iSK BM-600 as a donor mic?
« on: May 19, 2018, 08:45:39 AM »
Has anyone tried the iSK BM-600 as a donor mic before? It looks promising since it's multipattern, though I don't know how good it's stock sound is, but I assume it doesn't have corrective EQ so it's probably probably pretty bright since it looks like a U87 copy. I'm sure with a C12 style capsule it could become very usable but I'd like to hear from someone who has used it before if anyone has experience either stock or modded.


RuudNL

Re: iSK BM-600 as a donor mic?
« Reply #1 on: May 19, 2018, 11:48:57 AM »
I have modified several BM600 microphones.
Yes, the BM600 uses a K67-style capsule but it sounds less bright than most Chinese microphones do.
There is some signal to noise ratio improvement possible, the transistors aren't the most quiet ones.
Never used a C12 style capsule in this microphone, but as far as I remember there is no EQ in the circuit, so this should be possible. It might be a good idea to change some capacitors, because the frequency response drops at low frequencies.
But the microphone isn't really bad as it is delivered. (Keeping the price in mind.)
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: iSK BM-600 as a donor mic?
« Reply #2 on: May 19, 2018, 06:46:06 PM »
I have modified several BM600 microphones.
Yes, the BM600 uses a K67-style capsule but it sounds less bright than most Chinese microphones do.
There is some signal to noise ratio improvement possible, the transistors aren't the most quiet ones.
Never used a C12 style capsule in this microphone, but as far as I remember there is no EQ in the circuit, so this should be possible. It might be a good idea to change some capacitors, because the frequency response drops at low frequencies.
But the microphone isn't really bad as it is delivered. (Keeping the price in mind.)
I thought the frequency response didn't look terrible. It doesn't look like it has that super harshness a lot of the Chinese ones have (though it does like slightly coloured, but so are a lot of mics, my CM1 definitely isn't completely flat despite being Neumann style).  I just wasn't sure how accurate the specs are since a lot of OEM versions just copy the specs even if they're not quite right. But it seems like it would be completely usable. The only actual audio sample I've heard was a Japanese YouTube video comparing it to the Bluebird which I thought it compared to quite well for around half the price, but since I'm an English speaker I can't really judge how it sounds very well if the sample is in another language.

I've got a CM-20c coming in the mail soon because I only needed the supercardioid capsule of the Little Gem. Are there any recommended mods for that? Or is it also usable as is? I've heard EQ can take care of the weird lower mid thing it has going on around 3 KHz which I hear make cymbals and some guitars hissy, but I really just plan to have it as a travel and backup vocal mic.

Khron

Re: iSK BM-600 as a donor mic?
« Reply #3 on: May 22, 2018, 10:04:34 AM »
A few corrections there ;D

1) https://groupdiy.com/index.php?topic=61084.msg773828#msg773828
2) [quote from the first post in the above-linked thread] "You can find some lovely-looking internal photos of the stock mic (better than i can ever hope of pulling off) over here: http://groupdiy.com/index.php?topic=49389.0 - just scroll past the U87's."
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: iSK BM-600 as a donor mic?
« Reply #4 on: May 23, 2018, 07:09:40 AM »
A few corrections there ;D

1) https://groupdiy.com/index.php?topic=61084.msg773828#msg773828
2) [quote from the first post in the above-linked thread] "You can find some lovely-looking internal photos of the stock mic (better than i can ever hope of pulling off) over here: http://groupdiy.com/index.php?topic=49389.0 - just scroll past the U87's."
Looking at the thread the BM-600 does have corrective EQ. So could a capsule swap with a premium K67 type capsule make it a better mic, or are the EQ correction and transformer weak like the MXL V67G? (According to Microphone-Parts the V67 transformer is really low output and the de-emphasis circuit is really weak)

RuudNL

Re: iSK BM-600 as a donor mic?
« Reply #5 on: May 23, 2018, 07:39:58 AM »
Yes, Khron is right (as always!  ;D ), there IS a corrective EQ available in this microphone.
(It is a long time ago I modified the last one.)
If you remove the corrective network, a C12-style capsule will work fine.
Personally, I prefer a C12 over a K67 with correction, but that is strictly personal I think.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Khron

Re: iSK BM-600 as a donor mic?
« Reply #6 on: May 23, 2018, 08:02:00 AM »
Flattery will get you nowhere!..  ;) ;D

On a more serious note, i could be wrong, but i think you can get the Devine BM600 from Bax-shop for less(?) than the iSK BM600. Just a thought :)
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: iSK BM-600 as a donor mic?
« Reply #7 on: May 23, 2018, 02:13:30 PM »
Yes, Khron is right (as always!  ;D ), there IS a corrective EQ available in this microphone.
(It is a long time ago I modified the last one.)
If you remove the corrective network, a C12-style capsule will work fine.
Personally, I prefer a C12 over a K67 with correction, but that is strictly personal I think.
I actually like the C414 sound a lot, I just know nothing about electrical engineering which is why I'm mostly interested in capsule swapping. I'm pretty strapped for cash rn (college age and in between jobs) so I probably won't be buying mics with the intention of comprehensive modding until I have more saved up anyway.

Re: iSK BM-600 as a donor mic?
« Reply #8 on: June 15, 2018, 07:28:39 PM »
Would it be possible to just change the capacitor responsible for the HF attenuation? I heard that it's C3 in a V67, is there a single capacitor that can be changed to a lower value to reduce the corrective EQ, or do you just have to install a new PCB?

