Need help! Building 1981 VLF Project

[Op04]

I'm so glad that you post here dbanner because you're the one remind me about PCB error, I made French correction as I mention above. I receive info that the original design (the PCB) as said by someone here on the forum via my PM it was no error instead only tx frequency adjustment. I borrow the inductance meter, turn out by the owner said it is bad meter. Anyway It's my first VLF after tune a bit the gold up to 7cm for 2.5grams gold 18 carrat similar to nugget on the field, it purpose to be sell I'm not so happy but my buyer are happy for my price and its capability.

[Op04]

I can help you. But I would like to see both sides of the PCB. If you can, take some good hi res photos and upload them. We can have a look too see if everything is ok with the PCB. After that it becomes necessary to make and balance the coils properly, then we can have a chance at getting your project working great.
Don't recall anyone here ever building this project. The circuit schematic is very interesting for a number of reasons.

The noise is out when threshold is to big, if only 40% it is clean, I have some noise gate for that, perhaps in the future maybe will give limiter or compressor for audio result, this is my point of view, i regularly build guitar effects,,to clear/up rise small gold sounded (perhaps THAT Compressor / can't believe I've seen there are none MD schematic put compressor on audio stage!)
Thank you for your readyness to helping me but now is in the hand my buyer, unless he complaint I can reach modify again

[Op04]

I forgot to mention my improvement to reach 7cm for 2.5gr gold. Here are my setup:
Coil diameter 85mm @10.5mh
C2, C13 @477pf (330pf+147pf paralel)
TP is showing 3Volt
Discriminate is not working but it is more sensitive to Non-ferrous
The switches are gone except S1, with this coil it is useless (no need switch)
Point K-J jumper wire and Point I = NC
Point G-O jumper wire
P7 are better use multiturn
I forgot to get pictures for the 3 trimmers pot so...
R59 & R61 @2M instead 2M2 as French correction
Result is even 0.5 gram nuggett I can hear a little bit at 1-1.5cm
and noise are quiet below 40% threshold(tune)
Don't ask for coil frequency or how was the inductance meter error percentage because I found that later the meter are not accurate
So that's it...

[aft_72005]

Hi
I built MD elector many years ago . when I was yang .
This detector work correct but need change some thing . first working frequency was 5KHZ
pll didnt work well with 15KHZ .
Also change some parts .
Tune it in full resonance mode seam nexus MD .
My elector md can detect cion 50cm in air .
Stability was good . it was one of my best detector at past .
I try found some pictuers from PCB .
Regards.

[aft_72005]

35 years ago …!!!!!!

[Op04]

Hi
I built MD elector many years ago . when I was yang .
This detector work correct but need change some thing . first working frequency was 5KHZ
pll didnt work well with 15KHZ .
Also change some parts .
Tune it in full resonance mode seam nexus MD .
My elector md can detect cion 50cm in air .
Stability was good . it was one of my best detector at past .
I try found some pictuers from PCB .
Regards.

Incredible!! I'm glad someone put more information for this project. It needs a lot cables

[ATTACH]54885[/ATTACH][ATTACH]54883[/ATTACH][ATTACH]54882[/ATTACH][ATTACH=CONFIG]54881[/ATTACH]


35 years ago …!!!!!!

You did very good job Sir, thank you for uploading this It surely deep if put at low frequency. This is the only one that works with many coil. As of now I still in learning process. I hope someone put the right improvement for this project. I wonder to get 5khz, do you remembered what parts that is replaced? Coil configuration? If this project can work above 15khz it will be the most easiest vlf project available.

[aft_72005]

yes , working with 5KHz ... but was long time ago . I don't remember what I done now !!!
but change resonance frequency TR coils and set PLL on 5khz .
I hope you have success.

[Op04]

yes , working with 5KHz ... but was long time ago . I don't remember what I done now !!!
but change resonance frequency TR coils and set PLL on 5khz .
I hope you have success.

