The headphones usually supplied for use with metal detectors are dinosaurs. Heavy, expensive, and flimsy of make, the sound quality of these burdensome and ridiculous things is a joke, and thats not a good thing at all, because sound quality in metal detecting is really what its all about!
Until I figured this little contraption out, I never made much money detecting because I was replacing headphones yearly to the tune of 50-100$ per. Now I carry three of four extra headphone sets with me everywhere I go, and these cost me about 2 dollars each, or less.
I studied many varieties of metal detector sound amplifiers before coming up with this idea, and it sure works well, and is easy to accomplish. While reading over this article, and building your own super booster sound amplifier, remember that many other good things can be made by modifying equipment and machinery to fit your needs.
This project will give you super sound quality, and adjustability. I have had many people tell me that by being able to adjust their metal detectors closer to threshold frequencies, they actually gain an inch or more in depth, and that is a BIG advantage. I myself have experienced this, and more. Those hunted out areas become huntable again, and remember this: a lot of the best stuff at any site is the deepest stuff.
You will need to obtain a walkman-type cassette player, which will then be altered to serve as your metal detectors SOUND AMPLIFIER, and it will also allow you to use the lightweight and REAL POWERFUL ceramic-speaker headphones that can be replaced for a dollar or two. Usually these run on two AA batteries.
Other than this belt-mountable cassette player, you will also need this short list of supplies:
Soldering Iron, soldering flux, and rosin core solder — do not use acid core solder, because it will not work, or it will not work for long.
– Small phillips head screwdrivers.
– Wire stripping tool/knife.
– Propane torch or bic lighter
– Small diameter heat shrinkable tubing = 1/8″ . Henceforth called HST.
– Electrical Tape
– A hot glue stick
– A 1/4″ Stereo headphone plug — Its very important to get a STEREO plug vs. a MONO plug. A MONO plug will not work.
A two foot long piece of wire-wrapped two-strand electronic cable with about a 1/8″ inner diameter, and an outer diameter of around 1/4″. Co-axial cable with a braided wire mesh on the outside, and two separate wire strands on the inside, is what you are after. Strip an inch of this wires insulation totally off both ends, twisting the outer wire braid into a third wire. Tin all of these wire ends with solder (See page on soldering).
A lot of the above can be salvaged, and the total cost of the supplies should not exceed ten dollars. I have consistently bought walkman cassette players used and still working for 50 cents or a dollar at thrift stores. I have 5 or 6 here right now, I picked up just because they were there and practically free. Almost every one of the type of stores selling used items has a special section for used electronics, and many times they will have a box FULL of the radio/cassette players. Make sure you obtain a machine with a cassette player, do not get one that is just a radio. This is because the amplifier we are after requires the amplifying circuit of the cassette player, and also because the cassette player mechanism allows easy access to that circuit.
When you buy these, get them cheap, or free, but before doing any work put batteries in and see if you get at least a loud hum from the headphones, when the volume is turned up. If they work perfectly, thats better, but sometimes the little rubber bands running the mechanics of the tape-turner go to heaven, and the machine is then good for our purposes but its wheels will not turn.
If none of the above happens, then toss the thing, and get another. You can even buy new hipmount cassette players for about 5 dollars, but the older meatier machines are actually better, and, as stated, still plentiful.
The players are usually encased in two pieces, and it all comes apart after 6 little screws are located and undone around the outer edge of the back of the player. Save the screws and remember its all going to have to go back together when this is done.
Once you get the cassette player apart, find the motor on the circuit board and cut its power wire, otherwise it will cause interference during operations. Cutting the rubber bands does not accomplish the same thing, you must remove power to the motor. One or both wires running into the motor are clipped, and that is that. Make sure they cannot short out later. Hot glue any loose ends and fasten with a dab of hot glue somewhere out of the way. Do not make trouble for yourself when its time to put the machine back together though, and keep hot glue well away from the circuit board.
Now look for the shiny metal cube, which is called the cassette head. The wire we need to hook up to, runs right up to that shiny metal cube, the cassette head. Find it and cut it up as close to the shiny cube as possible. You need as much slack as you can get, and there will not be much. This is the same type of wire-wrapped 2 strand cable that you have obtained already, except that it is smaller in diameter. Strip the ends of this wire carefully, and tin each bare wire (see the page on soldering).
IMPORTANT******* Remember to place your HST (heat shrinkable tubing) on wires BEFORE joining any two wires. Cut the pieces small enough so they can be slid out of the way, and be unaffected by the soldering irons heat, but then can be pulled up over the join, to be shrunk in place permanently. Any heat will shrink that stuff so be careful. Double or triple applications of HST is a good trick for waterproofing and strengthening joined wires.
On either end of the two-strand wire wrapped cable goes the 1/4″ Stereo Plug. 1/4″ denotes the diameter of the plugs shaft, by the way. Inside this plug are three prongs, one being higher and usually larger in size than the other two. The outer wire wrapping of the cable, which has been already twisted and solder-tinned, gets attached to that largest of prongs. The other two wires you just solder where they fit best, at this stage, because correct polarities will be checked when it gets hooked up to the amplifying circuit in the cassette player.
