[zamproject]

Hello

I received a B&K 2230 from university clearance.
Obviously the unit was not used since long time, but after battery housing mess (leak and chain connector for the 4x1.5V destroyed) I was able to power it on via an external PSU

I have no idea If the unit still calibrated, and I have none of external B&K generator to check.
Service manual offer a calibration with internal oscillator, BUT I need to know a "Ko" factor of the microphone which is given in the initial documentation for each mic, and I don't have it...

Basically the calibration is done by setting "cal" to internal and adjust meter to read 94dB+Ko

Did someone have any idea of the magnitude of this Ko given with 2230 meters ?

I won't bother for a small factor and just cal to read 94dB, but if the factor can go from -10 to +10 I may have issue...

Best
Zam

[zamproject]

Side comment after few hours playing with the tool...

The "cal" pot have a range less than +/- 5dB around 94dB, so maybe Ko should not be high number.
I also find a picture on the web of a mic calibration/data sheet where the Ko is -0,3

Also, I build a cable to wire the "AC" output.
I try few plot with REW in my room to see how in work in this application (I usually use REW only line I/O to check and calibrate gears)

But the main new is that the mic seem to sound damn good 
I'll have to try it on some rec session 

Best
Zam

[Tubetec]

I have heard of people repurposing B&K sound level meters for recording with excellent results , omni pattern with very flat response. Calibration wont matter for recording purposes .
 

[zamproject]

I have heard of people repurposing B&K sound level meters for recording with excellent results , omni pattern with very flat response. Calibration wont matter for recording purposes .

Ok ! definitely try on the next recording...

I find another picture of the 4155 calibration chart with a Ko at -0.1 dB
This factor seem very low and mic manufacturing tolerance so tight
I think I can just ignore this, I don't need +/- 0.1 or .3 accuracy in my use case

Best
Zam

[Tubetec]

As luck would have it a model 2203 showed up for sale locally ,
It incorporates  what looks like a half inch capsule , cathode follower input stage , and I think germainium transistors in the output/meter driver circuitry ,
Its like an omni tube microphone and preamp combined into one ,all running off 3x1.5v cells .

Like you were saying it should also make a superb front end for acoustic measurements with REW , its within a fraction of a dB out to 40khz with the half inch capsule and the long term stability is astonishing .It should be possible to 'cal' things up to an extremely high degree of accuracy.

An interesting idea might be to add a usb audio interface into the 22xx series enclosure
another idea is bolt-on a hi-res Tascam or zoom recorder. 


 

[Tubetec]

Just finalising the sale now 

Thanks for flicking the switch on these units for us Zam.

Picture showing sub mini tube and capsule .





 

[zamproject]

An interesting idea might be to add a usb audio interface into the 22xx series enclosure
another idea is bolt-on a hi-res Tascam or zoom recorder.

Don't know for the model you just pick-up but mine have an line out called "AC".
Fortunately I have a miniplug coming with so I just wire a cable with a 6.35 at the other side, direct to my AD
The output is post pre and post EQ, with A and C curves, obvious for measures applications, but also two "flat" ones with 20Hz-20k cutout and a full allpass 10Hz-50k and for what I see at the curves in service manual, cutoff are given for -1 not -3dB 

Don't try to record music so far, but lot of play in my room with REW

But for sure next time I want omni recording I'll try it !!

Best
Zam

[Tubetec]

I found the documentation on the 2203 ,
the 'cal' pot basically allows the user to calibrate out the effects of the various supporting hardware that goes along with the measurement set , mic goose necks for instance add a specific capacitance which loads the response of the various capsules by a certain amount , each capsule has a given offset to begin with .

The model I got is older but externally identical to yours ,
and im sure spec is very much the same , its still light years beyond the spec of most microphones  even 60 years on . The freq.resp with the various different parts is also so well documented , predictable and consistant from specimen to specimen its easy to account for its effect on the overall performance , this is very good news for using it with REW .

A stereo set up is the obvious application , spaced omni's with a super high bandwidth/dynamic range recording format  , you just turn up at the cathedral or concert hall with a couple of mic stands and a hardcase 

[Tubetec]

In the end I got both the 2203 and 1 inch capsule for 25 euros 
according to the seller capsule is noisy but fingers crossed thats only moisture due to poor storage.
Its a later model ,so fet input stage as opposed to tube .

The proper B&K calibrator does come up for sale at reasonable price now and then , I'll be keeping an eye out for one as well as a second mic .

[Tubetec]

Unit arrived ,
pretty good condition ,  crack in the corner of the glass on the MC meter nothing to worry about , slight dent in the grill on the mic which I managed to tap out gently with a wooden drift and a plastic mallet , capsule membrane is intact.
Anyone whos ever used Bruel & Kjaer will know the quality ,engineering and design is first rate .
2203 was designated portable back in the day , its about the size of a brick and a similar weight .
Capsule is resting in a warm place for 24 hours before I attempt to power up the unit ,with the 1 inch capsule its good for upto 134db spl , surely good enough for almost any musical sound imaginable.
Might try get a sound out of it tomorrow , will report back .
 
 

[Tubetec]

Schematic for a Bruel & Kjaer 2203 (fet) spl meter wanted.
I did find one here but cant download it ,

https://www.radiomuseum.org/r/bruelkjae_praezisions_schallpegelm.html

Maybe someone here is already signed up and could get it for me .

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