TESORO GOLDEN SABRE

[eclipse]

Sounds like we need a modification that:
1. on strong signal -keeps the audio level at reasonable high but not too high, has to limit the signal to certain spot, which lets say the operator can adjust (like volume limiter)
2. on weak signal amplifies the signal again to high level but lower than the strong signal, lets say 1/2 of the level so the operator will know that it's a deep target.

[amtech2005]

TESORO GOLDEN SABRE

SimonBaker , Go back to around page 100 of this thread . Ivconic had the Tesoro Golden Sabre "1265 lite" working very good. I think if you are still having problems , 1. check your total current drawn off the battery , 35 m.a. in all metal mode and 55 m.a. in disc mode. 2. Also , no one ever mentions what they do with the i.c. chip un-used pins , noise / oscillations can happen from open pins on some type of i.c.'s . 3. check your audio section . Go back several pages and build your circuit to match schematic where Ivconic said his was almost perfect . Then make any mods , one at a time. You will get it perfect , sounds like your close..........Eugene

[Max]

for Ivconic

Hi Ivconic,
what's the last stable PCB version of TGSL you made ?

It's the one of page 95 or maybe there are a new one... I saw goldbug stuff !? What's this ?

Have you implemented the monostable mod on it ?

Kind regards,
Max

[simonbaker]

Sounds like we need a modification that:
1. on strong signal -keeps the audio level at reasonable high but not too high, has to limit the signal to certain spot, which lets say the operator can adjust (like volume limiter)
2. on weak signal amplifies the signal again to high level but lower than the strong signal, lets say 1/2 of the level so the operator will know that it's a deep target.

Agree, need "logarithmic amplifier", http://www.play-hookey.com/analog/lo...amplifier.html !

[simonbaker]

SimonBaker , Go back to around page 100 of this thread . Ivconic had the Tesoro Golden Sabre "1265 lite" working very good. I think if you are still having problems , 1. check your total current drawn off the battery , 35 m.a. in all metal mode and 55 m.a. in disc mode. 2. Also , no one ever mentions what they do with the i.c. chip un-used pins , noise / oscillations can happen from open pins on some type of i.c.'s . 3. check your audio section . Go back several pages and build your circuit to match schematic where Ivconic said his was almost perfect . Then make any mods , one at a time. You will get it perfect , sounds like your close..........Eugene

Thanks! I'm doing something crazy -- building TGSL on solderless breadboard first -- also using unshielded coil to start -- I know, demented!!! Not expecting good operation with this...

But very good to learn many things -

- How JFet TR2 and D2 zener affect TX coil voltage.

- How Neg supply works, how it creates voltage spikes.

- Effect of different Voltage regulators and batteries.

- How Diodes D3 - D5 and CD4024 make "AND" logic for narrow audio pulse.

- What is phase relationship of Lock-in amp control signals (gates of JFet TR4, TR5). All metal vs. Descrimination.

- How to connect RX coil for proper phase.

- Effect of coil shielding (will see later when add shields).

- Different effects with speaker, ear plugs

One mistake I found in my wiring -- put junction transistor instead of JFet for one lock-in switch -- doesn't work too good! Hard to read those little suckers...

So now I'm studying signal as it passes through op amps, etc. But may need to build on PCB for that, so many crazy noises, spikes, etc. But I do see amplitude changes when I put metal over coil, yea!

Goin' slo, but worthwhile because so much good information from this forum .

Some day maybe make a separate thread to show all my junk just for fun..

Cheers,

-SB

[Aziz]

Hi Simon,

..
- What is phase relationship of Lock-in amp control signals (gates of JFet TR4, TR5). All metal vs. Descrimination.
...
-SB

TGSL hasn't implemented the lock-in amplifier. It is only a synchronous detector. I am in doubt, that nobody really implemented a true lock-in amplifier in a VLF MD (of course, besides me)!

Aziz

[simonbaker]

Hi Simon,



TGSL hasn't implemented the lock-in amplifier. It is only a synchronous detector. I am in doubt, that nobody really implemented a true lock-in amplifier in a VLF MD (of course, besides me)!

Aziz

You and Max correct me -- but what is the real difference? Sin vs square reference?

-SB

[Aziz]

Hi Simonbaker,

You and Max correct me -- but what is the real difference? Sin vs square reference?

