microphone to check out

shop deals on amazon
Advertise with us
Shop deals on ebay
GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
G

Gus

Well-known member
Joined
Jun 3, 2004
Messages
5,264
Location
n
The MXL 890 and I think  CR89 VR89 and ? microphones have an interesting circuit.

I would do something a little different in some parts of the circuit. I might machine a new capsule mount and base.

I bought a 890 for the body and decided to listen to it.

I traced most of the circuit it might have better CMRR than the Schoeps type (look up how to calculate the output of an emitter follower) if the build out resistors are .1% I have not removed then to measure them with mult digit DMM.
Also look up how CMRR is degraded with small changes in output resistance when  being plugged into a nontransformer input preamp.
 
Interesting. Is the circuit flat? A lot of people report that it's flatter sounding than usual k67 suspects. I wonder if it's the capsule or the circuit.
 
The polarization voltage (70V)  is supplied to backplate so there is no usual capacitor between capsule and gate of the FET. In fact when looking at the images on Recordinghacks there doesnt seem to be any gate resistor (the usual 1G or less) either. So does it make it gate leak biased? Maybe they use a FET like 2SK596 or 2SK1578 with built-in resistor (like in electret mics)?

Google found this article about DC-connected (capacitorless) phantom powering with the list of such FETs and some noise measurements: https://www.edn.com/design/analog/4369073/Condenser-microphone-uses-dc-coupled-impedance-converter
Too bad the huge THD because of the limited biasing and internal diodes (usual reverse and forward on some) makes these FET's useless.
 
As in so many cases in life, "it's how you use it" ;) ;D

http://audioimprov.com/AudioImprov/Mics/Entries/2015/12/20_Modding_a_BM-800_Mic.html
https://groupdiy.com/index.php?topic=61079.0



mhelin said:
The polarization voltage (70V)  is supplied to backplate so there is no usual capacitor between capsule and gate of the FET. In fact when looking at the images on Recordinghacks there doesnt seem to be any gate resistor (the usual 1G or less) either. So does it make it gate leak biased? Maybe they use a FET like 2SK596 or 2SK1578 with built-in resistor (like in electret mics)?

Google found this article about DC-connected (capacitorless) phantom powering with the list of such FETs and some noise measurements: https://www.edn.com/design/analog/4369073/Condenser-microphone-uses-dc-coupled-impedance-converter
Too bad the huge THD because of the limited biasing and internal diodes (usual reverse and forward on some) makes these FET's useless.
Click to expand...
 
mhelin

Look at the picture of the back of the PCB

JFET PI to dual opamp as buffers.
 
Gus,

I can't see any pics or schematics on your initial post.

Are you refering to an external pic or something?

Thank you and kind regsrds!

HL
 
Images can be found here:

http://recordinghacks.com/microphones/MXL/890

Not too good resolution.

I've got a pair of BM-800s waiting for hacking into.

The 890 is still over EUR 200 in Europe but almost half in US (and some on GS have found it for $60 ),

Grabbed the image URL from the HTML code, it's actually much better:

http://cdn.recordinghacks.com/images//mic_extras/mxl/MXL-890-circuit.jpg
 
I bought them for the bodies

Might change the JFET and reset the bias

Check the match of the output resistors and change if necessary

Machine a new capsule base and mount and try different capsules like in one of the VM 1 threads

I can't tell what opamp is used. I checked the three I have wiping the sanded top with alcohol did not show anything different then when it was dry.
 

Similar threads

E
Tube Microphone SMPS with adjustable B+ and Heater
Replies
3
Views
205
rock soderstrom
rock soderstrom
Voyager10
Comparison of JFETs for mic applications
2
Replies
38
Views
3K
Voyager10
Voyager10
bluezplaya
Patchbay w/Mults
Replies
4
Views
391
john12ax7
J
A
I want to make a reliable clone of a C800G microphone
4 5 6
Replies
100
Views
9K
Khron
Khron
M
"Manleyish" Tube Microphone (ST51 + SCT 800)
Replies
0
Views
972
Mauritius89
M

Latest posts

Back
Top