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DD coils for the Goldquest SS

A

Anonymous

Guest
Lately Reg. Sniff has done a lot of research on coils to use with his modified Goldquest clone. Running things back, and forth with Eric, it appears that Goldquest SS users can utilize Minelab, Minelab type, SD coils on the Goldquest. There may be a little problem with the larger sizes running it at 10uS., but the 11" DD coil should be OK.
Owners of the latest Goldquest SS will only have to make an adapter to convert the Minelab type connector to the Goldquest style, or re-wire the SD coil to a Goldquest SS connector.
There is the possibility that some may require setting up on a scope for a little tweaking on the damping, but most should work OK.
Perhaps Reg. or Eric will chime in with additional information. Those who wish can email me at Mr.Bill@surfscanner.com
Thanks Reg, way to go <img src="/metal/html/super.gif" border=0 width=26 height=28 alt=":super">
Mr. Bill
 
right now ive got the 11 inch mono coil on the goldquest question what are the benifits of having a dd coil isnt it for heavy minerization or are they better seeking coils go deeper etc. im jest wondering what the bennys are right now the 11 inch mono works great and havent had to change the 10 us setting since i got it guess cause the mineral werte im at are ok more info on this for us laymen folks differences positive and neg. what am i missing switching to a dd coil larry ca
 
Hi Bob,
A question was asked a while back on another forum whether ML SD or GP coils could be used on a GQ. Well, I knew they wouldn't just plug in and work since the plugs were different, but I really didn't know whether they would work if the proper connections were made.
If a ML coil would work on a GQ, then much of the DD coil problem would be solved since there is a wide variety available for the ML's. This would open up a very wide range of coils for use.
Well, I decided to build an adapter that would allow me to test the ML coils and see what would happen.
Little did I know that Eric was already working on this idea also and had already tried a ML coil. He found out they worked on the GQ before I did.
The big difference that inhibits the immediate use of a ML coil is simply the difference in coil connectors. So, I built a very simple adapter that accepted a ML coil plug and had a connector that would work on my PI. This would allow a coil to be used without changing it at all.
What was required for my setup was a 5 pin chassis socket that mated with the ML plug and a regular coil plug I use. My GQ clone uses a 4 pin mic plug and not the regular GQ connector. So it was a matter of connecting the proper pins between the chassis socket and my plug. When done, I tried the one DD coil I had available, which is a ML 11" DD, and it worked quite well. Now, my test adapter is extremely crude and needs to be mounted properly, but it did allow me to test a ML coil.
All that was required was to make sure that the xmit coil was connected to the xmit circuitry and the receive coil connected to the receive circuitry.
Eric's design is very forgiving which allowed for the coils to work. That is one of the beauties of his machines.
One does have to remember that the new GQ 2's are modified to accept a DD coil. The older GQ's will require a modification before they can use a DD coil. Any mono coils built before the DD adapter was developed will have to be modified also. Once the older board is modified, a simple jumper will be required to be added in the mono coil plug to allow it to work.
One other little but important fact is the ML coils have a wider mounting "ear" assembly which will require a different lower rod. One can add a spacer and use the original rod but the proper rod is a better choice.
Reg
 
Hi Larry,
One of the advantages of a DD coil is they do not produce as much ground response as a typical mono coil. Now, in some places, the ground signal is minimal so a DD is of little value. In areas of little or no ground signal, the mono is the most sensitive of the two. However, the difference isn't that terribly great.
Now, in other areas, the ground signal can be a major problem which can seriously affect how the GQ works. In this case, the DD greatly reduces the ground signals allowing for easier hunting and generally provides the ability to detect much deeper targets.
I have found that in many of the gold producing areas, the DD is the preferred coil. It isn't perfect, but it greatly reduces the problems encountered with a mono coil.
The DD also adds something else. Surface iron trash is much easier to distinguish since it will either provide a double blip type signal or a much wider signal than a non-ferrous object. Checking a target by raising or lowering the coil can help one separate ferrous junk or some hotrocks from non-ferrous objects.
Some hotrocks will generate a strong positive response on a mono coils will generate a negative response on a DD. Other hotrocks such as basalt will still produce a positive response on a DD but will be much less of a signal. Also, moving the coil closer to the rock will cause a supressed signal which allows one to determine many of the rocks.
So, there are advantages to using a DD coil in certain areas. Some places almost require a DD while other areas will see little benefit from using one.
One last point is a DD is generally a little quieter than a mono coil. This is due to the isolation between the xmit and the receive and the fact the coils are simply smaller. So, in some noisy areas, just changing to a DD may mean the difference in being able to detect deeper objects and not being able.
I hope this helps.
Reg
 
