Need help with a TLM 102 sized PCB for DIY LDC mic

[JohnRoberts]

The suggestion to put as much gain in the first stage as possible to improve S/N is not without compromise. Too much front end gain can cause headroom issues.
====
I deleted a few posts that were stirring the pot... please play nice, and be kind.

JR

PS: I locked the thread because I just didn't feel like reading it last night. I read it today.. you're welcome.

 

[ccaudle]

Too much front end gain can cause headroom issues.

Both voltage, and potentially current available from the phantom power. 6dB voltage gain means twice the current delivered to the input impedance of the mic amp.

following low noise gain stages, rather than trying to do it in the mic

If you can get the electronics quiet enough that the capsule noise dominates, then it won't matter, if you add gain in the mic or in the pre-amp the noise floor will be dominated by the capsule noise, so then it makes sense to have the mic buffer as unity gain for simplicity and sake of headroom.
There may be a conversation which can be had about noise spectrum and audibility and the difference between the spectrum of the electronic noise vs. capsule noise, looking at the noise on a frequency range basis rather than a single number of integrated noise level, but in any normal acoustic environment you are getting pretty deep into the area of questionable relevance at that point.

 

[edenooo]

The suggestion to put as much gain in the first stage as possible to improve S/N is not without compromise. Too much front end gain can cause headroom issues.
====
I deleted a few posts that were stirring the pot... please play nice, and be kind.

JR

PS: I locked the thread because I just didn't feel like reading it last night. I read it today.. you're welcome.

I was worried why it was locked!! I had one last question I'll post later and was worried I'd have to make a whole new post to ask it lol

 

[Itsme]

The suggestion to put as much gain in the first stage as possible to improve S/N is not without compromise. Too much front end gain can cause headroom issues.

Apologies if my comments were misleading. My suggestion is to put as much as possible of the total desired gain into the first stage as this would reduce the added noise of the following instances significantly. This is in particular valid if an active inverter stage is implemented.

 

[pmfalcman]

Yes I'm aware! I'm have space to add those, I just didnt want to have to work around them while routing

Do not put it out for too long. It'll bite you in the as..tounding place.
Best practice is: mounting points first. You cannot move them, you have to have mounting holes/points in given places.
THEN route around whatever you're connecting. No matter whether traces, wires, pipes or other.
Drilling through an IC is doable but causes noise issues or adversely influences FR.
But then again - I'm not familiar with this body, mounting might be simple and straightforward.

 

[edenooo]

Ok so- looks like the "OPA1642AIDR" (Pictured on the right) I used in my schematic is out of stock on JLCPCB and their suppliers, but they have a ton of the "OPA1642AIDGKR" available, this version uses a VSSOP-8 footprint instead of an SOIC-8 footprint, my question is- the numbers used are simply in reference to the pin being used for the same function, correct..? Meaning the 8 on the "AIDKGR" variant is the same 'function' as pin 7 on the "AIDR" version..? I see the version on the OPIC42 project seems to have the same 'pinout' as the "OPA1642AIDR" on the right.

Is this correct..? Or is there any some reason that I'm not able to use the "OPA1642AIDGKR" variant? They seem to be totally identical based on what I can read from the datasheets, but I'm rather inexperienced.

 

[edenooo]

Do not put it out for too long. It'll bite you in the as..tounding place.
Best practice is: mounting points first. You cannot move them, you have to have mounting holes/points in given places.
THEN route around whatever you're connecting. No matter whether traces, wires, pipes or other.
Drilling through an IC is doable but causes noise issues or adversely influences FR.
But then again - I'm not familiar with this body, mounting might be simple and straightforward.

I had originally routed with them in mind luckily, I had kept them at certain points and had just removed them temporarily so they weren't in the way while I was working, but I absolutely agree.

And mountng should be fairly simple, I'm very component at 3D printing and have the necessary tolerances for the circuit inside the body, despite how utterly tiny the body is.

 

[Khron]

my question is- the numbers used are simply in reference to the pin being used for the same function, correct..? Meaning the 8 on the "AIDKGR" variant is the same 'function' as pin 7 on the "AIDR" version..?

Google - "opa1642" - datasheet (should be among the first couple of results) - pinout should be within the first few pages.

