Minelab Audio Enhancements/Speaker Units?

[bklein]

I want to make a speaker unit for my GP Extreme and see some offered with supposed enhancements. What are the features of the enhancements? BB Sailor mentioned in an older post he thinks there is the potential for audio-side improvements. What would they be?

[Mechanic]

Hi Barry,

I made myself a small booster for using an external speaker. Well when I say made..... I had an old pair of amplified computer speakers. I removed the amp and trimmed the board size down until it was minimal. Popped it in a small box with a 9v battery, added a switch and led and it was done! For the volume control I used the one that was on the board. I think it cost less than $10

If you want it to be powered by the detector battery you will need to use a small audio transformer or series capacitors between the detector and amp.

Don't know what the actual "enhancements" are apart from amplifying the audio making it boom in louder. If the signal doesn't come out of the detector in the first place no amount of after amplification will do any good!

I only ever use my booster if I am detecting with others and we want to compare detectors. I normally just use earplug under chin headphones, the ones with the rubber bits that actually go into your ear and seal up.

Cheers Mick

[bklein]

I'll probably do something similar just to get something done in time for a trip I hopefully will undertake to Arizona in a few weeks. I was looking through Texas Instruments' Audio selection of parts on their site (now combined with National) and they have some parts that have added features that kind of got my mind pondering...
First they are operating as a digital class amplifier and also some have dynamic power tracking to minimize power demand. Some have AGC circuits. And some have a "mini-DSP" that might be really interesting to play with. Their software app for the PC looks really simple.
I suppose I could just record sample outputs from my GP Extreme and then see what processing may be worthwhile using my music synths (including a Symbolic Sound Capybara 320).
The commercially available units like Gold Screamer seem to have an audio threshold circuit. This could be more trouble than its worth depending on how it is designed. I haven't yet characterized the GP audio but it seems to have both amplitude and frequency variable characteristic upon detection. I could build in PLL frequency tracking, and audio expander functions and have some fun with them...

[ivconic]

I made small booster with LM386, for GP3000 i had once. Problem is in signal level and impendance, so small audio transformer must be used. I hadn't at the time so i tried something to achieve with resistance and capacitance coupling between GP and LM386. Results were satisfactory but not perfect, on louder signals i had distortion. There are no improvements nor advantages in using speaker, except more comfort (no additional cables and no headphones). Small booster box, 9v batt operated, can be mounted on GP easily. Sound level is good. 9V battery can last long. It did job for me. I don't know why Minelab never included speakers in those series.

[satdaveuk]

I made small booster with LM386, for GP3000 i had once. Problem is in signal level and impendance, so small audio transformer must be used. I hadn't at the time so i tried something to achieve with resistance and capacitance coupling between GP and LM386. Results were satisfactory but not perfect, on louder signals i had distortion. There are no improvements nor advantages in using speaker, except more comfort (no additional cables and no headphones). Small booster box, 9v batt operated, can be mounted on GP easily. Sound level is good. 9V battery can last long. It did job for me. I don't know why Minelab never included speakers in those series.

Hi Ivconic
Did you try putting a 10uf cap between pins 1-8 then try diffrent resistors series with it ie: 1.2k = 50x gain and so forth.
Used that chip with various projects and it works quite well.
using that chip with just a cap will give you 200x so will get distortion

[ivconic]

Hi Ivconic
Did you try putting a 10uf cap between pins 1-8 then try diffrent resistors series with it ie: 1.2k = 50x gain and so forth.
Used that chip with various projects and it works quite well.
using that chip with just a cap will give you 200x so will get distortion

Yes i tried several options on LM386. It is better with less gain. Right now i have dozen TDA7231 for such purposes.
Main problem in boosting GP out is impendance.
Impendance matching transformer is desirable in that particular case.
Or; more skilled diy'er (more brave one ) can open GP and trace audio path, add another audio driver and small internal speaker!

[ivconic]

Here is SD2000 audio output. I assume GP series couldn't vary much in this stage, most probably those have pretty similar audio stages. So, on this particular schematic; lowering R7,R12 and R13 (do experiment very carefully with R7 !!!) i am sure this audio stage can drive directly speaker . So instead headphones; high impendance speaker can be plugged in to socket. On second thought; more better is to add audio driver, MPSA13 or simillar, base via 27k to pin 7. on NE5532JG, collector via 22ohms to plus rail, emitter to speaker + and gnd to speaker -. There is plenty room inside GP box for so few components.

[bklein]

This "Superfix" thing looks like it has all my ideas rolled into one (but for over a grand!):
http://www.finders.com.au/Finders_Ar...t_SuperFix.htm
Seems they went out of business...

[Mechanic]

Don't even think about it! Not long ago they were selling on ebay for less than $10. They are the biggest piece of poo you will ever try. The latest lot on ebay I think have come from the chinese knock off co. If you ask around the forums you will get one at a pretty good price <$50.

Better just do what you want to do, at least if you don't like it you will be able reprogram it till you do!

