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

[micolas]

Thanks, @micolas, so it's slightly bigger than even an actual 87. There you go @Wordsushi, "the best Ali 87 might actually be an Ali 193"

That is if the seller is not lying. They tricked me with u87 and tlm103 bodies. In reality they were smaller than in the description on the website

 

[svyet]

I guess there's only one way to find out..

EDIT: i.e. wait for the next @Wordsushi review haha

 

[micolas]

I guess there's only one way to find out..

That's @RuudNL 's famous reply

 

[Wordsushi]

https://a.aliexpress.com/_Ew2jWkv

Interesting! That would mean it's the exact same size as the HL-77 body from the New 87 body thread (https://groupdiy.com/threads/new-u87-body.84622/post-1131223), with the exception that this one is black and doesn't have the cutout in the headbasket rim for the fake pattern indicator. Thank you for pointing that out.

I had initially thought it was in one of those smaller cheap u89 sized bodies that are everywhere, like @micolas said, but either way, it most likely wouldn't be too much of a pain to transplant it into a more standard sized 87 style body (like the HL-95), if these measurements were incorrect.

Yeah, @svyet, I'm really thinking about it, but trying not to be as impulsive about it as I normally am.

 

[micolas]

Interesting! That would mean it's the exact same size as the HL-77 body from the New 87 body thread (https://groupdiy.com/threads/new-u87-body.84622/post-1131223), with the exception that this one is black and doesn't have the cutout in the headbasket rim for the fake pattern indicator. Thank you for pointing that out.

Or,
No one stops us from replacing the components on the PCB with higher quality ones, the transformer and the capsule

 

[svyet]

Yeah, why bother transplanting? Sure, it's not the exact dimensions of an 87 so it can't be called a "clone" but it's pretty darn close, and if that's not what you're after then it doesn't matter. Could be something you implement Ruud's tweaks (which doesn't even involve changing the capsule) and be done. At $200 plus a few component tweaks, it would certainly be an affordable 87, just maybe not as fun as swapping the capsule or anything else. But that's not me pressuring you to buy it, no matter how much I'd love to see a video. $200 is not small money in any case. Perhaps you could raffle off a few pieces from your collection with a $1 entry fee for each mic? Could be good for viewer engagement anyway..

 

[Wordsushi]

Or,
No one stops us from replacing the components on the PCB with higher quality ones, the transformer and the capsule

Exactly. It appears the pre-installed 7.5k bias resistor is visible in the upper right of the PCB on the faux 193 and the other caps Ruud mentioned are fairly easy to find, so it's probably par for the course if the experiment were to happen.

@svyet, True. If it were the same size as the HL-77, my reason to transplant would be dependent upon if it has the same body resonance issue as the HL-77, or if I wasn't quite as satisfied with the headbasket geometry as I am with my results using the HL-95 body.
And no raffles. I'm not ready yet to part with any of my "Island of Dr. Moreau" *******ized mic babies. LOL.

 

[svyet]

Haha! And right..resonance. Has anyone ever simply tried packing the bodies with adhesive sound dampening pads? I feel like I've seen people even place stuff inside the headbasket running up along under the headbasket frame as to not obstruct anything. Back when I was asking about making improvements to the black Rode NT1, @kingkorg showed measurable improvements simply by stuffing foam into the slot in the capsule mount to tame low-freq resonance. I'm sure he could speak more to solving other resonance issues in light/thin mic bodies.

 

[micolas]

@svyet, True. If it were the same size as the HL-78, my reason to transplant would be dependent upon if it has the same body resonance issue as the HL-78, or if I wasn't quite as satisfied with the headbasket geometry as I am with my results using the HL-95 body.
And no raffles. I'm not ready yet to part with any of my "Island of Dr. Moreau" *******ized mic babies. LOL.

I think you mean the HL-77 body not the HL-78

 

[micolas]

Haha! And right..resonance. Has anyone ever simply tried packing the bodies with adhesive sound dampening pads? I feel like I've seen people even place stuff inside the headbasket running up along under the headbasket frame as to not obstruct anything.

I think @ Wordsushi stated that the most annoying resonance occurs in the headbasket of HL-77. Any modification inside it will change the micro-acoustics and move the sound away from the Neumann.

 

[Wordsushi]

I think you mean the HL-77 body not the HL-78

Thank you for catching that. Corrected. I suppose I thought it was one better than it is.

And as I took a 2nd look at the faux 193 product photo, I noticed that there is a notch on the XLR base that is identical to the one on the HL-77 to prevent the body tube from rotating freely. This further makes me believe they are the same.

And yes, regarding the resonance, I think it's something that is happening with the way vibrations are being transferred from the headbasket ring to the capsule deck. I had tinkered a bit with trying to tame it until I discovered the HL-95 body, which does not suffer from the same issue.

 

[living sounds]

Thank you for your assessment! What errors, in particular, do you notice? What in your opinion could be improved here?

For some reason they use a 470p cap in parallel with the 1M resistor for the high frequency correction. Replacing that cap with a 220p cap (as in the U87i) corrected the problem. The polystyrene looking cap in the middle of the PCB has nothing to do with the audio circuit, it's a 470p PSU bypassing cap. Best to replace that with COG ceramic.

I went pretty deep into it a couple years ago until I had the response very close to my Andreas Grosser modded U87ai:

1. Replace the tiny trafo with a UTM0587.

2. The fake TLM103 has a headbasket with U87 dimensions. The capsule needs to be raised higher and ideally a dome or some foam (like Basotect) added below to deflect/dampen reflections from the metal bottom.

