An Interesting GQ mod

[Anonymous]

Hi All,
I just thought I would pass this info along for those interested in trying to add a little sensitivity to their GQ, Beachscan, etc. Actually, it adds a little volume but does appear to make things more stable and quieter, which in turn allows weaker signals to be heard.
Now, the trick is to do what many ML PI owners are doing and that is to use a Radio Shack mini amp between your PI and the headphones, or simply as the output out of the PI.
If you just use the mini amp speaker, then simply clipping the amp on a shoulder or suspend it around your neck will allow one to hear the speaker quite well. Just set the threshold of the PI such that you can just hear it via the speaker and you are at max sensitivity.
If you decide to use headphones, then a stereo to mono adapter or headphones with a switch are needed if you want to sound in both ears.
Either headphones or just listening to the RS speaker really helps.
Obviously, there will be places where using just the speaker could cause problems, so one probably should be able to use both setups.
Reg

 

[Anonymous]

Hi Again,
I should have listed the Radio Shack part number of the mini amp. It is 277-1008. One can do a search for a mini audio amplifier on the RS website and it should show the litle amp. Measurement of the mini amp is aobut 2 1/2" by 3 1/2" by 1 1/2".
It really does help under the right conditions.
Reg

 

[Anonymous]

Here’s a little circuit that could be used. It would boost the faint signals, at the same time attenuating the loud peaks. Plugging the headphone in would turn it on, removing turn off.
Mr. Bill

 

[Anonymous]

Hi Reg,
Could this mini amp be wired directly to the GQ battery, being it requires 9 volts to operate? If so how would I go about doing that?
Thanks
Bob

 

[Anonymous]

stopped today at radio shack and checked out the mini- amp i noticed it had a jack for rechargable 9 volt battery im supposing you would have to buy the charger or just use a regular 9 volt battery also a imput in and and external speaker out (so im assuming this is were the headphones plug into ) so you would need a 1/4 inch jack to plug into the audio output(headphone jack) on the gq with the other end 1/8 inch jack into the mini-amp then you need and adapter 1/8 inch male jack to 1/4 inch female with which you plug your he3adphones into it turn it on now the question ? on the gqv2 it had volume control which i have up all the way up and adjust sound thru the headphones so im assuming using the mini amp this would be the same so do you think you can turn on the mini amp volume all the way up and the gq the same and then use the volume control on the headphones i hope this is making since and the other thing is have to figure out how to hold it to the web belt i guess by taking apart the mini jack and drill holes thru the plastic and mount a way to put it on the belt that way all the stuff is there interesting i didnt get one yet cause i was getting all confused on the jacks and adapters so what your saying is the mini amp will enhance the faint signals for the deep ones with a little more umpfhh and mellow out the threshold a bit so its not to wavey so you could tell the diffence in a solid signal than a waving threshold hope i didn't confuse any body
me and electronics any way more disccusion on this topic indeed the price is 12 bucks and a couple of adapters 4 or five bucks apeice not bad price for a mod hh larry ca

 

[Anonymous]

would that be in and extenal box which would somehow be mounted close to the headphone jack or web belt or built into the electronics on the gq all thumbs in electronics let me know if your in the mood to solder im looking at the schematic it looks like parts from radio shack what you think let me know i think you still have my #phone and addy or email me hh larry

 

[Anonymous]

Hi Bob,
I am sure the mini amp could be wired to the GQ battery, but that would defeat one of the main reasons for using the amp. The addional gain is one thing, but an important second issue is to let audio vary or affect a different battery.
Regardless of just how the audio works, it will have an impact on the pulse circuitry if the audio drives a speaker, headphones, or other current hungry device and is tied to the same battery as the transmit circuitry. About the only way around this is to regulate the power supplies.
When the audio drives headphones, or a speaker hard, one can see the battery voltage change. This does have an impact on the transmit circuitry.
Now, take that fluctuation away and the pulse circuitry has every opportunity to be more stable. That is basically what the mini amp does. It reduces the current loading on the PI battery by placing it on a different battery.
I don't recommend tying this little amp to the GQ battery at this time. Besides, all is not perfect. Some times the little preamp will pick up nearby radio stations or signals which will cause its own problems. In such cases, it may be best to not use the mini amp. The little preamp could use a little shielding of its own.
Reg

 

[Anonymous]

