B5 microphone

[Gus]

Anyone trace behringer b5? I friend asked me to look at two and I don't feel like tracing it.

Looks like a Schoeps type DC to DC converter with a J305 fet and a transistor (48 volt version of a fet 70 type circuit?)

 

[eriksmusicproduction]

I'd be interested as well.

I think they are pretty much a version of the studio projects c4, made by the same company. Maybe someone has traced that circut?

Erik

 

[GermanTech]

I´ve just repaired a Behringer B5 with through hole PCB. Failure : small output and lot of crackling and hiss noise. First stage was a J305 FET and I replaced it with a J201 N-Channel general purpose FET . Now it works fine and no sound difference to the other original B5 I have in use.
It was a try..... a first shoot in the dark ....but that was the solution of the problem.

​

 

[k brown]

I have two; one thru-hole and one SMD - they don't look like fun to trace.

Didn't think much of them till I put the omni caps on - they're actually quite good.

 

[cyrano]

This what I've collected over the years. Origin and author unknown. As far as I can remember, there are at least four different versions.

 

[k brown]

Anyone have mods/upgrades for B-5 electronics?

 

[Khron]

Anyone have mods/upgrades for B-5 electronics?

In order to achieve what?

 

[k brown]

In order to achieve what?

Just curious what anyone has done, to achieve whatever they were trying to . . .

 

[jp8]

View attachment 121315

This what I've collected over the years. Origin and author unknown. As far as I can remember, there are at least four different versions.

FYI: The LTspice schematics are mine and are available from the Behringer schematics thread here: Behringer.

Being a single ended output stage circuit with poorly (RF) executed impedance balancing, it is very sensitive to cell phone radiation and somewhat to hum as well. If you like Schoeps style circuits, copy the Takstar CM-63 circuit including the output common mode choke, but replace the 2SK208Y by a 2SK208GR to get into the right bias range for the 2k drain and source resistors. Btw, I don't have the CM-63 circuit diagram.

I can check if a TS-8 or similar size transformer will fit, but I'm afraid not.

Jan

 

[Emil C]

I found replacing FET (BF245A) with 2SK208 to drastically reduce RF interference in t.bone EM700 - a similar input configuration.

 

[jp8]

FYI: the interference I was referring to is AM demodulation of cell phone RF signals by the output transistor(s). JFETs do not have this issue. But maybe there was RF leaking through your headbasket or capsule and the JFET type did matter.

I have tested several BJT output circuit topologies for cell phone RF sensitivity. Worst ones were single-ended outputs, like the B5. Then symmetrical Schoeps and by far the best one was the Takstar CM-63 with Schoeps circuit and with common mode choke and beads and XLR with short ground connection to the tube. Through-hole/wired output caps for RF suppression proved largely ineffective in my test, even when mounted on the XLR. They may have been usefull in the pre-cellphone era, but not anymore now.

Jan

 

[Emil C]

I have a surveillance camera antenna nearby and in a particular place the RF field is very strong. In that place B-5, EM700 and t.bone SC140 are all affected. Only C-2 (Behringer) was ok. All of them share the same input topology. Some of them are inbalanced in the output stage (both branches are of the same series resistors value, not taking in consideration transistor output impedance), so at first I tried correcting that, with no effect. But changing FET (trying to obtain a lower white noise) led to this surprising effect - the RF interference was gone. I cannot explain why, even the FET-s Cgd are similar, but in that position 2SK208 (from AliExpress!!!) was better. C-2 did not suffer from RF interference from the begining, so it must be the printed board. All those mics are made by 797 Audio.

 

[jp8]

Well, neither do I have a plausible explanation for your observations. But in my 40 years of hardware design experience, I've encountered enough miracles to start believing in Black Magic. And the higher the frequencies, the blacker the Magic seems to get.

Ja

 

[Emil C]

I agree. I wouldn't believe myself either, but I can't deny my own experience. And to add something to the miracle, 2SK30A, on paper perfectly identical to 2SK118, has a more annoying self noise. Just play with k118 when possible.

 

[jp8]

I only play with SMT JFETs, so I would have to source those first before I could do any experiments. But I know many people select the JFETs with lowest noise from a batch, so there could be part-to-part variations.

Jan

 

[Emil C]

Possibly, I found S/N variations around 1.. 1.5dB for different k118 in C-2. I buyed many times from different vendors on AliExpress, all of them were very good. Maybe I was just lucky. 2SK208 is the same cip in a SMD package.

 

[dai h.]

I don't have the CM-63 circuit diagram.

hi, someone's apparently drawn one over on micbuilders:

https://groups.io/g/MicBuilders/message/35478

 

[jp8]

Ah, that was from Stephanie. I rememver now, indeed. I just did not store the schematic on my PC. Thanks for freshing up my mind! She also painstakingly reverse engineered the SC140, btw.

Jan