elskardio
Well-known member
I haven't thought of that, and it makes sense!
Now.. Should I re-bias all my mics?
OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87
- Thread starter Wordsushi
- Start date
Help Support GroupDIY Audio Forum:
Now.. Should I re-bias all my mics?
AdamFrisen
Well-known member
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:
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:
Attachments
AdamFrisen
Well-known member
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).
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).
Last edited:
AdamFrisen
Well-known member
... 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
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
Last edited:
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
Well-known member
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.
Last edited:
