Tesoro - Make it deeper

[dbanner]

I dug some more and found some TL062's from TI which I purchased from a local supplier, they don't have the notch and I am now thinking they are not genuine. The writing on them seems to have faded away very quickly. I can barely read it.

[ivconic]

I bought my chips from a credible local provider. That still doesn't mean they're original... but it's unlikely.
However, it is possible.
All I have to do is find a rail to rail chip and see if there is any difference with a simple replacement.
Luckily I have another blank pcb so I can put together another Bandido to try Carl's ideas on.
Unfortunately... I don't have any other factory coils worth such an experiment at the moment.
I had a dozen coils but I don't have them anymore.
It's like that with me; "conveyor belt" for detectors, coils and parts...
I'll try to get some factory low inductance coils for that task.

[ivconic]

This is interesting and educative!
A friend sent me a PDF with his testings and experiences.
I took the liberty of trying to translate into English.
I am attaching the original and the translation:

[ArchibaldSTM]

You can watch the video (several parts on the channel). There are subtitles in English.

[dbanner]

The crossover distortion is curious. I wonder what's going on there. Is there a defect in the chip itself or is there something involving the test setup that's causing it, which doesn't seem to be the case, since the other chips don't show this behavior.

[Carl-NC]

Early opamp designs sometimes had crossover distortion due to the output stage becoming debiased at 0V. Newer opamps don't have this problem.

[dbanner]

Early opamp designs sometimes had crossover distortion due to the output stage becoming debiased at 0V. Newer opamps don't have this problem.

I noticed that the crossover distorion is occurring below 0V (scope pics). It would seem due to the internal circuit of the op amp, it continues to sink current to the output even below 0V during transition or crossover. So there is some internal current source which allows this to occur. This, it would seem, is typical of many of these jellybean op amps.

Anyways, this gives a clue why this distortion is occurring.

There is no resistive load at the output. Followed by a coupling cap then to the scope. Am I correct or what? I don't think this has anything to do with fake or defective op amps but rather the test circuit itself is flawed.

[dbanner]

Maybe I'm way off base on this one, but I don't like mysteries.

[Nightryder]

Could it be "fake" or relabeled ICs? I'm asking because nowadays a man can hardly tell. Even the old trusty store you are used to buy from can be ripped off buy the supplier. This scenario happened to me when I was building the first IDX. It could detect most coins 18-25 cm in air for most coins and I thought that was it regarding depth. After watching many videos I knew there was something wrong. I got ICs from a different source and guess what! detection increased to 35-42 cm for the same coins.

Good luck!

[Maurizio2]

The Bandido design appears to me to be lacking gain in the G channel. In newer analog VLF designs the R channel (and G channel) are run with gains 4-8 times higher than the X channel because they are substantially ground-free, and the G channel is what we use for targeting. Also, if this is the design that uses a 6mH TX coil then you can get a boost from lowering the LTX.

Hi Carl!

1) About the lacking gain in the G channel, I think it is possible to change the gain of op-amp.
What do you propose to solve the problem?

2) When you tell is possible a boost from lowering the LTX, do you intend to use a coil with a lower mH for TX as Musketeer IGSL for example?

[Carl-NC]

1. On many newer detectors the R channel is 4x-8x the gain of the X channel, and R is used for targeting. As I look again at the B2uMax, the G channel is used for targeting and its gain may already be boosted. It's hard to tell because it is a static single-stage channel so you can't directly compare with X & R. I would sweep some targets and compare, then see if it's possible to boost the G channel.

2. I would try 500uH - 1mH.

[ivconic]

A lower TX coil resistance logically means a higher "radiated" power through that coil.
Carl gave good advice, 0.5mH - 1mH is a good optimum for diy.
IGSL is perhaps the best example of this.
The first version used stock coils and I noticed that it works very well but does not have enough "depth".
The second version with Musketeer coils (1mH) kept the same quality of work but gained in depth.
But any more drastic increase in TX power carries with it serious consequences.
IGSL was built on the Tesoro core design.
Increasing the TX power will drastically disrupt the signal processing in the further stages.
You need to find the right measure. The same applies to all other detectors.
As time passes I am more and more convinced of one thing; good winding of coils is very important for "depths" as well as for the quality of work.
My poor DIY conditions were never good enough to wind quality coils.
That's why over time I started planning and building detectors that would use stock coils.
I'm looking at the ML Vanqish coils I have. The thing is brought to perfection!
I can't even dream of imagining how I would manage to wind such thin and precise coils, it's impossible in a DIY version.