BM800 capsule mod
- Thread starter Technotech
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I'm guilty of not reading the whole thread in detail ... but Technotech's comment in his original thread tells me his problem isn't gain staging in the interface but the mike itself overloading.
If that is the case, swapping the capsule for a 'better', larger, louder capsule like TSB 2555 is likely to make his problem worse ... though the sound at lower levels would be improved.
The 'cure' is to reduce the gain INSIDE the mike itself. Some circuits cannot reduce gain below a set limit so you might have to reduce the signal from the capsule itself .. eg by putting a small capacitor across a capsule if it doesn't have a built in FET.
If the capsule has a built in FET, things are more complicated. You would need to modify the circuit so the FET operates as a Source Follower (the infamous Linkwitz mod) or better still ...
turn it into a Charge Amp type circuit. I've got details of details of how to do this in simpleP48.pdf. But not every (??) capsule is easy to modify unless you are a brain surgeon
Incidentally, though I designed microphones for a living in da late 70s & early 80s, I probably haven't listened to as many capsules as k brown.
This Millenium, I like the cheapo JLI/TSB 140 & 160 capsules (as well as TSB 2555 of course). Properly mounted & in suitable circuits, they outperform some famous big name German SDCsIt might be easier to use TSB 140/160 (no FETs) and stick your own FET on the back which you can configure as a Charge Amp.
Technotech
Active member
Oddly, this is more expensive than Amazon. The CM-63 listing you posted is also unfortunately out of stock. I've found another that's the same price though.
I'm reading good things about the C-2, and the NT1-A as well.
Interesting. I don't think there's much to work with in the current mic though, so I think either way, I need to buy a new one to record non-vocals.
Hi @ricardo - which circuit and headbasket would be your preference to pair with a TSB 2555 or 140/160?I'm guilty of not reading the whole thread in detail ... but Technotech's comment in his original thread tells me his problem isn't gain staging in the interface but the mike itself overloading.
If that is the case, swapping the capsule for a 'better', larger, louder capsule like TSB 2555 is likely to make his problem worse ... though the sound at lower levels would be improved.
The 'cure' is to reduce the gain INSIDE the mike itself. Some circuits cannot reduce gain below a set limit so you might have to reduce the signal from the capsule itself .. eg by putting a small capacitor across a capsule if it doesn't have a built in FET.
If the capsule has a built in FET, things are more complicated. You would need to modify the circuit so the FET operates as a Source Follower (the infamous Linkwitz mod) or better still ...
turn it into a Charge Amp type circuit. I've got details of details of how to do this in simpleP48.pdf. But not every (??) capsule is easy to modify unless you are a brain surgeon
Incidentally, though I designed microphones for a living in da late 70s & early 80s, I probably haven't listened to as many capsules as k brown.
It might be easier to use TSB 140/160 (no FETs) and stick your own FET on the back which you can configure as a Charge Amp.
I would choose the simplest solution which is on page 10/11 of SimpleP48.pdf
FET harvested from a PUI AOM 5024.
First I would try the RCA version (page 12) and if the mike still overloaded, the slightly more complicated version in Fig4 with C4/J3.
Schoeps aim for 135dB spl overload on their mikes and the above would easily give 130dB spl or more.
But the simplest solution is simply to mod a BM800 like audioimprov
https://audioimprov.com/AudioImprov/Mics/Entries/2015/12/20_Modding_a_BM-800_Mic.html
You don't need a bigger capsule as that would be louder and make the overload worse. Or the Hartley oscillator.
So just add
- C12, the Charge Amp capacitor. Bigger cap = less gain
- R2 / C6 the Noise Filter
If you want to change the headbasket, you need to be able to measure frequency response of mikes. Naive removal of mesh etc will change the sound but usually not for the better.
Good Day Mr. @ricardo !!
Hmmmm ... um ... er ... that makes sense and I take your comment very seriously. And yet, after sleeping on this for a couple of days, I still think it COULD be a gain staging type thing - Here is the pitch:
I believe he has a USB microphone. One can adjust its output signal level in the Windows System Sound settings. To me, this is tantamount to the initial gain on a simple analog mixer, where you set mic volume coming in to the mixer. Similar to gain staging a mic on a mixer, you can easily set it too high and run out of headroom right away. Reducing the input level provides headroom for additional tweaks and level adjustments later in the audio chain. Here the recording application is further down the chain.
If the USB computer microphone is set to high as to run out of headroom, it will sound bad everywhere else in the chain - and nothing later can fix it. I consider this sort of, almost analogous to using a high gain high distortion effects pedal ahead of my super clean Fender Super Reverb amplifier, or even my Peavey Special 130 Amplifier. The signal is dirty and overdriven from the front panel input jack all they way through the amplifier, and there is no setting that can clean it up.
Thus, reducing the device's input volume in the Windows System Sound menu might reduce what the recording application manages, my point is, I do believe there may be a device driver setting we have over looked. Set to high, it overdrives everything down the line. We see this with Zoom and conference calling applications. The Zoom application has an automatic level control - but it does not matter if the mic is overdriven and there is already no headroom, you can lower the volume in Zoom but it will still be distorted. Capisce?
Does this not make sense? James
That may well be true ...
But from the usual cheapo circuits for electrets with built in FETs, I'd expect the FET to overload on a brass instrument "even somewhat close and at a quiet volume."
If you can identify the FET and get at it's terminals, adding a NPO/COG ceramic between Drain & Gate (as in my Fig 4 C4/J3) would reduce the gain, THD etc. That's essentially what audioimprov does in the #85 link with his C12
Technotech
Active member
Yes, it's a USB microphone. I hadn't considered the Windows microphone level settings, I thought it was just the mic peaking. I'll try it out, although I suspect the frequency response of this mic will be all over the place. Wonder if I can test it..?
That's what I thought, but I don't have any experience to know if this is what's happening here.
