Is there anyone who knows more about this microphone? (BM-700)

[RuudNL]

Recently I bought this microphone for somebody, who wanted to start a homestudio:

It is a McCrypt BM-700. Sold by Conrad. It costs only 72 Euro ( ~ $94), so I did not expect very much of it.
To my surprise this microphone sounds great! It is a real large diaphragm cardioid microphone (no electret!), the electronics look like the Schoeps circuit (with a DC converter for the polarisation voltage). Self noise is very low and the overall impression is that you are listening to a N****nn with a price tag over at least $1000...
Semiconductors in the audio path are 2SK30A and 2 x 2N5401. It it probably manufactured in China.
Is this microphone a relabeled version of an other (better known) type?
Does anyone have more experience with this microphone. Just curious!

 

[tommypiper]

Looks like it might be one of these.  http://www.groupdiy.com/index.php?topic=48061.0

Good to know it sounds good.  I was wondering about that.  Does it have the pattern selection switch, hi pass and pad switches?

EDIT: Here it is on this page, from a Canadian retailer or distributor. http://www.procanaudio.ca/Large_Diaphragm_Condenser.html

Can you tell us what is below the PCB, so we can know if we can fit a different transformer there, please?  Is there a plate, or something?  Is it possible to put a transformer near the XLR connector wiring in the bottom of the mic?

Would love to see pictures! 

 

[RuudNL]

Yes, in the meantime I found that this microphone is also sold as ISK BM-700 by a British company.

To answer your questions:

- It is a cardioid-only microphone, so no switchable patterns.
There is no -10 dB switch or a low cut filter. (I don't like to use low-cut on microphones anyway.)
The opening angle is not too wide, just as I would like to see this for music recording. It will give you good acoustic separation.
- Inside the microphone are two PCB's, mounted back to back. One holds the DC-DC converter for the polarisation voltage (~ +45V), the other one the head amplifier and balancing circuit.
- There is not very much space for a transformer. Maybe there is room just above the XLR connector (if you use a small transformer), but I would have to check this. What would be the advantage to add a transformer?

I will try to make some pictures in the near future.

 

[RuudNL]

The inside:

There is a hand drawn schematic on the Internet.
There are some errors: one transistor should have C-E reversed (emitter to output) and a 2K2 source resistor is not drawn.

 

[ksor]

I have just got two of this type MC200 and the look exactly liker yours !

http://www.groupdiy.com/index.php?topic=48164.0

The picture doesn't show it as gold plated but it is - exactly like yours !

I have not yet torn it apart to take pictires of the inside - but soon I will.

It's my first BALANCED mics so I have "only" my cheap unballances to compare with and ... wav the MC200 is much better !

Probably "Made in China" both of them with one label "MC200" on mine and "BM-700" on yours 

Nearly same price too !

 

[RuudNL]

Yes, this microphone is great value for money!
I bought it for somebody else, but now I have ordered one for myself too!  ;D

 

[PRR]

.

 

[RuudNL]

That's a better (=correct) schematic than I found on the Internet! 

 

[PRR]

Same schematic, just clearer and with your notes applied.

 

[ksor]

I've taken some pictures of my MC200 ...

http://kelds.weebly.com/3/category/mikrofoner/1.html

 

[RuudNL]

It looks like a different design. Is there a schematic diagram on the Internet of this microphone?
(It seems there are two FET's near the input ?  :)

 

[ksor]

Yeah, but I think the outside is almost the same - but inside is a big difference !

Maybe it's the chineese company logo - UR - are the same too ...

I haven't found any schematic - I even wouldn't know where to search for it - Google comes up with a "motor"  :-\ !

Anyway ... I'm very satisfied with the two !  ;D

 

[RuudNL]

I am very curious to know the idea behind the two FET's (??) on the top of the picture.
As I can see on the picture, the lower one is marked 2SK30.
What is the identification on the PCB for the upper one? Are they simply parallelled? (Maybe to lower the noise on the input?)
It seems they have put the head amplifier and balancing circuit together with the DC/DC converter on one single PCB.
As far as I can see component values are much the same as in my BM-700.

( I used the microphone today and again I was amazed by the quality and the extreme low noise!    )

 

[ksor]

I am very curious to know the idea behind the two FET's (??) on the top of the picture.
As I can see on the picture, the lower one is marked 2SK30.
What is the identification on the PCB for the upper one? Are they simply parallelled? (Maybe to lower the noise on the input?)
It seems they have put the head amplifier and balancing circuit together with the DC/DC converter on one single PCB.
As far as I can see component values are much the same as in my BM-700.

( I used the microphone today and again I was amazed by the quality and the extreme low noise!    )

The YELLOW arrows points to 2SK30

The RED arrows points to 2N5401

The last I think you can read but it's a 2N5551

Maybe some day I'll do the schematic but not today 

 

[RuudNL]

Mmmm.... so an 'extra' 2SK30, compared to PRR's schematic. (And my BM-700!)
They are close together and at first sight I don't see much additional components...

 

[Dan Kennedy]

Looks like the top FET is the amplifier, it's gate is connected to the bias resistor and the teflon insulated terminal.

Maybe the second one is cascode?

 

[Blue Jinn]

Old topic revival. These microphones are US$30 or so on Ebay, with shockmount. I am going to grab one or two. According to recordinghacks, they have SMD boards now, and a small capsule. (Probably like the newer MCA mic.) It does look like RuudNL's boards will fit in there though. So it is basically a body and shockmount.

 

[RuudNL]

I have indeed seen microphones with the same type number (BM-700) on Ebay.
But these can't be compared with the McCrypt or ISK BM-700!
Thin aluminium body, crappy small electret capsule and a small PCB with SMD components.
I tried to connect them to a mixer, but I didn't get sound at all... (Apart from a lot of noise!)
The cable that comes with it, has a XLR-3 connector at one end and a 3,5 mm stereo jackplug, with tip and ring connected together at the other end. So it seems, it is not even intended for phantom powering.
All I kept was the (rather crappy) aluminium body.
Even for the body, the price is too high!