Dear Aft,, It's a pleasure to see you again.Sir, how time flies.... It did works and somehow I have to sold it, but since then I learn a lot from so many2 project in this forum, build so many,,, metal detector is a hobby drug, keep fail but keep making it hehe I spend thousands dollars for many projects half of it was failure I have 5kg copper coil that messed up, failures for PI and VLF countless projects I've done till now. To me VLF is too difficult and I kinda late join this forum, back then when I first enter this forum I still remember KT315 show his barracuda pcb but my brain couldn't catch up 11+ years ago. Anyway.., I'm glad the magz give a step by step guide and some help from Skippy back then it was a big help, If I knew tesoro eldorado back then its far more easy, but I let go VLF and my head are full with 100 different mosfet and coil parameters for PI now,, I can't remember about this project too...thanks for your updates Sir Aft, same pray for you too...
Warm Regards

[aft_72005]

Hi again
I made that circuit 15 years ago. I am very busy and forgot what I did then. I think I still have it in my storage room.
Yes, making a VLF is not easy.. and I agree, yes, you have to spend a lot of money... but it is very interesting to make and experience. Making pi metal detector is easier. I apologize for my late reply. I am less here.
Your sincerely .

[Op04]

Hi again
I made that circuit 15 years ago. I am very busy and forgot what I did then. I think I still have it in my storage room.
Yes, making a VLF is not easy.. and I agree, yes, you have to spend a lot of money... but it is very interesting to make and experience. Making pi metal detector is easier. I apologize for my late reply. I am less here.
Your sincerely .

Thank you for reply. umm if there's no available premade cheap clone, VLF machine would be more interesting to build, now everything has change,, but the real problem is world situation now is making every cost went up, anyone will think twice to get their hobby.

[aft_72005]

Thank you for reply. umm if there's no available premade cheap clone, VLF machine would be more interesting to build, now everything has change,, but the real problem is world situation now is making every cost went up, anyone will think twice to get their hobby.

Here is my country... Chinese VLF metal detectors are so cheap that you don't think about making them... Handmade metal detectors are much more expensive... but in my opinion... when you make a metal detector yourself And it works much better if you set it carefully.. I made many circuits from VLF and pi years ago.
iviconic and sascho circuits work well.

[Op04]

Oh I see your country. So when we have opportunity by builds many project, it's all about voltage we're watching and for PI we control mosfet behavior. Yes you're right, but PI is more predictable result, I don't want to put risk no more on VLF. Ivconic has giving his work so many we must thank him. Sascho project I don't want put a risk. TGSL Minipulse Barracuda GS4-5 SD2000 Surf Hammerhead Andy'sEldorado TD3X they all work to me. TDI schematic I still unsure, wish Altra can confirm his scematic on that thread still confusing. For future build I hope I can buy the book and make Voodoo, I wish George put his analog version of it that using N-ch FET. I became out of topic. But just conclusion of the thread, this 1981 machine is working device but it just too big and heavy, eldorado is a good start for beginner. I see compadre recently I believe it will work.

[ivconic]

I made that detector long time ago. One among first diys. I got more/less the same behavior. It won't get any better.
It is obscure design, belong to its time and it will need many serious modifications to make it so so usable.
I think it is waste of time, since there are many better projects on this forum.

[Op04]

I made that detector long time ago. One among first diys. I got more/less the same behavior. It won't get any better.
It is obscure design, belong to its time and it will need many serious modifications to make it so so usable.
I think it is waste of time, since there are many better projects on this forum.

Back then my electronic skill was awful at that time (still tll now), when I saw that schematic it's the power supply I could catch up, other seem(now I realized) using charge pump I don't familiar with, so that was chosen. To get discrim with it, I'm not able to achieved, it just work in all metal mode, I just got tricked when it says on the line it can feel gold, silly me why choosing to build that just because it has step-by-step guide. My head can't catch up with TGSL too that time. It took 3 years to get familiar with metal detector on how it works, from coil tx rx timing sound etc..but now we must prepare the worst, end days has come we're all gong to miss days of hunting and detecting. I'm glad this forum exist, ahh sorry I talk too much