 

[Itsme]

Ok so- looks like the "OPA1642AIDR" (Pictured on the right) I used in my schematic is out of stock

It looks like you are mixing it up. The 1642 is a dual, the 1641 is the single. The pin numbering across the package options of the 1641 is the same fortunately .

 

[edenooo]

It looks like you are mixing it up. The 1642 is a dual, the 1641 is the single. The pin numbering across the package options of the 1641 is the same fortunately .

HOW DOES THIS KIND OF THING KEEP HAPPENING

I must be actually going insane, thank you lol

 

[Itsme]

It's getting less with experience, but never goes completely away...ask me how I know .

 

[JohnRoberts]

Apologies if my comments were misleading. My suggestion is to put as much as possible of the total desired gain into the first stage as this would reduce the added noise of the following instances significantly. This is in particular valid if an active inverter stage is implemented.

It is a useful rule of thumb but as with most engineering decisions there can be competing interests.

JR

 

[Itsme]

It is a useful rule of thumb but as with most engineering decisions there can be competing interests.

Almost always...

 

[rogs]

As @Itsme has mentioned, you are confusing the OPA1641 and OPA1642 devices.

Couple of points....
The pin outs for the OPA1641:
• inverting input - pin 2
• non-inverting input - pin 3
• - ve supply (gnd) - pin 4
• output - pin 6
• +ve supply - pin 7
The other pins are not connected.

OPA1642: all 8 pins are used, but only pins 2, 3 and 4 perform the same function as the OPA1641.
OPA1641 and OPA 1642 are not interchangeable.

• The SOIC and VSSOP footprints have different pin spacing, and are also not interchangeable.

 

[edenooo]

As @Itsme has mentioned, you are confusing the OPA1641 and OPA1642 devices.

Couple of points....
The pin outs for the OPA1641:
• inverting input - pin 2
• non-inverting input - pin 3
• - ve supply (gnd) - pin 4
• output - pin 6
• +ve supply - pin 7
The other pins are not connected.

OPA1642: all 8 pins are used, but only pins 2, 3 and 4 perform the same function as the OPA1641.
OPA1641 and OPA 1642 are not interchangeable.

• The SOIC and VSSOP footprints have different pin spacing, and are also not interchangeable.

Yeah, can't believe I somehow completely overlooked that despite how much I've looked at these schematics.

 

[Khron]

Yeah, can't believe I somehow completely overlooked that despite how much I've looked at these schematics.

Google - "opa1642" - datasheet (should be among the first couple of results) - pinout should be within the first few pages.

Straight from the horse's mouth But I guess that would've made too much sense(?)...

 

[MidnightArrakis]

Ok so- looks like the "OPA1642AIDR" (Pictured on the right) I used in my schematic is out of stock on JLCPCB and their suppliers, but they have a ton of the "OPA1642AIDGKR" available, this version uses a VSSOP-8 footprint instead of an SOIC-8 footprint, my question is- the numbers used are simply in reference to the pin being used for the same function, correct..? Meaning the 8 on the "AIDKGR" variant is the same 'function' as pin 7 on the "AIDR" version..? I see the version on the OPIC42 project seems to have the same 'pinout' as the "OPA1642AIDR" on the right.

Is this correct..? Or is there any some reason that I'm not able to use the "OPA1642AIDGKR" variant? They seem to be totally identical based on what I can read from the datasheets, but I'm rather inexperienced.

[the "OPA1642AIDR" I used in my schematic is out of stock on JLCPCB and their suppliers] -- While using the assembly services of your PCB-fabricator is convenient and understandable, but you are also limiting yourself to whatever their current inventory of parts on-hand is. When being involved with DIY projects, another item that you need to learn about is how to specify and source your components. Fortunately for you in today's world, you have the Internet to very easily locate "who has what"!!! (See chart further on down below).

In related news.....all of the PCB-fabricators that also offer PCB-assembly services that I have used and/or are aware of, will also accept receiving components from their customers (like YOU), simply due to the fact that it would be physically impossible for them to have readily available stock of nearly every electronic component manufactured for the past 20-years. So.....contact JLCPCB and find out if you can send them (or, have "drop-shipped" to them) this OPA1641 IC-chip for use on the assembly of your PCB. You will also need to find out if they can place the part -- manually -- if you are only having 1-to-10 boards assembled or what is their minimum -- Tape-Reel -- length or quantity is should you be having some limited small prototype production run made.

