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VCO Mod

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16 years 2 months ago #1271 by Ismael
VCO Mod was created by Ismael
This mod is for a fine frequency adjust through different ranges to overcome noise and stability. I have had this mod on my detector for quite a while now (over 2 years) and I never released it publicly due to it being necessary to use 2200 end caps and also one part was extremely hard to find and that is the multi-turn external adjustment extension. I only sold one detector with this on and that was my original detector to a fellow in the US that wanted to try it. This is my detector:





In the above picture you can see the controls and following is an explanation of them.

Starting from the top (power socket) is the standard fixed frequency - On/Off switch (I just have a couple of extra frequencies). To the bottom left is a switch to change from Fixed to Variable system and on the opposite (bottom right of Fixed Switch) is the fine tune adjustment. The next knob numbered 1 - 9 are the variable frequency ranges. The reason for so many is to allow a greater range. If I had less the fine tune would be greatly reduced and therefore be rather coarse. Below is another picture of the frequencies:



As you can see I have a large range that I can cover and so far it has worked well in reducing interference and to a degree noise of operation. I haven't managed to use it much over the last 2 years and have really only been out for a few times totaling maybe only 3 weeks to a month. If I can make this work externally with a multi pin connector then I may release it publicly.

For those of you interested the other knobs are just Tone /Threshold and my inbuilt Audio Amplifier.

:woohoo::woohoo::woohoo:
Regards Ismael
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14 years 3 weeks ago #1876 by Mechanic
Replied by Mechanic on topic VCO Mod
Hi Ismael, I am very interested in the VCO mod. I can easily make a new end cap. Are you still going to release the diagram for the VCO? I have been looking for a circuit to build my own, but due to my limited electronic knowledge I have been unable to find what I need. Even the main IC no. would be enough.
Cheers

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14 years 3 weeks ago #1877 by Woodyfrankston
Replied by Woodyfrankston on topic VCO Mod
Hi Ismael, I had the pleasure of looking at one of your modded SD2000 detectors with the VCO mod done to it. I am amazed that it is so stable, you really did a fantastic job on the detector. Keep up the good work.

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14 years 3 weeks ago #1884 by Ismael
Replied by Ismael on topic VCO Mod
Hi Mechanic and Woody, The IC is LT6900 or LT1799 I may post the schematic but at the present would rather not due to it still being a current mod. I hope you understand. Thanks also Woody, yes it definitely quietens and stabalises the detector. Which type did you see? My original detector as in the photo (sniff, sniff my baby!!:( ) or a single turn pot on standard covers?

:woohoo::woohoo::woohoo:
Regards Ismael

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14 years 3 weeks ago #1885 by Woodyfrankston
Replied by Woodyfrankston on topic VCO Mod
It was the one Michael bought from you.
You did a great job on it.

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14 years 3 weeks ago #1886 by Ismael
Replied by Ismael on topic VCO Mod
Yeah that's my baby. A very good detector that one. I certainly miss it!

:woohoo::woohoo::woohoo:
Regards Ismael

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14 years 3 weeks ago #1887 by Mechanic
Replied by Mechanic on topic VCO Mod
Hi Ismael,
Thanks for your input on this, it is greatly appreciated. While looking at the data sheets, I found one that does 40khz to 4Mhz. I might try a few experiments with the different VCOs.
Cheers

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14 years 2 weeks ago #1898 by Mechanic
Replied by Mechanic on topic VCO Mod
Hi there again, I have another question for you guys.
By changing the frequency which the detector runs at, you also change the the pulse train timings. Is it possible to adjust the timings without remaking the logic circuit. And would there be an advantage if the pulses could be adjusted?
The reason I ask this is that there is a 15ms delay between transmit and the first sample on Ch2. Slow the detector down this period is longer speed it up it is shorter. Also if using a coil with a higher Q value than standard, the timings could be set to sample earlier, therefore finding more small gold?

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14 years 2 weeks ago #1899 by Woodyfrankston
Replied by Woodyfrankston on topic VCO Mod
It depends on the detector. M/L detectors use crystal control for MPU but on most models use L/C for pulse timing and Audio as well.

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14 years 2 weeks ago #1900 by Mechanic
Replied by Mechanic on topic VCO Mod
Hi woody, this is in reguards to the sd2000 detector.

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