Barracuda Legend Kit Problems

[Old cart]

The signal chain ends at the output of the first stage, and after that the signal must be above the threshold to generate an audio tone. So the second stage only serves to boost the audio amplitude. In other words, if you increase the gain in the first stage you will increase sensitivity, albeit with an increase in instability. If you increase gain in the second stage, you will boost the sensitivity of the audio to a signal that exceeds the threshold.

Of course, don't know how I can be so stupid! Thanks for setting this straight.

[Impulse]

Hey all the barracuda is in the post! hopefully we will get to the bottom of the issues we have had

[6666]

Here u go.. Top trace is pin 2. Bottom is pin 4.
Sweep = 50uS/ div
Y axis is 2V/ div.

Pulse is essentually returning to ground from -5V. I have my scope ground reference on the minus lead of C1.

Just looked at my bara pulses, pin 2 pin4 and mine are nice and clean like Dons, remember that - Batt is ground for P Fet.

[green]

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.

I get a sampling gain of .0256(640 x .000040). What is the correct formula?

[Michaelo]

I think it's been mentioned before but there's no actual pre-amp, it's just a single stage high gain amplifier (gain = 1,000).
The remaining circuitry deals with the manipulation of the resultant signal, basically audio...
A pre-amp (with decent filtering) would be a welcome change...

[Qiaozhi]

I get a sampling gain of .0256(640 x .000040). What is the correct formula?

I seem to have had some "fat finger trouble" (FFT), as your calculation is correct. Must have hit too many buttons at once to get 0.0267.
Also, 127,000 * 0.0267 = 3390 (not 7209) ... I certainly cocked that up!

So, with the correct values (thanks Green - at least someone was awake) we have 127,000 * 0.0256 = 3251. Which means that a 1uV signal at the input results in 3.25mV at the output.

Hopefully it's right this time.

[ivconic]

I seem to have had some "fat finger trouble" (FFT), as your calculation is correct. Must have hit too many buttons at once to get 0.0267.
Also, 127,000 * 0.0267 = 3390 (not 7209) ... I certainly cocked that up!

So, with the correct values (thanks Green - at least someone was awake) we have 127,000 * 0.0256 = 3251. Which means that a 1uV signal at the input results in 3.25mV at the output.

Hopefully it's right this time.

Too much simulators ... and there what you get !
Leave simulators and took soldering iron in your hands instead.
Feel the heat!

[ivconic]

No heat yet?
Any discoveries on that faulty Barra?

[Qiaozhi]

No heat yet?
Any discoveries on that faulty Barra?

In actual fact, the soldering iron is often in use here. I regularly use a combination of hand calculations, simulations and real hardware.. You really do need to be proficient in all areas to achieve good results.

I have the Baracuda here, and gave it a cursory glance a few nights ago. The unit was very unstable and with poor detection depth. The first thing I noticed was that the MOSFET was very hot, so I detached the coil and found it to be 166uH which is far too low, and the reason for the excess heat. Power supplies were all in the correct range, but the TX oscillator output was distorted and the main sample pulse was false triggering and giving two separate pulses. During further testing the CD40106 went kaput, with the result that the -5V supply was being pulled down to -3.84V. Literally, a few minutes ago. the postman arrived with a bag of parts including the CD40106 replacement. However, there's Bank Holiday weekend imminent here in the UK, and I have guests coming to stay. Hopefully I can get another look at the Baracuda some time next week, as long as real work doesn't get in the way.

[ivconic]

In actual fact, the soldering iron is often in use here. I regularly use a combination of hand calculations, simulations and real hardware.. You really do need to be proficient in all areas to achieve good results.

I have the Baracuda here, and gave it a cursory glance a few nights ago. The unit was very unstable and with poor detection depth. The first thing I noticed was that the MOSFET was very hot, so I detached the coil and found it to be 166uH which is far too low, and the reason for the excess heat. Power supplies were all in the correct range, but the TX oscillator output was distorted and the main sample pulse was false triggering and giving two separate pulses. During further testing the CD40106 went kaput, with the result that the -5V supply was being pulled down to -3.84V. Literally, a few minutes ago. the postman arrived with a bag of parts including the CD40106 replacement. However, there's Bank Holiday weekend imminent here in the UK, and I have guests coming to stay. Hopefully I can get another look at the Baracuda some time next week, as long as real work doesn't get in the way.

"...166uH..." !!

That explains a lot.

[Old cart]

"...166uH..." !!

That explains a lot.

That is why I proposed some small standardized test coils be made available, maybe through Silverdog. If this was desirable what coils would we need? Maybe a 100mm in diameter 300uH, 450uH, others?

[kt315]

maybe through Silverdog
--
WHO is Silverdog? why always as a trouble there is poping-up the name silverdog?

[kt315]

KEEP THOSE TABLES ANYWHERE. i give them again and again and again. i gave them 10th times.
you dont need a calculator and calculate

[Old cart]

KEEP THOSE TABLES ANYWHERE. i give them again and again and again. i gave them 10th times.
you dont need a calculator and calculate
[ATTACH]35652[/ATTACH][ATTACH]35651[/ATTACH]

Sorry KT, I have never seen those tables, and I spend a lot of time on this forum.
But that is not exactly what I was looking for. I think it is a table that you published that showed the L and R of coils listed by the name of the detector they go with. I can not find it now. As we say in America- I have my **** together, I just can not lift it! ( I do not know if that wil translate well)

Silverdog is the guy who has a web site that sells detector kits like Chance, Baracuda, Surf PI, Minipulse, and others. Google Silverdog and you will see!

[Polymer]

Hi Old cart,

This might be the list you are looking for. I found it accidentaly whilst I got "lost" clicking around on this site ...

http://www.geotech1.com/cgi-bin/page...oils/index.dat

I know I have a very comprehensive coil parameter list from this site on hard disk, It'll take a bit to find it, but I will post once found ...

Cheerio