If you have done the conversion, maybe you can share with us the parts needed (connector type and source?) and a brief wiring diagram (dummy's guide to converting an SD coil to a GQ).
Thanks!
JT
 
No disrespect meant, but it sounds like you would need to send the unit in to be modified. The modification requires cutting the circuit trace, and re-wiring the connector. Changing out the coil connector.
If your using the unit for beach hunting, it
 
Larry
I doubt there would be any benefit for you to change to a DD coil. The most sensitive coil to use in your hunting condition is the mono coil. From the results you say you are getting now, the performance would drop down a bit by changing.
Mr. Bill
 
Hi JT,
Lets see if I can make a very simple conversion into something complex or something like that. The reason I say this is because it is somewhat difficult to get the Amphenol plug used on the GQ's here in the US. I was able to finally track them down at Newark but that was well over a year ago, so I don't know if they are still available.
This is the reason I converted to a different type of plug on my PI. Presently, I am using a simple 4 pin plug commonly used as a mic connector. I picked this plug and socket setup because it was simple and easy to get. Now, it turns out, I find this setup is very similar to the plug used by ML, except ML uses a 5 pin plug.
So, if I had to recommend something to those who want to make the mod by themselves to use ML coils, would recommend simply changing the plug and socket on the GQ to match the ML setup, rather than make a conversion assembly.
However, for those who still prefer to simply make an add on conversion assy, then I will try to explain that also.
By now, it should be obvious the big difference between the ML coils and the GQ coils is the plugs and sockets. So, to make a ML coil work we need to match things such as TX to TX and RX to RX and to know just what has to be done to allow the use of a DD coil. So, basically what has to be done is to provide a 5 pin socket to match the ML coil plug connect this socket to a plug that matches the GQ. I used a piece of S Video cable made by Mogami as my dual coax wire connecting the socket to the plug. If this cable is very short, then most likely other Cables could be used but it should be quality cable.
Now, there are two versions of the GQ which makes things a little more difficult since they are physically different in appearance. Fortunately, the V2 versions are already wired for a DD, so it is just a matter of matching plugs.
Finally, there is the matter of what has to be done on the original GQ's to allow the use of a DD coil.
So, for starters, the GQ is almost like the Beachscan so I can use a decent pic I have of that board as a reference to show what trace has to be cut and where the extra wire has to be connected.
Before providing the specific ML DD mod info, I need to state that any mods will most likely void any warranty, so keep that in mind. If in doubt, please contact Mr. Bill.
Also, anyone who attempts this mod is solely responsible for any possible damages that may occur for any reason. So, again, if there is any doubt, then I recommend you contact Mr. Bill to have him make the DD mod change.
For those who still want to continue on their own, please email me for more details and let me know what plug they will be using and I will try to provide as much info as I have available.
I can post them on this forum but that is up to Mr. Bill.
The mod isn't really that complex, but does require decent soldering skills.
I can be contacted at rgsniff@comcast.net
I hope this helps.
Reg
 
I agree with Mr Bill,
I've compared both for wet sand and the mono coil is more sensitive for smaller conductors, The DD coil if "water proofed" would be a great coil to help any pi operate smoother if the users Pi is not operating as stable as it should. You may lose sensitivity with using the DD coil but it should help the Pi operate better under rough soil conditions.
My GoldQuest is set-up for both the DD and mono coils, Currently it's hard wired with the 11" mono coil which is the best over all coil for my GoldQuest searching the Ca. wet sand beaches. Now that's with my Pi and can change with other pi's which may do better with a DD coil.
JT, If you still prefer going to a DD set-up which is fine just make sure the DD coil is waterproof and as Mr. Bill said you need to cut a trace on the circuit board. The conversion is not hard just need to be handy with a soldering iron and understand what's involded with changing over the plugs.
Since you mainly search ocean wet sand with your GQ and need a waterproof coil it would be best to wait until a waterproof DD coil is made. The Minelab DD coils would be best used for inland searching such as nugget hunting since these coils are not waterproof.
HH, Paul (Ca)
 
