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
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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 seem to be ok. For the 60V board it was kinda given considering it switches at +100 KHz.
I will put the complete KiCad projects if someone would be interested in using these. There are gerber-zipfiles which work for JLCPCB. Make sure to remove the order number when putting the order as it might be printed where I removed the ground pour and silk screen from high impedance area.
The 60V board with SMD, the sizes are 0805 as the smallest except the LTC3290, which is in MSOP10. It will be hard to see without magnifier if it's soldered properly. I have removed the solder mask on the bottom side and put bigger via holes so you can use solder iron from underneath to solder the chip.
In EEVBlog, there is a technique you can use do solder the bottom of the chip just as LTC3290.
How to solder SMD with bottom as ground:
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)
The microphone gets sensitive to tapping on the grill without the NFB capacitor. The sound level almost always gets clipped (even in U87 ORS PCBs).
I prefer the sound with it. The simulated frequency response with it gets more like U87. Without it, more like U87AI.
Testing little with 60V to the capsule compared to with only 45-48V before, I think it's worth trying.
Double check all if you think of using the project I attached. C8 and C9 is supposed to be placed on the backside if big polyester/Vishay Sprague are used. C5 polyprop axial needs to be placed right above the resistors as low as possible as in the picture. Components should not be higher than at most 11 mm on the board. The RV1 trimpot should have the screw on the side and not on the top as in the picture. I tried with the screw on top but it then touched the body shell.
I will put the complete KiCad projects if someone would be interested in using these. There are gerber-zipfiles which work for JLCPCB. Make sure to remove the order number when putting the order as it might be printed where I removed the ground pour and silk screen from high impedance area.
The 60V board with SMD, the sizes are 0805 as the smallest except the LTC3290, which is in MSOP10. It will be hard to see without magnifier if it's soldered properly. I have removed the solder mask on the bottom side and put bigger via holes so you can use solder iron from underneath to solder the chip.
In EEVBlog, there is a technique you can use do solder the bottom of the chip just as LTC3290.
How to solder SMD with bottom as ground:
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)
The microphone gets sensitive to tapping on the grill without the NFB capacitor. The sound level almost always gets clipped (even in U87 ORS PCBs).
I prefer the sound with it. The simulated frequency response with it gets more like U87. Without it, more like U87AI.
Testing little with 60V to the capsule compared to with only 45-48V before, I think it's worth trying.
Double check all if you think of using the project I attached. C8 and C9 is supposed to be placed on the backside if big polyester/Vishay Sprague are used. C5 polyprop axial needs to be placed right above the resistors as low as possible as in the picture. Components should not be higher than at most 11 mm on the board. The RV1 trimpot should have the screw on the side and not on the top as in the picture. I tried with the screw on top but it then touched the body shell.
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