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

[edenooo]

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.

I'll absolutely keep all this in mind, thank you!!! I got 5 PCBs ordered today (with proper mounting), I'll post here again with any updates as soon as they're here, I'll send sound samples too assuming I didn't bork anything (which is rather unlikely despite how simple this board is)

If they work though, they're small enough to fit in virtually any mic body given you figure out or print mounting, which is SUPER nice, that also means I won't have a bunch of extras lying around if they work, and I can actually put them inside other mics instead of letting them sit around and be unused !!!

 

[Екатерина]

Oh, my friends, I am very interested in this OPIC.45, but I have a few questions that make me confused. I haven't seen the amplification factor, which is often around 30db in other microphone circuits. Of course, I am not good at amplifying circuits, and there is a high possibility of my negligence. Another issue is that the frequency response curve of the current circuit is flat. Can we connect a 0.1 μ F capacitor to ground after the R2 47R to form a simple Low Pass, which can be adapted to the K67 capsule

 

[Khron]

I haven't seen the amplification factor, which is often around 30db in other microphone circuits.

That's probably the case in mics that also have a high-ratio step-DOWN transformer on the output...

The OPIC.45TX, IF you had read any of the text description (or googled the NTE-1 transformer datasheet) employs a 1:1 ratio output transformer.

Correlation is not causation

Can we connect a 0.1 μ F capacitor to ground after the R2 47R to form a simple Low Pass, which can be adapted to the K67 capsule

That should be feasible, although i'd go with a higher-value resistor and a lower-value capacitor. Opamps are rarely very happy driving heavy capacitive loads...

 

[Екатерина]

That's probably the case in mics that also have a high-ratio step-DOWN transformer on the output...

The OPIC.45TX, IF you had read any of the text description (or googled the NTE-1 transformer datasheet) employs a 1:1 ratio output transformer.

Correlation is not causation



That should be feasible, although i'd go with a higher-value resistor and a lower-value capacitor. Opamps are rarely very happy driving heavy capacitive loads...

Khron always appears in a timely manner. I know NTE-1 does not attenuate sound by more than 1db, but will the OPIC.45 circuit make the sound very small? If it needs to be better, then it should be used

 

[Екатерина]

If the output sound becomes very small, then a better microphone amplifier is needed to use it, right

 

[Khron]

but will the OPIC.45 circuit make the sound very small?

How do you mean, "small"?

 

[Екатерина]

Sorry, there may be an issue with my statement. If I record using U87AI and the microphone amplifier requires a gain of 50db, do I need to gain more decibels using the OPIC.45TX circuit

 

[Khron]

Sorry, there may be an issue with my statement. If I record using U87AI and the microphone amplifier requires a gain of 50db, do I need to gain more decibels using the OPIC.45TX circuit

Technically, the sound ends when it enters the capsule; after that, it's an electric signal But i'm pretty sure @rogs can answer that more accurately.

Needing 50dB with a U87Ai sounds like the sound you're recording is very quiet..? But the OPIC stuff should need +/-6dB gain compared to most other mics, i think; the noise should be lower, though.

 

[MidnightArrakis]

How do you mean, "small"?

[How do you mean, "small"?] -- I was wondering the exact same thing. Then, I thought.....maybe a "lower (smaller)" signal level?

By the way.....I also wanted to take a moment here to -- compliment -- you on your knowledge of audio circuit design and also of so many specific details about so many particular electronic circuits and devices. As a direct result of my personal respect of your circuit design knowledge, I have frequently recommended other members on this forum to contact you in hopes that you would be able to resolve whatever issue they are having with their particular audio circuit designs. I hope you don't mind me doing this.

Because I am unable to design a circuit "to save my soul", I then have the greatest respect for people such as yourself, RuffRecords, Matador and others. My expertise is in taking a schematic and then being able to design it "six ways to Sunday" into the physical world that we all live in. But, what it is that I do is directly dependent upon what it is that people like you do, so I cannot but help myself to have the highest respect for anyone who is able to take complex mathematical equations and somehow turn them into a schematic!!! I "bow down" to you and all of those who are similar to yourself!!! THANK YOU SO MUCH!!!.....

