GP Extreme all in one VR/Speaker/Booster build

Hi all, after recently aquiring a GP Extreme i KNEW i was not going to be a happy chappy being tethered to it, especially after using vlf units with everything built into the box. My other issue was weight, lugging around the 6v SLA will feel like having a car battery strapped to your back by days end.
After having read as much info as i could find on the net & speaking to electrical minded people i opted to build my own all in one box, which will run off a 8.4v 6800MA Li Ion cell once it arrives, a lightweight cell, it will be strapped to the detector in it's own case case. The box of goodies build was next.
1 project box
1 adjustable VR, it will step down the voltage & hold it constant at whatever range its is set at.
1 audio amplifier, 4-12v input, 3.5w power, compact & sealed.
A power socket in, i opted for a standard type fitting for convenience sake.
1 on/off toggle switch
1 Audio out socket, to use with h/phones if desired
1 Speaker, ratted from a incar phone kit speaker
1 volume pot
and finally a standard 4 pin out socket for power/audio to detector box.
After carefull laying out & drilling an assortment of holes it started taking shape, it took an afternoon to build.

Project box with speaker fitted.
https://i.servimg.com/u/f83/18/28/25/09/p1080416.jpg

Adding components.
https://i.servimg.com/u/f83/18/28/25/09/p1080417.jpg

More Bits
https://i.servimg.com/u/f83/18/28/25/09/p1080419.jpg

Have set output voltage to 6.82v, currently powered by a 16.4v li ion cell.

Finished product, have also made new insulated 4 pin power/audio lead. waiting for battery cell to arrive now, will make custom pouch to strap all of it to detector box.
https://i.servimg.com/u/f83/18/28/25/09/p1080420.jpg


battery cell
68mm X 37mm , 6800Ma, 8.4v with carry case
https://i.servimg.com/u/f83/18/28/25/09/t2v1yy10.jpg

vmaxx, you've made a ripper of a system there. The 6v SLA is a shocking and back breaking system, but back in the days the GP came out , Li-ion were still a costly dream. I'm sure it'll serve you well as I ran a similar system on my SD but in component form rather than a neat package like yours. Only thing that I would also probably look at is to get a second battery and external charger for it, that way you can have one charging, whilst detecting with the other as some Li-ions can take a while to charge. Best of luck with it and let us know the outcome.
Cheers

nice job vmaxx I made a booster using the same kemo amp, it worked and was very loud but I could hear the amp through the speaker and it didn't sound the same as headphones so I stoped using it.

make sure you turn the volume pot wright down if you plug your headphones in, that little kemo amp has balls and will turn a set of koss
headphones into a set of external speaker's and will probly blow them up.

lockie

I've yet to actually plug it in, just need to confirm speaker pin outs on detector box first before i take the plunge. i worked it out as top left batt +, top right batt -, bottom left spk +, bottom right spk -, or doesn't matter on speaker pinouts from det. box?
I'd hate to fry the unit before i got to use it....
Also, would maybe using a 20k pot instead of 10k reduce speaker volume ?
I'm not an elec engineer, but know enough basics to get by
Any knowledgable input from wiser members appreciated.
cheers

The one under the +volt is the audio+ but I don't think it's too critical with the audio side of it. I myself would stick to the 10k as I think you will find that it's not a reduction in the speaker volume that you'll desire. I say this because I run my volume control at about 3/4 of the way to full and I run 2 speakers placed fairly high on my shoulder straps. 10k will give you more bandwidth of the usable area, rather than more of the low (useless) area and only a very sensitive and short upper section. But it's all personal preference...

HI Vmax,

You might need to connect the detector audio to the amplifier with either an audio transformer of a capacitor on series with each input line to the amp(unless the amp has this internally. Don't hook the audio- up to battery-, it needs to be kept separate.

It will be interesting to see if the noise from the switchmode supply you have used has any effect on the smoothness of the detector threshold. Make sure you take your original battery setup out bush to test the difference and as a backup, just in case.
Also the battery you are using, does it have a built in shut off device for when the battery gets to its critical low voltage level? You don't want to go over discharging li-ion cells, they don't like it. Another thing worth doing too is to put a 1.5A thermal breaker on series with the power output to the detector, just in case something goes wrong, it will help keep the smoke contained

Let us know how you get on with it.....

Cheers Mick

Well, after 2 types of audio amps, neither being suitable, very unstable audio response & poor volume control etc...
I'm back on the drawing board. Might easier to get a spare DETacc enhancer, gut it & rehouse it in the kit box with existing volt reg & speaker, at least i will know it will (should) work then.
My sole purpose is to contain all the ancillary bits & pieces in one compact box & do away with heavy batteries & leads everywhere.......