Cheers Mick

[ivconic]

Don't even think about it! Not long ago they were selling on ebay for less than $10. They are the biggest piece of poo you will ever try. The latest lot on ebay I think have come from the chinese knock off co. If you ask around the forums you will get one at a pretty good price <$50.

Better just do what you want to do, at least if you don't like it you will be able reprogram it till you do!

Cheers Mick

Mick you took my words!
Hot price indeed!
And, inside there is nothing so special that descent diy'er can't make himself.

[bklein]

What's the issue with them - the audio demo's seemed like it did what it should (or what I'd like it to do).
Are you saying what is sold now are knock-offs and don't perform like the original?
I had bid on one currently on ebay (bid ~$50) but now I see they made a mistake in the ad quoting shipping as $18 but later in the description they say $78. I'm overbid now anyway and don't want to spend that much as my brain seems to be discriminating ok I think. But if you guys come across one for $10 I want it! That is cheaper than any amp'd speaker I've found and I'd just like to try it anyway.

Barry

[Mechanic]

Hi Barry,

I too was once curious to try a superfix. A kind soul had one at a club camp in his box of JUNK and let me try it out. He had bought it and used it for a bit but just could not make any sense out of it. Instead of hearing the threshold hum you hear silence. When you wave over a target you are meant to hear a bip. Only trouble is the thing seems to bip randomly. It does bip over a target but in general it would be easily identified on the normal audio. The whole random bipping was enough to turn anyone off. Much easier to decipher the original audio using your ears. Same goes for ground noise, learn to deal with it, over time you will learn to identify it. Just sweep from different directions and listen to the detector. The chinese copies will most likely be just a copy of the case, not the internals. The original superfix has a micro controller, doubt that they would have copied that. It is probably just an amplifier inside the superfix box. Bit like the fake chinese Minelab 4500's. The only thing that is 4500 about them is the case and end caps. A lot of the time there are mistakes on the endcaps which makes them fairly easy to identify. Inside they are just some crappy vlf. They will pick up targets in air(if you are lucky) but in mineralized just completely hopeless.

Get yourself a small nugget and bury it till you can just hear it, then play with the threshold knob. If you have the threshold set too high you will miss targets at the near limit of detection depth.

The audio output is a square wave which changes frequency as a target is swept past the coil. The volume also changes/increases as the target is swept.

Ivconic, The audio cct on the gp is kind of similar to the 2000 but not the same. It is best not to try and get more from the existing audio cct. The problem is if you start drawing more current from the internal +-5v supplies you will effect the operation of the other ccts and start causing inter modulation. If an external amp is used running off the detector battery, it must be connected using a high impedance audio transformer or capacitors in series with the audio lines. The amplifier will be on a different voltage level as to what the detectors internal amplifier runs at which is why the transformer or caps must be used. Alternatively if a small amp is made up and runs off of its own battery the audio can be directly coupled to the amp.

Cheers Mick

[Finderskeepers]

sd2000 audio circuit

hello all,
I have recently tried to assemble an sd2000 on breadboard and have had no success in making it work. The search coil (minelab 11 inch monocoil) is humming, but there is no audio. After studying photo's that i have obtained from the internet, there is a component on the audio circuitry that looks like a electrolytic capacitor but not shown on the schematic - it is positioned above the ne5532. I would like to know if this part is crucial and if so, how it fits in. I'm not dissappointed that it does not work, it's a very complex and time consuming project (was bored on new years day and was curious to know if it would work). I'm confident that all the connections are correct - have checked them countless number of times and the only substitutes part i have is the ssm2210 in lieu of the lm394 and a tn2405l in lieu of a vn2410. Also the pinout connections for the lt1057 differ between the dip and smd package.

[ivconic]

Yes Mick, that makes sense.
Conventional audio driver, like on other machines, can pull descent momentum current and affect supplying on the rest of machine.
Also speaker can produce loopback interferences and intermodulations through power lines.
To void that; more serious approach is desired. I would experiment with Musketeer/Relic Hawk audio kind, including famous (mentioned few times here on forums) audio transformer. Such audio driver usualy can pull not more than 15-20mA with strong signal and less than 10mA with average signals. Hopefully it will not affect much power supply.
Of course; audio should be supplied directly from accu, from own regulator, but not through existing regulators on GP.
However, all this means more components and more space. Additional box than should be considered.
I think Minelab did not include such audio and internal speaker because SD,GP and GPX machines are considered as "profy" and for "serious" metal detecting, especially nugget hunting, where slightest change in treshold can make huge difference and we know that such changes are not easy to hear via ordinary speaker. Good old headphones are not easy to compete with.

[WM6]

Also speaker can produce loopback interferences
I think Minelab did not include such audio and internal speaker because SD,GP and GPX machines are considered as "profy" and for "serious" metal detecting, especially nugget hunting, where slightest change in treshold can make huge difference and we know that such changes are not easy to hear via ordinary speaker.

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I am trying to avoid this by using metal housing and pop-up bigger (5cm dia) piezo ceramic summer outside.