AMX Schematics & Layout

[Olly]

I am in stage of re-drawing your schematic in different software. So I want perfectly accurate schematic according to which I will draw my pcb.
And I want to pick best option. In your schematic you put all together, all the options. And it is confusing.
Why would I want to remove IC2? What are the pros&contras of that.
Is the coil same at both options? Single coil or coil with center tap?
At Tinkerer's schematic R1-4 are with values and at your schematic with zero values. If zero values then why those exist on schematic? Placeholders?
Also at Tinkerer's schematic there is significantly higher amplification than on your schematic; I guess it is due loss because of the R1-4 resitors.
We will agree that R1-4 will introduce more noise in signal path, so imho is better to omit them and use lower gain at opamps, as you did.
But than I should omit even the placeholders or not?
Can you (if not asking much) separate both options in two separate schematics and explain in short both options, pros and cons for each one.
This way is little bit confusing. I don't want both option on my pcb, I want clear one option and to avoid placeholders for componentes I will probably not use in option i picked.
I am sorry if I ask too much. But two separate option as schematic of RX will reduce any further confusion.
Things will evolve, hopefully more people will join, same questions will be asked all over again when topic grows to several tens of pages and more.
If you not sure about the component if you gonna use it or not; than it is better not to be present on pcb.
This reminds me on your first HH attempt, you put "dozen" options on one sch draw and one pcb draw. It was so confusing then. And my first two attempts to make it; failed so bad.
You must understant that I don't hide back in your head and I can not see your thoughts. Many of us do not.
Split your work on two separated and perfectly clear options and everything will be clearer and better to understand.
Your character seems to be like that; lazy on words, not only do you adore incomprehensible abbreviations in writing; you also like to put everything on one schematic and one pcb.
Like a pot with stew. Everything inside, so you guys pick what you want from it!
Imagine me, after a lot of effort to make it, after "100" new pages on the topic, a lot of effort (and money) in the end
it doesn't work for me, because I discover that I mixed up the options.
There are also people like me, who are stupid, not all of us are super smart to read other people's thoughts and immediately understand
everything "what the writer wanted to say"...
I sincerely apologize for these remarks, but it is better to say them now than much later.

Hi Ivconic, respectfully I think that Carl has done an amazing job with the experimental platform. There are a lot of optional parts and footprints on this first development version to aid experimentation and so allow convergence on an optimal solution. Research first - Then development..

I for one can’t wait to get started playing with the board.

Kind regards,
Olly

[ivconic]

I am in stage of re-drawing your schematic in different software. So I want perfectly accurate schematic according to which I will draw my pcb.
And I want to pick best option. In your schematic you put all together, all the options. And it is confusing.
Why would I want to remove IC2? What are the pros&contras of that.
Is the coil same at both options? Single coil or coil with center tap?
At Tinkerer's schematic R1-4 are with values and at your schematic with zero values. If zero values then why those exist on schematic? Placeholders?
Also at Tinkerer's schematic there is significantly higher amplification than on your schematic; I guess it is due loss because of the R1-4 resitors.
We will agree that R1-4 will introduce more noise in signal path, so imho is better to omit them and use lower gain at opamps, as you did.
But than I should omit even the placeholders or not?
Can you (if not asking much) separate both options in two separate schematics and explain in short both options, pros and cons for each one.
This way is little bit confusing. I don't want both option on my pcb, I want clear one option and to avoid placeholders for componentes I will probably not use in option i picked.
I am sorry if I ask too much. But two separate option as schematic of RX will reduce any further confusion.
Things will evolve, hopefully more people will join, same questions will be asked all over again when topic grows to several tens of pages and more.
If you not sure about the component if you gonna use it or not; than it is better not to be present on pcb.
This reminds me on your first HH attempt, you put "dozen" options on one sch draw and one pcb draw. It was so confusing then. And my first two attempts to make it; failed so bad.
You must understant that I don't hide back in your head and I can not see your thoughts. Many of us do not.
Split your work on two separated and perfectly clear options and everything will be clearer and better to understand.
Your character seems to be like that; lazy on words, not only do you adore incomprehensible abbreviations in writing; you also like to put everything on one schematic and one pcb.
Like a pot with stew. Everything inside, so you guys pick what you want from it!
Imagine me, after a lot of effort to make it, after "100" new pages on the topic, a lot of effort (and money) in the end
it doesn't work for me, because I discover that I mixed up the options.
There are also people like me, who are stupid, not all of us are super smart to read other people's thoughts and immediately understand
everything "what the writer wanted to say"...
I sincerely apologize for these remarks, but it is better to say them now than much later.

[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.

[Carl-NC]

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

[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]

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]

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 ???

[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.

[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.

[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.

[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?

[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]

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

[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:

[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.