Hi Larry,
Yes, you will need some different plugs and possibly different headphones, depending upon what you have at the present time.
Ok, lets take the issues a piece at a time.
First, you will need a cable that connects the GQ output to the input of the mini amp. The length of the cable depends on how you mount the GQ and the mini amp. On my unit, control unit, thus the audio connector is mounted on the S rod so I needed a longer cord if I want to have the mini amp near my shoulder.
The GQ output is a 1/4" stereo plug connection. So, one end of the cord should be a stereo plug. The other end can be a 3.5 mm stereo plug or a 1/8" mono plug. Either will work.
What I did was buy a surplus 10' coiled cord equipped with a 3.5 mm stereo plug connector on one end and a female connector at the other end from All Electronics. The cost was about $2.65 for the cord. I cut off the female connector and installed a male 1/4" stereo connector. I made sure that the outer tip of the 1/4" stereo connector was electrically connected to the outer tip of the smaller connecter at the other end of the cord, the middle connections were the same and the inner or ground connections matched from end to end. With this setup, the cord worked fine.
That took care of the cord problem and allowed the little mini amp to work. Now, since I had a nice long coiled cord, I could simple toss the little mini amp over my shoulder around my neck and let it just hang there.
Rather than just relying on the cord sticking in the jack as a means of holding things together, I used my trusty method of attaching things. VELCRO!!!! I attached a piece of self adhesive velcro to the back of the mini amp, and then used a piece of double sided velcro strap and simply held the cord in place with the velcro. Now, it would take some serious effort to tear things apart.
The little amp still just hung over my shoulder by the cord, but the cord was snuggly held to the amp. I would use the amp near one ear and later just reverse how the amp was tossed around the backside of my neck so the amp sort of hung near the other ear.
This technique is simple, quick to do and very easy to change. Looks ugly, but what the hey.
If I were to mount the mini amp on or very near the GQ housing, I would use Velcro there also.
Ok, now for the headphones. The mini amp has a 1/8" mono plug connection so a pair of headphones with a 3.5mm stereo plug would work, except only one ear would produce a noise. Fortunately, my headphones have a switch so I can change them to mono. They worked fine then.
For those of you who do not have headphones that can be switched from stereo to mono, a simple plug/socket can be made. You will need a a 1/8" mono plug, a small piece of 2 conductor cable, and a 1/4" stereo or 3.5 mm female in line connector, depending upon your headphones. Just connect the two connection points on the 1/8 mono plug to the two outer connection points on the female connector and it should work.
Reg

 

[Anonymous]

It's availble commericialy for $89.95. I have them in stock. There in a little box that fits velco's to the side of the detector, with it's own battery, and a on/off switch.
Mr. Bill

 

[Anonymous]

It also comes with it's own headphones.
The brand name is "Depthmaster"

 

[Anonymous]

[No message]

 

[Anonymous]

Hi All,
After reading my posts, I realize I could have been a little clearer in my description of how the mini amp attaches to the GQ.
Basically, the mini amp will attach to the GQ or BS the same way any headphones do and that is, to simply plug in the stereo plug connector mounted on one end of the special interface cable into the audio connector on the GQ. There is no need to get inside the GQ or do any mods on the GQ at all.
The only thing that really has to be done is to build up an interface cable that will be used to connect the GQ to the mini amp.
I hope this clears up any confusion. If some exists, feel free to email me.
Reg

 

[Anonymous]

That little single transistor amplifier really does three things to help pull a little more audio sensitivity out of the weak signals.
1. It is a headphone to metal detector output circuit interface by offering a 1K ohm load to the normal series resistance (several hundred ohms typically) used to reduce full speaker power to the headphone circuit. The 1K load reduces the voltage divider losses caused by the series resistance and the headphone impedance.
2. It is an amplifier to add gain in the low signal area. You an tell that there is more gain because you can hear the background noise in the metal detector audio circuit better. You can also pick up the radiated s1gnal from the metal detector coil if your wires or the amplifier is not shielded.
3. It is an audio peak limiter because of the low voltage (1.5 to 3.0 Volt) supply. This limits teh full dynamics of any target that is in the range above the peak limit imposed by the battery voltage. One improvement to compensate for this is to modify the circuit as follows.
Modification: This modification will allow you to bypass the amplifier and directly connect the headphones to the amp module input circuit, effectively connecting it to the metal detector without the amp. To do this simply get a momentary DPDT push button or a DPDT toggle and switch the input on one half of the switch and the headphone on the other half of the switch. When in position 1 the switch connects the metal detector output to the amp input and the amp output to the headphones. When the switch is in position 2, the metal detector output goes directly to the headphone. This is the classic by pass circuit.
I have used the Depthmaster effectively on my ML detector. This should work on any detector to pull a little more sensitivity out of the detector. One more tip; build the circuit in a metal box and use shielded cable.
bbsailor

 

[Anonymous]

Mr Bill,
I built your circuit but was not able to get that transistor in Au so the electronics shop gave me an equivalent (hope their right) C32725 W39 .
It works but not as I expected. The threshold is smoothed but signals large or small give about the same volume in the headphones which is not as loud as without the amplifier.
Anyway just thought I would let know how it went.
Billm
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[Anonymous]

Mr Bill,
Found the problem with my circuit,just a wrong connection. Works good now.
Billm