Questions about BM800 modding

[mikeylemur]

I want to take on this small project to develop my soldering experience. As I have no knowledge of electric engineering, I will be following this this guide as it seems pretty beginner friendly. Only three parts to solder, not too bad. There are probably more optimal ways to improve the BM800 PCB, but this guide has pictures to refer too and I don't need to read and pcb schematics.

So the guide suggests a small NPO ceramic or mica capacitor of 20 to 30 pF, an electrolytic capacitor of 250 to 1000 mF at 16V or more, (small enough to fit inside the mic.) and optionally but recommended, a 270 to 470 ohm, 1/8 watt or higher, resistor. OP used an 22pF, 1000mF / 16V, and 330 ohms 1/4 watt resistors.

Here are some parts I found on AliExpress:
-ceramic or mica capacitor of 20 to 30 pF: 1, 2, 3,4 The guide doesn't specify a voltage. I have found ceramic capacitors rated at 50v, 1kv and 3kv, which should I go for?
-electrolytic capacitor of 250 to 1000 mF at 16V or more: 2, 3, 4, 5, 6, 7 (this is 16v470uf and not the 1000uf that the OP used)
-a 270 to 470 ohm, 1/8 watt or higher, resistor: 1, 2, 3, 4, 5. The product listing labels each product skew with 'r'. I'm assuming that means ohms?

All of the resistors and capacitors are rated the same, I assume the only difference is the quality of parts. How can I tell which one is better? OP has also given a wide range of resistances to choose but which resistances are optimal. For example, I found the 16v470uf for cheap but OP chooses a 1000 uf capacitor instead.

https://audioimprov.com/AudioImprov...0_A_Low-Cost_Beginners_Mic_files/IMG_0925.jpgIn this part of the guide, OP removes a trace on the PCB and solders a resistor there. Is there a simpler method of doing this? I thought about soldering the resister on the trace itself and slowly spicing off the solder and trace together. I also thought about splicing a trace first and holding the razor in between the trace . That way, I can stop the solder from making contact to the other side. My last idea is to solder points further apart from each other.

''Finished printed circuit, both sides.The last change is to swap the wires at the output going to pin 2 & 3 of the XLR connector. All of these mics I’ve looked at have phase reversed from studio standard.'' In my case, I would be switching the yellow and green cables right?

---

Here are some budget capsules I've found after scouring the forums: this, this, this, this, this and this.

Questions:
I've seen mics with foams just below the capsule holder, is this worth including in my mod?

This PCB has been built for electret mics in mind. I assume that electret capsules can be interchangeably swapped, but not DC capsule that uses high voltage (50-70 volts). Do the the three LDC's I linked above use high power voltage? 1, 2, 3

I haven't seen any other budget capsules recommended but I'm open to more suggestions.

Any advice is greatly appreciated!

 

[Андрій Чубака]

-ceramic or mica capacitor of 20 to 30 pF: 1, 2, 3,4 The guide doesn't specify a voltage. I have found ceramic capacitors rated at 50v, 1kv and 3kv, which should I go for?

in this circuit not more than 50v

-electrolytic capacitor of 250 to 1000 mF at 16V or more: 2, 3, 4, 5, 6, 7 (this is 16v470uf and not the 1000uf that the OP used)

about this kind of capasitors in some case better have it with low ESR. But not always it is important.

-a 270 to 470 ohm, 1/8 watt or higher, resistor: 1, 2, 3, 4, 5. The product listing labels each product skew with 'r'. I'm assuming that means ohms?

yes r in this case it is ohms

the Chinese market is a lottery, unfortunately it is impossible to be sure of the quality of what is bought there. maybe with resistors is no problem there but about other not always all good.

I now also thinkig about this problems, but at this moment looks like I won`t continue all this searching on ali.

 

[Андрій Чубака]

I can say for you. You can't just buy any kind of capsule and place it in bm800 body with standart pcb or even modified pcb.

https://groupdiy.com/threads/saddle...or-3d-printing-done-models.84271/post-1096339
There i am tested this thing with fine capsule. Maybe you can reduce level of noise with modifications of circuit. But level of sound will be too low anyway and sound will be not very good. Standart bm800 pcb looks like good for electret capsules only. Maybe somebody know more about it but i can say only this right now.

 

[Khron]

Regarding adding that resistor across the sliced trace - instead of soldering the legs of a through-hole resistor to the very thin trace with the scraped-off solder-resist, i'd much rather solder the legs to existing solder pads of components along the respective "halves" of that trace.