/

 

[Khron]

I also wanted to take a moment here to -- compliment -- you on your knowledge of audio circuit design and also of so many specific details about so many particular electronic circuits and devices.

All it takes is a couple decades of messing around with things (up to and including in a slightly autistic manner), coupled with a severe sense and determination regarding cheapskate-ness, and a thorough aversion to programming / coding (so no microcontrollers, wherever they can be avoided). Thirst for knowledge helps, as does a healthy helping of self-criticism and/or setting certain standards (and/or challenges) for one's self. Asking "why" a lot is also useful - technology often has good sound (no pun intended) reasons for the solutions adopted. Oh, and complete and utter disregard for worshipping "classic" and "vintage" circuits / components / other physical or technological devices - i'm not religious (quite the contrary), but wasn't the 2nd commandment all about that?

Despite all that though, i'll be the first to state that i myself am in no way an expert. A bit more experienced than your lay-person, but i'm yet a child still playing in the sandbox, in the grand scheme of things.

Regardless, we now return you to your original scheduled programming (as it were)...

 

[MidnightArrakis]

All it takes is a couple decades of messing around with things (up to and including in a slightly autistic manner), coupled with a severe sense and determination regarding cheapskate-ness, and a thorough aversion to programming / coding (so no microcontrollers, wherever they can be avoided). Thirst for knowledge helps, as does a healthy helping of self-criticism and/or setting certain standards (and/or challenges) for one's self. Asking "why" a lot is also useful - technology often has good sound (no pun intended) reasons for the solutions adopted. Oh, and complete and utter disregard for worshipping "classic" and "vintage" circuits / components / other physical or technological devices - i'm not religious (quite the contrary), but wasn't the 2nd commandment all about that?

[All it takes is a couple decades of messing around with things] -- Is THAT all??? Shucks!!!.....you make it sound all too easy!!!

/

 

[Khron]

[All it takes is a couple decades of messing around with things] -- Is THAT all??? Shucks!!!.....you make it sound all too easy!!!

/

Well, as with so many other things (especially in tech), "it's how you use it" *** - just because you're at it for a long time, doesn't mean you're 1) progressing, and if you are, 2) (even) in the right direction Hence the long(?) list of other things i mentioned...

---

*** Not mine, but felt sort of relevant, "in context"...

 

[Екатерина]

Technically, the sound ends when it enters the capsule; after that, it's an electric signal But i'm pretty sure @rogs can answer that more accurately.

Needing 50dB with a U87Ai sounds like the sound you're recording is very quiet..? But the OPIC stuff should need +/-6dB gain compared to most other mics, i think; the noise should be lower, though.

I roughly understand, does the output impedance of OPIC.45TX have 200R? Can we use a 1:2 transformer like a dynamic microphone to increase the signal level

 

[rogs]

Sorry, there may be an issue with my statement. If I record using U87AI and the microphone amplifier requires a gain of 50db, do I need to gain more decibels using the OPIC.45TX circuit

As I have mentioned in other posts, the OPIC project is primarily an impedance converter. It is a simple circuit, and is not intended to provide any gain, nor is it designed to accomodate internal frequency control modifications easily.

You will find latest version of the OPIC.45TX version documents here: https://www.jp137.com/lts/OPIC.45TX.pdf
Note that the circuit now includes an extra 470R resistor across the transformer secondary, fitted to damp the tendency for the transformer to 'ring' at high frequencies.
This graph shows the effect of the resistor when a 10KHz square wave is applied to the ciruitry (without the capsule fitted):


That additional resistor will also attenuate the signal by c. 1dB.

The inclusion of a transformer is an experiment, to see how how the OPIC circuit performs with a fully balanced output. The Neutrik NTE-1 was chosen as it is easily available , and not expensive.

Fited with an Arienne Audio flat 47 capsule - biased with a 65V polarisation voltage - the OPIC.45TX circuitry will require about 45dB of preamp gain.
So quite a lot. The circuit itself has a noise figure of c.8dBA, so it is reasonably quiet, and can provide a signal with an excellent S/N ratio when used with a low noise, high quality mic preamp.