RuudNL

Re: iSK BM-600 as a donor mic?
« Reply #9 on: June 16, 2018, 03:58:41 AM »
C3 is responsible for the HF rolloff. Lowering this value = more HF.
C1 is responsible for the LF rolloff. Increasing this value = more LF.
There is a solution for every problem!

http://www.vansteenisaudio.nl


Re: iSK BM-600 as a donor mic?
« Reply #10 on: June 16, 2018, 02:29:23 PM »
C3 is responsible for the HF rolloff. Lowering this value = more HF.
C1 is responsible for the LF rolloff. Increasing this value = more LF.
Is there a recommended value for C3 for C414 clones/C12 style capsules? Or is there a way to easily bypass the HF rolloff without building a new circuit?

Khron

Re: iSK BM-600 as a donor mic?
« Reply #11 on: June 16, 2018, 04:44:11 PM »
What about just disconnecting one end of the 470nF capacitor coming off the JFET drain?

(See the U87 schematic for reference)
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: iSK BM-600 as a donor mic?
« Reply #12 on: June 16, 2018, 11:14:49 PM »
What about just disconnecting one end of the 470nF capacitor coming off the JFET drain?

(See the U87 schematic for reference)
Would that be the capacitor C4? C1 and C4 are the only 470s I see on the schematic.

Khron

Re: iSK BM-600 as a donor mic?
« Reply #13 on: June 17, 2018, 05:16:52 AM »
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: iSK BM-600 as a donor mic?
« Reply #14 on: June 19, 2018, 05:26:45 PM »
Anyone know the stock value of C3 in the BM-600?

Khron

Re: iSK BM-600 as a donor mic?
« Reply #15 on: June 19, 2018, 06:20:50 PM »
C3 on the BM600 board, i guess?

Describing its circuit location / function might be more helpful / clear than just a part designation (imho) :)

Anyone know the stock value of C3 in the BM-600?
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Re: iSK BM-600 as a donor mic?
« Reply #16 on: June 20, 2018, 05:04:59 AM »
C3 on the BM600 board, i guess?

Describing its circuit location / function might be more helpful / clear than just a part designation (imho) :)
I mean is it worth it (as in will it make a noticable difference) to upgrade C3 to an 820 pF WIMA capacitor like this one?
https://www.mouser.ca/ProductDetail/WIMA/FKP2-820-630-25?qs=sGAEpiMZZMv1cc3ydrPrF%252b32GxjiTRYH5KVsjK79ez0%3d

Khron

Re: iSK BM-600 as a donor mic?
« Reply #17 on: June 20, 2018, 06:42:46 AM »
I guess i didn't make my question / tip clear enough :)

"C3" doesn't really mean anything, in itself ;) That's why i was asking about its function (or role) in the circuit. That, and my BM600's are at the "studio", so out of reach.

Is it the coupling capacitor for the capsule (going by the 820pF of that Wima)?
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: iSK BM-600 as a donor mic?
« Reply #18 on: June 20, 2018, 08:02:13 AM »
I guess i didn't make my question / tip clear enough :)

"C3" doesn't really mean anything, in itself ;) That's why i was asking about its function (or role) in the circuit. That, and my BM600's are at the "studio", so out of reach.

Is it the coupling capacitor for the capsule (going by the 820pF of that Wima)?
I think C3 in these circuits controls the HF de-emphasis, though if I'm wrong someone please correct me. I don't know the stock value of it, but in some threads on modding similar mics people someone mentioned that using a higher value capacitor helps tame the high end more, so for mics using a K67 and weaker corrective EQ it's supposed to help.

Because I don't know how good the stock capacitor there is, or how close the stock BM-600 sounds to an actual U87 (I don't think it sounds like crap though) I want to replace whichever capacitor is responsible for the HF de-emphasis if that's necessary/makes a noticeable improvement. Haven't bought the mic yet but I'd like to use it over some of the other cheap multipattern mics out there because the BM-600 is around half the cost of the the Behringer B2 Pro and CAD GXL3000.

Basically my goal is to turn it into a usable versatile work horse mic (main use will be cardioid). So for now I just want to do a couple small improvements if I can and later on I'll invest in a better capsule.

Doesn't have to be a C414 clone either, just has to be a non-harsh sounding versatile mic. I nothing about electronics design, but I'm sure I can solder in replacement capacitors.
« Last Edit: June 20, 2018, 08:12:11 AM by Icantthinkofaname »

Khron

Re: iSK BM-600 as a donor mic?
« Reply #19 on: June 20, 2018, 08:27:50 AM »
I guess that makes a certain amount of sense, then.

As you may or may not have noticed in one of the links i've posted before (namely this one - https://groupdiy.com/index.php?topic=61084.msg773828#msg773828 ), i've lifted the schematic of the whole thing, albeit didn't really bother renaming all the parts to fit the designations in the actual BM600, so the HF de-emphasis cap value is 220pF, and is (fortunately) located on the bigger signal board (as opposed to the preeeeeeetty cramped input / switch board).

I myself am kinda skeptical about the whole "this film cap sounds worlds better than that film cap", although i do try to not have ceramics in series with the signal path. In other words, just about any film cap is preferable to a (non-C0G / NPO) ceramic, imho :P

820pF might be a bit heavy-handed, starting from 220pF, but i suppose it's worth a shot. Worst case, you'll end up with a dark(er)-sounding mic - ribbons anyone? :D
Might want to consider also getting a 470pF one, or perhaps a 680pF one too, and see which value you like best. Or if you're feeling particularly adventurous, MacGyver a switch for that, too ;D
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