Whenever I am having 1-to-5 prototype PCBs fabricated and assembled by a company like JLCPCB, I go ahead and purchase all of my components, sort them out into little ZIP-LOC bags, label each bag with their component -- REF DES -- while also providing them with a hard-copy print-out of the "PCB Component Assembly Drawing" and a print-out of the BOM. With all of that information at-hand, it is a rather easy and straight-forward process for one of their assembly technicians to correctly assemble one of my prototype PCBs with no errors. In addition to learning how to create schematics and design PCBs, you will also need to learn how to create and provide proper "PCB Documentation" to outside vendors, so outside companies can know and understand not only what it is that you want to be done, but also in -- HOW -- you want things to be done.

Of -- ALL -- of the PCB GERBER-files that are shared here on this forum, there isn't -- ONE -- set of GERBER-files that I have seen on here that contains -- ANY -- of the information that I have always included in all of my PCB-fabrication files and that is.....a DOCUMENTATION layer!!! Meaning, in addition to all of the GERBER-files generated for a PCB that includes the copper layers, the soldermask/pastemask/silkscreen layers, drill files, etc., etc., etc.,.....my PCB-design background has also included providing the PCB-fabricator with a -- DOCUMENTATION -- layer, as well. Something like this:


This specific fabrication information simply provides the PCB-fabricator with my "design intent" information as to how I would like a PCB to be fabricated and it is also easily included as -- just another GERBER-file -- so they have this information "right there, right then" as they are reviewing the other GERBER-files and getting my files setup for fabrication. Meaning.....they don't even have to open up and refer to a PDF-file in order for them to have and review this information. On their part, they can either turn-off or even delete this layer, if they want to. But, at least it's -- RIGHT THERE -- for them to see and they CAN'T MISS IT!!! And, you know what??? ..... Because of this.....I've never had a PCB-fabricator either call me up or send me an e-mail message asking me any questions about how I want my PCBs to be fabricated. Just sayin'.....

Now.....as far as the IC-chip goes that you're looking for, here's a list of U.S. distributors that all have your OPA1641AIDR in-stock in the quantities shown in the chart below:



>> It seems as though your best bet would be to purchase this chip directly from "Texas Instruments" ( TI ) and at the price of only $0.79 each, I would go ahead and get at least $5 or $10 worth or more if you are planning on making a bunch of your PCBs.

But.....what do I know, huh???

/

 

[JohnRoberts]

Almost always...

The discipline of design engineering routinely involves managing multiple variables to realize an optimal result.

JR

 

[edenooo]

[the "OPA1642AIDR" I used in my schematic is out of stock on JLCPCB and their suppliers] -- While using the assembly services of your PCB-fabricator is convenient and understandable, but you are also limiting yourself to whatever their current inventory of parts on-hand is. When being involved with DIY projects, another item that you need to learn about is how to specify and source your components. Fortunately for you in today's world, you have the Internet to very easily locate "who has what"!!! (See chart further on down below).

In related news.....all of the PCB-fabricators that also offer PCB-assembly services that I have used and/or are aware of, will also accept receiving components from their customers (like YOU), simply due to the fact that it would be physically impossible for them to have readily available stock of nearly every electronic component manufactured for the past 20-years. So.....contact JLCPCB and find out if you can send them (or, have "drop-shipped" to them) this OPA1641 IC-chip for use on the assembly of your PCB. You will also need to find out if they can place the part -- manually -- if you are only having 1-to-10 boards assembled or what is their minimum -- Tape-Reel -- length or quantity is should you be having some limited small prototype production run made.

Whenever I am having 1-to-5 prototype PCBs fabricated and assembled by a company like JLCPCB, I go ahead and purchase all of my components, sort them out into little ZIP-LOC bags, label each bag with their component -- REF DES -- while also providing them with a hard-copy print-out of the "PCB Component Assembly Drawing" and a print-out of the BOM. With all of that information at-hand, it is a rather easy and straight-forward process for one of their assembly technicians to correctly assemble one of my prototype PCBs with no errors. In addition to learning how to create schematics and design PCBs, you will also need to learn how to create and provide proper "PCB Documentation" to outside vendors, so outside companies can know and understand not only what it is that you want to be done, but also in -- HOW -- you want things to be done.

