Preamp modifications

[Magman116]

Hello to all. Things definitely did not start out well here, and it is mainly my fault for letting things get out of hand, plus I was really posting in forums that I should not have. I am sorry to have offended anyone or any manufacture here.

For commercial detectors I really favor the Tesoro detectors. They perform consistently and are very light weight. I own several Tesoro detectors and have found the Silver Saber uMax to be the best all around detector on the market for the price.

I would like to discuss the design and or modification of the receive preamp in detectors.

This I will stress. The preamp needs to be as low noise as possible to allow more of the signal through without being affected by the circuit noise of the preamp. If there is excessive noise in the preamp stage, all following stages will be affected.

Resistors are a source of circuit noise and resistors in the preamp need to be selected carefully. There are formulas that define the noise of a resistor. The lower the resistance, the lower the noise.

Another main contributer to noise in the preamp, is the amp itself. Many manufactures tend to use fairly hi-noise amplifiers even if they (component datasheet) state the components are low noise. LOW is relative.

I would like to post a preamp as an example to go through and outline the noise and how to modify the preamp to minimize the noise and maximize the signal.

For some, a very small PCB can be made and wired by hand, then added to the detector circuit in place of the current preamp. This will greatly enhance any detector's receive sensitivity.

I'll get my example preamp and a revised preamp to go over with everyone; that is if people are interested. It is a fairly easy mod once you understand exactly what is going on in the preamp section.

Thanks for reading.

-Chris

 

[Mr.Bill]

Post away.

Yes, the component may have the same model #, but comparing specs. between component manufactures do show difference's. Looking forward to reading your info.

 

[Sven]

Hi Chris,

You took a beating in the other forum. It was going to happen.
This forum, Modifications Forum would have been the right one to start your post in. About how you took the popular Bandido/Silver Sabre, modified it and improved upon it's circuitry to make it a better; deeper machine. There was no need to tell about the Ultimate,
until you actually had one built to show the world.
Your post would have been rec'd much a better response, than it did.

At any rate, I read all your posts and would like to see what you have to share with us.
As a project I thought about building a Bandido per posts on Geo but, haven't been able to say for certain the schematics posted
are 100% accurate without errors. If you can give us a better clue that we can build the machine, give us a list of parts....etc. that would be of real help. Some or many of us tinkers would be tinkerers have no real electronic schooling. I learned from reading books and probably only know about 5% of what you or any other tech knows. So we are looking for reliable info to help us.
I can solder parts and components...............can't make a PC board. Would love to purchase a pre-made one.

Give us some how to build articles, reliable info........we will listen. If we can successfully use what you supply, you get the recognigition you deserve.

When you get a better video up on YouTube, I will look at it again.

Happy Treasure Hunting.

 

[Beachcomber]

n/t

 

[WilliamJB]

I purposely bought an older rig a Bounty Hunter 8400 just so I could modify things. I do not have the gear to work with SMD's so I figured if I went with an older device I could play around more. Now instead of trying to build seperate pcb's to add to the OEM circuits which probably the better way to go I was tinking about componet selection. Today we have a lot more componets inthe form of transitors to chose from then they did 15-30 years ago. I have consistently modified two way radio equipment by up gradeing pre drivers,drivers and finals with transistors that have higher signal to noise ration,disapate more heat watts, and that have better inter mod specifications. Then I usualy like to replace cheap diodes with much faster ones. Capacitors tend to dry out so I either replace those or better yet replace them with Japanese soild caps! Upgrade any torrid assembly,voltage regulators and turn up the juice a little bit. Before you know you it you have improved out put power, recieve sensitivity, switching speed, and voltage reulation easily 30% or more for just a few bucks. When you can make the unit run cooler at a higher output level with more stability,less noise and more sensitivty you basicly end up with a macine that will kick most detectors teeth in! For under $100 dollars. Case in point I saw a Whites 6000 Pro on ebay going for around $50 put another $50 in parts to up grade it and you can easily go head to head with any of the $800+ machines of today. The best part is that these older machines have much better shielding then these new all plastic enclosed machines. The metal lunch box design act's like a faraday cage and helps to keep all the random stray EMI/RFI out of the electronics! I am alread considering getting an older Whites 5000-6000 and doing some modifications. With these their are stillplenty of coils to be had.

 

[thebeatmachine]

I've had luck updating detector op amps in the front end. I used a eight pin socket on one and tried several op amps that were interchangeable with one another. Sometimes there are op amps that are the same chip but one is a general version and the other is for Audio applications. ( on 6.95 khz anything with an "A" on it is a good thing) The same goes for transistors, your detector may use a npn type in the tx stage but with a quick to the radio store you can have a hand full of npn of different varieties. The faq sheets for each of them are available on the Internet. If you make a way to switch transistors out for test purposes, (Like use part of an eight pin socket) you can find out which ones work the same, better, or not at all. This is all risky stuff but I have made improvements on my detectors using my amateur methods. There are also schematics available on the Internet but they can be hard to find and are often posted in foreign languages and sometimes they just arn't accurate. When you find a good one hold on to it.

Modifying detectors is a great hobby, the best around.

 

[prospector 55]

one of the biggest things you can do to improve a metal detector pre-amp is to replace all 5 and 10 percent tolerance resistors with 1percent resistors and replace all of the op amps with discreet components ,single transistors have much better gain, stability,heat disipation,much lower noise,and distortion than any op amp on the market today, also replace all cheap capacitors with silver mica caps if possible, I have worked on industrial metal detectors for a number of years I am an electronics technician, I would also be really interested in your pre amp mods, it is always fun to learn new things

 

[GOLD&OLDIES]

Like i read from someone else i don't know much about electronics, but would be real interested in what you come up with good luck and keep us posted Kevin

 

[king-ghidorah]

Keep me posted too. I like tinkering with things.