Lets go over what we have done so far: You have taken the player apart. You have soldered the 1/4″ Stereo plug on one end of the wire-wrapped 2 strand cable from your supplies list. You have also stripped and tinned the wire wrapped 2 strand cable inside the player, which runs from the cassette head (Shiny Cube) to the printed circuit board/amplifier circuit.
Now we need to test this set up, and its tricky, but the end product is very well worth all this trouble, believe it.
Plug the stereo plug into your metal detector. The wires on the other end of it now need to be tested with the wires running to the circuit board of the cassette player. The outer wire wrapping will connect to the outer wire wrapping of the cable inside the cassette player. The two other wires must be tested with the cassette player on and hooked up to the metal detector. You can turn it on by hitting the players PLAY button, and you have to have the headphones on to hear all this.
Turn the volume to about 1/4 or 1/2 but don’t blast your ear drums. Turn the metal detector on, with tuner at #1 preset level, and turn the detectors volume all the way up. Again, the cassette player is also on. Make sure the batteries are hooked up and there is power. Put the headphones on and attach the outer wrapped wires from both cables together. Now test the two wires out of the center of this wirewrapped cable with the two corresponding wires running into the player.
When you get it right you will know, as long as everything is hooked up with power. If you can’t get any sound either way, you have a bad solder join/connection somewhere, or a switch is off. Go back over this until you get it right. Once you have tone and variability coming through the headphones, solder the wires as is, shrink their HST, wrap with electrical tape, and re-assemble the cassette player.
Before doing any soldering remember to correctly place the stereo plugs cap, and any HST, in their correct spots before joining.
You can make an egress point for this outbound wire going to the detector, wherever it is needed, by melting the plastic casing of the cassette player with a lighter or even the soldering iron. Attach this wire inside the cassette player with hot glue, so that any pull on it is not on the soldered join. Do remember to keep hot glue away from the circuit board too.
This finished super booster now gets strapped to your metal detector with rubber banding or whatever you can deduce for your own particular set up. Mount it on the detector so there is not a lot of trauma replacing the batteries.
Practice getting just the right amount of volume that will let you adjust your threshold frequency as low as it will go. This increases field size of the coil and you will gain many advantages, including increased depth. The differences between round targets and not is more easily discernible too. Ferrous and nonferrous have much more clear signatures when listening with the increased sound quality. You will love it. Be careful with the sound though, you have much more than your ears need, or can even handle. Do not make yourself deaf by trying to get more from the machine than it can give. If you use this to its best utility, you will increase your finds exponentially over time, and will save a lot of money.
The ability to solder is important in all electronics work, and for other work too, like plumbing, or jewelry.
The correct way to solder is to clean all the metal to be soldered first, then coat the metal well with rosin soldering flux. Different work requires different soldering fluxes, but all electronic work uses ONLY rosin flux, and most of the solder comes in wire and is called rosin core solder, because it has this type of flux running right through the middle of it.
Apply the soldering gun or soldering pencil to ONLY one cleaned and fluxed wire or terminal at a time, simultaneously applying the solder itself to each area being heated. As soon as high enough temperature is reached, the solder will melt and flow across the entirety of the heated wire or terminal. This is called Tinning. You will see the solder coat the wire or terminal entirely. It should be bright with no dull spots. If there are dull spots apply heat until shininess is achieved. Do not confuse burnt flux with areas of dull cloudiness. Dull cloudiness is the result of insufficient heat. Burned flux may appear dull but when scratched off the solder will probably be bright underneath. If there is excess solder on the part it can be shaken off carefully at this stage of treatment.
Two tinned pieces of metal only require a minimum of flux and heat to join together when the soldering iron is applied to them. This is how the professionals do it, and the minimum heat at this stage allows for the use of heat shrinkable tubing, and protects delicate components.
In electronics only rosin core solder is used. Do not use acid core solder unless your job specifically calls for it. Acid core solder will never be used to make electronic connections.
A necessity in soldering is to expose only the amount of metal necessary for a good soldered joint. Any excess exposed metals just crate greater possibilities for short circuiting down the road.
Good soldering skills are usually the difference between good work, and only so-so. practice on scraps until you get good, and perfect soldering is not hard once you get the hang of it.
Editor’s Note: Bill Gallagher originally sold this report, but has decided to make it public domain through DetectorBase. The original article was written in 1991. We would also like to emphasize that the opinions expressed in this article are of the author and no way reflect the opinions of DetectorBase.
Author: Bill Gallagher
Bill Gallagher sold his first treasure hunting article when he was 19, to Western and Eastern Treasures magazine then of Arcata California (Coral Fever). He then proceeded to publish magazine articles with them on a steady basis through the mid 90’s, as well as with several other magazines. Subjects included metal detecting, rock hounding, numismatics, bottle collecting and much more. Bill turned 48 in 2007, and is still treasure hunting strong.
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