Of -- ALL -- of the PCB GERBER-files that are shared here on this forum, there isn't -- ONE -- set of GERBER-files that I have seen on here that contains -- ANY -- of the information that I have always included in all of my PCB-fabrication files and that is.....a DOCUMENTATION layer!!! Meaning, in addition to all of the GERBER-files generated for a PCB that includes the copper layers, the soldermask/pastemask/silkscreen layers, drill files, etc., etc., etc.,.....my PCB-design background has also included providing the PCB-fabricator with a -- DOCUMENTATION -- layer, as well. Something like this:

View attachment 147626
This specific fabrication information simply provides the PCB-fabricator with my "design intent" information as to how I would like a PCB to be fabricated and it is also easily included as -- just another GERBER-file -- so they have this information "right there, right then" as they are reviewing the other GERBER-files and getting my files setup for fabrication. Meaning.....they don't even have to open up and refer to a PDF-file in order for them to have and review this information. On their part, they can either turn-off or even delete this layer, if they want to. But, at least it's -- RIGHT THERE -- for them to see and they CAN'T MISS IT!!! And, you know what??? ..... Because of this.....I've never had a PCB-fabricator either call me up or send me an e-mail message asking me any questions about how I want my PCBs to be fabricated. Just sayin'.....

Now.....as far as the IC-chip goes that you're looking for, here's a list of U.S. distributors that all have your OPA1641AIDR in-stock in the quantities shown in the chart below:

View attachment 147622View attachment 147627

>> It seems as though your best bet would be to purchase this chip directly from "Texas Instruments" ( TI ) and at the price of only $0.79 each, I would go ahead and get at least $5 or $10 worth or more if you are planning on making a bunch of your PCBs.

But.....what do I know, huh???

/

I plan on doing this in the future if my initial board doesn't work (which I should expect even if I've solved all the problems I can think of, just to curb being disappointed)

I'm aware having my board assembled by JLC isn't the most economical way of doing things, but this is a learning process for me, and I'll do much better if I can learn these things one thing at a time, I've never had to solder chips as small as this one before, so I plan on doing that AFTER I've learned from any of my initial mistakes from PCB building.

Ordering PCBs without components on them is also much cheaper, so I would love to be able to do that instead of having any board manufacturer assemble them in house (and by doing so, drive the price up by a factor of 10x)

but like I said, I learn better in stages.

 

[pmfalcman]

but like I said, I learn better in stages.

Very amendable. Slowly but surely, baby steps etc.
Let me help with these stages, I went through them myself:
1. Order a bunch of unpopulated PCBs from a supplier. With some to spare (read: destroy beyond recognition. Naah, not even this.)
Most probably extra 3 will do unless you've absolutely no manual abilities.
Similar OPIC circuit cost me $5 for 10 pcs. It's a whopping ¢0,5 apiece. Round ones may be a bit more. $1? Even a poor Pole can afford that

2. Order parts. Most expensive are 1G resistor and IC. All the rest is sold in minimum qts of 10 or 20 just to reach less than $1 in price. Dunno 'bout US, might be more expensive. $1,5 for 10? Get.... 3 IC extra (as above). OK - buy 5 more. Get wild and spendy!! YOLO etc. It's... les than 5 buck learning expense. Less then 10 buck total.

3) Now it gets nasty 'cos truly expensive - a soldering station..... I paid a whopping ~$20 for mine and were soldering AtMegas32. Not one a week... More. With ease. (No fancy tips, mind you!). Temperature control is of the "somewhere around here" type. No trendy digital displays.
Or, for a bit more you can buy a hot air station. It's even easier to solder ICs and SMDs. I guess I saw somewhere a combine: soldering iron plus hot air for... $35? 40?
Sure, one for $400 will serve you for ages and make your work fast and efficient.
If you're a pro. Soldering 8 hrs a day. 7 days a week. OK - 6. Like god.
(Mine works since ca 2010)
(Soldering station, not god)

4) Turn it on, don't be afraid, start soldering.
You'll ruin a board or two. So what? You'll fry an IC or two. So what? Still you spent +/- what you'd pay for couple of populated PCBs and you're left with a soldering station and a new skill for free.
And self made mic boards.

5) There's plethora of "how to solder" videos on YT. Watch a few and start experimenting.
You do not need another lenghty, boring and twisted write up.

But if you like reading ....

See? 5 easy stages. As promised.