Noise-Reduction for Fisher 1266-X (evtl. 1270-X & 1236-X2)

[satdaveuk]

I got the 1265x which was givin to me a while ago in exchange for repairing a Arado and apart from changing the on/off pot 10k and battery holders x2 the machine works like a dream, still dig crap mind you like any machine.
They were certainly ahead of there time compared to most others on the market, correct me if im wrong in saying the 1266x is the same but SMD devices were used.

Regards

[Funfinder]

Because I opened the Fisher 1266-X for the above picture
now I also took a second one from the PCBs back:

On the left side the already know 40 nF capacitor and the
both connection wires to the variable push pull resistor.

http://www.geotech1.com/forums/showp...9&postcount=20

As far as I can remember the 1 MegaOhm Resistor in the
middle also has to do with reducing the noise.

And the very low value cap (I guess around 5-20 pF)
was soldered parallel to either the transmission or
reception coil contacts (I guess reception) so the
Fisher 1266x no longer discriminates very small rusty
iron parts (5mm diameter).

btw this mod also slightly improves the sensitivity to other
finds by some percent (iron ca. 10% < - -> silver ca. 5 %).

Perhaps the 8'' spider coil finds such stuff by default
because of slightly different "calibraton" (coil impedance)
but I haven't this 20cm coil that's why I can't test it.


One big advatage of the Fisher 1266-X is:
It uses just a few electrolyte-condensers (or just 1 - 2)
and those are not too big. With some luck this machine
still works very good after 30 years.

Only the coils cable isn't very flexible enough and could
break - especially if the temperature outside is very low.

But it's a really well made machine and it's "magic spirit"
lives on in the great improved bulgarian Blisstool circuits.

[Funfinder]

> the threshold keeps drifting

If this drifting is too strong you should find the culprit.
Bad batteries, the voltage stabilisation circuit, changing
electrosmog, bad resistors or even lose soldering contacts.


Have no idea where you can find such a special push-pull resistor,
but you could attach 2 seperate pots somehow (if you don't need
this battery-check button, there would be space enough).

If you're skilled you also could try to repair the push pull tags:
Use a little knife and remove the plastic around the region
where the tags broke off until you have enough metal for
soldering contacts. But you have to fix the wires for this
contacts first with glue etc. or they may break off again.

I could already repair an IC with broken leg with this method.


btw. the PCB I have is different, theres just 1 variable resistor in
the corner. Perhaps yours now has 2 different pots for presetting
each of the both discs.

[dejavuband]

RE

Hi any ideas where i can get a push pull sensitivity pot as two tags have corroded and snapped off on mine,using a linear 100k pot with resistors to get the gain but for some reason the threshold keeps drifting,any ideas as to why this would happen ,cheers,are you in uk or states?

[Funfinder]

thx dejavuband you liked this thread and
great that the mods are working fine for you!

Also haven't any idea for what the yellow pot is.
But so far I have the following describtion and
would be great if someone could complete it.

[dejavuband]

re barreter

Thanks for speedy response,any idea what the small trim pot with yellow insert does,and any ideas as to why my threshold sometimes speeds up and slows down and sometimes goes completely?

[Altra]

I never heard of Barretter or don't remember.

After looking it up, yes it works the same.

[kt315]

Altra, in the case the bulb is working like BARRETTER.

[Altra]

That light bulb is part of a battery charging circuit. So it won't light under normal operation.

Its an old trick to regulate current while charging nicad batteries. A charger is connected through a series diode and light bulb to B+. When a low battery is connected to the charger there is a large voltage differential. This causes the bulb filiment to heat up and the series resistance to increase. As the battery voltage increases to full charge the voltage differential, and series resistance decreases. This creates a constant current over the full charging cycle. I know too much information

[dejavuband]

Can you identify these components please

Hi ive done pretty well much of the mods on this thread(and by the way what a great thread)few mods left to do,but for now i pretty much know what all the trim pots do except the one with yellow insert by the wired ribbon, closest trim pot to it would be the tone pot,does anyone know what this little trim pot does?and ive noticed up by the ribbon hidden away at the top by pots there's a bulb or a valve,any ideas as to what the bulb is as it don't light up and is bothering me now, that's it for now ill leave it with you boys,but im not finished not by a long way,cheers

[Qiaozhi]

Hi, I,ve just joined the forum and I can,t seem to message member funfinder I have read some of his threads on the fisher 1266x detector and would like to ask his advice , can someone help me contact him thankyou, neil.. If some one could pass my mobile number on I,ll call him straight back, thankyou, neil.. 07948344482

You cannot contact other members until you have made at least one post. You have just done that, so please try again.

