Fisher Gold Bug

[ivconic]

Yellow dots are -V layer and White dots are +V layer.
Next one update:

[ivconic]

Coil i have is original coil for Gold Bug 2, not for Gold Bug.
Today i realized that, by randomly finding totally stripped original pcb from Gold Bug 2.
Gold Bug works on 19kHz while Gold Bug 2 on 71kHz.
So actually i am having coil for 71kHz. All the time trying to make my diy work with it.
Now...
i gave up from further messing up with Lahr schematic as i posted earlier.
Noticed several errors.
But now i will in spite do the reverse engineering on pcb that i have.
It is stripped long time ago. No components on it. So this will be long term hobby joy.
Also discovered that this pcb is multilayer. 3 or 4 layers, not sure yet.
In spite all the odds, i proclaim "war on Gold Bug 2". It will be stripped down to ground zero and totally disclosed at the end.
In spite to it's arrogant designers and makers, who had funny pitiful delusion that are smart and that can stop this from reverse engineering.
This will be done. With or without any help from any random third party.
...
I just started:

[dbanner]

It would be nice to know the details of the RX coil and what resonance it is tuned at. Simply put, the scheme of the search head with internal components.
You should put the scope shots of the tx waveform with the RX waveform BEFORE the preamp side by side for comparison to see what's going on at null.(phase of RX coil residual voltage)
Hopefully you can return to project soon.

[dbanner]

Ok.

I found that some component values look quite wrong on lahr's schematic. Up to the ground balance pot the circuit is flowing nicely, so long as the component values are corrected and the offsets are correctly trimmed, the circuit should work fine up to this point.
After that seems where there are even more errors.
Will keep at it.
BTW, Ivca, have a look at the Troy shadow X5 schematic, pretty similar topology around the synchro- demods.

[kt315]

I wonder why they didn't just use an opamp chip instead for the RX front end, performance? Price?

noise factor.

[dbanner]

I wonder why they didn't just use an opamp chip instead for the RX front end, performance? Price?

[dbanner]

That CZ-6 pre-amp WILL have a noticeable phase/gain behaviour, it's mostly defined by the R's and C's in the feedback network.
The 1K0 & 4n7 pair give a low-pass roll-off at f_c = 34 kHz , and the high-pass roll-off, determined by the 47R & 1u0 pair, give an f_c = 3.4 kHz.
There may be some additional contributions from the input filter ( the 47R + 47R etc low-pass filter circuit ), and the 200pF stability cap will affect things at high freqs, I don't know what, though.

Thanks for the info. Nice circuit.

[dbanner]

I applaud you for your efforts.
I'm going to scrutinize the schematic for errors in the area of the channels. I'll run some simulations and post them.

Whatever errors are on original schematic will be found!

[ivconic]

"So i am giving up from this by now. Because i have several parallel works that are waiting on the bench."

I know that. Im wondering since a while how you manage it, to work on several projects at the same time;-).

So my last question is: Is there another PCB Layout for a high frequency unit with discrimination available ?

I don't know about Gold Bug.
Maybe Tesoro Lobo.
KT315 posted links many times on forum.
...
I don't give up only because of other projects that are waiting on the bench.
Mostly i give up because "original" schematic consist many errors.
I will look up forward to obtain either Gold Bug detector... either more accurate documentation if such exists among colleagues.

[Prospekteur]

"So i am giving up from this by now. Because i have several parallel works that are waiting on the bench."

I know that. Im wondering since a while how you manage it, to work on several projects at the same time;-).

So my last question is: Is there another PCB Layout for a high frequency unit with discrimination available ?

[ivconic]

I discovered more mistake and discrepancies on "original" schematic.
So i am giving up from this by now. Because i have several parallel works that are waiting on the bench.
So far with present information that we have; Gold Bug attempt is pure waste of time.
So today i decided to give up by now. Until i get new more accurate information.

[Prospekteur]

Ok...Thanks Ivconic;-)

[ivconic]

Im also interested in this project. Is there a working PCB-Layout available? Some say its working and others have errors;-).

I haven't posted my pcb and it is good thing, because of the mistakes i am discovering now.
Any other pcb, drawn by other people? I can't tell. So far i didn't see neither one for Gold Bug.
If you have link to someone else's work; please post here.

[ivconic]

I also use the CD4060 to drive the crystal. Last year I tried it so hard and without succes but now I know that the amplitude from CD4060 needs to be trimmed. It works just fine with the TGSL coil 10.5Vpp from +5 volts, pretty clean. My o-scope is a Hantek DSO5202P it's a decent one, had succes with it bringing to life many failed projects before I had it.
What about the Q of the coil, Less Q is better for forced driven coils right? Seen some Fisher coils on eBay.
I wish I could give you tips have a great time doing the Fisher Gold Bug!
regadrs

Obviously the schematic that flows around for years; consist some mistakes.
I can't count them yet, until i make working devices.
Above those i made additional mistakes when drawing pcb.
Would be great to find original Gold Bug on Ebay by affordable price.
Coil for Gold Bug differs a lot from all other Fisher coils.

[Prospekteur]

Im also interested in this project. Is there a working PCB-Layout available? Some say its working and others have errors;-).