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

[homero.leal]

No concerns for the high-impedance area of the circuit? And for longevity's / reliability's sake, it's customary to connect the wiper of a trimpot to either end (so things don't completely "blow up" if the wiper happens to go open-circuit / intermittent).

All in all, a pretty... convoluted(?) layout.

I'll leave the questions about the 1KV-rated output cap for a later time, though...

Regarding HI-Z area, I placed a small thru-holes near the junctions, so teflon turrets could be used.

Regarding wiper, I updated the schematic/pcb with your recommendation.

Thank you!

HL

 

[homero.leal]

Here is the PCBWay Shared Project URL for this PCB:

https://www.pcbway.com/project/shareproject/OPEN_SOURCE_DIY_Mic_Project_ORS_87_5bff5d94.html

Please keep in mind this hasn't been tested yet. If you are willing to give it a shot, try it and help confirm if it works, you are welcome.

Thank you!

 

[Khron]

Regarding HI-Z area, I placed a small thru-holes near the junctions, so teflon turrets could be used.

Could've possibly considered not-routing those two signals, to eliminate / minimize confusion? "If those are already connected on the board, what's with the isolation pin?" etc. But i AM a self-confessed nitpicker - if something's worth doing, it's worth doing right (imho)

But then again, there seem to be no noise issues with Mihi Fuchs' boards, despite no particular concern with the high-impedance connections there either..?

 

[homero.leal]

Could've possibly considered not-routing those two signals, to eliminate / minimize confusion? "If those are already connected on the board, what's with the isolation pin?" etc. But i AM a self-confessed nitpicker - if something's worth doing, it's worth doing right (imho)

But then again, there seem to be no noise issues with Mihi Fuchs' boards, despite no particular concern with the high-impedance connections there either..?

As you can see, I always have liked to have my options open, that's the reason the multi-option design. So, if you you want to solder HI-Z components and do a truthfully cleaning or you want to air-solder the junctions, it's ok. If you want to use one or another output cap, it's ok. If you want to use a transformer with center TAP, and not to use the 2k2 resistors, just solder the jumper and it will be ok.

Anyway, if there is a winning combination of components that could render the other options non-justifiable, I will update the PCB with a more fixed design.

Regards!

 

[OneRoomStudio]

As you can see, I always have liked to have my options open, that's the reason the multi-option design. So, if you you want to solder HI-Z components and do a truthfully cleaning or you want to air-solder the junctions, it's ok. If you want to use one or another output cap, it's ok. If you want to use a transformer with center TAP, and not to use the 2k2 resistors, just solder the jumper and it will be ok.

Anyway, if there is a winning combination of components that could render the other options non-justifiable, I will update the PCB with a more fixed design.

Regards!

Ultimately, I don't think this matters all that much, but just for discussion's sake - typical FR4 substrate (the industry standard PCB material) has a surface resistivity of around 150MΩ/cm...so keeping the board clean isn't the only issue. When we're dealing with impedances as high as 1GΩ, the board itself presents a significantly lower impedance path between pads than air.

 

[mrchapp]

Here is the PCBWay Shared Project URL for this PCB:

https://www.pcbway.com/project/shareproject/OPEN_SOURCE_DIY_Mic_Project_ORS_87_5bff5d94.html
[...]

Just FYI, the PCB is not rendered correctly there. Looks like some holes are drilled correctly, but all other layers are scaled down.

 

[Khron]

typical FR4 substrate (the industry standard PCB material) has a surface resistivity of around 150MΩ

And that's just the substrate; then you have the solder-resist, at the very least...

 

[homero.leal]

Just FYI, the PCB is not rendered correctly there. Looks like some holes are drilled correctly, but all other layers are scaled down.

Could it be possible this could be a problem with PCBWay viewer?

I checked the PCB at gerber-viewer.com before creating the shared project page, and everything looked fine:



Also, i did the process to order it, and it passed the review:



Really strange...

HL

 

[OneRoomStudio]

Ultimately, I don't think this matters all that much, but just for discussion's sake - typical FR4 substrate (the industry standard PCB material) has a surface resistivity of around 150MΩ/cm...so keeping the board clean isn't the only issue. When we're dealing with impedances as high as 1GΩ, the board itself presents a significantly lower impedance path between pads than air.

