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

[elskardio]

I think 11(or more) years ago, it was less common to have accurate spectral analysis in plugins, and hardware spectral analyzers are crazy expensive. A lot of people have oscilloscopes though, so looking for symmetrical clipping made sense.

I haven't thought of that, and it makes sense!
Now.. Should I re-bias all my mics?

 

[AdamFrisen]

I was not happy with how I secured the U87 ORS board(s) in the U87-ish body I had so I made my own PCB.

I followed the U87AI original schematic closer and I also wanted to get 60V to the capsule.

The LTC3290 seems to work after 2 failed attempts (I needed to connect it directly to the phantom power in to the mic in order to get to work).
It doesn't require any inductors and was the smallest solution I could find.

So comparing to the mic using U87 ORS PCB (Homeros) and the PCB tailored for the mic body:




And mic built using the new PCB with 60V addition:

 

[AdamFrisen]

The poured ground planes in the main board seems to be no worse compared to U87 ORS board(s). But needs to be measured properly some day. Benefit of the ground planes for the 60V board was expected, given that it operates at a frequency above 100 kHz.

I will share the full KiCad projects for anyone interested in using them. Gerber files (in .zip format) are included and are compatible with JLCPCB. When placing an order, ensure to remove the order number, as it may be printed in areas where I've removed the ground pour and silkscreen from high impedance zones.

The 60V board utilizes surface mount components, with 0805 packages as the smallest size, except for the LTC3290, which comes in an MSOP10 package. Due to its small size, it may be difficult to confirm proper soldering without magnification. I've exposed the solder mask on the bottom side and enlarged the via holes to facilitate soldering from beneath using a soldering iron.

For reference, EEVBlog describes a method for soldering the underside of chips like the LTC3290, which feature a bottom thermal pad/ground plane:



The U87 mini body used for the PCB: https://www.aliexpress.us/item/1005...ain.22.21ef1802SWOLj5&gatewayAdapt=4itemAdapt

... and UTM-transformer UTM0587, 0547f or 0547 (if you add the NFB capacitor 4-10 pF, C13 in the schematics attached)

Without the NFB capacitor, the microphone becomes more sensitive to tapping on the grill, and the sound level tends to clip, even on U87 ORS PCBs. I prefer the sound with the NFB capacitor in place (in U87 ORS), as it brings the simulated frequency response closer to that of the U87. Without it, the response is more like the U87AI. I haven't tried yet on my board.

After some testing, applying 60V to the capsule (instead of the previous 45-48V) seems to produce noticeable improvements, so it's worth considering.

Before using the attached project, double-check everything. For instance, C8 and C9 should be placed on the backside if large polyester/Vishay Sprague capacitors are used. The C5 polypropylene axial capacitor must be positioned as low as possible above the resistors, as shown in the picture. Ensure that no components exceed 11 mm in height on the board. The RV1 trimpot should have a side-mounted adjustment screw, not a top-mounted one, as the latter can interfere with the body shell.

NOTE: In the ltc3290_dc_v0 schematics, C6 should be rated > 60V. I used 4uF/100V. R6 should be 1M and not 10K. I suggest to use X7R or COG for all SMD capacitors (if too large or expensive, go for X7S).

 

[AdamFrisen]

... and regarding capsules I have used,

the "green" one suggested by @Papa Tango Charly

single: https://www.aliexpress.com/item/100...order_list.order_list_main.106.33061802FX8QDt

I have hard time to distinguish the sound from Vamisound's alleged Takstar CTS-2 (dual) capsule compared to the green one in the spoken word.

There is also dual version now: https://www.aliexpress.com/item/100...list_main.59.4cec1802nUOCL3#nav-specification

I have not tested dual yet but it will be interesting while I am waiting for Arienne's K87.

If Vamisound's capsule is Takstar CTS-2 and as it is considered to be in top 3 of K87 'replica', then the green one is a very good value for spoken word.

I have 797 Audio CY002 waiting to be installed and compared to Takstar and Arienne's.

While waiting I noticed the similarity in the picture to Takstar for this capsule so I felt an urge to get it too:
https://www.alibaba.com/product-det...spm=a2756.trade-list-buyer.0.0.34df76e9MmIcll

 

[Papa Tango Charly]

... and regarding capsules I have used,

the "green" one suggested by @Papa Tango Charly

single: https://www.aliexpress.com/item/100...order_list.order_list_main.106.33061802FX8QDt

I have hard time to distinguish the sound from Vamisound's alleged Takstar CTS-2 (dual) capsule compared to the green one in the spoken word.