-SB

The difference between synchronous detector (in TGSL and most of the VLF MD) and lock-in amplifier is as follows:

Synchronous detector:

The transmit oscillator signal acts as a reference. This will be shifted through ground balance and/or discrimination pot. The sine wave is then converted to a digital rectangle wave form via a comparator with some hysteresis (or schmitt-trigger, zero crossing detector) which triggers an analog switch (FET). Only the half of the time-domain signal is passed through. The other half is not processed.
There are more possibilities for processing the synchronous signal:
- averaging over the gated window
- integrating over the gated window
- sampling over the gated window (last signal will be used)
Averaging or integrating over the gated window will increase the signal-to-noise ratio. TGSL uses the averaging method (=low pass filter, C15, R30)

Lock-in amplifier:
Lock-in amplifiers use the whole time-domain signal with some time constant (TC) back to past. The RX signal is multiplied (=mixed) with two reference signals Ref1, Ref2. Ref2 is a +90 degree phase shifted of reference Ref1. The mixed two channels are then low pass filtered. You will have a channel called in-phase (I) and another channel called quadrature phase (Q). The two channels represents a complex signal where the magnitude and phase can be extracted directly (computing, very expensive to implement this in analog hardware).
As the lock-in amplifier uses all the time-domain signal the signal-to-noise ratio will increase dramatically and will give a better sensitivity. You don't have a gated window anymore but a window of interest of time constant length. The more the time constant, the better the SNR.

Implementing the true lock-in amplifier via analog hardware is quite complex. Particularly for two channel lock-in amps (I & Q). Most analog lock-in amps use only a single channel implementation to keep the hardware simple and cheap. Taking pure sine waves for the reference increases the SNR.

That's the main difference. I haven't seen yet a true VLF MD which implements a true lock-in amplifier.

Aziz

[ivconic]

Hi Ivconic,
what's the last stable PCB version of TGSL you made ?

It's the one of page 95 or maybe there are a new one... I saw goldbug stuff !? What's this ?

Have you implemented the monostable mod on it ?

Kind regards,
Max

Actually all of those are very stabile, very sensitive and with almost perfect disc (keeping in mind working conditions and limitations and comparing with most of other models).
I did various pcbs just for one reason; it was hard to establish one and only enclosure for TGSL, so i made pcbs according to enclosures which came handy to me, CZ5....1265...etc.etc.
Recently i got a constant supplying source of those enclosures so i decided to stuck on those, therefore pcb size i am using is related to original Fisher 1265/66...
Gold Bug is just lonely case, ha,ha,ha....i got pretty broken Fisher Gold Bug 2 and after a while decided to use it's enclosure for TGSL. Since Bug original pcb is a bit smaller than 1265 i had to draw new one to suit those dimensions.
Since i do keep all the previous works (files) in SP format, it was easy to me later to "play" and mod. existent files and apply various mods.

There are just few major changes actually in all this mess;
I decided to reject TX "fuse" part from design. Zener 4V3,1N4148,Fet,330K,100K and cap are omitted. Actually it never played any role in all my handmades so far, so...who need those!? Excellent space saving on pcb.
TX 2N2907 just need 47K on base to gnd and that is all.
Second...i played arround treshold part...changing 330K and 2K2.. Not some benefits so far so i retreived original setup at last schematic.
Monostable....hmmm... turned to be some improvement, especially as you described it in your last post, yes you are absolutelly right. Very good mod if used with good understanding, so it is good to have it on pcb (main or piggy, never mind)...
Last important mod is replacing MPSA13 with 2xBC547 and 1xBD140.
Now... i do suggest this mod. Power drain reduced and audio is louder significantly. Excellent mod! Best so far!
Need to be included on main pcb....i am finishing the draw these days.
Even if we later find real source of audio problems this last mod should be keeped, great benefit from it and no drawbacks at all.
....
Battery check...ha, i rejected it long time ago. Pretty obsolete and anoying. If somebody really need batt. check i suggest to take any other...many posted on this forum so far.
...
Ok..back to main problem;
i am now almost sure what is the real cause of the audio problem.
All the signal paths are problem! Ha,ha,ha!!!
Signal is significantly attenuated from very start - LF353.
Remember my previous post where i related this to coil? Yes...with some coils louder audio and with some dont.
It is not only important to null coil and respect inductances.
I think latelly i "overnulled" to much my coils. Signal is totally choked there.
Either to null coil a bit "loose" with slice higher residual voltage either to rethink and include some extra amplification in existing design.