Hi All,
On the Beachscan and the GQ, the circuitry is designed for the use of a mono coil only. As such, the transmit coil is also the receive coil, so the receive circuitry is connected directly to the transmit circuitry.
The conversion that allows the GQ to use a DD coil is really quite simple. What has to be done is to simply disconnect the receive circuitry from the transmit (xmit) circuitry. Once that is done, then the disconnected receive circuitry has to be connected to a new pin on the coil plug socket so the receive coil can be connected to it via the plug connection.
Now, the easiest way to disconnect the xmit from the receive is to simply cut the pc board trace connecting the two. This is a very small trace that connects the damping resistor (damper on the pic) to the receive input resistor.
The pic uploaded displays a basic Beachscan pc board which is almost identical to the GQ. The GQ does have an extra pot and resistor in the general area, but the coil connections are physically in the same position. Now, on the pic I have noted three things, the damper (damping resistor), the receive input resistor and the trace. Actually, the trace cannot be seen since it is on the bottom side of the pc board but runs directly under the point of the arrow between the damping resistor and the receive input resistor. This trace has to be severed so there is no connection between the damping and the receive resistors. My recommendation is to cut and scrape away about 1/8" or more of the pc trace to assure there is no connection.
Now, the red wire just above and to the right of the red arrow pointing to the damping resistor is the xmit lead going to the chassis coil connector. The copper shield wire connected to what is listed as "SCRN" is the other lead, normally called the common or ground.
Ok, once the small trace is cut, a new wire has to be soldered to the receive resistor at the end or point where the blue arrow touches the receive resistor. This new wire will ultimately connect to the chassis coil connector also and will connect to the receive pin.
So, once done there will be three connections to the chassis connector used to connect the coil. First, the red wire from the pc board to the connector is the xmit wire. The copper colored wire connected to the "scrn" connection point on the pc board is the coil common. The third wire I will label as the blue wire is the new added wire that connects to the receive resistor is the receive pin.
So, as a summary: the existing Red is the xmit wire; the existing scrn wire is the common; and the new blue wire is the receive connection.
As a special note, on the GQ, the Red and copper shield wires as noted on the pic may be a green and black wire and may be connected to posts instead of directly to the pc board. Regardless of the color or the actual mounting, the wire connected to the point noted as scrn is the common. The lead connected to the other post is the hot xmit lead.
If this is not clear, please let me know.
Two final items, first I have directly ommited the specifics of the coil chassis connector at this time but will post more later since there are many options available and second, one might wonder why only three wires are needed when the transmit and receive coils each have two wires. Well, one wire of both is ultimately a common, so the commons can be connected at the chassis plug and only one wire brought back to the pc board. Two separate commons can be brought back from the chassis plug to the pc board but there will not be any significant benefit as long as the leads are short. So, for simplicity, only one common is needed from the chassis plug to the pc board.
Reg
 
Hi All,
First of all, I would recommend that all pic's be down loaded for reference since they do disappear after a period of time.
Now, my last posting, I explained the basics of what has to be done to modify the GQ to use of a DD coil. Once the conversion is done, a new problem is created. That problem is, the mono coil will not work.
The reason the mono coil will not work is simple, it is acting as a transmit coil only and there is no receive connection.
So, something has to be done to reconnect the xmit back to the receive. This is a very simple task and can be done in the coil plug attached to the mono coil cable.
As mentioned in the previous post, the receive circuitry has to be connected to a pin on the coil chassis connector so a receive coil winding can connect to the receive circuitry.
As a simple solution, all that has to be done to make a mono coil work is simply connect the xmit pin of the mono coil connector to the receive pin with a small jumper. This will effectively reconnect the transmit (xmit) to the receive again. It will now be done in the connector and not on the pc board.
I have attached a copy of a pic sent to me of the GQ pc board. Note that this board initially looks different because of the placement of a few parts and the direction from which the pic was taken.
However, one can use the "SCRN" notation as a reference. In this pic, the xmit is a green wire and the common is a black wire.
Now, if one looks at the chassis connector, you will note the spare pin. Just for reference, one could connect the receive wire mentioned in the previous post to this spare pin. If the DD connection is done this way on the chassis connector, then what would have to be done in the coil cable connector would be to connect the center (xmit pin) to the pin that connects to the left chassis spare pin. This would then reconnect the xmit to the receive.
Again, I hope this makes sense.
Reg
 