BTW, for the nerds out there, I looked it up, and dry air has a resistivity of around 2×10^16Ω⋅m, or 20,000GΩ/cm...so more than 133 thousand times higher than FR4.

Edit: my maths was off by a few zeros the first time

 

[Papa Tango Charly]

C'est ce qu'on appelle « DIY Layout Creator » (DIYLC). Vous pouvez le télécharger ici : http://bancika.github.io/diy-layout-creator/

Thank You Best

 

[Papa Tango Charly]

FWIW, même si je ne l'ai pas noté, lorsque j'ai mesuré la résistance de chaque côté du T-13, parce que les fils ne sont pas marqués, j'ai remarqué que la résistance CC était d'environ 440/20, très très similaire à celle de l'AMI. dit la littérature.

Vous voyez tellement de ces boutiques proposant des transformateurs de style T très similaires et maintenant, je pense simplement qu'ils sont tous fabriqués dans les mêmes usines et que les boutiques leur mettent leur propre emballage. Ce n'est pas comme si tout le monde faisait le sien.
Il semble avoir à peu près la même taille exacte que le 3u, et étant donné que Guosheng ne semble pas faire valoir qu'ils fabriquent également des transformateurs originaux à côté de leurs capsules, j'ai tendance à croire qu'il est possible qu'il les sous-traite.

Il est également possible que ces T-13 sur Aliexpress soient du stock B,

Hello, the manufacture of guossheng transformers is incomparable with those found on alibaba or aliexpress. The quality of lamination and winding of Ali transformers etc... is very poor. Guosheng is also a microphone manufacturer and a passionate guru. best

 

[Wordsushi]

Hello, the manufacture of guossheng transformers is incomparable with those found on alibaba or aliexpress. The quality of lamination and winding of Ali transformers etc... is very poor. Guosheng is also a microphone manufacturer and a passionate guru. best

I just don't know if he makes his in-house or he's getting them OEM'd for him by someone else.

 

[Wordsushi]

So, if C6 is omitted, there's no de-emphasis, right?
So couldn't this circuit also be used with a C12 or 47-style capsule?

 

[micolas]

I just don't know if he makes his in-house or he's getting them OEM'd for him by someone else.

Hi, how does the diy U87 sound using the $18 Ali T-13 compare to the 3U GZT-87 and Neutrik NTE 10/3?

 

[micolas]

So, if C6 is omitted, there's no de-emphasis, right?
So couldn't this circuit also be used with a C12 or 47-style capsule?

If you omit C6 there is still de-emphasis on the bass

 

[micolas]

So, if C6 is omitted, there's no de-emphasis, right?
So couldn't this circuit also be used with a C12 or 47-style capsule?

if you want to use c12 or k47 style capsules then convert u87 topology to km84, but adapted for the capsule with the large diaphragm, so with a larger output signal

 

[Khron]

So, if C6 is omitted, there's no de-emphasis, right?
So couldn't this circuit also be used with a C12 or 47-style capsule?

if you want to use c12 or k47 style capsules then convert u87 topology to km84, but adapted for the capsule with the large diaphragm, so with a larger output signal

... Which is the FET847 project, as long as you skip the unnecessary 1G resistor.

 

[micolas]

... Which is the FET847 project, as long as you skip the unnecessary 1G resistor.

FET847 project
Thread 'FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop' https://groupdiy.com/threads/fet847...-jonathan-burtner-pcb-layout-by-poctop.61057/

 

[Khron]

Some corrections to that:

https://groupdiy.com/threads/fet847...urtner-pcb-layout-by-poctop.61057/post-843994

 

[OneRoomStudio]

What some of you might be realizing now is how similar the KM84 and U87 circuits are (aside from the deemphasis). They're both just a JFET 'common source' amplifier (with high input impedance) feeding a step-down transformer (for low output impedance), in addition to bias voltage for the capsule. Capsule > impedance conversion > output. Powered by 48V phantom power.

That's it. No magic here.

The signal-path capacitors, as well as any negative feedback/deemphasis allow you to tune the high and low frequency response for the capsule you're using. You can mess with the headroom and gain by changing the FET voltage and bias. You can improve the noise level by choosing a low-noise FET and/or ensuring your high impedance connections are floating. Other than that, your capsule will make the biggest difference in sound, followed by the transformer (might saturate or have limited bandwidth if it's too small). These are simple circuits.