[hoardhunter]

Hi, I,ve just joined the forum and I can,t seem to message member funfinder I have read some of his threads on the fisher 1266x detector and would like to ask his advice , can someone help me contact him thankyou, neil.. If some one could pass my mobile number on I,ll call him straight back, thankyou, neil.. 07948344482

[detectoman]

hi funfinder for great link, i came of see here, and this good site for obtain extense information on 1266 x fisher but not for 1225 x, btw, i appreciate very much, so i obtain other things for my needed, thanks of new, i understand 25' is bigfather of those, i am very amazed whit my fisher, due these is in any fields major than xlt, due the xlt, faulth in hot sun, but good discriminative function in fresh, i look the circuite of fisher 25" x, is intermedium in old and news models , very strong and fine sound, lightweight, problem is hot" receptor sistem, so detect mineral in any times, go far whit pinpoint sistem push botom, ok i await for new tips of other users on modification of 25 x" but exist no much 25" dinosaur earlier in the world, wtb, whit mineral disase, i prefer my fisher to other
economic batery duration, sound stronge, weight, dinamic, body balancead, 2 simple knob, check batery simple, shock resistant, not bss etc an embrace and of new thanks

[Funfinder]

Yesterday I had time to mod the 66 again - realizing a good new idea that really works:

a much larger sensitivity spectrum

The sens.-knob uses a 100k variable resistor which is in line with a second 100k, means a variarability from 100-200kOhm. This is fatal when you need a huge sensitivity-spectrum. You'll get a much broader one if that second 100k is replaced by a 10k - from absolutly no background noise to the most sensitivity.

Next I found out that it's possible to alter the still "saturated" electro-smog beeps, easy confusable with good target sounds into thinner ones by placing a 100k-1000k resistor into the audio-output stage.

And for even more powerful performance it's possible to interrupt the wire of those 560 Ohm resistor that shortcuts the receiving coil to ground directy where the incoming cable is soldered to the board.

But the most important is a real huge sensitivity range which doesn't exist by default and can make the trusty rusty 1266x almost worthless by too much and not deletable background noises.

Especially because the sensitivity changes with discrimination. While in all metal mode the background noise ist very high, at disc level 10 it is completly gone - but together with the maximum sensitivity! And if the usual sensitivity range is too small for re-adjusting all of this, first the MD loses depth and misses important targets, while second in iron mode too heavy background noise can render good signals worthless.

However, the best would have been Fisher had used from the beginning a circuit which is completly immune against all those electromagnetical influences. But even alot modern MDs from other brands still have the same problems.....

[Funfinder]

Hi detectomen,

if I'll experimenting again with my Fisher and find a way to reduce mineralisation I will post the info here.

Because alot minerals are mixed with metal on a molucelar basis - quote from wiki "Aluminium":

>> Aluminium is too reactive chemically to occur in nature as a free metal. Instead, it is found combined in over 270 different minerals. <<

most detectors just do adjust the disc level to small iron objects and discriminate everything below.

The 1266x forwards the "raw" signals that's why you hear everything - even the discriminated metals often still "snap crackle and pop".

This is good to have the full control but also can drive you insane if the background noise reaches your own psycholgical threshold level. Thats why I modified it - sometimes I just want to have the detector to be quiet!

btw. detectoman - check out this thread:
http://forum.treasurenet.com/index.php?topic=166574.0

Very good and a huge amount of practical info about the 1266x from experienced treasure hunters.

btw. I found some 5cm / 2'' in diameter mineralized stones transported by an glacier at ice-age time 100km far away from the alps near to my village so I can make some tests. I'm also having bigger mineral-stones up to 5kg but I doubt the 1266x will ever remain silent over them, even at highest disc and lowest sens.


There would be a way to blend those signals out but this would need a complete different digital timing circuit. I wrote already about this possibility. Minerals create doubled audio output signals and if those additional circuit could detect it "live", it could be discriminated.

But because such a signal in total takes ca. 0,5seconds it would need a relative slow sweep and pace speed.

A better way would be to add some electronical parts so the coil gets completly overloaded by minerals so it outputs "out of range"-signals that no longer gets processed any further.

btw. I checked out already the "give a large beep"-circuit where the signal goes next after the bias-level. Its possible to "delete" those longer beeps but for a reasonable use more testing had to be done.


So far the best method to eliminate disturbing mineralic noise just is to add that 40nF capacitor and then trim the var. bias resistor to a level so the 1266x is as good as quiet at minimum sensitivity if minerals are near (at that discrimination level you like to search).

Just try it! Good targets no longer will get drown in a sea of "snap crackle and pop", even in mineralic areas.