There is also dual version now: https://www.aliexpress.com/item/100...list_main.59.4cec1802nUOCL3#nav-specification

I have not tested dual yet but it will be interesting while I am waiting for Arienne's K87.

If Vamisound's capsule is Takstar CTS-2 and as it is considered to be in top 3 of K87 'replica', then the green one is a very good value for spoken word.

I have 797 Audio CY002 waiting to be installed and compared to Takstar and Arienne's.

While waiting I noticed the similarity in the picture to Takstar for this capsule so I felt an urge to get it too:
https://www.alibaba.com/product-det...spm=a2756.trade-list-buyer.0.0.34df76e9MmIcll

Getwin on Alibaba.com puts a pictures of a Taskar capsule then on the seconde picture you have an other brand with red wire. I have bought these capsule. JLI and Getwin sells the same capsules I have bought a both C12 and a K87 at Getwin Alibaba and JLI they are the same. They are not Taskar capsule. There C12 is very dark and the K67 is a bit sibilant and not very warm. Best

 

[AdamFrisen]

Getwin on Alibaba.com puts a pictures of a Taskar capsule then on the seconde picture you have an other brand with red wire. I have bought these capsule. JLI and Getwin sells the same capsules I have bought a both C12 and a K87 at Getwin Alibaba and JLI they are the same. They are not Taskar capsule. There C12 is very dark and the K67 is a bit sibilant and not very warm. Best

Thanks.

So these:

https://www.alibaba.com/product-det...spm=a2756.trade-list-buyer.0.0.34df76e9MmIcll

... could be JLI TSC-2?

https://www.jlielectronics.com/microphone-capsules/tsc-2/

Good cause I was curious about them as well but too expensive to import to EU directly from JLI.

Well the very capsule that looks exactly like Takstar CTS-2 (AND confirmed to be it) still eludes me.

 

[AdamFrisen]

The 60V board using the LTC3290 unfortunately introduces switching noise. I can hear it as clicks occurring about twice per second when I set the mic gain to about +60 - 70 dB.

 

[mic test]

Hello, I find the mic a little quiet when I measure pole and sgnl, I can't get more than 10.8V. Is that right and could I get it louder?
https://www.pcbway.com/project/shareproject/OPEN_SOURCE_DIY_Mic_Project_ORS_87_5bff5d94.html https://www.micandmod.com/microphone-parts/microphone-capsule/k87-capsule/

1​	LSK189​	JFET​	Ultra Low Noise, Low Drift, Single N-Channel JFET​	722-LSK189TO923LBK​	LSK189-TO-92-3L-BK​
1​	D1​	Zener Diode​	36 Volt 1.3 Watt 5%​	625-BZX85C36-TAP​	BZX85C36-TAP​
1​	-​	Audio Transformer / Signal Transformer​	1:10 MIC​	568-NTE103​	NTE10/3​
1​	R7​	Metal Film Resistor​	1GOhms 1.2W 5% High Volt Axial​	708-HVA12JA1G00​	HVA12JA1G00​
3​	R9, R14, R16​	Metal Film Resistor​	1/4 WATT 10K OHM 2%​	660-MF1/4LCT52R103G​	MF1/4LCT52R103G​
2​	R18, R19​	Metal Film Resistor​	2.2 Ohms .5% 100ppm .50 Watt​	279-H42K2DZA​	H42K2DZA​
1​	C7ABCD​	Film Capacitor​	1uF 1% 160V​	75-MKP1839510161​	MKP1839510161​
3​	C7, C8, C10​	Aluminum Electrolytic Capacitor​	22uF 63V​	667-ECA-2CM220B​	ECA-2CM220B​
2​	C11, C13​	Multilayer Ceramic Capacitor​	0.01uF 100volts X7R 10% 2.5mm L/S​	75-1C10X7R103K100B​	1C10X7R103K100B​
1​	-​	Trimmer Resistor​	25Kohms Sealed 6mm SQ 12turn​	81-PV37W253C01B00​	PV37W253C01B00​
1​	C6A​	Film Capacitor​	150pF 630 Volts10%​	505-FKP2J001501DKI00​	FKP2J001501D00KI00​
1​	C5A​	Film Capacitor​	0.033 uF 250 VDC​	505-FKP3F023304D0KJ0​	FKP3F023304D00KJ00​
1​	C9​	Film Capacitor​	1 uF 100 VDC 5%​	505-MKS2D041001K00JI00​	MKS2D041001K00JI00​
3​	R8, R13, R15​	Metal Film Resistor​	1M OHM 1% 200PPM 1/4W​	594-VR25000001004FA5​	VR25000001004FA500​
1​	R12​	Metal Film Resistor​	33K OHM 1% 100PPM 1/2W​	594-SFR16S0003302FR5​	SFR16S0003302FR500​

past not to the board and had to be soldered from the back
505-MKS2D041001K00JI00 0.033 uF 250 VDC

 

[Voyager10]

I can't get more than 10.8V.

