Fisher Gold Bug

[Nandor]

Post #25 at previous page, "ps.jpg", have you missed it?
With it i simply ended any more brainstorming around power supply.
Period.
...
But i also understand what you want to say.
I don't think that 0.5V difference (if exist in reality) will make any significant differences in detector behavior.
Remember TGSL?
It has even larger difference between the rails! Yet it worked just fine.
Comparing to that; 0.5v is nothing.
Your points are making sense to me.
But with "ps.jpg" all the doubts are ended... at least at my side.

I think I have seen this kind of powersupply at the Relic Hawk. Why not? My good old TGSL consumes only 29mA, with 2 Lipos it could last long. Maybe the oscillator would need some kind of regulation, a 6 volts regulator or so it can make 10-12 volts pp. If i remember well you said once that most commercial detectors operate between 12-16Voltspp.

[MartyJ1963]

@Ivconic,,,,Looking forward to seeing ths GoldBug project come to life,,,you have always amazed me ever since the day I joined the Forum in 2016,,,I always read every one of your posts and have never missed one,,I wish I had the knowledge and skill that you have in building and designing/re-designing Metal detectors as I guess would most of the members on here wish they were as good as you too. I, for one, sincerely look forward to learning from your posts, at the present, and hopefully in the future. I really admire the countless projects you have given freely here on Geotech and thank you for making this hobby the most enjoyable hobby I've ever had. Don't despair Ivconic,,,You're the best! Best regards,,,Marty.

[ivconic]

Funny, I never thought of my contributions to your thread as crap.
That being said, I'll leave you to your task.

But than again... it is pointless to try to do anything on these forums any more.
Good old times like 10-15 years ago will never repeat.
People changed a lot. Super sensitive on every benign word and expression you make.
Could this be due covid19 stress? And overall bad situation worldwide?
I can't tell. But obviously things has been changed dramatically in peoples minds.
I am sorry, but i don't intend to measure each word that i will post here.
I am free man. Free spirit. Benign in my acts and words. No hidden agendas.
I have huge respect to majority of people here.
But i see things are changing rapidly in pretty wrong directions.
So to spare my self on the first place and others too; from further situations like this one;
i think is better to chill out for some time and take a longer rest from forum-ing.
Cheers and Good luck!

[ivconic]

Funny, I never thought of my contributions to your thread as crap.
That being said, I'll leave you to your task.

Nooooooooo!
It was not addressed to you and your contribution.
Let's cut the crap again and do talk on important things here.

[dbanner]

[ATTACH]53411[/ATTACH]

And yet...
THE HELL with "mumbo-jumbo" solutions from 40 years back in the past.
New technology today allows us much better solution.
This is pretty much straightforward power supply with all the positive sides and none drawbacks.
Two LiPo , 18650 type, with nominal capacity at ~1A will last much longer than two 9V batteries.
Since there are ready balancing chargers for two batteries; we are sure those will be in pretty much the same state when charged.
I've been working a lot lately with those batteries and i notice some tendencies in their behavior.
Fully charged usually are 4.2V. Discharged are 3.7V.
But when fully charged and than used; it drops very fast to ~3.9V and than stays there for looooong period of use!
Hours of working with low power metal detector.
Also now we don't need any voltage regulator to introduce more hum in the rails.
Also now we don't need any virtual ground "generator" to make all this more complicated.
With this kind of setup we have all the benefits you may want from one power supply stage.
Later on is maybe good (or maybe redundant) to add simple voltage monitor on both batteries.
But than again it is redundant.
Such batteries are already including small protection circuit and will immediately cut off when discharged.
With least ~1A per battery... we are sure that this will provide us more than enough working hours.
So... let's cut the crap and focus on more important stages on schematic!

Funny, I never thought of my contributions to your thread as crap.
That being said, I'll leave you to your task.

