer I use to drive standard phones, I get a rectangular pulse of 2V amplitude which goes up to 3.5kHz on full signal. Personally, I think a max of 1.5kHz is high enough.

Eric.