Behringer B2 Pro Electronics upgrade

[ln76d]

Ok, there's last PCB track to cut (marked with red X on the pic) after that check is there continuity between PCB point and switch pin (marked black arrow).
My eyes hurts checking these connections from the pic
Need a while for this.

 

[user 65018]

Hi!
I did cut  PCB track off from bottom and check for continuity .
There is no continuity  from  that switch's pin and open hole in the center after cut made.

 

[ln76d]

Remove these three parts.

 

[ln76d]

Remove these two wires

 

[user 65018]

Hi!
Caps and resistor removed.

 

[user 65018]

Hi!
Milky jump wire and blue wire removed.

 

[kingkorg]

Wow! I had to join the forum to report my results.



Can you please, please, please give us idea how to get that high end roll off like on U87, just like a famous Studio Projects mod done by Microphone Parts:

 

[RuudNL]

Can you please, please, please give us idea how to get that high end roll off like on U87, just like a famous Studio Projects mod done by Microphone Parts

The (MP) rolloff is the result of two 10K resistors in series with the base of the output transistors (to the previous stage, so in series with C6/C7 ), and a series circuit of a 100 K trimpot and a 1000 pF capacitor between the base connections of the output transistors. When using this modification, you may (or may not) want to remove C25 and C26. The setting of the trimpot now determines the amount of HF rolloff.
It's no rocket science... More about this: http://www.audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html

 

[micaddict]

Wow! I had to join the forum to report my results.

I didn't have much time, but i managed to remove C1, C2, and two unmarked caps between diodes and resistors. Noise to signal is so much better. Here are the examples before and after with preamp cranked:
Before
https://app.box.com/s/7ldcy2rwav4jqkc74dqlv8uyymak48n9
After
https://app.box.com/s/xyavy5prc3yicb4gdbkgg081ianqy2ni

Sound wise it didn't do much, but there is less rumble in the lows after. Just a drum loop played through my monitors, with preamp cranked.

Before
https://app.box.com/s/mpud3bwlax1bidvctnoq6cd0rz08y463
After
https://app.box.com/s/t1hd9h498qq790z74lrp0s65tb9ico9q

Can you please, please, please give us idea how to get that high end roll off like on U87, just like a famous Studio Projects mod done by Microphone Parts:

https://microphone-parts.com/products/studio-projects-c1-circuit-upgrade-kit

Welcome! 

And thanks for sharing your findings.

 

[ln76d]

Try something different.
Put 10nF from FET source leg to ground.
I will soon update final modification.

 

[ln76d]

yes

 

[RuudNL]

what about R8 and R9, should they be removed as well?

No, leave R8 and R9 in place! (Otherwise the output transistors won't get biased.)

 

[micaddict]

Fixed with some body kit, primer and spray

I feel this thread will make this mic highly desirable.

Better late than never. 

 

[RuudNL]

10 nF didn't do much, so i went with 22nF, and got these results.

Did you measure (HF) distortion after adding the 22 nF capacitor?...

 

[kingkorg]

I did measure harmonic distortion with REW, if that is what you mean. Seems fine.

 

[RuudNL]

Is that the result of an acoustic measurement? (Microphone+speaker?)

 

[ln76d]

For k47 there's no need to use any capacitor for LPF.
Problem is elswhere.  Behri behri headbasket isn't the best option for k47 and definately you could rebuild input topology, i will update "tutorial" soon.  Any capacitor for filtering cause phase shift.
Anyway this kind of body (headbasket) is much better for K67.
For filtering also you can try single cap from drain to ground or two capacitors -  one from source and one from drain - both to ground.

Could you measure something for me?
I need voltage value from R17/C13 junction and R20/C15 junction.

Did you changed C6/C7 to higher values?
Did you removed C1/C2, C25/C26?

 

[micaddict]

Don't underestimate the original (797 Beijing Audio) capsule, especially when comparing to an RK.

 

[ln76d]

****, i missed 24V diode somehow...
108V, not bad
Anyway that change my input topology mod...
Now it's easier to make.
So here's update.

 

[ln76d]

Could you measure R15/R16 voltage?