3.1. Remove the two 2.2k resistors, replace them with through hole components of the same value mounted upright and summed together. From there take a 56k resistor (I used 47k, which is fine, you need to isolate the stage otherwise there can be oscillation on the outputs) to cathode of a 24V zener, which should be in parallel with the cap filtering the drain voltage. I added an additional filtering stage with a 10k resistor + ca 5uf cap, this is all per the v16 U87 schematic (you can find it online). From there it goes through a 100k resistor, which also needs to be taken out and replaced with 47k (I used through-hole again). Now you have a clean voltage feeding the drain side of the FET.

3.2. Remove the source resistor and replace it with a 10k variable resistor (trimpot). Set the bias per the instructions (availible online) via the Messeingang (6.8k and 560 ohm resistor were flipped on all of my mics, so exchange them).

I've attached a photo of the fully modded PCB with the parts named as in the old Neumann schematic also attached.

3.3. A simple pad (as in the U87) can be achieved by adding a cap in parallel with the capsule. Neumann used 560pf.


Much of the secret lies in being very diligent with the fet bias setting. I used a 256B transistor, like Andreas Grosser.

Ultimately this mic sounds very close to the real thing, but lacking some of the detail sonic sophistication. This would be down to the capsule (which is much better on that mic already than the average cheap chinese mic) and maybe the mesh structure, which is a little different on the Neumann mic.

 

[living sounds]

Don't use a "better" cap for the cheap output electrolytic. It sounds better this way for some reason.

 

[Wordsushi]

For some reason they use a 470p cap in parallel with the 1M cap for the high frequency correction. Replacing that cap with a 220p cap (as in the U87i) corrected the problem. The polystyrene looking cap in the middle of the PCB has nothing to do with the audio circuit, it's a 470p PSU bypassing cap. Best to replace that with COG ceramic.

I went pretty deep into it a couple years ago until I had the response very close to my Andreas Grosser modded U87ai:

1. Replace the tiny trafo with a UTM0587.

2. The fake TLM103 has a headbasket with U87 dimensions. The capsule needs to be raised higher and ideally a dome or some foam (like Basotect) added below to deflect/dampen reflections from the metal bottom.

3.1. Remove the two 2.2k resistors, replace them with through hole components of the same value mounted upright and summed together. From there take a 56k resistor (I used 47k, which is fine, you need to isolate the stage otherwise there can be oscillation on the outputs) to cathode of a 24V zener, which should be in parallel with the cap filtering the drain voltage. I added an additional filtering stage with a 10k resistor + ca 5uf cap, this is all per the v16 U87 schematic (you can find it online). From there it goes through a 100k resistor, which also needs to be taken out and replaced with 47k (I used through-hole again). Now you have a clean voltage feeding the drain side of the FET.

3.2. Remove the source resistor and replace it with a 10k variable resistor (trimpot). Set the bias per the instructions (availible online) via the Messeingang (6.8k and 560 ohm resistor were flipped on all of my mics, so exchange them).

I've attached a photo of the fully modded PCB with the parts named as in the old Neumann schematic also attached.

3.3. A simple pad (as in the U87) can be achieved by adding a cap in parallel with the capsule. Neumann used 560pf.


Much of the secret lies in being very diligent with the fet bias setting. I used a 256B transistor, like Andreas Grosser.

Ultimately this mic sounds very close to the real thing, but lacking some of the detail sonic sophistication. This would be down to the capsule (which is much better on that mic already than the average cheap chinese mic) and maybe the mesh structure, which is a little different on the Neumann mic.

WOW. Interesting!
Could you try to repost the photo of the modified board since it didn't seem to come through? I'm not sure I understand exactly what's going on in 3.1 above.

 

[Khron]

I'm not sure I understand exactly what's going on in 3.1 above.

Sounds like recreating the U87A / KM84 JFET stage and power supply, to me.

 

[living sounds]

WOW. Interesting!
Could you try to repost the photo of the modified board since it didn't seem to come through? I'm not sure I understand exactly what's going on in 3.1 above.

Sorry, copied this post mostly from an older PM. Indeed, this is about recreating the older U87's stage and PSU. I'm not 100% sure what I tried back then, but it sounded best this way. Look at the old U87 schematic and it should become clear.

I have yet to try an Arienne Audio K87 capsule in there, this should decrease the delta to the real U87 quite a bit.

 

[Wordsushi]

Sorry, copied this post mostly from an older PM. Indeed, this is about recreating the older U87's stage and PSU. I'm not 100% sure what I tried back then, but it sounded best this way. Look at the old U87 schematic and it should become clear.

I have yet to try an Arienne Audio K87 capsule in there, this should decrease the delta to the real U87 quite a bit.

Oh well. Thank you for the input. If you ever do find that old photo of the PCB, please feel free to drop it here.

Sounds like recreating the U87A / KM84 JFET stage and power supply, to me.

Yeah, I just can't picture what this new batch of parts looks like on the board. I need visual aids. I'll probably just stick to what Ruud did.

 

[OneRoomStudio]

Oh well. Thank you for the input. If you ever do find that old photo of the PCB, please feel free to drop it here.


Yeah, I just can't picture what this new batch of parts looks like on the board. I need visual aids. I'll probably just stick to what Ruud did.

Everything he said in "3.1" has to do with the part of the circuit that derives B+ from phantom. There were a few different versions of this over the years.

Here's the 24V version:

Here's the 33V version:

My guess is that the Chinese version uses the 24V version.

 

[living sounds]

Oh well. Thank you for the input. If you ever do find that old photo of the PCB, please feel free to drop it here.

It looks a little wild, I remember it was very fiddly work.

 

[Wordsushi]

It looks a little wild, I remember it was very fiddly work.

View attachment 124132

Thank you very much. Love it. Really appreciate you taking the time to dig it up. I hadn't realized you were talking about this mod on an Ali 103. I imagine attempting something similar would be a bit easier on a faux 193 or 87 that already has through hole components.