TESORO GOLDEN SABRE

[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!

[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

[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 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]

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

[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 !

[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

[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

[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.

[Max]

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?

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?

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?


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).

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 .

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

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 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?

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.

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

Cheers,

-SB

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).

That's cause the goal is providing user with informations about strongness/weakness of signal... thus providing hints on e.g. target depth or size...

Most of the times is good that way: on bandidoII I feel happy having that kind of audio... but sometimes, and expecially at TGS, this often results in poor audio response on deep stuff... so you'll simply miss stuff... unless using e.g. hi quality headphone set and not internal speaker stuff.

The monostable mod solve that issue, providing a sound that last for a while, no matter of weakness of output signal... but this will cut away any additional informations like at Compadre. Simply a switch can solve that issue, commutating on-off the monostable stuff and so letting you hear the original audio signal when you already found an hot spot.

But you have to switch it manually all the times... that's why I think Ivconic isn't satisfied of it... also on worse soil the monostable will trigger more false signals than original output stage... cause hot magnetic stuff concentrations will give fast transients on not perfect geb tuned device and so will trigger a sound just like a good target...

In normal audio you'll hear that cracks... but usually you'll not dig at them cause will simply reject as "noise" (so rejecting also deep, small and good stuff): but you'll dig less empty holes also.

So... the best will be a proportional strong audio... but seems till now we haven't.

It's sure a drawback of TGS... that, indeed, was never made for such a sensitivity we found by tweaking... so I think that's due mostly cause we wanna locate stuff out of the normal range of original TGS.

That's true also for BandidoII : with headphone it's great MD...can locate stuff at deep... but on speaker is not that good at the end... that's why most people think it's just average MD... they wanna full audio response from ANY target... and it isn't in that old Tesoro designs with proportional audio.

Kind regards,
Max

[nakky]

Hi SB,this is not good dont ask me why but it is.Grt Nakky.

[simonbaker]

Friends,
despite all the mods included so far, i am not satisfied at all with audio!
Last mod with monostabile is good enough as it is, yet its main drawback is constant and target (signal strenght) independable last,pitch and delay.
So...here i am back again on the start
Original audio seems to be best so far, better than all mods we included. Why? Simply, operater can take most of informations on target, from it.
I would be more happy if it is more amplyfied and more loud.
One thing also noticed; when speaker 8 ohms is used (without mods) "depth" in air is reduced significantly. At very end of detection, audio start with cracks. For example; coin at 35cm - 40cm producing just "cracks" not pleasant "beep". And even than those cracks are so mum and silent.
When resistor 10 ohms added in serie with speaker, those cracks turns to "beep" very pleasant and fine, but very mum and silent. I have to put speaker on my ear close to hear those beeps.
Closing coin to coil, beeps are rising in amplitude. 15cm away from coil and closer beeps are loud enough and very pleasant.
Damn!
During last year, making over 25 TGSL's so far, (and over 30 coils) i noticed one very interesting thing;
With some coils audio is better and louder, with most of coils audio is weak!?
Does this depend on coil itself??? Other words, depends on signal amplitude?
Cose...i am confused,mostly i make same coils using same datas. Even than some coils "producing" better audio and some worse!?
So.....problem with audio is still here and it is not solved.
How to solve it? How to mod audio arround MPSA13 and make it louder (much louder) but to maintain simplicity and limited pcb dimensions?
Working on it...damn!

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?

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?

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?


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).

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 .

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

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 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?

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.

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

Cheers,

-SB

[ivconic]

Hi,
the use of earplugs and pot could be the cause of lowered / bad audio.

The electrical contacts inside the earplugs are the things to consider better... they can waste energy cause they are not perfect electrical contacts with zero resistance.

The earplug sure modify also impedance matching between speaker and output stage, this is related also to the bad electrical contacts inside.

Usually using headphones the things go better cause both you hear better the small audio variations but also the load of headphones is usually much higher than the earplug one.

In the case of speaker, instead, the few ohms maybe added by earplug contacts and joints could easy interfere with speaker operations... also cause there's much more current involved to drive speaker... and it's reduction will mean just you hear big hot bangs and not just fine movements of the speaker's cone.

The pot is similar issue: even at full conduction one side... there are always some few ohms that make things worse... this is true for all cheap carbon pots...

Kind regards,
Max

Yes, i tried somehow to overcome the problem. I added 150 ohms via plug...no results.
I cant explain, but have feeling that somehow plug presents some huge parasitic element. This not supposed to be an issue at conventional detectors. All of them do have earplug and usually speaker is connected via that plug and its inner switch - once you plug eraphones, speaker is off and vice-versa.
Plugs i am using are brand new from a shop. Medium quality. Also have in mind that original TGS DO have earplug. So.... must be something wrong or missing on origin schematic of TGS from the first pages on this thread?
Look...if it was my first device, i would have most of doubts in my own hand works. But it is 26'th so far. All components are respected as on schematic. Never mind all the mods so far, i am talking now about original TGS.
So...from very first device to the last one...all of them worked more than good, i dare to say fantastic. I never expected to achieve such good performances. Yet...when packed in enlosure with ear plug and vol pot included...in most of cases audio turns degraded somehow...!?
So i am usually making a bad compromise. I do void earplugs and pot for adjusting volume. In that case TGSL works excellent.Although i could be more happy with a slice louder audio...
My goal now is not to make another TGSL (enough is enough ), but to solve the main catch here, on this design. As you already seen, i ve been tried many things so far. Quite a fun it was. Still no perfect solution.
I also want to void to much complicated audio stage. Need to keep limited pcb dimensions. Besides...if we integrate quite new and complex audio in TGS...it will need much other changes in previous stages too. At the end it will turn to a quite new design...which is not what i am intend right now.

So i think...nevermind the plug and pot...problem still coming from device itself!? Where,why? Tough question.

At last LM358 output...signal varrys from -0.5 to -0.01 V. -0.5V stands for no detection, -0.01V stands for full detection. That range is what interests me mostly.
Signal at output is so weak? Why? Tracing signal from the switching fets to audio i couldnt find out where it is been attenuated. Dont have a clue.
Signal at LF353 output looks enough good.
Base of MPSA13 "receive" pretty weak signal.Short and weak.
I met in other designs simillar audio and there MPSA13 producing such loud audio that it almost screaming. Classic III for example...
Hmmmm...
Sooner or later we will find right solution....

Regards!


P.S.
Thanks friends....dont tell nobody that i am 42 !!!! Sheeesh!!
I fell exactly like i am 22....

[simonbaker]

Correction

My "low spike" calculations for R11, R12 only good for no load, please disregard.

Load (37 mA) makes spikes happen in negative supply always - we just live with them as Max says. Maybe not a problem anyway.

CD4024 is clever design because ripple and spikes synced with lock-in amplifier, probably just make an offset, can be adjusted. A separate DC/DC converter might have beat frequency, bad.

But if we get coil oscillation from DC/DC converter freqency somehow -- good!

Sorry for confusion on resistors.

-SB

(P.S. with 37 mA current draw, best resistors seem to be R9 = 5.6K, R10 = 12.5K for spikes, but I'd stick with original, Tesoro smarter than me )

[Noemio]

happy birthday



How many?