HI Vmaxx,

Have you tried an audio transformer to isolate the detector electronics from the amplifier electronics? The biggest problem is that the audio voltage levels and ground are at a different voltage to what you would expect. Either an audio transformer or or a 1uf or 10uf capacitor(s)(have a fiddle) in series with the input to the audio amp should do the job.

The best way I have found with amps is to run the amp from a different power source. I made my amp from an old(new) pair of computer speakers from the warehouse(cheapie shop), cost $10. Removed the amp and trimmed off the excess components and un populated board to make it fit into a small box with a 9v battery. Then the detector audio just hooks straight up to it. The battery lasts days. There is no buzz in the audio background either.

Cheers Mick

hi vmaxx. minelab pi machines have a 2 channel audio output, so you will need to use 2 mono audio amps (one for each output) or get one stereo audio amp. i have built an audio booster using 2 kemo 3.5 watt amps and works very well. you will also need a dual gang 10k pot

I tried the same amp, Kemo, i assumed it was mono output, being only 2 wires out......??
after lifting the lid on the sla battery & checking the speaker wiring also, only runs 2 wires to the h/p jack.
what am i missing here....
any chance of a wiring diagram or more info on how you wired it?
appreciated
alex

Not sure, maybe I'm wrong, but I think it's mono audio.

Your right Costas, it is mono, however, one line the square waves go positive and the other line the square waves go negative, so its kind of differential.

Audio transformer <<<< Get one and use it

Cheers Mick

when you say poor volume control is it to loud or not loud enough?

how many volts are you putting into the amp?

with the Kemo 3.5 amp, volume initially was faint & not progressive using the pot, it would cut out on half a turn of the pot, Supplied Kemo amp diagram runs speaker earth & amp earth back to batt neg. i played around with earths & managed to get a louder audio response with spk earth isolated from batt neg, but still s**t. Gave up on the kemo amp.
Then tried a Jaycar kit build 2w amp, much better volume, but same deal, volume would cut out at 1/2- 3/4 pot turn & sound very unstable, just didn't sound right. Connected DDETacc booster to recheck audio of unit, normal as it should be...i'd love to open my DETacc unit & see what's inside , but box is glued shut, i'd destroy it trying.
I'm a bit sus on the 10k pot...maybe its been the culprit all along..turning it, the volume output does not seem to progress smoothly.
Am i wrong in thinking, 2 pins out for audio on det box, one pos & one neg ?? should connect up like any normal speaker out?
Excuse my ignorance Mechanic, but there is obviously more to it if you say i need to add audio transformers etc to the circuit, well above my electrical knowledge...can anyone enlighten me some more.?
cheers

Lockie, voltage is 6.8 v, (voltage i have set my VR to) amp will run with 4-12v from memory, but the audio is somewhat unstable, hard to describe, but you certainly would not try detecting with it.

mate looking at your pics again it look's like you have your volume pot controlling the sound going in to the amp. you need it controlling the sound coming out off the amp.

the two in wires from the amp should be connected to the 4 pin plug.

power should be connected to the arrow with the + next to it

your earth and neg speaker wire connected to the arrow with the - next to it

and your + speaker wire going to the wire with the pic of a speaker next to it, this is also the wire you want to put the volume pot on.

Hi Vmax,

The problem arises because the audio circuit has its own artificial ground which is about half battery voltage. When there is no audio signal from the detector, there is still say 3.5v going to the input of the amp. The amp then tries to amplify this which in turn will set the output into overload causing crap audio as well as guzzling heaps of battery power. The audio transformer acts as an interface between the detector and the amp, isolating them from each other. When there is no audio from the detector, the input of the amp will see 0v, when there is an output from the detector, this will be picked up by the amp and amplified as it should be.

http://www.jaycar.com.au/productView.asp?ID=MM2534

Don't worry about hooking up the centre tap, just use the outside pins.

Cheers Mick

You are dead right Lockie, that's how i wired it, as the instructions that came with said so, Input into the pot, then then to the amp. So you're saying it should be on the output & only use the 2 outer pins on the pot?

yes vmaxx I think the volume pot should go on the output + and would use the middle and outer pins on the pot.

im not 100% mate, I made mine over a year ago and have sold the machine with that setup but that's how I remember it


you should be able to get it to work mate, it was a useable setup, I just prefer the way my coiltek external speaker with built in amp sounded.

