Coil RX signal Equinox, Manticore, CTX3030

[bklein]

I’d like to know if the coil RX signal on these detectors are unprocessed or if perhaps they are converted to digital or amplified by the in-coil PCB. My interest is in experimenting with an added amplifier.

[Altra]

I don't think any of these do processing in the coils

See post #502 for the pre-amp and #516 a scope shot for the Equinox.

https://www.geotech1.com/forums/foru...e34#post435400

I believe the CTX3030 coil has a pre-amp and security chip. It is BBS technology so it uses hardware demodulators vs DSP demodulation in the Manticore and Equinox

[bklein]

I'll let you in on what I'm wondering about - I'll read that thread when I get more time.
Back in the 70's I was a technician for Music Man, a guitar amp company. I was looking at ways to reduce EMI issues our amps had.
The most beneficial thing I found was to use a BIFET op amp as the first amplification stage. Bipolar op amps would rectify the RF and you'd get the audible interference.
So now we have BIFET type or J-Fet type op amps with higher slew rate than the 5532/4 so I'm wondering if using one after the coil signal would reduce EMI.
It would be interesting to play with increased gain too while I'm at it.
Has someone already done this and have results?

Barry

[Altra]

Hi Barry, did you ever get to meet any famous musicians at Music Man?

Not sure how much you could tweak the Manticore or Equinox. They are very sensitive to minor changes in phase and amplitude. The idea is to have a flat frequency response across approx. 2khz to 40khz. You could increase the gain, but would probably lose your target ID accuracy, GB, and salt elimination. Keep in mind that the pre-amp, ADC run on 3.3v so don't feed it anything higher.

I have no idea what the Manticore coil has inside. But assume it is a continuatation of Equinox technology. The coils are not interchangeable, not sure if this is marketing or some improvement to the Manticore? The only thing I have seen others do is use a donor pre-amp boards to build their own coils.

The CTX3030 probably has a better chance to get improvements. But I have not seen a schematic for the pre-amp, only photos.

Mark

[bklein]

Yes I met several but I was a young nerd that didn’t socialize well. Could have gone out for drinks or dinner with them but they were too outgoing for the introvert I was.

[JoyJo]

Greetings. Has anyone already managed to measure the inductance and active resistance of the TX and RX coils for the Manticore search coil?

[JoyJo]

Maybe someone has a photo of the manticore board?

[Carl-NC]

Greetings. Has anyone already managed to measure the inductance and active resistance of the TX and RX coils for the Manticore search coil?

There is a preamp in the search coil so you cannot measure the RX coil without breaking open the assembly.

[JoyJo]

Yes. I know that. I should at least find out the inductance of the transmitting coil so that I can determine the number of turns. The winding of the TX coil is made of litzendrate. I tried to calculate... I know the inductance of the TX coil from deus2, there is also a winding with litzendrate. Based on the length of the turn of one coil (approximately 61 cm), I estimated and received 8.8 turns of litzendrate for the TX coil. I suspect that there will be something like that in Equinox and Manticore. Although, the transmitting cascades of equinox and manticore are different. Judging by the fuzzy photo of the mantleboard, the TX cascade in it resembles the transmission cascade Fisher CZ5.

[nordic]

I have made an RX amp using dual opamp and 5x gain. I don't think I have got any more depth tbh. The VDI stayed the same, no issues with EMI. The sound was a little distorted though on shallow objects.

[bklein]

See if you can try different op amps like I mention above and note any difference around EMI. To be honest though all this focus on noise cancel doesn’t seem to make a lot of difference in me hearing targets. The Manticore is the only detector I can say does a good job reducing EMI. CTX…no.

[nordic]

I actually don't have much issue with the EMI, also looking at the scope, all what Equinox does to combat the EMI is offsetting frequencies in some fixed incremented + or -. Eg from 5KHz to 4.99KHz or so.
In case of Nox 800, the coil outputs differential signal centered at 1/2 Vdd, which is 1.6V. In the control box RX signal goes through an LCR filter and then into ADC PCM1662. This LCR filter plays major role on target ID. Any modification to it skews IDs, except iron discrimination. In fact any additional external filter will probably effect target IDs.

[nordic]

Also if it helps someone, Nox 800 output cascade is made of HIP2103 + AO4882 combo. Mosfet power supply is around 25V via LMR64010 switcher. It can be increased to almost 29V before software protection kicks in. I have been running mine at 27.5V without any problems, even in 4kHz. Battery life is effected severely though.

[JoyJo]

Can you measure the supply voltage hip2103? I've been looking for its analogue for a long time. More precisely, a good driver for an n-channel half-bridge, so that you can adjust the supply voltage of the half-bridge, you need to apply a constant voltage to the driver separately.
Recently I got my hands on a board from hterra pro. On it, the transmitting cascade is assembled on ao4882 and driver ncp81155. The driver is controlled by a signal. In general, judging by the scheme of the xterra pro, I can say that this is a shortened version of Equinox.

[nordic]

Hi there, yes, there is a logic level signal going to the HIP2103, there is even a test pad for it. Possibly directly from the MCU. If I recall correctly it was 5V or just under, I could not find where on the board this supply is formed, perhaps I didn't look long enough. Perhaps a lot of Minelab machines share similar design. They are close if not identical to datasheet recommended designs. Nothing extraordinary in these circuits, engineers took signals into digital realms, all the magic happens in the software.