Behringer B2 Pro Electronics upgrade

[user 65018]

Hi!

By removing C1 and C2 which on XLR pin 2and3 mic input.
All i know is mic sound better but no clue what it does to mic input signal.

Could you explain why .


Thank you.

 

[RuudNL]

C1 and C2 are there for RF suppression.
The value of 22 nF may be  at bit high, and cause HF rolloff.
But I would never remove them completely.
Substitute them with a lower value.
1 to 4,7 nF will still give you RF suppression, without noticable HF rolloff.
(The output impedance of the output transistors in series with the 20 ohms resistors is low.)

OR:

Remove the capacitors en replace the 20 ohms resistors with 47 uH mini inductors.

 

[micaddict]

Hey Ruud, good to see you in this thread.

@ Piotr and Ruud.
Wouldn't a slight HF roll-off be a good thing to keep, given the K67-style capsule?

 

[user 65018]

C1 and C2 are there for RF suppression.
The value of 22 nF may be  at bit high, and cause HF rolloff.
But I would never remove them completely.
Substitute them with a lower value.
1 to 4,7 nF will still give you RF suppression, without noticable HF rolloff.
(The output impedance of the PNP transistors in series with the 20 ohms resistors is low.)

OR:

Remove the capacitors en replace the 20 ohms resistors with 47 uH mini inductors.

Thank you.

C1 and C2  was Wima 0.022-63 not sure if its the same value as you mention.
C25 and C26 was Wima 1000-100

After removed these parts my mic sound more cleaner and more open.

Thank you  ln76d

 

[micaddict]

Regarding RF, the B2 Pro has a dual mesh headbasket. Not triple like the Neumanns and not single like the AKG C12, but one coarse and one fine layer. Best of both worlds IMO.

 

[RuudNL]

Wouldn't a slight HF roll-off be a good thing to keep, given the K67-style capsule?

Some form of rolloff may be a good thing, combined with a 'K67-style' capsule, but not at this point of the circuit.
22 nF at the output represents a rather heavy load at high frequencies.
It would be better to introduce some HF rolloff in the phase splitter stage, just before the two output transistors.

 

[ln76d]

All of these caps also affect phase.
All four are not needed.
In case of hf damping as also RF 10nF  between FET and first BJT to ground.
Many microphones don't have RF filtration at all and they works.
If owner had no problem with RF after removing caps then why should it be used?
Ruud, this isn't typical schoeps topology, similar somehow but there is no PNP pair at the output.
It's combination PNP/NPN.
I also don't recommend to use caps before them

 

[jasonallenh]

I turned this thing into a u87. Check Poctop's u87 thread ;D

I added documentation specific to this version of the B2, if you decide to go that route.

 

[micaddict]

I turned this thing into a u87. Check Poctop's u87 thread ;D

I added documentation specific to this version of the B2, if you decide to go that route.

Yup, that's an option, too.
Thanks for the reminder. 

Oh, unless it happened today, it helps to add a post #. 
Long thread.

 

[jasonallenh]

Oh, unless it happened today, it helps to add a post #. 
Long thread.

It's in the Meta on the first page

 

[user 65018]

All of these caps also affect phase.
All four are not needed.
In case of hf damping as also RF 10nF  between FET and first BJT to ground.
Many microphones don't have RF filtration at all and they works.
If owner had no problem with RF after removing caps then why should it be used?
Ruud, this isn't typical schoeps topology, similar somehow but there is no PNP pair at the output.
It's combination PNP/NPN.
I also don't recommend to use caps before them

Thank you !

I would like to order these parts from Mouser.
but  like to make sure i order the right part.

2x 1nF Wima FKP (small size min.100V rated)  1nF Is the same as 1000pF?
1x 4.7nF can be wima fkp or mkp (small size)  4700pF ?
1x10nF can be wima fkp or mkp (small size)  .01uF?
2x 68uF/63V electrolytic caps (panasonic FC or FM


Thank you.

 

[ln76d]

Everything is correct, but wait with order, there will be few things more. I'll let you know later.

 

[user 65018]

Everything is correct, but wait with order, there will be few things more. I'll let you know later.

Ok! Thank you.

 

[ln76d]

Ok, here's a full list of parts:

2x 1nF Wima FKP (small size min.100V rated)
1x 4.7nF can be wima fkp or mkp (small size)
1x10nF can be wima fkp or mkp (small size)
4x 68uF/63V electrolytic caps (panasonic FC or FM, BC components etc.)
10x 2n5087
10x2n5088 (from the same manufacturer as 2n5087)
4x470nF/63V capacitors (wima, ero, anything which would fit PCB - fkp, mkp, mkt, mks), best 5% tolerance
1x7.5V Zener (0.5W-1W)

I assume that your multimeters have options for HFE and capacitance mesurements?

 

[user 65018]

Ok, here's a full list of parts:

2x 1nF Wima FKP (small size min.100V rated)
1x 4.7nF can be wima fkp or mkp (small size)
1x10nF can be wima fkp or mkp (small size)
4x 68uF/63V electrolytic caps (panasonic FC or FM, BC components etc.)
10x 2n5087
10x2n5088 (from the same manufacturer as 2n5087)
4x470nF/63V capacitors (wima, ero, anything which would fit PCB - fkp, mkp, mkt, mks), best 5% tolerance
1x7.5V Zener (0.5W-1W)

I assume that your multimeters have options for HFE and capacitance mesurements?

HI!
Could you verify these parts if it is correct?


http://ca.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f43c9cdc58

Thank you

 

[ln76d]

Everything would be correct except 1nF and 4.7nF. Buy FKP not FKS type.

 

[user 65018]

Hi!
This is an updated list.

http://ca.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=6e4d0ea604


Will order soon,

 

[ln76d]

Here's next step - measurements with fluke.

Try to find most matched 470nF and 68uF caps.

Measure HFE of each transistor.  Take a sheet of paper and note value of each.
Overall we are looking for highest HFE, you need to find also matched HFE between one 2n5087 and one 2n5088.
If you will find it then also choose other two 2n5088 with highest HFE, no need to match it.
Q1/Q2 is pair of 2n5087/88
Q3/Q4 two other 2n5088 with highest HFE.

 

[micaddict]

Amazing that this mic didn't get a dedicated mod thread sooner. Like a decade or more ago.
Seems like such a good candidate.

But hey, better late ...

 

[ln76d]

Yeap Henk, mic is pretty good for mod, similar circuit you will find in studio projects.
Finally something different than molested schoeps in transformerless chinese microphones.
Lack of schematic was true pain in the three letters to make more advanced mods. 
I was always too lazy to draw schematic.
Only thing which i don't like in this mike as the donor is engraved logo and headbasket shape (both types).