I have attached a diagram of how i wired together the two mono amps. For volume control a 10k dual gang pot is used on the input lines. The power supply runs straight from the 6 volt sla battery. I think you have connected the circuit ground of your mono amp with one of the detectors audio output.

Hi Vmaxx, Lockie and Blacksand,

Blacksand, years ago I built an amp for my 2000 in that exact configuration and it worked.

However just a simple audio transformer between the detector output and mono amplifier input is all that is needed.

See the little yellow transformer, thats it!
This is a bottom view of the board with some (really)rough diagrams!
Basically, detector audio into the transformer, then the other side of the transformer is connected as follows:
One end of the winding to amp input -/batt-
The other end of the winding to one side of your potentiometer, 1K should be sufficient.
The other side of the potentiometer connects to amp input -/batt-
The middle pin of the potentiometer connects to amp input +


Cheers Mick

Hi Mick,

That is a very simple circuit. Is that a lm386 chip on there? looks like the part number has been scratched off.

Blacksand

HI Blacksand,

Yes I would say that it is an lm386, the pinout is correct for that ic and it would work in that configuration. Very simple, effective and commonly used. Oh and its also battery friendly.

Cheers Mick

Finally got it working, have added audio transformer to circuit & am using a Jaycar 1w kit audio amp, it did not work at first, was same result as others. After researching net, found pot wiring was back to front, contrary to wiring schematics supplied with all the Kemo amps. It now adjusts correctly & has proper control. Volume is more than adequate. Have wired amp to dir batt power, bypassing voltage reg also.
Thank you to all for their input to my problem, now to go find some GOLD.

Hi Vmaxx,

Glad you got it going

I'm just curious as to why you have connected the amp directly to the battery and not to the output of the switchmode(dc/dc converter) supply?
Was the power supply causing noise on the output of the amp?

Cheers Mick

I had that thought in mind Mechanic, when doing final connections, but had not tried it with the VR to see if it was noisy, also running from direct battery gives the amp a couple more volts to run with. (whether it makes difference with the extra volts don't know ??....i'm just an amature)

Cool mate! Thinking about it bit further, it is probably better the way you have done it as it will stop the voltage to the detector from being modulated(from varying) when you go over a large target, as this could potentially lower the voltage on the output of the regulator briefly. Though when you go over a large target it probably would not matter if the detector became a little unstable.

As for the higher voltage putting out a bit more punch, well it probably won't make that much of a difference. You should be getting enough volume out of the 1W amp to wake the neighbors and alert everybody within 1k to your position

To test if the new power setup causes more noise at the output of the detector, do this:
Put on a mono coil, the smaller the better. Set the coil switch to cancel. Turn the threshold until the noise(warble/minor response) just starts to break through. Then turn the detector off, leaving the threshold in the same position and reconnect the original battery. See if the threshold starts to break in the same position or if you have to move the threshold knob further for it to start to break.
I hope that makes sense!

Cheers Mick

I will try that on weekend, the volt reg is set at 6.82v constant output, running off a 8.4v 6400ma li ion cell, not the camcorder batteries others use, this one has a higher initial amp rating so won't need resetting or turning the det. on first before the power etc like all the others, that would p*** me off.

I wonder if there is a market for something like i built, with everything in 1 box, which would easily be contained on the side of your det housing along with a decent battery cell, can also get 12000ma 12v, slightly larger.
Would have a decent Li Ion cell, proper regulated voltage to suit sd or gp series, inbuilt loudspeaker, h/p socket & could also add usb out to charge your phone in emergencies....ha!....but i guess most folks now have GPX units, so i'm probably several years too late

Well, after some more trial & error with different batteries, amps etc i finally have a good combination, all in one unit, and yes, i ended up using the common camcorder li-ion batteries you see around. Total weight all up 573G as apposed to 1.8Kg for the standard battery on its own...not to mention leads, remote speaker etc..etc..
Amp is 2w, kit built, the detector voltage is controlled by a variable voltage reg, ( can set voltages to suite SD, GP, etc) keeping a constant stable supply. have added a led for power also, inbuilt speaker, h/p jack, volume control.
Now just need to get the missus to sew up a side pouch to house the unit. I can also detach battery & run from a 2 battery power pack housing, which clips to your belt if one needs extended power. All up i've probably spent more than what it would have cost to buy a a/market battery solution, through several trial & error build attempts, but then you still needed to run a booster amp, and remote speaker etc, and not to mention the satisfaction of doing it yourself....so end result, i'm happy.
Thanks goes to board members for advice during the build process, much appreciated.

Feel proud there vmaxx, looks really, really good!!!