Voodoo Main Discussion

[surfdetector]

Hi surfdetector,
I am at the preamp stage of the voodoo tonight i will progress.

I tested the Voodoo preamp with a 300 uh 30 awg flat planar coil I knew was pretty fast.
Just trying to get a idea of the Pi front end portion of the voodoos capability.
the following shot is with a Maxim 412, I also tried a 4562, it was faster but it wasn't as clean.

[ATTACH]53973[/ATTACH]

I have only tested the dual d on the Mpp but I took off my preamp and went to stock except for a 4562 amp.
this shot is of the coil balanced on a signal gen it worked pretty well but further testing and playing with the Rx coil I was able to get a little better performance bringing the nugget into play.
This coil is pretty forgiving I can even stack the rx right on top of the inner tx.
I don't know what to even call it it could be considered everything from a omega to a concentric and dual d. All depending where you put the Rx coil.
I'm building two larger size Rx d coils to see what happens to the depth and sensitivity of this coil where the trade off is.

[ATTACH]53974[/ATTACH]


Thanks again for the great job on your videos.

Thanks for the images. I do like the 4562 as well. You are doing good work with the coils.

[ivconic]

Finally arrived...

[ivconic]

Reading a book...
thoroughly and meticulously done... nothing less i expected from George.
My hat down to this!
...
Preparing order, component lists, tomorrow will place order to local supplier.

[Matt_Rowe]

Sent you a PM

Pmed you back, thank you,

[lamoiz]

350 uh well damper with litz threads .. it works hard.

[surfdetector]

350 uh well damper with litz threads .. it works hard.
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Hi Lamoiz, which coil is this one?

[lamoiz]

Hi Lamoiz, which coil is this one?

hi surf; it is a 175/46 litz wire coil that I use on my mpp beach.It measures 31 cm. this test is on the voodoo

[ivconic]

White's Spectrum
Rx 1,2 36mH 123 ohms
Tx 4,5 540uH 1.4 ohms

White's DFX concentric
Rx 1,2 13.8mH 36 ohms
Tx 4,5 540uH 2.7 ohms

White's DFX DD
Rx 1,2 14.2mH 55 ohms
Tx 4,5 680uH 3.5 ohms

Am i wrong to assume these would be perfect coils for Voodoo detector... PROVIDING that coil is cut open and those TX tuning caps are stripped out?
...
Still reading a book. Close to the end. Impressed with the idea but more important with materialization of the idea.
Of course nothing is perfect and always can be improved further.
Morphology of this detector allows precisely that; easiness of further improvements.
I want answer on this; if we omit (usually noisy) NE555 and connect directly RC3 to R61 ; we'll have probably simpler audio, but 100% synchronized and totally noise free, right?
Not to mention affect on power consumption too, which will be somewhat lower. But at this particular moment i am focused only on S/N.
Second; i fully understand why LT1054 is chosen instead 7660. All the arguments truthful and mentioned in the book.
But generally 2 main are ; sync frequency and input voltage. If i decide to supply my detector with anything less than 12v, or put 7812 to keep it there, than second argument goes away and only first one, the sync frequency stays unsolved.
Is there any way to properly sync the 7660 with ~1kHz and less?
I am forcing this question for simple reason, LT1054 is harder to obtain and some 5x more expensive than 7660.

[Qiaozhi]

Am i wrong to assume these would be perfect coils for Voodoo detector... PROVIDING that coil is cut open and those TX tuning caps are stripped out?

I didn't know there were tuning caps in the White's coils. I thought the DFX was wideband. If true, at least the TX cap will need to be removed.

I want answer on this; if we omit (usually noisy) NE555 and connect directly RC3 to R61 ; we'll have probably simpler audio, but 100% synchronized and totally noise free, right?

This might work, but the audio tone will then be 1kHz instead of 430Hz.

Second; i fully understand why LT1054 is chosen instead 7660. All the arguments truthful and mentioned in the book.
But generally 2 main are ; sync frequency and input voltage. If i decide to supply my detector with anything less than 12v, or put 7812 to keep it there, than second argument goes away and only first one, the sync frequency stays unsolved.
Is there any way to properly sync the 7660 with ~1kHz and less?
I am forcing this question for simple reason, LT1054 is harder to obtain and some 5x more expensive than 7660.

In the past I've experienced some issues when trying to synchronize a 7660 directly from the TX oscillator, but recently I was able to sync a 7660 to a 1000pps TX even when the pulse width was 50us. The previous problems may have been with pulse rates below 1000pps. I cannot be certain, so it might be worth trying.
You should use a 7660A though, and not a basic 7660 as it only has a max input voltage of 10V.

[ivconic]

"...I thought the DFX was wideband..."
Sorry if i made confusion, i mostly had Eagle Spectrum coils on my mind, the "Blue Max" and the "Black Max" so called coils and especially those with the rainbow lookalike stickers.
Those certainly do have several TX tuning caps inside. TX inductance is just perfect for fast PI coil and other good things that comes along (earlier sampling etc).
Whats even better; those are frequent and affordable coils today... what's even better; we had chance to see them opened so far, many times, on forum.
So is easy doable; the stripping. When it comes to DFX coils; i must say i am not sure about those.
Are those having anything from the caps inside or not.
Sorry for confusion.

"...This might work, but the audio tone will then be 1kHz instead of 430Hz...."
Yes, that would be the "catch 22"... but who ever had and got used on Musketeers; will not mind higher pitch. In time it becomes even pleasant.
We only have to put pros and contras in equation and see what is the real benefit from NE555 absence.
Personally, i don't like to see them on the same power supply with more delicate stages in the detector.
So 7660A will be! Thanks for the tip!

[Carl-NC]

DFX coils do not have tuning caps.

[ivconic]

DFX coils do not have tuning caps.

That's even better, no need for opening it.
With inductance ~540uH makes it good choice for Voodoo.

[ivconic]

"...This might work, but the audio tone will then be 1kHz instead of 430Hz...."

Check this out: https://szynalski.com/tone#1007,squ,v0.75
Not that bad at all!

[godigit1]

350 uh well damper with litz threads .. it works hard.
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Hi Lamoiz,

what pre amp are you using?
That doesnt look like a 5532.
Testing on the voodoo with a fast coil
I've had to damp it back to sample properly since the voodoo only goes to 15 us.
did you try any mono coil tests before disc assembly.
My R2 3r3 is getting hot did you have this Issue?

Has anyone had this issue?

Thanks

[surfdetector]

My R2 3r3 is getting hot did you have this Issue?

Has anyone had this issue?

Thanks

So far, I have not had any excessive heat on my project. What wattage resistor are you using?