B&K 2230 (SPL meter) calibration.

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zamproject

Well-known member
Joined
May 11, 2010
Messages
1,502
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
 
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
 
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 .
 
Tubetec said:
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
 
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. 


 
Just finalising the sale now  ;)

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

Picture showing sub mini tube and capsule .





 

 

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Tubetec said:
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  :eek:

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
 
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  8)




 
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 .





 
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 .


 
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 .


 
I just managed to find a second 2203 without accessories ,
its on route as we speak ,
sold as 'Defekt' , as it doesnt calibrate to spec according to seller .
I posted the Service manual in documents section for anyone whos interested .
I contains the full schematic , below is just the mic head amp ,first stage and psu
The capsule that came with the original unit I purchased is noisey , so Im on the hunt for a pair of new 1 inch capsules and a few other odds and ends to complete the set .

Im looking forward to trying the units with the Cosmos ADC , the pre filter output on the B&K looks like it will match reasonably well with the Cosmos as its designed to work with< 600 ohm load . The ADC could be mounted on the baseplate/battery cover of the meter ,meaning the entire signal path is measured in inches rather than yards . Of course you still have the meters AC output to use as a monitor send if required ,although thats limited to 10k minimum load.

The powersupply from 3x1.5volt D cells is quite an acomplishment , It manages not only to supply the 1khz reference tone but also -9 v , +/-20 , 48 and 200 volt rails. Head amp(48 and 200) and first stage (-9v)are discrete transistors all the way , final output and meter drive are op amp based dual rail.

Im not sure how the noise of the 2N3457 and modern Fets compare , I'll bet B&K have cut close to the theroretical limits in any case .

I might be able to blag my way into the cathederal when they have a recital on the pipe organ for proof of concept later . But I'm also a big fan of pairs of omni mics closer in recording smaller folk or trad instruments and vocals especially given favourable acoustics.

I'm thinking of getting a pair of Cosmos ADC's from Ivan and equip each B&K unit with one , allowing a total of four inputs, although that may pose clocking issues for recording that need to be ironed out .
 

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I own two of these, both the valve front-end version. One arrived in great condition, in a nice case with a bunch of accessories. The other one looked like it had been stored in a shed in the tropics for years, had leaking batteries and a noisy capsule, yet to get it going. If anyone has any tips on fixing these types of capsules when they're noisy I'm interested. (or are they a write-off?)

The working one has astounding dynamic detail on transient sources like drums and acoustic guitar. I had it about 1m in front of a drum kit at chair height (literally sitting on a chair) in a quick test and it picked up everything beautifully. Combined with dynamic close mics it added a level of detail and 'air' that I'd never heard before on a kit, without sounding at all thin or harsh on cymbals. As an acoustic guitar room mic it was similar, jaw-dropping levels of detail without sounding clinical. I'm keen to get the other one going to try stereo pairing.

Be aware that the outputs have some DC on them, so a blocking capacitor is required. The one that is designed to go out to the filter module is after the first gain stage and I find it has plenty of gain available and is much quieter than going through an attenuator and into another gain stage. They fit standard DC barrel plugs (can't remember the exact size but I think it's the standard 'Boss guitar pedal' one) so you don't need to source the proprietary B&K plugs.

I'm pondering building a quiet external DC supply so I don't have to mess about with big batteries and maybe putting a balanced output buffer into the battery compartment so it can drive a standard line out.
 
I have one with a noisey capsule also , I dont think theres much hope of repair . Still waiting on the second unit to arrive . Lots of ebay sellers seem to break up the the measurement sets and sell the individual parts , often they havent even the brain to realise the mic is worth less when seperated from its associated spec sheet . From what I gather theres three main versions of the 2203 the one with the valve was first , then one using mostly germainium ,then the one with the op amps . One of mine is in the region of 480000 serial number , the one in the post is around 270000 , I think the model with the valve only went as far as 175000 . There is a couple of the earlier schematics available @radiomuseum but his sign up isnt worth wasting your time on . B&K themselves might send you the service manual if you get in contact .
 
I stripped the faulty one down for a look inside, assess the condition of caps etc.. the 3D engineering is astounding, difficult enought to make everything fit these days with 3D modelling!
 

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Wow quite a job to fit all the components in the discrete version , the later one with the op amps saves a lot of complexity . The fact that the model 2203 was produced for more than 25 years stands as testament to the supreme engineering of the B&K guys , top notch stuff indeed.
 
Item arrived , typical German diligence regarding packaging for safe transit ,there are good people left on this god forsaken planet after all .

I have to admit I'm a little jellous you have a pair of the valve/germanium/inductor based units Noon's , I suspect in terms of cold hard measurements theres little or no difference but the older model has better mojo and I suspect it when you hit above 120db spl it distorts a little nicer .

I've still a bit of a 'guzz eye' on me after last nights festivities , a little early to start messing with high voltage rock and roll yet so I'll leave the tear down of the new unit till later

Back in the old days at a studio I used work we used a pair of B&K's pointed at the lid of the grand piano , seperated by a baffle , close on 30 years later it still resounds on national radio

Heres a taste of it , to go with the morning coffee , easy listening might not be the correct term , thought provoking kind of sound maybe , and the ornamentation might not suit everyones taste . Not sure if I was credited for my small part as chief tea maker , runner/assistant to the engineer or not , I must check the sleeve notes . The caliber of the musicianship on the sessions was awe inspiring, more like a religious experience .

 
They're basically buffer, attenuator, gain stage, attenuator, gain stage so not that difficult to overdrive the gain stages. Unfortunately it's pretty nasty when it breaks up and it does it quickly rather than gradually, best left in the clean zone. I like to imagine there's some nice mojo in the valves and germaniums but realistically it's probably too well engineered for that. :)
 
Try setting yourself up with a really long headphone cable and having one of these on a really sensitive setting. You can hear your own thoughts from across the room!
 

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