AMX Schematics & Layout

[ivconic]

And the files Carl posted in post #35 I just tried and those opens with no problems at all:

[KingJL]

I have re-created the AMX V1.1 in Kicad V7.0 (NO EASY TASK), if anyone is interested.

[KingJL]

I have re-created the AMX V1.1 in Kicad V7.0 (NO EASY TASK), if anyone is interested.

Anyone who has downloaded from the link prior to 9:45 AM EST Monday, April 24, 2023, please redo the download... there were many MB of extraneous backups included previously.

[ivconic]

The AD797 is too expensive a chip for a tight budget. But the bigger problem is getting the original chip.
Because "cross-eyed" manufacturers have flooded the market with some chips that bear the same markings but are sold at suspiciously low prices.
And now imagine the suffering of the average "European" from a country that is not a member of the EU, therefore as a consumer he is not completely protected
from fraud and cannot easily exercise his consumer rights.
I don't have a problem paying a lot of money for the AD797, but my problem is doubting that I will get what I paid for.
Some of you will say: "If you don't mind paying; then order directly from the manufacturer..."
And there follows an even bigger problem; shipping and import taxes, which are very high above certain limits,
should then be added to that price at the manufacturer's, which is high.
Specifically, two chips give a price that exceeds the import limit.
And finally with customs paid; the price would exceed the price of a solid metal detector from a reputable manufacturer... just two chips!
So I am forced, with a heavy heart, to look for an alternative solution, some adequate replacement.
In recent months, everyone has gone crazy with the euphoria surrounding AI. So I asked ChatGPT AI about this:

[ivconic]

Simplified, it goes like this (only two from the list I can obtain at local supplier):

[ivconic]

I have already obtained two of LME49720, for some other project.
Which is gonna be now: LME49720 or LT1115 ?
Which one is more sutiable for this purpose?
Or none?

[ivconic]

Carl I have a couple of questions. The answers to these questions can be very educational.
Why MAX412? Why not all 4 be AD797? Or instead of MAX412 some other opamp?
Since I already have the LME49720, which is a dual opamp; can all 4 opamps in RX stage be LME49720?
Will it affect performance and how?

[Carl-NC]

I have taken a look at your gerbers and would need to make some recomendations.

I took a look at the videos (30 min of Rick's, I'll finish it later) and I'm aware of the issues. Back when I use to design eval boards for GSM and ultrasound chips I spent a lot more time & effort on PCB layout, doing all the things Rick mentioned. That was about 20 years ago at Analog Devices, and even then we were paying close attention to ground return currents. I admit that metal detector design has made me a bit lazy and I've fallen back on some bad habits. The purpose of this first board is to just roughly evaluate what actually needs to be done; raw performance is secondary. When I finalize the design I'll spend more time on the layout.

[Carl-NC]

Carl I have a couple of questions. The answers to these questions can be very educational.
Why MAX412? Why not all 4 be AD797? Or instead of MAX412 some other opamp?
Since I already have the LME49720, which is a dual opamp; can all 4 opamps in RX stage be LME49720?
Will it affect performance and how?

The 49720 looks like it will work just fine, probably even for the input amps. Voltage noise is slightly higher but I wouldn't worry about that now. The MAX412 is a placeholder, not a final selection. I was lazy and didn't go searching for a better chip. I have a bunch of 412s so I will probably start out using that until I see a need to use something better.

[ivconic]

The 49720 looks like it will work just fine, probably even for the input amps. Voltage noise is slightly higher but I wouldn't worry about that now. The MAX412 is a placeholder, not a final selection. I was lazy and didn't go searching for a better chip. I have a bunch of 412s so I will probably start out using that until I see a need to use something better.

That help me in decision! Thanks!
I will try to draw through-hole pcb for my work.
Or I might decide for two layer due the recent talks.
But as you said; "a proof of concept" and just for testing can be done more relaxed by now.


AD797 specified power supply voltage range of ±5 V to ±15 V.
LME49720 specified power supply voltage range of ±2.5 to ±17V.
So no changes in power supply needed too.
In fact I can supply it even with ±2.5 if conditions allows that.

[ivconic]

The role of RX3 DNS, RX5 DNS, R1, R2, R3 and R4 ???
RX2 and RX4 I can understand, can be 10R or less.
CX2 47P "Comp" is specific only to AD797 or...?
RX6 1K exist at IC3B and don't exist at IC3A ???

[Carl-NC]

RX2-RX5 are options for different opamps. Some have an enable pin, some have a disable pin. The AD797 uses that pin for compensation, so that's why CX1,CX2 are there.
RX1,RX6 are for a single-ended preamp option (omit IC2).

[ivconic]

...RX1,RX6 are for a single-ended preamp option (omit IC2).

You just lost me here!
So... both are present or not present at single-ended preamp option?
This way with only one present; does not make much sense to me???

[Carl-NC]

If you remove IC2 then you have to install RX1,RX6 (and eliminate a couple other resistors).

[ivconic]

AMX RX topic , post #35 , You explained it. I wasn't read it.
That's the problem, because I have to re-read all over again to avoid asking the answered question.