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

[micolas]

View attachment 131372
Sound test done at home (birds included).
Left: MicParts capsule + 180pF on the top end.
Right: 797audio capsule + 220pF on the top end.
Both using Aliexpress T13 transformer. Raw file, no EQ no compression.

What model is capsule 797?

 

[anvl]

CY002 capsule

 

[micolas]

CY002 capsule

Thank you!
I also chose 220pF for CY002 in the headbasket / body of B2-PRO new model

I think the R channel sounds closer to character 87.

 

[anvl]

I usually enjoy making the whole process by my own (KiCad design, PCB burning ...) -- Old Style.

 

[micolas]

View attachment 131377
I usually enjoy making the whole process by my own (KiCad design, PCB burning ...) -- Old Style.

It would be good if the Gate of the jFET and the red wire from the capsule are connected isolated from the PCB, its traces, etc.
There is a huge impedance here. It can compromise the correct operation, sound quality, introduce all kinds of noises, worsen the signal/noise ratio. A turret
(ptfe insulated terminal), isolated from the PCB must be used to connect.

As in the pictures.

 

[Khron]

A turret
(ptfe insulated terminal), isolated from the PCB must be used to connect.

... Or in free air...

 

[micolas]

... Or in free air...

@Khron , right!
Building in the air, point-2-point is my preferred method.
Air is my favorite dielectric.

 

[micolas]

@anvl
If you executed the PCB manually, by corroding with ferric chloride, various acids, etc., then the PCB surface may remain electrically conductive, you must clean it very well with isopropyl alcohol. And after soldering the components as well.

 

[anvl]

One more question regarding this. In my circuit, red wire from the capsule is not directly connected to JFET gate. I use C4 470pF, R6 1G, R7 1G as you can see in green. Where should I use isolated terminal then?

 

[micolas]

View attachment 131383

One more question regarding this. In my circuit, red wire from the capsule is not directly connected to JFET gate. I use C4 470pF, R6 1G, R7 1G as you can see in green. Where should I use isolated terminal then?

At both ends of the 470pF coupling capacitor.

 

[anvl]

Thanks. Let's do it !!!

 

[micolas]

Thanks. Let's do it !!!

Careful! Do not heat the jFET too hard or too long. It can be totally or partially damaged (it can change its parameters). Same caution with all components (especially styroflex capacitors are very sensitive to temperature)

 

[anvl]

Regarding this, I should change my layout to place JFET as near as possible to this C4 470pF, right?

 

[micolas]

Regarding this, I should change my layout to place JFET as near as possible to this C4 470pF, right?

That would be good.
The wires from the capsule should be as short as possible. They are like parasitic capacitors(or even as antennas that could pick up disturbances of all kinds)
Some designs even moved the jFET into the headbasket, positioned on the capsule, reducing the length of the wires

 

[micolas]

@anvl
As a general rule, the output side must be positioned as far as possible from the input side, to avoid unwanted couplings, self-oscillations, etc.
I would place the transformer away from the input side ~ with huge impedance (billions of ohms), towards the XLR.

 

[anvl]

Thanks, micolas. It was a great idea to show you some pictures !! I have to work over my layout then.
Anyway, I have beautiful sound on this mic, as you could hear previously (no noises or disturbances), right?
This mic on the picture is the one on the R channel using 797 capsule that I posted before.

 

[micolas]

Thanks, micolas. It was a great idea to show you some pictures !! I have to work over my layout then.
Anyway, I have beautiful sound on this mic, as you could hear previously (no noises or disturbances), right?
This mic on the picture is the one on the R channel using 797 capsule that I posted before.

Yes, I like channel R, it's closer to 87.

But I also liked the song. It made me nostalgic and reminded me of my good musician friends with whom I spent some wonderful years in the south of extraordinary Spain.

 

[micolas]

Thanks, micolas. It was a great idea to show you some pictures !! I have to work over my layout then.
Anyway, I have beautiful sound on this mic, as you could hear previously (no noises or disturbances), right?

If the isolation of sensitive high-impedance components from the PCB surface is not respected, or if PCB is not covered with special protective materials (how does Neumann, Rode, etc.),
the quality of the sound can worsen over time, due to contamination with oxides, dust, dirt, other various particles, moisture, etc.

 

[cello4u]

I see you don't have a trimpot installed in that 3-pin footprint in the middle, OR an R* in its footprint next to C8(?). So the JFET has no connection between its source pin and ground. That's gonna be AT LEAST part of the reason why this is "no bueno".

Circuits rarely work when they're incomplete, and as this has already been trimmed down from the original Neumann schematic, there's not all that much room (or need) for Muntzing anymore anyway...

https://en.wikipedia.org/wiki/Muntzing

 

[cello4u]

Thank you for your reply. Now I know where the trimpot goes. Since I bought enough for 2 boards, and my BOM did not include an R*, is there one of the other resistors that I could throw in there(since I bought enough for 2 circuits). I searched R* in the thread and could not find anything useful.