[ivconic]

Post #25 at previous page, "ps.jpg", have you missed it?
With it i simply ended any more brainstorming around power supply.
Period.
...
But i also understand what you want to say.
I don't think that 0.5V difference (if exist in reality) will make any significant differences in detector behavior.
Remember TGSL?
It has even larger difference between the rails! Yet it worked just fine.
Comparing to that; 0.5v is nothing.
Your points are making sense to me.
But with "ps.jpg" all the doubts are ended... at least at my side.

[ivconic]

Yes we are in agreement. But in previous original schematic, ground sits at 2.5 volts, negative rail sits at 0 volts and positive rail sits at 6 volts. So there is more headroom on the positive side(6-2.5=3.5volts)
Shifting to 3 volt virtual ground changes this so now it sits at the mid point. Just an observation. So now all signals are level shifted by 500mV and are now closer to to positive rail of 6 Volts.
Not that the signal will clip, but it has 500mv less headroom on the positive transition, that's all I'm saying.

Actually not. Simulation proves that ground sits at precise 3V, which is exactly half of 6v.
So even in original; it is quite symmetrical power supply.
If simulator is to be trusted.
The similar power supply was on 1265.
I had few of 1265 in very good shape.
I measured the symmetry at rails, +/-4v.

[dbanner]

Consider those 3V as ground, GND.
and +v (+6v) is than +3V.[/FONT]

Yes we are in agreement. But in previous original schematic, ground sits at 2.5 volts, negative rail sits at (-2.5V)and positive rail sits at 6 volts. So there is more headroom on the positive side(6-2.5=3.5volts)

Shifting to 3 volt virtual ground changes this so now it sits at the mid point. Just an observation. So now all signals are level shifted by 500mV and are now closer to to positive rail of 6 Volts.
Not that the signal will clip, but it has 500mv less headroom on the positive transition, that's all I'm saying.

[ivconic]

And yet...
THE HELL with "mumbo-jumbo" solutions from 40 years back in the past.
New technology today allows us much better solution.
This is pretty much straightforward power supply with all the positive sides and none drawbacks.
Two LiPo , 18650 type, with nominal capacity at ~1A will last much longer than two 9V batteries.
Since there are ready balancing chargers for two batteries; we are sure those will be in pretty much the same state when charged.
I've been working a lot lately with those batteries and i notice some tendencies in their behavior.
Fully charged usually are 4.2V. Discharged are 3.7V.
But when fully charged and than used; it drops very fast to ~3.9V and than stays there for looooong period of use!
Hours of working with low power metal detector.
Also now we don't need any voltage regulator to introduce more hum in the rails.
Also now we don't need any virtual ground "generator" to make all this more complicated.
With this kind of setup we have all the benefits you may want from one power supply stage.
Later on is maybe good (or maybe redundant) to add simple voltage monitor on both batteries.
But than again it is redundant.
Such batteries are already including small protection circuit and will immediately cut off when discharged.
With least ~1A per battery... we are sure that this will provide us more than enough working hours.
So... let's cut the crap and focus on more important stages on schematic!

[dbanner]

But shouldn't make much difference since it applies throughout the circuit. Don't know.

[ivconic]

Consider those 3V as ground, GND.
-v than is -3V and +v (+6v) is than +3V.

[dbanner]

Shifting from 2.5 V to 3V leaves less headroom on the positive going side, hopefully this will not matter in the end.
Lm317 regulated at 6.5V will restore the default of the original design.
Notice the non inverting inputs of the 404's after the preamp are referenced to Vdd ie 2.5V
Changing to 3V will level shift the RX signal, decreasing the headroom by 500mV.

[dbanner]

Looking good, I'll do the same in ltspice, just for comparison. How about a load on the 3V output.

[ivconic]

If Proteus is to be trusted; this is more like it!
Instead BC327 i put now BC558 and instead MPSA there are two diodes.

[dbanner]

LM393 is more commonly known for the quad comparator. TLC374 can only be a recipe for fake chips on the market.