We must keep in mind that TGS is rather old and obsolete design...dating from 198...and some!? Sheeesh! Now i realised this!?
Even that, TGS/TGSL performs good and oftenly better than many of modern designs.
So i was thinking to analyze again and again schematic and find proper spot where i can include one more amplicication stage. Should it be before or after switching fets? Should i replace fets with 74hct4016?
Should we mod LF353?
We must think on S/N ratio and try to void funny situation to amplify more internal hums than signal itself...ha,ha,ha!!!
Winter is coming...a lot of funny job is waiting me than!

Regards!

[ivconic]

Aziz thank you on splendid explanation!

The way you put it there, now, many important things said in a few simple sentences! Bravo!
Thanks again! I learned few things more!
Best regards!

[simonbaker]

Hi,
the audio of TGS is "proportional". Like in e.g. bandidoII ou get stronger audio signal with stronger signal from target... so shallow target are very easy detected but deep ones are usually listened as very small audio beep (most often "crack" using speaker).

...

Kind regards,
Max

When you look at circuit, you wonder: why is audio proportional? Comparators U106 make a binary signal, original signal amplitude is forgotten -- right?.

(Also look at gain of final U107a LM358 op amp - about 50 in latest schematic - very high considering input is 10 volt pulse from comparators! Earlier schematic has gain of only 3 -- Who changed it and why? But let's see...)

So, if audio volume is proportional, it must be due to pulse width from comparator output, not strength of RX signal. So deeper coins must be making quicker pulse as coil passes over.

Capacitor C25 will make very skinny pulses into a lower voltage due to rise time through 100K pull-up resistor R40. But notice, fall time is very fast because pulled down directly by comparator outputs through diode. Quick pulses never get very big or stretched, pulled down quickly.

I watched pulses at U107a non-inverting input for a long time on my oscilloscope. Mostly as expected when a square pulse charges capacitor -- rise quickly and start leveling off. Then drop suddenly with trailing edge of pulse because diode makes shortcut to V-.

This is basically a good shape because it is like logarithmic amp -- shorter pulses charge faster relative to their width, longer pulses don't add that much extra per time.

But I think maybe problem is on trailing edge - pulse drops too fast, so quick pulses don't have time to sound in speaker. We want to stretch short pulses. Maybe C25 needs a slower discharge path. The 4K7 resistors R47, R55 make a slower discharge, should make audio tone longer, especially for quick pulse. Note that R47, R55 (mystery resistors) are not on PCB.

I think some tuning can be done with these resistors and capacitor 25. Gain of U107a may need to be adjusted if resistors attenuate all the pulses.

There may be an idea with positive feedback through RC filter on U107a to hold pulses longer too...

-SB

(I love the smell of frying LM7808 in the morning...not! 33 ohm 10W resistor is now in series with battery V+ for boneheaded breadboarders...)

[simonbaker]

Hi Simonbaker,



The difference between synchronous detector (in TGSL and most of the VLF MD) and lock-in amplifier is as follows:

Synchronous detector:

The transmit oscillator signal acts as a reference. This will be shifted through ground balance and/or discrimination pot. The sine wave is then converted to a digital rectangle wave form via a comparator with some hysteresis (or schmitt-trigger, zero crossing detector) which triggers an analog switch (FET). Only the half of the time-domain signal is passed through. The other half is not processed.
There are more possibilities for processing the synchronous signal:
- averaging over the gated window
- integrating over the gated window
- sampling over the gated window (last signal will be used)
Averaging or integrating over the gated window will increase the signal-to-noise ratio. TGSL uses the averaging method (=low pass filter, C15, R30)

Lock-in amplifier:
Lock-in amplifiers use the whole time-domain signal with some time constant (TC) back to past. The RX signal is multiplied (=mixed) with two reference signals Ref1, Ref2. Ref2 is a +90 degree phase shifted of reference Ref1. The mixed two channels are then low pass filtered. You will have a channel called in-phase (I) and another channel called quadrature phase (Q). The two channels represents a complex signal where the magnitude and phase can be extracted directly (computing, very expensive to implement this in analog hardware).
As the lock-in amplifier uses all the time-domain signal the signal-to-noise ratio will increase dramatically and will give a better sensitivity. You don't have a gated window anymore but a window of interest of time constant length. The more the time constant, the better the SNR.