That allows for more mechanical reliability (larger surface area connecting the copper to the glue and the board substrate). A through-hole resistor has considerably more mass than a surface-mount one, and in the interest of longevity, not to mention much less fiddly mounting, try to follow this idea.

 

[mikeylemur]

about this kind of capasitors in some case better have it with low ESR. But not always it is important.

What do you mean by ESR? is that different to resistance

the Chinese market is a lottery, unfortunately it is impossible to be sure of the quality of what is bought there. maybe with resistors is no problem there but about other not always all good.

So the resistors should be fine but capacitors can be hit or miss? In terms of quality, are you referring to the longevity of the capacitor or are you talking about the stated values - actual values.

There i am tested this thing with fine capsule. Maybe you can reduce level of noise with modifications of circuit. But level of sound will be too low anyway and sound will be not very good. Standart bm800 pcb looks like good for electret capsules only. Maybe somebody know more about it but i can say only this right now.

That's fine, it'll be interesting to see if it will outperform my sm58. I will most likely buy another microphone with good circuits to capsule swap in the future.

 

[mikeylemur]

Regarding adding that resistor across the sliced trace - instead of soldering the legs of a through-hole resistor to the very thin trace with the scraped-off solder-resist, i'd much rather solder the legs to existing solder pads of components along the respective "halves" of that trace.

That allows for more mechanical reliability (larger surface area connecting the copper to the glue and the board substrate). A through-hole resistor has considerably more mass than a surface-mount one, and in the interest of longevity, not to mention much less fiddly mounting, try to follow this idea.

If I follow the traces, I would solder to either 1, 2 or 3 right?

 

[Khron]

Not quite.

The "before" / "upstream" side is actually at the emitter of the transistor just "north" of 1.

https://www.direnc.net/bc846-80v-100ma-npn-en-sot-23-kilif-smd-transistor-philips-54756-69-B.jpg
On the "after" / "downstream" side, either 2, or one end of the 2k2 resistor connected to that same trace.

 

[mikeylemur]

Not quite.

The "before" / "upstream" side is actually at the emitter of the transistor just "north" of 1.

https://www.direnc.net/bc846-80v-100ma-npn-en-sot-23-kilif-smd-transistor-philips-54756-69-B.jpg
On the "after" / "downstream" side, either 2, or one end of the 2k2 resistor connected to that same trace.

So it would be

 

[Khron]

That looks better indeed.

 

[mikeylemur]

That looks better indeed.

https://www.direnc.net/bc846-80v-100ma-npn-en-sot-23-kilif-smd-transistor-philips-54756-69-B.jpgOn the "after" / "downstream" side, either 2, or one end of the 2k2 resistor connected to that same trace.

When you said the 2k2 resistor, you didn't mean number 4 but number 2 right? I reckon number 3 would be the easiest to solder but it looks like it is ''after'' the 2k2 resistor [2]

 

[Khron]

If you cut the trace between 1 and 4 (which is where you should), it makes absolutely zero difference.

 

[KZhack14]

Check out the mod i recently did on a used BM800 i acquire based off this other Henry Spragen's Article here.

Depending on what you're going for, even a mod as simple as swapping out the capsule and adding a larger cap to filter the voltage regulator's noise should suffice.

I do think adding some dampening material onto the body as well as inside the mesh grill will further improve the stray resonance/reflections from such a light body.

My next step of mod is probably going to repaint the body to something other than the whacky pink color. For now I'm calling this mic "Hot bubblegum"

 

[mikeylemur]

I do thinking adding some dampening material onto the body as well as inside the mesh grill will further improve the stray resonance/reflections from such a light body.

In the picture you sent, is that dampening material that you put inside the body or the grill?

Could you send me a link for that capsule if the QC is good.

What is the resistance of the green capacitor? I also saw that you didn't add a 270 to 470 ohm, 1/8 watt resistor but a 50v150uf capacitor + a second ceramic capacitor instead. Is there any particular reason you did that and where would I put a a 50v 150uf capacitor in my circuit?

Would love to hear some audio recordings of the mic if you have any!

 

[kingkorg]

Bit more elegant and better solution, using the same parts.

I think this was my last attempt that was working OK (using the original TSB-160A capsule), though I didn't had the 47uH inductors and the PNP's were what were there already (2N5401 smd versions) - also the zener is 9V1 one actually.

