OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87

[untamedfrontier]

Is there any 2N3819 where the pin layout for TO-92 case is different from this?

View attachment 132877

Not 1,2,3 - SGD but 123 - DGS instead.

These ones from mouser have your desired pinout : https://www.mouser.com/ProductDetai...r/2N3819-PBFREE?qs=OlC7AqGiEDla/gXW0b%2BF8A==

I used them in my first ors87 build and they work as expected

 

[AdamFrisen]

These ones from mouser have your desired pinout : https://www.mouser.com/ProductDetail/Central-Semiconductor/2N3819-PBFREE?qs=OlC7AqGiEDla/gXW0b%2BF8A==

I used them in my first ors87 build and they work as expected

Thanks. I should have searched little more before posting.

Maybe it doesn't matter if symmetrical.

 

[Khron]

Maybe it doesn't matter if symmetrical.

It really doesn't, unless it's somehow THAT difficult to just turn the thing around

 

[AdamFrisen]

It really doesn't, unless it's somehow THAT difficult to just turn the thing around

I looped the leg of the transistor around the 1G resistor hanging freely in the air and crimped it down hard, then soldered it.

 

[AdamFrisen]

Trying to measure using REW to adjust the bias for minimum distortion and wondering about the results.

PCB outside mic body, output connected to UTM0547f
Input sine 1KHz, 100mV RMS

With drain bias of 14.41V, I get "flat" 2nd harmony higher than 3rd (fine with me, 2nds are ear-candy, odd harmonies not), but the THD+N is higher. About -60dB.

With drain bias of 12.51V, the 2nd is much lower but not "flat" and 3rd are higher. THD+N is lower than above. About -68dB.

What could explain this (and which bias should I pick) ?

 

[Khron]

With drain bias of 14.41V, I get "flat" 2nd harmony higher than 3rd (fine with me, 2nds are ear-candy, odd harmonies not), but the THD+N is higher. About -60dB.

With drain bias of 12.51V, the 2nd is much lower but not "flat" and 3rd are higher. THD+N is lower than above. About -68dB.

What could explain this (and which bias should I pick) ?

"The real world" is the explanation, and the imperfect nature of electronic components - in this case, the JFET.

You know, you COULD consider setting one bias, reassembling the mic, and THEN taking a measurement - it would make that noise plot a LOT more meaningful... Pretty sure you don't care about the 50Hz mains hum and its harmonics (and neither does anyone else).

At 100mV in, how does the output look (with the Scope tool in REW)?

 

[AdamFrisen]

[...]
At 100mV in, how does the output look (with the Scope tool in REW)?

Thanks. The output signal is flat above, at -20 dBu. I built it without de-emphasis.

 

[Khron]

Thanks. The output signal is flat above, at -20 dBu. I built it without de-emphasis.

View attachment 132962

And i can only assume you HAVE measured the physical output (with a hardware voltmeter) to be indeed 100mV RMS, at whatever output volume setting you used?

 

[AdamFrisen]

And i can only assume you HAVE measured the physical output (with a hardware voltmeter) to be indeed 100mV RMS, at whatever output volume setting you used?

Fluke 79III True RMS. I just measured 1 KHz output to be 100 mV RMS from my external audio interface and relying on the fact the self-calibration showed flat frequency response.

Below is sweep loopback on my Focusrite Clarette+ 2Pre.

 

[AdamFrisen]

I measured two commercial stock microphones with the one I built with same setup (not too scientific as I don't have any anechoic chamber) and wondering about the results.

The two commercial microphones measured phase shifts around 19KHz and 20 KHz (several), but on my U87 ORS build as flat circuit (no C6, shortcut C9), I get phase shifts around 7KHz-9KHz.

I am using K47 flat capsule. When I measure without any capsule (outside mic body), I get no phase shift so I am wondering if I built or measuring wrongly?

Mavis MPA-81 stock capsule:



Stellar X3 stock:



U87 ORS no C6, shortcut C9 with K47 flat capsule:

 

[kingkorg]

I am using K47 flat capsule. When I measure without any capsule (outside mic body), I get no phase shift so I am wondering if I built or measuring wrongly?

All good, don't worry. Measuring phase of acoustical signal is quite difficult. And in this case irrelevant.

