surf p.i headphones issue

[dbanner]

My home built surf p.I works good with piezo, however when I plug in the headphones the sensitivity goes all crazy. I think the coil starts to ring. I'm using 32 ohm headphones. What could be the issue here?

[homefire]

Did you make any changes to the Schematic as SilverDog shows ?

[dbanner]

Yes, that's the exact circuit I used. I made no changes.

[homefire]

Wasn't set up so well in the Audio department. I think High impedance would help. Piezo.

[kosacid]

what i done was put the headphones in line with the buzzer without using the switch on the headphones socket just straight through

[dbanner]

OK.will try that. The audio is not loud enough to hunt without headphones,especially beach hunting.

[homefire]

By hand no solder, short across R-34 and R35 one at a time with a .47uf Cap. See what happens to audio levels. There was a Fix posted some time back Replacing one of those Resisters but I can seem to locate it.

[dbanner]

My issue is not volume level, but somehow connecting headphones affects coil damping, the specific symptoms are a delayed response to a target with reduced sensitivity. I have no problem when driving just the piezo. But with headphones connected things go awry.

[homefire]

What type of Battery are you using . ??

[dbanner]

8x"AA"=12volts Duracell alkaline.

[homefire]

That's good. Or should be. Check the Voltage the FET is seeing with and without the Head Phones. They may be loading but I can't see how unless it's taking down your voltage.

[dbanner]

What FET? I will use seperate battery for audio output to see if makes any difference. I'm also trying to get tgsl working optimum, also delta pulse, also cloneing Garrett ads deepseeker for beach hunting, working on lobo and baracuda PCB etching at moment. Maybe too many projects at same time not so good. Better to focus on one at a time.

[homefire]

The FET that drive your Coil. You said it was messing with your Damping ?

[dbanner]

Ah yes the MOSFET, well it works fine with just piezo connected. I think I will have a closer look with scope to see what's going on when headphones are connected. I suspect that somehow it could be affecting my sampling pulses.