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

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Wordsushi, your Youtube videos where you replaced the capsule with Arienne flat K47 in BFL V47 and MPA-81S convinced me to get MPA-81 myself.

MPA-81S replacement sounded so good. I am waiting for the capsule to arrive. I am thinking of putting the ORS 87 circuit board with the modification suggested in this thread for flat K47.
 
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I am posting pictures of MPA-81S if anyone would be interested and maybe figure out what classic design it might have followed:

MP-81S_A.jpg
 

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AdamFrisen said:
Wordsushi, your Youtube videos where you replaced the capsule with Arienne flat K47 in BFL V47 and MPA-81 convinced me to get MPA-81 myself.

MPA-81S replacement sounded so good. I am waiting for the capsule to arrive. I am thinking of putting the ORS 87 circuit board with the modification suggested in this thread for flat K47.
Click to expand...
Hi Adam! Wow! That's fantastic! the MPA-81 is a ridiculous value for the money and the Arienne Flat K47 is like strapping a booster rocket onto it to the next level.
Take into account that the ORS 87 is cardioid only so you'd lose the ability to do fig-8, which I think is the sweet spot with this combo. The Flat K47 in Fig-8 is sublime. Try it on the stock circuit first and see if you like it. Thank you for posting and please feel free to comment back on your thoughts once you've had a chance to play with it.
 
AdamFrisen said:
I am posting pictures of MPA-81S if anyone would be interested and maybe figure out what classic design it might have followed:

View attachment 130953
Click to expand...
This is a fairly decent implementation of a standard transformerless Schoeps circuit and you may have actually seen this same circuit before in the.... drum roll please....
IMG_0194.jpg
IMG_0196.jpg

Vanguard V4
 

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Wordsushi said:
Hi Adam! Wow! That's fantastic! the MPA-81 is a ridiculous value for the money and the Arienne Flat K47 is like strapping a booster rocket onto it to the next level.
Take into account that the ORS 87 is cardioid only so you'd lose the ability to do fig-8, which I think is the sweet spot with this combo. The Flat K47 in Fig-8 is sublime. Try it on the stock circuit first and see if you like it. Thank you for posting and please feel free to comment back on your thoughts once you've had a chance to play with it.
Click to expand...
Yes, I should try it of course when I think about it. And then maybe buy another flat K47 later if I wanna keep it that way but build U47 style microphone.

It was almost 30 years ago I held a solder iron way back when lead was used and multi-bit PCM DAC was a thing (Burr-Brown PCM1704).
This DIY microphone thread sparkled my interest to build something again. Thanks for that. My older Weller seems to work still so it will be exciting.
 
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micolas said:
Black - primary
Yellow - secondary
Click to expand...

I'm confused by that screenshot and the description in some Aliexpress items. The Chinese there, if Google Translate is correct, says that the left side of the transformer is yellow with the right side being black. Is the Ali T-13 (ASTDS) reversed compared to the AMI T-13?
 
mrchapp said:
I'm confused by that screenshot and the description in some Aliexpress items. The Chinese there, if Google Translate is correct, says that the left side of the transformer is yellow with the right side being black. Is the Ali T-13 (ASTDS) reversed compared to the AMI T-13?
Click to expand...

Just measure the resistance between all four wires. Larger resistance side goes towards the circuit, lower resistance side goes towards the XLR. If it turns out to be out of phase with a standard mic, swap the two wires going to the XLR. No need to assume or wonder or anything...
 
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micolas said:
Not related to AMI T-13.
Follow @Khron 's directions
Measure ohmic resistance with DMM
Between the wires that measure more, (aprox 395...483 ohm), is the Primary that connects to C7.
The other two wires connect to the R18 and R19.
Click to expand...

Thank you, both! This Ali T-13 (ASTDS) measured 448 Ohms between black wires (thus primary), so it's wound like the AMI T-13. Oh, well!
 
Can someone review my BOM? I'm about to embark on this project using a BM-800 donor, using OneRoomStudio's schematic from post #71 and the BOM listed on post #160.

Resistors are not too bad, I think:
R7: 1G
R8: 1M
R9: 7.5K (vs 7.3K)
R10: 30K trimpot (vs 25K)
R12: 47K
R13: 330K
R14: 10K
R15: 300K
R16: 56K
R18 & R19: 2.2K

GR1: 1N4749A Zener

Q1: 2N3819

Capacitors is where I'm most unsure about:
C5: 47n (multilayer ceramic)
C6: 220p (multilayer ceramic)
C7: 1u (250V axial MKP CY0G L21mm)
C8: 22u (25V electrolytic)
C9: 470n (multilayer ceramic)
C10: 4.7u (35V electrolytic)
C11: 4.7u (63V WIMA MKS4 P22.5mm)
C12: 10u (63V)
C13: 10n (multilayer ceramic)

I believe in Homero's PCB some of the ceramics capacitors I have are film or electrolytic instead. Would that make a big difference?

Transformer is the aforementioned Ali T-13 (ASTDS). Capsule is BaiFeiLi U87.

Thanks in advance!
 
Imagine my novice surprise when I get the boards and none of the part #s match the parts I ordered...

Can someone point me to the BOM for V1.1 so I can sort them out? Also, with C5a & b and C6a & b are these now series caps where a single part 1/4th of the value would suffice?

Thanks,
eso
 

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