Questions about BM800 modding

[MicMaven]

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.

Good Day! I sounds much better, cleaner and more articulate without the thicker foam.

I suggest lining the grill with a light gauge, closely woven cotton fabric to protect the element from dirt and debris, and allow better acoustic transfer. My wife sews that into little "wind socks" in the shape of a sock toe, so they easily line the grill, without crowding the microphone element. I often use a lovely red fabric to make them. See the attached photos which give an idea of the fabric type and gauge, and the attractive result. Use a light weight, many threads per cm/inch cotton fabric, like a bed sheet or even finer gauge material for good accoustic transmission and effective protection. Good luck. James - K8JHR -

 

[KZhack14]

@MicMaven , woven fabric I do not have atm, but I have some 120-200 mesh stainless steel filtration nettings that I could use atm. I have been combining them with some thin foam as pop filters on some of my other dynamic mics with various level of success.

 

[mikeylemur]

Good Day! I sounds much better, cleaner and more articulate without the thicker foam.

I suggest lining the grill with a light gauge, closely woven cotton fabric to protect the element from dirt and debris, and allow better acoustic transfer. My wife sews that into little "wind socks" in the shape of a sock toe, so they easily line the grill, without crowding the microphone element. I often use a lovely red fabric to make them. See the attached photos which give an idea of the fabric type and gauge, and the attractive result. Use a light weight, many threads per cm/inch cotton fabric, like a bed sheet or even finer gauge material for good accoustic transmission and effective protection. Good luck. James - K8JHR -


View attachment 111504View attachment 111505

Is there any difference between using normal cotton compared to the woven fabric?

 

[mikeylemur]

@MicMaven , woven fabric I do not have atm, but I have some 120-200 mesh stainless steel filtration nettings that I could use atm. I have been combining them with some thin foam as pop filters on some of my other dynamic mics with various level of success.

The second test sounds better. I will probably line the inside with what MicMaven suggest but put a pop filter ontop. Do foam pop filters affect HF's more than foam ones?

>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.

Where would I solder a 150uF cap if I wanted to do that to my PCB?

 

[KZhack14]

The second test sounds better. I will probably line the inside with what MicMaven suggest but put a pop filter ontop. Do foam pop filters affect HF's more than foam ones?

>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.

Where would I solder a 150uF cap if I wanted to do that to my PCB?

in parallel to the original cap w/ zener dioide

 

[Drosselmeier]

 

[MicMaven]

Is there any difference between using normal cotton compared to the woven fabric?

Sorry for the delayed reply ... YES I find there is a difference. The fabric is quite thin and acoustically transparent, whereas cotton batting can have a significant restriction on higher frequencies. Happy trails to you. James

 

[Paul W]

So it would be

For any other clueless paint-by-number noobs who might be reading, it took me a while before I realized that this trace goes from the pad on the far right edge of the PCB and goes right between the legs of the "1UF" capacitor without contacting it, as highlighted in yellow here. It needs to be cut anywhere between the (black) transistor on its lower left end and the resister marked 2K2. The new resistor needs to bridge between the left and right parts of the divided trace, but can contact them anywhere along the respective halves.

Spragen says to attach the positive leg of the new big electrolytic capacitor to the pad on the right end of that trace (the topmost of the pads along the right end of that trace), but that rightmost part of the trace and the top pad do not exist in some variants of the circuit. I assume you can connect the big cap anywhere along the right part of the divided trace. (More on that in another post.)

EDITED TO ADD for handy reference, I'm doing the "A LOW-COST BEGINNER’S MIC" a.k.a. "A LOW-COST DIY MIC UPGRADE" rom the Audiomprov blog post of SATURDAY, OCTOBER 20, 2018:

https://audioimprov.com/AudioImprov/Mics/Entries/2018/10/20_A_Low-Cost_Beginners_Mic.html

 

[Paul W]

I took Kron's hesitations about just soldering the new resister to the divided trace, which is a pretty delicate little bit of cladding, and thought (against my better judgment) I'd try making my own through-holes to mount it more securely. I figured if I just drilled a couple of holes adjacent to the traces, I could use those, as long as I didn't short to the backplane layer on the opposite side of the PCB, which I assume is just a big ground.

So I drilled a couple of holes with my smallest Dremel drill bit, and scraped away the insulation on the traces adjacent to the holes I'd drilled, and scraped circles in through the backplane on the back side, which was more of a pain in the *** than I expected. So I whipped out the Dremel and an abrasive bit and crudely gouged donuts around the holes, leaving small bits of backplane, now isolated from ground and ugly as Hell.

Then I mounted the resistor into the holes from the back, and soldered it in place... which was a ridiculous pain in the ***.

