ETI1500 metal detector main speaker - low volume

[Ace]

This unit since day one on construction has had a low main speaker volume. The phone jack that has a 470 ohm resister in series has sufficient volume.

Checked through the schemeatic and tested all wires and speaker and found it is correctly setup.

Was there possibly an omission to the schematic or perhaps a fix to this.

I am posing to add a 470ohm resister inseries to the main speaker to determine if this brings up the volume.

Strange so it may seem but perhaps this has happened to someone else that has an explanation.

Only difference between the jack and main speaker is the jack and a 470 ohm resistor. All componets have been checked thoroughly and are as per the schematic

thanks
in advance
cheers

[Sean Goddard]

Re: ETI1500 metal detector main speaker - low volume

There is no guarantee that the schematic is correct.

ETI were, towards the end, notorious for typos in their projects, and thus this resistor value might be quite a way out.

If you have found a value which works, then I would suggest that you "go with it".

[Allan]

Re: ETI1500 metal detector main speaker - low volume

Ace , adding a resistor in series will only make it quieter. The resistor in the headphone circuit is to reduce the power available to the headphones. Try another preferably higher impedance speaker, or get an old telecom style earpiece insert, the aluminium enclosed sort from the old coloured dial phones. They are very efficient, due I think, to the rocking armature design. DC resistance about 40 ohms I think.
I guess another possibility is that you have wired up the headphone socket in some wierd way. Try the speaker alone from output capacitor to ground.
Hope that helps cheers, Allan in Gympie.
By the way , how does it perform. ?

[Ace]

Working - Know of any mods for the ETI1500?

Got it all working now. The connection to the board was soldered one side and not on the other so resoldered and up came the sound.
With the unit working - having issues with tuning and balancing the ground at mid to high sensitivity. Requires a lot of reset of the tune button.

I think I might purchase a couple of 10 turn pots for the tune and balnce controls to see if I can get better correlation.

Generally unit picks up at 600 mm in sand no problems. Yet to finish it of as working correctly but am wanting to see if any mods do exist for this unit

cheers

[Allan]

ETI1500 Ace, What is your regulated supply voltage? 10 volts.

A May 1982 letter to the editor of ETI suggests making R53 2.2k instead of 12k. This will increase the zener current to about 2ma and the regulator will work better and the tuning will be more stable. Anyway, thats what the man said. Worth a try. Another constructor says IC4b needs its inputs reversed . By the way this circuit seems very similar to an old Garrett Fortune Hunter. Anyone got a circuit of that? Cheers,Allan.