IGSL

[Davor]

I gave this a second thought and made a LTspice sim to compare my vision of a future Tx with the existing ones. From top to bottom are:
- balanced H-bridge cross-coupled oscillator, draws about 4.5mA, very clean, no 2nd harmonic, works fine without adjustments (look Ma, no hands )
- Musketeer IGSL, works fine, a bit less current draw, about -40dBc 2nd harmonic, requires adjustment
- TGSL IGSL, draws very little current, but the coil current is also small, quite touchy, I had to change a resistor between base and positive rail to be able to tune it - perhaps it is the source of a no tuning with TR3 problem, when it oscillates in full rail regime the 2nd harmonic is whooping -30dBc

The first two use a Musketeer coil with my odd specifications (mine was built that way), and the third one is a TGSL, and it also works on ~double the frequency.

Lo and behold, but please give me some feedback as well:

[axljackass]

guys just to clarify some simple questions ii hope you dont mind.

1.Is it possible to use my lipo battery which is 14.8v?do i need to change any parts? any negative effect to my circuitry? by the way my speaker is 6-24v
2.can you guys show me how to put my headphone i guess imight fried up it ill connect it parallel to my speaker right?

thanks guys

[Davor]

14.8 V goes to the audio amp only, but as it is operated in current mode I don't expect anything spectacular to happen. Just go for 14.8V. Your headphones will be terribly loud this way or another, but I must confirm that headphones with a potentiometer on them works just fine. I thought of various methods of making them quieter, but Ivconic's tip on the phones with volume control did the trick just fine.

[bernte_one]

hello

i have currently 2 versions of igsl musketeer layout files here
1st from the version of silverdogs pcb (first layout ehich was public made here)
2nd 2.1 layout of igsl musketeer which was published some times later

which one is recommended to build for next pcb i etch and does anyone know the improovements of version 2.1

regards bernd

[Biogas]

Hi All!

Please tell me what is the different between the IGSL and TGSL?

Thank you!

[Davor]

There is an additional discrimination channel with independent adjustment for Fe-like targets. It can be adjusted so that you have a notch at, say Al foil, or you can overlap both channels to have a "double tone" indication for small gold, Al foil and nickels. Otherwise it is very much like TGSL. In addition, there is a variant that works with "Musketeer" coils.

[axljackass]

can anyone post the link on how to make "musketeer" coil?i can only find the tgsl coil.thanks guys

[Davor]

You can check how selim did it here: http://www.geotech1.com/forums/showt...824#post131824

[giuhalftrack]

....choice of opamps in gain stages as well. In case you used LM324's there, you'd lose some significant distance.....

yes I had LM324 on my board, when i went to get LF347 in shop they give me an "equivalent one" :\ TL .... something
I need to get only LF347 (listed in igsl schematics parlist)?

i know this is a stupid question, please be patient.

[Davor]

No, this is not a stupid question at all. It deals with offset problems of various families of opamps.
In general you have two flavours of op amps, those with FETs and those with BJTs on their input. BJT input opamps have transistor bases directly at their inputs, and those require some base current.
In case of a TGSL (and IGSL) configuration, and using LM324 as PNP BJT input opamp, the final gain stage has a non-inverting input nailed to the signal ground, while the inverting one passes the base current through a considerably high resistance, which results in about -15mV offset at the output. With Disc Sens control starting at 3mV, you need a signal that is 18mV instead of 3mV to give you a beep, and that accounts for some serious depth loss.

FET opamps have negligible bias current and their offset is typically not related to input resistance mismatch and you don't have such loss.

In case you insist on using LM324, because of low power consumption, voltage flexibility etc. - you'd have to do something about the offset problem. But frankly, the easiest thing is to just replace the opamp with a FET input one.

[ivconic]

yes I had LM324 on my board, when i went to get LF347 in shop they give me an "equivalent one" :\ TL .... something
I need to get only LF347 (listed in igsl schematics parlist)?

i know this is a stupid question, please be patient.

LF444 should do too. I guess it is easier to obtain.

[Davor]

Mine works happily with TL064 and it uses a fraction of LF347 current. It is noisier, but it is not much of an issue here. LF444 is practically the same thing as TL064, and also uses little power.

[Hahhaa]

Hi all,
My 1st post here
I'm planning to build TGSL version of IGSL and Davor's mod. I'm making my own coil but didn't have proper equipment and wire. So, I'm making TGSL for now. For musketeer version, I'm sparing some space in the same board, separating 'oscillator stage' by a toggle switch (6 pins DPDT).

I read somewhere, "replace TL062 with TL072 or TL082, cause they have less noise"
Maybe this apply to TL064 too. If too concern about the noise, replace with TL074 or TL084.
LF347 and LF444 is not available near my place (small shops). I'm getting TL064 instead, and TL084 too, just in case.

[giuhalftrack]

No, this is not a stupid question at all. It deals with offset problems of various families of opamps.
In general you have two flavours of op amps, those with FETs and those with BJTs on their input. BJT input opamps have transistor bases directly at their inputs, and those require some base current.
In case of a TGSL (and IGSL) configuration, and using LM324 as PNP BJT input opamp, the final gain stage has a non-inverting input nailed to the signal ground, while the inverting one passes the base current through a considerably high resistance, which results in about -15mV offset at the output. With Disc Sens control starting at 3mV, you need a signal that is 18mV instead of 3mV to give you a beep, and that accounts for some serious depth loss.

FET opamps have negligible bias current and their offset is typically not related to input resistance mismatch and you don't have such loss.

In case you insist on using LM324, because of low power consumption, voltage flexibility etc. - you'd have to do something about the offset problem. But frankly, the easiest thing is to just replace the opamp with a FET input one.

ok very interesting !!! I was disappointed when the guy at shop said: "they are equal".

[golfnut]

You will not need to worry about noise and swapping chips around.

You will need to concern yourself with..

A suitable housing
soldering all the parts correctly
Wiring all the pots the right way
Obtaining a 9" DD coil shell
A shaft plus fittings and handle/grip
Appropriate battery technology
Coil shielding techniques
Coil Nulling process
Sourcing quality screened cable to coil
Trouble shooting if things go bad
Setting up
Finally learning how to use it properly - to get something out of it.

In 3 months time when you are up to snuff, start swapping chips around.

Steve