Implementing the true lock-in amplifier via analog hardware is quite complex. Particularly for two channel lock-in amps (I & Q). Most analog lock-in amps use only a single channel implementation to keep the hardware simple and cheap. Taking pure sine waves for the reference increases the SNR.

That's the main difference. I haven't seen yet a true VLF MD which implements a true lock-in amplifier.

Aziz

Thanks Aziz, you are the prof!

My thoughts:

Integrating and averaging are the same thing for square wave gate signal.

As mentioned in literature, difference between multiplying by square wave and sine wave is a square wave just has extra harmonics - with proper filtering, I think only adds 10% more noise.

TGSL does use quadrature I believe, two channels but not sure what phase difference is yet, maybe not exactly 90 deg.

Synchronous Detector also uses whole time domain because low pass filter is a Markov process and theoretically includes signal all the way in the past. Your digital lock-in amp has advantage in that it is much easier to make filter which is not Markov process (finite time sample), and can make really fancy filters of any kind. But how much advantage? Is it really that dramatic? I say TGSL JFets are not really gated window but rather integrating with a sine wave and many harmonics -- the time window is still the low pass filter time constant.

You point out an interesting design weakness -- TGSL "synchronous detector" only uses half the signal. I have thought about adding a second gate to each channel with a "low noise" inverter feeding the extra gate. But will the inverter add more noise than the extra gate takes out? A good question for experimentation.

So I stick with opinion that synchronous detector is very similar to a lock-in amp, maybe within 10 or 20 percent (maybe that was using hardware), and mathematically quite similar. But your software lock-in will win, no question about it.

Now back to frying parts...

Cheers,

-SB

[ivconic]

"So, if audio volume is proportional, it must be due to pulse width from comparator output, not strength of RX signal. So deeper coins must be making quicker pulse as coil passes over."

This is true. Yet not explaining fact that same detector gives different audio (width,strenght and decay) with 2 "different" (almost the same) coils??
I hardly can claim 2 handmade coils "same". Almost impossible.
There is one more preference of coil needed to suit to make detector sing louder and wider, but which one?
The rest of your post is more than interesting. Now, with posts like yours and Aziz's this forum get real sence! Thanks much!
Man can learn here...finally!

[ivconic]

I hope to experiment with audio because I agree that it should give as much information about target as possible.

I wish we could hear what Ivconic is hearing -- can you post audio or video of it?

As soon as possible i will record and post here. Need to fix some pc microphone first

First, there are questions about schematic that affect audio, nobody answers yet:

1. Schematic from "Gift Pack" shows R47, R55 on output of last LM393 comparators, but other schematics do not have. They must affect audio I think, but has anyone tested?

I tested those already. I havent spotted any difference than.


2. I have one schematic of TGSL which shows R40 connected directly from output of LM393 instead of after diode D12 -- but most schematics show it connected after diode. Which is correct?


Right way is after diode.

On speaker vs. earphone:

Maybe speaker is very different from earphone as follows: speaker has very large inductor. Audio signal is very narrow pulse, small duty cycle. Speaker coil stores energy from pulse and spreads it out, making rich sound. Earphone has less inductance, cannot spread pulse as well, therefore more loss goes into volume pot or other part of circuit (sucks away energy).

No. I reffered plug thing in situation ONLY when plug exist,connected in setup but speaker is used. Cracks appeared on speaker - not on ears?? Funny and strange? Once plug removed - speaker sounds perfectly!? Funny!?

It is sort of related to concepts in this link: http://www.tinaja.com/glib/msinprop.pdf .

But then Ivconic says speaker gives cracks on deep coin and adding resistor helps -- that seems opposite to my thought. Maybe resistor helps self-bias the Darlington -- I give up .

What bias? Resistor was in serie with speaker, usually 10 ohms. Looks like speaker forming some sort of "loopback" and distort something at previous stage. Not sure what is going there, but noticed various speakers do distort more or less.

Try removing Diode D3 on CD4024 Q3 output -- should make wider pulse, how does it sound?

Actually....yes. Removing one (or even 2) of 3 transients will add a bit of loudness, yet not enough. This is true. Amplifying one "clean" frequency is always easier than amplifying composite signal - less losts.


Maybe for very deep objects, output of LM358 is very small and you start hearing the voltage spikes from the V+ rail (yes, those pesky voltage spikes!).

You really hate those spikes!? Dont you?

