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

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
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.
The value of R* regulates the proper operation of the circuit, i.e. it achieves the BIAS of the 2N3819 jFET transistor. Its value varies depending on the parameters of the jFET, the most important being Idss.
2N3819 has a large dispersion of parameters, therefore we use for R* an adjustable resistor, a trimpot.
Do you have a 20...25Kohm trimpot in the BOM?
 
The value of R* regulates the proper operation of the circuit, i.e. it achieves the BIAS of the 2N3819 jFET transistor. Its value varies depending on the parameters of the jFET, the most important being Idss.
2N3819 has a large dispersion of parameters, therefore we use for R* an adjustable resistor, a trimpot.
Do you have a 20...25Kohm trimp
I did, and that is what I had in the JFET, until I figured that out. It is now in the trimpot. I thought Khron was saying I would need an additional resistor in the R* to complete the circuit as well.
 
I did, and that is what I had in the JFET, until I figured that out. It is now in the trimpot. I thought Khron was saying I would need an additional resistor in the R* to complete the circuit as well.
Ok, so you have the trimpot correctly connected to the jFet source and to GND.
Do you have all the components soldered on the PCB?
And also connected to the XLR
output?
Put a picture of the current situation again, but as well focused, bright.
 
I do have the trimpot soldered in. I am unclear which leg of the jfet to connect to the ground insulated pin (which I also have, but not in yet). Is that a wire jumper? solder? also, the orientation of the jfet on the 1.1 board is different?
 
I do have the trimpot soldered in. I am unclear which leg of the jfet to connect to the ground insulated pin (which I also have, but not in yet). Is that a wire jumper? solder? also, the orientation of the jfet on the 1.1 board is different?
Post pictures though.
 

Attachments

  • 82420-408108276963742f3400c8c3cf3f3cf9_1719346960656.jpg
    82420-408108276963742f3400c8c3cf3f3cf9_1719346960656.jpg
    59.1 KB · Views: 0
  • 1719347010991_1719347080978.jpg
    1719347010991_1719347080978.jpg
    499.2 KB · Views: 0
I do have the trimpot soldered in. I am unclear which leg of the jfet to connect to the ground insulated pin
Gate (middle pin of jFet) connects to turret pin (isolated from PCB). It bends very carefully, not to touch the plastic body of the jFET and connects directly to the pin of the turret, in the same place as the wire from the capsule and with the end of R7=1G which is not connected to GND.
 

Attachments

  • Screenshot_2024-06-25-23-40-22-583_com.atomicadd.fotos_1719348057173.jpg
    Screenshot_2024-06-25-23-40-22-583_com.atomicadd.fotos_1719348057173.jpg
    543.6 KB · Views: 0
  • 1719347443397_1719347496738.jpg
    1719347443397_1719347496738.jpg
    2.8 MB · Views: 0
Last edited:
You can't expect a very cheap capsule to sound like a premium one.
For tests and to familiarize yourself with the peculiarities of the construction of the microphone, you can use any capsule you want, as cheap as it may be, it is even possible to destroy it by mistake.
When you progress you will want better quality, then you can invest more.
They are personal choices.
 
ok buy the good one directly, the others will only come from the reskin in 4-5 weeks
Best recommendation: Arienne K87.

Budget solutions:
If you are in Germany, look on ebay Kleinanzeigen.de or other similar sites, a second-hand microphone model Behringer B2-pro,for maximum 50..70 euros.It has a very good 797 capsule that will take you to the U87 sound. The microphone is good, body/headbasket etc.
Or from JLI, the excellent TSC-2 (Takstar) capsule, the one used in the AKG P420.
 
PS: Anyone interested in a 53.5x38mm (~2.1"x1.5"), single-layer, multi-donor-body-compatible, etch-at-home ORS87, with pad & high-pass?

View attachment 131370

Although truth be told, it's not all that much of a "stripped-down U87" anymore... :LOL:
That looks nice. Ground plane and all. Yes I am interested.

I see there are plenty online services like PBCWay to 2-, 4- 6-layered circuit boards manufactured for reasonable fee?
I wonder which might be suitable free PCB/schematic software and what manufacture service to try out nowadays for DIY?
 
Last edited:
That looks nice. Ground plane and all.

More copper left on the board = less needs to be etched off, goes quicker, etchant lasts for more uses 👍🏻 And wider traces stick to the board better, less chance of peeling them off. Of course, you can still burn them off with a too-hot iron, but that's probably a bit beside the point 😁

"Any machine is a smoke machine, if you use it wrong enough"...

I wonder which might be suitable free PCB/schematic software and what manufacture service to try out nowadays for DIY?

KiCad seems to be quite popular, and free & open-source.

For board manufacture, all(?) the far-eastern board houses are about as good as the next. I've ordered from Itead Studio, back when they still made boards; JLCPCB is one of the most popular, and i think i've had some made at PcbGogo as well; haven't noticed any (quality) differences in the simple boards i needed. They all have the "$5 for 5-10pcs of (up to) 100x100mm 1/2-layer boards" deals, so whatever differences might only show up in the shipping options / costs.
 
More copper left on the board = less needs to be etched off, goes quicker, etchant lasts for more uses 👍🏻 And wider traces stick to the board better, less chance of peeling them off.
In addition, more copper on PCB representing GND provides a reduction in 50Hz hum.
I can say this from my own experience.
In this regard, I have seen amazing examples of PCB designs that, without full shielding , were impressively immune to hum.
I often execute my p2p builds on a thin metal plate. I can work, adjust, etc., with full access to the experimental prototype in real time, without additional restrictive shielding, having a reasonable hum.
Of course, in the case of microphones, in the high-impedance area, care must be taken not to create parasitic capacitances that affect the signal level, the signal/noise ratio.
 
PS: Anyone interested in a 53.5x38mm (~2.1"x1.5"), single-layer, multi-donor-body-compatible, etch-at-home ORS87, with pad & high-pass?

View attachment 131370

Although truth be told, it's not all that much of a "stripped-down U87" anymore... :LOL:
It is an excellent PCB design. On my taste. It has a clear electronic logic, I don't even need a schematic. And very versatile, you can use it in any body with any geometry, you can populate it with a wide variety of components (chosen rationally, technically, not under the influence of black magic👹) it can adapt to everyone's requirements.
Regarding the J113, thanks for the info posted earlier, in the meantime I've looked into it a bit and I think it's a good candidate for microphone circuits. I have a lot of 2N3819 CENs, most of them are suitable for 87, but in the next Mouser order, I will definitely include the J113, it has an unbeatable performance/price ratio and is available.
So yes, I like this PCB and it really is an attractive solution for getting great results.
 
Back
Top