I discovered that when you drill your own through-holes and don't have a super-teensy bit, the hole is WAY too big, and that makes soldering problematic. Whichever side you're soldering from, the solder tends to just run down through the hole and make a glob on the other side, leaving nothing but flux on the side you're working. I wanted both sides soldered---the front side for the electrical connection, and the back side for mechanical stability, and it took several tries to get something I decided had to be acceptable, ending with soldering the front side with the board in a vertical plane, and accepting a cold-looking joint on the back side which I hope is fine for mechanical stability. Ugh.

(If I try this again I will stuff the hole with something-or-other so that the solder can't just play keep-away. I guess it doesn't matter if it's electrically conductive or insulative; it just needs to be heat tolerant and not liquefy. Any suggestions? Is this a dumb thing to do?)

 

[Paul W]

One of the reasons I wanted to try making my own through-holes for mechanical stability is that I bought a couple of BM800s which at first I thought had the same circuit---it looked very familiar---but once I got them I realized the PCB differed in important ways, like lacking the aforementioned pad that Spragen says to connect to. I also saw that the PCB was simpler in other ways on the right-hand side, and thought the circuit was different. Whoops.

But then I looked more closely, and it appears to me that the circuit on those mics is the same, and the PCB just lacks some unpopulated pads and unused bits of trace. Here's what I'll call the "classic" that looks like what's in Spragen's main BM800 mod article, above what I'll call the "variant" PCB, and a rear view of the variant PCB.

I figure that if I mod the variant PCBs that I've got, I should try to get the through-hole thing to work, to connect the big electrolytic capacitor securely as well as the resistor; they connect to the same part of the divided trace and can use the same hole.

BTW, I suspect this variant circuit is fairly common, because the two mics I bought that have it came from very different channels, and I've seen pictures of this variant PCB in some thread about modding BM800's. (I thought that was some thread on this site, but can't find it.)

[EDITED TO ADD: Oh, hey, I just noticed that Drosselmeier provided a picture of one of these variant PCB's, along with a picture of the classic PCB, a few posts back in this thread. With no comment, as if it were obvious the circuit was the same...]

(BTW the classic PCB in the upper part of the first picture has already been partially modded, with a blue ceramic cap betwen the middle and bottom pads (of 5) along the right edge; I take to them to correspond to the bottom 2 pads in the variant PCB.)

 

[MicMaven]

I discovered that when you drill your own through-holes and don't have a super-teensy bit, the hole is WAY too big, and that makes soldering problematic.

Boy, I feel you pain! My hind-sight advice is twofold:

Serving Suggestion 1. Purchase a set of itty-bitty bits for $3-6 US on eBay. You may not use them very often, but they are well worth having.

(Some tools are worth the cost, even if you seldom use them because nothing else works as well for the particular job. Years ago, my young bride gave me a bench top grinder as a present. At the time, I thought would never use it. And yet, every time I DO use it, I realize it is the only tool for that particular job, and I am lucky to own one. These itty bitty bits are that sort of tool.)​

​

Serving Suggestion 2. Occasionally, I solder the part lead to the circuit, and physically secure the piece with a bit of CA glue, hot glue, or some other glue - usually what I have on hand. Back in college, my girlfriend's father gave me a handful of Locktite sample tubes, and they work well for this application (although I will not repeat his ill-timed advice to to be careful with it during *** ...) In any case, make electrical connection with solder, and physically secure the part an appropriate adhesive.

Just my take. James

 

[Paul W]

Boy, I feel you pain! My hind-sight advice is twofold:

Serving Suggestion 1. Purchase a set of itty-bitty bits for $3-6 US on eBay. You may not use them very often, but they are well worth having.

(Some tools are worth the cost, even if you seldom use them because nothing else works as well for the particular job. Years ago, my young bride gave me a bench top grinder as a present. At the time, I thought would never use it. And yet, every time I DO use it, I realize it is the only tool for that particular job, and I am lucky to own one. These itty bitty bits are that sort of tool.)​

​

Serving Suggestion 2. Occasionally, I solder the part lead to the circuit, and physically secure the piece with a bit of CA glue, hot glue, or some other glue - usually what I have on hand. Back in college, my girlfriend's father gave me a handful of Locktite sample tubes, and they work well for this application (although I will not repeat his ill-timed advice to to be careful with it during *** ...) In any case, make electrical connection with solder, and physically secure the part an appropriate adhesive.

Just my take. James
View attachment 125167View attachment 125168

I will definitely be ordering have already ordered some teeny tiny bits!

I thought about using glue, but was worried about being able to un-do it if I got things wrong need to desolder & redo a part.

I'm also wondering about glues and their possible conductivity; I figure most glues are basically plastics and most plastics are insulating, so I might use them for mechanical support w/o too much worry about shorting something, but for the high impedance part of a mic I'd think any slight conductivity could be A Bad Thing. At this point I'm painting by number and don't really know which parts of the circuit I need to worry about, or what glues are good enough insulators.