You know, some Tesoro models have "all-or-nothing" audio, like my Compadre. All targets have same volume. Weak targets break up. Do we know how TGS was supposed to sound?

Ha! I have idea for you; try to locate and remove 1M resistor parallel to diode at last stage! (if there is any 1M resistor there in Compadre). Than you will get same audio as on TGSL.


However, looking at schematic, it looks like R45 from U107a LM358 output is the pull-up voltage for the audio, so audio signal voltage equals output of LM358 -- I would expect varying volume depending on output of LM358.

This is what i thought also. I experimented with R45....no significant differences....sheeeeeshh! That's why i suggested extra amplification, in my last post...

I keep working furiously to try to get a working TGSL so I can have fun with these problems...

You will have it in no time. Just do a proper pcb.

Cheers,

Double Cheers to you man!

-SB

REGARDS!

[Max]

When you look at circuit, you wonder: why is audio proportional? Comparators U106 make a binary signal, original signal amplitude is forgotten -- right?.

(Also look at gain of final U107a LM358 op amp - about 50 in latest schematic - very high considering input is 10 volt pulse from comparators! Earlier schematic has gain of only 3 -- Who changed it and why? But let's see...)

So, if audio volume is proportional, it must be due to pulse width from comparator output, not strength of RX signal. So deeper coins must be making quicker pulse as coil passes over.

Capacitor C25 will make very skinny pulses into a lower voltage due to rise time through 100K pull-up resistor R40. But notice, fall time is very fast because pulled down directly by comparator outputs through diode. Quick pulses never get very big or stretched, pulled down quickly.

I watched pulses at U107a non-inverting input for a long time on my oscilloscope. Mostly as expected when a square pulse charges capacitor -- rise quickly and start leveling off. Then drop suddenly with trailing edge of pulse because diode makes shortcut to V-.

This is basically a good shape because it is like logarithmic amp -- shorter pulses charge faster relative to their width, longer pulses don't add that much extra per time.

But I think maybe problem is on trailing edge - pulse drops too fast, so quick pulses don't have time to sound in speaker. We want to stretch short pulses. Maybe C25 needs a slower discharge path. The 4K7 resistors R47, R55 make a slower discharge, should make audio tone longer, especially for quick pulse. Note that R47, R55 (mystery resistors) are not on PCB.

I think some tuning can be done with these resistors and capacitor 25. Gain of U107a may need to be adjusted if resistors attenuate all the pulses.

There may be an idea with positive feedback through RC filter on U107a to hold pulses longer too...

-SB

(I love the smell of frying LM7808 in the morning...not! 33 ohm 10W resistor is now in series with battery V+ for boneheaded breadboarders...)

Hi,
"When you look at circuit, you wonder: why is audio proportional? Comparators U106 make a binary signal, original signal amplitude is forgotten -- right?."

No, it isn't. In theory any comparator has a binary output (+Vcc or -Vee) but it really isn't on practice: simply doesn't exist a comparator that give output at 2 discrete levels of voltage... not considering also that you have also output stage voltage drop... in real devices.

What happens really: you have an op amp that works in open loop at highest possible gain... that is similar in behaviour to an ideal comparator ...that doesn't mean you have really, always 2 discrete levels at output and no intermediate voltage.

When you consider gain you have the answer: consider +8 and -8V as supply voltages and open loop gain of 200000 (as typ of lm393)... how much differential input voltage is required to saturate device ?

deltaV+ = +8/200000 = +40uV
deltaV- = -8/200000 = -40uV

So... you have full saturation voltages out the interval +40 to -40uV at differential inputs.

But what you'll get inside the interval, what if you have e.g. +10uV there ?

V=10uV --> Vout = +10uV*200000= +2V

+2V , not +8 or -8V... so it's an "intermediate" voltage out of discrete limits.

Why I'm doing all this ? Simple... you actually HAVE 10uV and similar voltages there... expecially when you'll measure submicrovolt influence of a small coin at 30cm from coil bottom! So you'll get not full saturation at comparators... but intermediate values and then (sadly) intermediate sound... cracks.

So, when you consider solid signals... like coins at 15cm... you'll get full sound... and real saturation of device, but on weak signals you have linear amplification and intermediate values, thus resulting in poor sound.

This explains why the audio on TGS is proportional... after a particular depth/size combination... so input level threshold... the device will give you a proportional tone related to weakness of signal or the far/small target.

Kind regards,
Max