You stumbled upon a thing i've been ranting about for ages. People are getting obsessed about how one capacitor can introduce phase shift, and should be avoided. When in reality all sorts of phase shifts occur between source and mic. Quite unpredictable, random.

 

[AdamFrisen]

Thanks, it sounds good subjectively the best microphone I have of the three. It has some nice "ringing" making it pleasant to listen to. As it is in a small body, I might try go with what Micolas suggested:



Pics of my build (I will fix pins for Dupoint connectors in second build as they are obstructing but convenient to use at the output):








I am completing all three different PCB board using same or very similar to Duffy's BOM (as that was the first order I made in Mouser and get 3-4 copies of each).





Already fun to measure and compare. I am waiting for Arienne K87 and Vamisound's capsule (the one that is supposed to be Takstar CTS-2).
I can post picture of Vamisound's later. For those I add the de-emphasis ofc.

 

[Khron]

I am completing all three different PCB board using same or very similar to Duffy's BOM

That's a very interesting zener you've got on my board there...

 

[AdamFrisen]

That's a very interesting zener you've got on my board there...

Hehe, yes. I was thinking to follow the original U87 ORS schematic (Or Duffy's which is identical to ORS first schematics except for C11 with bigger capacitance) so I am violating your design intentions gravely.

I am gonna put the zener on the backside entangled to that capacitor. Couldn't get both in the same spot.

But next build, I will follow your BOM (Except for some parts I might find in my decades old stash of components).

 

[Khron]

I am gonna put the zener on the backside entangled to that capacitor. Couldn't get both in the same spot.

It's arguably pointless to have capacitors directly in parallel with zeners, though. They're usually way lower impedance than the capacitors, and even upping the capacitance by 10-100x yields barely any extra noise attenuation, so... Makes way more sense to have none in parallel with the zener, but a larger value (or multiple ones) "behind" a series resistor, "downstream" of the zener.

 

[soliloqueen]

I measured two commercial stock microphones with the one I built with same setup (not too scientific as I don't have any anechoic chamber) and wondering about the results.

The two commercial microphones measured phase shifts around 19KHz and 20 KHz (several), but on my U87 ORS build as flat circuit (no C6, shortcut C9), I get phase shifts around 7KHz-9KHz.

I am using K47 flat capsule. When I measure without any capsule (outside mic body), I get no phase shift so I am wondering if I built or measuring wrongly?

Mavis MPA-81 stock capsule:

View attachment 133040

Stellar X3 stock:
View attachment 133044


U87 ORS no C6, shortcut C9 with K47 flat capsule:

View attachment 133042

that's the same exact phase plot, it's just delayed by 120 degrees. the wrapping is confusing you

 

[AdamFrisen]

that's the same exact phase plot, it's just delayed by 120 degrees. the wrapping is confusing you

Ah thanks, I found 'Unwrap Phase' in REW. https://www.stereonet.com/forums/topic/121663-understanding-phase-plots-in-rew-etc/

 

[AdamFrisen]

Looking at U87A and U87AI schematics, I notice the power supply is better regulated than in ORS using even capacitance multiplier.


Not needed anymore? Considering phantom power is specified to max 48V/10 mA, not much power but still.

https://www.edn.com/simple-circuits-reduce-regulator-noise-floor/

 

[Khron]

Looking at U87A and U87AI schematics, I notice the power supply is better regulated than in ORS using voltage multiplier.

* Capacitance multiplier

Not needed anymore?

This ORS87 project was meant as a stripped-down, simplified version of the U87 circuit for cardioid-only capsules.

That being said, given the noise profile of zener diodes, that particular arrangement does raise questions (imho), but that's one reason i shuffled things around in my version of the U87A circuit...

 

[AdamFrisen]

I noticed some drop in drain bias voltage during frequency sweeps and even bigger in the three different commercial microphone amplifiers I have. About 20-30 mV.

The zener is using very little current in ORS schematics , maybe operating where the impedance is varying and temperature sensitive?

https://toshiba.semicon-storage.com...e/what-is-the-impedance-of-a-zener-diode.html

I started to look about zener diode noise thanks to your comments Khron. I found another interesting diy forum .

https://www.diyaudio.com/community/threads/some-noise-measurements-for-leds-and-zener-diodes.35821/