Hi Again,
Now, before anyone can get the ML compatible coils such as a Coiltek coil to work on a GQ, they need to know just how the ML compatible coil plug is wired. This information allows a person to wire a matching chassis plug properly.
At this point, I need to give a special thanks to Allan Carson of Australia for providing me with a simple but clear pic of the ML coil wiring. I have attached the pic he sent me. From this pic, it is quite simple to wire a mating chassis connector.
One just has to remember that the pic attached is a pic of the back side of a ML plug. By backside, I mean the side the wires are soldered to.
Now, if a person just wants to build an adapter, this pic will give the info as to which pin does which on the ML side. The key to making everything work is to simply wire the 5 pin chassis connector correctly so all leads connect properly. By this I mean that the xmit connects to the xmit and the receive connects to the receive, and the common to common.
Up to this point, I have not mentioned the specifics on the GQ side of the adapter. The reason is simple, it all depends upon just what you use for a chassis connector, the type of plug, and more specifically, just how you wire the existing or any new chassis connector. If you use the existing connector and just wire the receive pin to the spare pin, then any adapter will have to have the proper Anphenol 3 pin connector. The wiring of that connector will simply match how the chassis connector is wired.
Now, a real simple solution, rather than build an adapter is to replace the connector on the GQ with a 5pin ML compatible chassis connector. This requires one to buy a 5 pin male chassis connector like those commonly used for CB microphones, remove the existing connector and mount and wire the new connector. If the xmit, receive and common are all matched across the plugs, everything should work just fine.
One place to find the 5 pin connectors is at www.hosfelt.com. Once at the website, search for mic connectors. (Don't forget the s on the end of connector). Now, the results will indicate 1, but that one is a bunch so select it and drop down to the 5 pin chassis connector, part number 5PMCS. A compatible coil connector is the 5 pin MC5P in line female connector.
Obviously, there are a lot of places that carry the proper connector so it is just a matter of tracking one down. The 5 pin is a common connector used on CB mics, so many CB repair shops will probably carry them. One other place that has better pics of the types of plug and chassis socket necessary is the following site. http://www.wearecb.com/connectors.htm
At this site, just drop down the the mic jacks and plugs and farther down to the mic chassis jacks.
Remember in the last post where I mentioned the easiest way to make a mono coil work once the DD conversion was started? What was mentioned was to add a jumper between the receive pin and the xmit pin to tie the xmit back to the receive. Well, if you look at the attached pic, you will see that ML does just that. If you look at the DD wiring first, you will see that the receive pin (RX)is the second pin up on the right. This is the pin connected to the center lead of the right coax. The xmit (TX) center lead is connected to two pins, the second up on the left and the top pin.
Now, the mono coil uses the same connector as the DD but the center coax lead now connects to the two TX pins just like on the DD coil, AND also connects to the rx pin where the DD receive coax was connected. So, basically, ML or ML compatible coils also use a jumper connecting the xmit pin and the receive pin together and do so in the coil plug.
Again, I hope this post is clear.
Reg
 
Hi All,
I think I found the part number for the 3 pin Amphenol connector used by Eric. This part would be required to build an adapter to connect a ML coil to a GQ using the original connector.
The Newark part number is: 16F6901. Hopefully, the following link will take you directly to the part listing where one can look at a pic, and other info as well as the price.
http://www.newark.com/NewarkWebCommerce/newark/en_US/support/search/searchResults.jsp?action=0&First=0&QText=16F6901&x=24&y=11
The column just to the left of the part number has 3 selections which will provide more info about the item.
Hope this helps.
Reg
 
Hi all,
One thing that has to be mentioned is the GQ and the GQ V2 are wired slightly different when it comes to wiring of the coils and chassis connector. So, the coils from the original GQ and the new GQ V2 are not really interchangeable without a minor wiring change. They will probably work but most likely will act very strangely.
Please note in the GQSS V2 pic (attached), the xmit and common leads are reversed when compared to the original GQ. On the V2, the pc board ground or SCRN pin is CONNECTED TO THE CENTER PIN of the chassis connector. On the GQ, the SCRN pin is connected to the right pin when looking at the back of the chassis connector. This is important when trying to build an adapter and very important if you should purchase a used coil.
Reg
 
Hi Again,
Sorry to take so long to get to this point, but the previous info really needed to be mentioned so people would better understand the differences in GQ's.
Since the GQSS V2 is the latest design, I have made a simple pic of the wiring of an adapter that will allow the use of ML compatible PI coils on the GQSS V2. By building an adapter, no changes have to be made to the coils or to the GQ. The adapter will simply plug into the GQ and the ML coils will plug into the ML compatible chassis adapter.
The logical thing to do is to mount the ML 5 pin compatible chassis connector in a small box and then connect the ends of a dual coax to that connector and the other ends of the dual coax to a GQ compatible plug that will fit the GQ coil chassis socket. It is probably a good idea to have at least a few inches of dual coax so the adapter can be readily mounted and not put excessive strain on the leads.
Well, this pretty well completes the necessary info needed to build an adapter for the GQ. I hope my explanations have been clear enough.
Reg
 
Is that the mounting hole diameters are different, if you want to replace the stock Goldquest plug with the 5 pin ML type. The hole diameter for the ML type is 16mm(0.63in), while that for the Amphenol is 18mm(0.71in). The ML type will be a very sloppy fit, unless a packing bush is made.
Eric.
 
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