What are you measuring here? Voltage on the drain of Q1?

The very first thing to check is whether the pinout of the LSK189 FET you're using matches the PCB. TO-92 FETs use pretty much all 6 permutations of source, drain and gate.

 

[mic test]

I measured at pole and sgnl, is that correct?

 

[Khron]

I measured at pole and sgnl

Why between those points?

 

[OneRoomStudio]

I measured at pole and sgnl, is that correct?

That's not the information you need.

First, measure the voltage at the R14/R12/C10 junction (as referenced to ground). Next, measure the voltage at the R12/C7/C9/Q1 junction (again, referenced to ground). The second voltage should be roughly half the first voltage, and should be in the ballpark of 10 volts.

Edit: In case you were trying to measure the polarizing voltage between "pole" and "signal," you can't measure that with a standard DMM - the impedance is way too high. The voltage there can't be easily measured, but should be right around 48V, unless you messed something up.

 

[homero.leal]

R18, R19 are 2k2 Ohm resistors, not 2.2, it's an error on the label, not on the part number from Mouser.

So, If you ordered part 279-H42K2DZA from Mouser, it is ok as this is the right part, but if you placed your own 2.2 ohm resistor then you should replace them for 2k2 instead.

Regards!

 

[mic test]

Hi, I bought them all as in the listing, so it should be correct, checked it and it's 279-H42K2DZA

I soldered a new pcb gnd and Q1 are 44.6V, do you think that's okay?
Khorn I measured it because I thought I could measure the polarizing voltage there
Thank you for the help I'm just learning it

 

[OneRoomStudio]

I soldered a new pcb gnd and Q1 are 44.6V, do you think that's okay?

Which leg of Q1? None of them should have 44.6V on them.

The drain should be around 10 - 20 volts (depending on the zener and FET you used), the gate should be at near ground potential, and the source should be a few volts (~1.5 - 3V). If you really have 44.6V on one of the FET pins, something is very wrong.

 

[Khron]

If you really have 44.6V on one of the FET pins, something is very wrong.

I measured it because I thought I could measure the polarizing voltage there

Well, what could've happened when applying a 1-10meg resistance between the capsule bias voltage, and the JFET gate?

[Spoilers - *bzt!*...]

 

[pasarski]

Well, what could've happened when applying a 1-10meg resistance between the capsule bias voltage, and the JFET gate?

[Spoilers - *bzt!*...]

I've done this now twice lately
and I can confirm that you see about 45v at the drain after that (the max voltage ratings don't seem to be a joke )

 

[mrchapp]

Well, what could've happened when applying a 1-10meg resistance between the capsule bias voltage, and the JFET gate?

[Spoilers - *bzt!*...]

I've done this now twice lately
and I can confirm that you see about 45v at the drain after that (the max voltage ratings don't seem to be a joke )

Oh, my. Can you elaborate? It looks like I was planning on making that mistake later this week.

 

[Khron]

Oh, my. Can you elaborate? It looks like I was planning on making that mistake later this week.

Look through the dataaheet of any JFET, in the "Absolute maximum ratings" section.

After that, recall how a multimeter works, and some of their characteristics, and what measuring a voltage involves

This is in the context of @mic test 's attempt of measuring the capsule bias voltage, by measuring between the "Pol" pad (where that voltage is present) and the "Sgnl" pad (which is the JFET gate, as it unfortunately happens in this case).

 

[OneRoomStudio]

As a general rule, you should always measure from GROUND to the pin you're checking voltage on. 1) Because generally, voltages are referenced to ground, and 2) because then you won't be inadvertently introducing a higher voltage at that point through the meter.

If you measure JFET pin voltages relative to ground, nothing bad will happen. DO NOT measure JFET pins relative to B+.

(obviously, there are some situations where you really do want to read relative voltage between two points, but those situations are far less common, and you need to know what you're doing)