GS 5 THRESHOLD PROBLEM

[Jose]

change all TO-220/TO-92 stabs on impulse chinese converters. set a converter between batt and board. i see you just are seeking up problems on bare places.

A DC / DC converter is possible, but it takes more current from the battery.

[Jose]

My thoughts are that the -12v regulator(79L12) sets the dc bias of transistors in audio vco stage. What would happen if this were to change? Would this affect the threshold in some way? Lm2990t-12 is low dropout.

It is possible, you can try a low-drop regulator, (-12v) or connect the two resistors of 47K, directly to -10 vol to clear doubts.
I think this scheme was added to solve the problem of changing the audio level, which originated when activating the high or low conductivity mode.
See the proto scheme.

[kt315]

I did not have the same problem with the threshold but other problems, such as high temperature in the TX stage, so I decided to feed the detector with 12 volts, besides being more practical, since you can use a gel battery.
For that reason, I use a low-drop regulator in the -10 volts line.

change all TO-220/TO-92 stabs on impulse chinese converters. set a converter between batt and board. i see you just are seeking up problems on bare places.

[dbanner]

My thoughts are that the -12v regulator(79L12) sets the dc bias of transistors in audio vco stage. What would happen if this were to change? Would this affect the threshold in some way? Lm2990t-12 is low dropout.

[Jose]

Hi jose....did you have the same problem with a GS 5 ????

I did not have the same problem with the threshold but other problems, such as high temperature in the TX stage, so I decided to feed the detector with 12 volts, besides being more practical, since you can use a gel battery.
For that reason, I use a low-drop regulator in the -10 volts line.

[kt315]

look my topic again http://www.geotech1.com/forums/showt...ly-mod-offered

[daverave]

ive used li-ion batteries so should get about 4 hours running time which is ok for a normal search....the threshold problem is annoying as cannot zero (silence) below 13 volts supply....i only ever had this problem before with the surf pi and only if i used too much feedback on the dc amp.

[dbanner]

Nice low current audio booster can be had from old computer cd-rom drives, the audio chip and associated circuit is on small circuit board to the front along with headphone jack and volume control pot, all self contained. Easy hack

[dbanner]

Yeah well, you've got yourself a battery killer. Low dropout devices may not help as much as you'd like. Rechargeable batteries discharge curve I suspect is not too linear. It may go from 13v down to 10v a lot faster than say from 14.4v down to 13v (maybe exaggerated, but you get my meaning). You may only get a few minutes worth of extra hunting, that's not much at all. A combination of higher capacity battery and some more efficient linear devices is one way to go maybe.

[daverave]

I think I saw 79L12 reg. as well for audio stage. You'd have to maybe change it too.
I wonder what the overall current consumption is like for the entire unit. Maybe you could rationalise the entire power supply for more time in the field. A good mod solution for entire unit, whilst keeping it lightweight.

Hi dbanner...with my GS 5 the current consumption is around 650 mA cause i added a amplifier stage to boost the audio.

[dbanner]

I think I saw 79L12 reg. as well for audio stage. You'd have to maybe change it too.
I wonder what the overall current consumption is like for the entire unit. Maybe you could rationalise the entire power supply for more time in the field. A good mod solution for entire unit, whilst keeping it lightweight.

[daverave]

Try a negative, low-drop regulator.
I use LM2991T.[ATTACH]44665[/ATTACH]

Hi jose....did you have the same problem with a GS 5 ????

[Jose]

Try a negative, low-drop regulator.
I use LM2991T.

[dbanner]

Battery voltage needs to be kept healthy for device to function properly. The regulators need more juice.

[Hyena]

I always expect problems when I am under drop voltage of regulator Stable mean you already checked with scope in mV scale?