Let's hope the chinese manufacturers will find the below schematics and change their PCB's, and forget the PC computer use. and bundle the mic with a proper mic cable with XLR-3's on both ends - you can't actually just change the mini jack to XLR on the cable currently bundled as it's only single core lead.

 

[KZhack14]

In the picture you sent, is that dampening material that you put inside the body or the grill?

Could you send me a link for that capsule if the QC is good.

What is the resistance of the green capacitor? I also saw that you didn't add a 270 to 470 ohm, 1/8 watt resistor but a 50v150uf capacitor + a second ceramic capacitor instead. Is there any particular reason you did that and where would I put a a 50v 150uf capacitor in my circuit?

Would love to hear some audio recordings of the mic if you have any!

I simply added the 150uF cap to in parallel to the zener's capacitor just to increase the capacitance of the filter cap. The other green cap is around 1500uF i think. The 2nd ceramic cap is just for me to get a 11pF value because I only had 22pF caps lying around.

So you can see inside the mesh head I had a foam windscreen + additional steel mesh to hold it as well as to dampen the plosives even further. The strip of PU packing foam is to hold the inner mesh in place. Might have an added effect of damping the highs a bit but I think its worth the trade off.

Here's a recorded clip of the microphone! Honestly I think if you're going to use the 25mm Chinese electrets don't be afraid to try a bunch of them to see which one you like. One more thing to note is that the QC of the capsules will vary quite a bit as mine had a tiny ding on it (i got it for less than USD8 (converted from my local currency) and it came in a plastic bag w/o any form of protection at all. So I think its fortunate that the capsule survived the trip.

 

[Андрій Чубака]

I want place here some interesting thing. This is my old test of cheapest bm800 mic without any rebuilding, also it was mic with small pcb with 1 tansistor only on it, and fet was already mounted in capsule. Capsule was 9,6mm size. This sound recording on ukranian language but now I don`t have this mic for recording something new. I am already using it like body for my mic for testing.

Spoiler: bm800

I keep mic in my hand when I am recorded it. So sorry about it.

 

[Андрій Чубака]

So you can see inside the mesh head I had a foam windscreen

I guess you absolutely no need it with your type of capsule. You don't have any high frequencys with it. Not good solution at all. Looks like there sounds is already too much on low frequencys even without this foam.

 

[MicMaven]

I do thinking adding some dampening material onto the body as well as inside the mesh grill

Great! I use the same type of packing foam sheet to dampen noise in my mic builds. I would, however, use less or thinner batting material in the head basket, as (I suspect) it may reduce high frequency response. But, that is just MY take ... your mileage may vary.

And ... er ... ahem ... while the Bubblegum Pink is ... um ... attractive in its own way, I would paint over that to make it less distracting ... um ... just saying. Not that there is anything wrong with pink, mind you! /// James ///

 

[KZhack14]

I guess you absolutely no need it with your type of capsule. You don't have any high frequencys with it. Not good solution at all. Looks like there sounds is already too much on low frequencys even without this foam.

I just tried with the red foam removed and kept the metal mesh in, there's a somewhat discernable lift on the high frequencies. I originally had it in there to try to further reduce dirty elements from getting into the capsule.

Great! I use the same type of packing foam sheet to dampen noise in my mic builds. I would, however, use less or thinner batting material in the head basket, as (I suspect) it may reduce high frequency response. But, that is just MY take ... your mileage may vary.

And ... er ... ahem ... while the Bubblegum Pink is ... um ... attractive in its own way, I would paint over that to make it less distracting ... um ... just saying. Not that there is anything wrong with pink, mind you! /// James ///

LOL I gotta admit Bubblegum Pink is kind of cute tho. I did mention at some point I would change the paint, but I'm waiting for inspiration to strike hmmm

Anyway did a quick test again with no foam this time round... You guys tell me whether it sounds better.



Forgive the singing. Anyway, no HPF no processing whatsoever done on all tracks. Recorded while my bedroom's ceiling fan's still spinning.

 

[Андрій Чубака]

Anyway did a quick test again with no foam this time round... You guys tell me whether it sounds better.

Now i can check it only on headphones. Sound is much more live anyway. I can't now hear it on my regular acoustics. But there difference will be very big. So what is preferred here depends from acoustic for listening. On smartphone is any sound here is good. But as usual i am preferred more live sound. And for editing frequencys balance better use eq and not a big layer of foam which is reduce contrast of sound so hard.