As I say though, things like frequency correction and gain circuitry are best applied outside the microphone with this circuit.

 

[Екатерина]

Perhaps I am a bit far from the microphone, and my sound card requires a gain of 40-50 dB to have sufficient signal level

 

[Екатерина]

As I have mentioned in other posts, the OPIC project is primarily an impedance converter. It is a simple circuit, and is not intended to provide any gain, nor is it designed at accomodate internal frequncy control modifications easily.

You will find latest version of the OPIC45TX version documents here: https://www.jp137.com/lts/OPIC.45TX.pdf
Note that the circuit now includes an extra 470R resistor across the transformer secondary, fitted to damp the tendency for the transformer to 'ring' at high frequencies.
This graph shows the effect of the reistor when a 10KHz square wave is applied to the ciruitry (without the capsule fitted):
View attachment 147661

That additional resistor will also attenuate the signal by around an extra 2dB.

The inclusion of a transformer is an experiment to see how how the OPIC circuit performs with a fully balanced output. The Neutrik NTE 1 was chosen as it is easily available , and not expensive.

Fited with an Arienne Audio flat 47 capsule - biased with a 65V polarisation voltage - the OPIC45TX circuitry will require about 45dB of preamp gain.
So quite a lot. The circuit itself has a noise figure of c.8dBA, so it is reasonably quiet, and can provide a signal with an excellent S/N ratio when used with a low noise, high quality mic preamp.

As I say though, things like frequency correction and gain circuitry are best applied outside the microphone with this circuit.

Wow, this is a fascinating plan, but it requires a high level of microphone amplifier

 

[Khron]

the OPIC45TX circuitry will require about 45dB of preamp gain.

... For what? A soft voice a foot away? A snare drum from a couple inches away?

Perhaps I am a bit far from the microphone, and my sound card requires a gain of 40-50 dB to have sufficient signal level

Well, how far from your microphone ARE you? And what voltage is the capsule supplied with?

 

[Екатерина]

As I have mentioned in other posts, the OPIC project is primarily an impedance converter. It is a simple circuit, and is not intended to provide any gain, nor is it designed to accomodate internal frequency control modifications easily.

You will find latest version of the OPIC.45TX version documents here: https://www.jp137.com/lts/OPIC.45TX.pdf
Note that the circuit now includes an extra 470R resistor across the transformer secondary, fitted to damp the tendency for the transformer to 'ring' at high frequencies.
This graph shows the effect of the resistor when a 10KHz square wave is applied to the ciruitry (without the capsule fitted):
View attachment 147661

That additional resistor will also attenuate the signal by c. 2dB.

The inclusion of a transformer is an experiment, to see how how the OPIC circuit performs with a fully balanced output. The Neutrik NTE-1 was chosen as it is easily available , and not expensive.

Fited with an Arienne Audio flat 47 capsule - biased with a 65V polarisation voltage - the OPIC.45TX circuitry will require about 45dB of preamp gain.
So quite a lot. The circuit itself has a noise figure of c.8dBA, so it is reasonably quiet, and can provide a signal with an excellent S/N ratio when used with a low noise, high quality mic preamp.

As I say though, things like frequency correction and gain circuitry are best applied outside the microphone with this circuit.

At present, the simplest way to increase gain is to add two resistors and turn the follower into a in-phase amplifier. The level signal will increase by 6dB, and of course, the noise will also double with the amplification factor. Have you measured the output impedance of this circuit? I made a diagram and I feel sorry for altering your picture

 

[Екатерина]

... For what? A soft voice a foot away? A snare drum from a couple inches away?



Well, how far from your microphone ARE you? And what voltage is the capsule supplied with?

About 1.5 feet, my voice is indeed a bit low, and the voltage of the capsule is 60V. My habits are not very good

 

[Khron]

About 1.5 feet, my voice is indeed a bit low,

You must have a really nicely treated room, if you can afford to be that far away (especially when singing / speaking softly) without "room sound" becoming an issue.

Have you measured the output impedance of this circuit?

Is that important?