Bluebird mod

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shiftreturn

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Joined
Dec 31, 2015
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5
first thread here. I'm mostly a musician that likes to tweak a little with my gear if I can make them better.  I can solder and understand the basics of electronics but I'm far from knowing more than just a little. Well, I picked up some useful info from this thread: http://groupdiy.com/index.php?topic=52306.0 and did some slight mods to my mic. I'd already turned the capsule 180 degrees which made the mic better. I did take the mesh out but it worsened the interference to the capsule so I put it back (it picked up a clear AC hum from somewhere when I did the mod). So my mod.. I put in 470n Wima mks2-5 for c1 and c3 which audible lowered the low freq filtering, which I liked. I put in some slightly higher values for the C8 and C9, some ceramic 3,3n caps (code 332) which I don't know the name of. All in all, the sound actually got even brighter and now I'm a bit confused. Should I just put the original components back and forget about it or should I use other brands for the components? I wan't this mic to be less sibilant, darker, not so pronounced proximity effect in the HF but in general I like it in the frequencies from mid to below. The capsule itself could of course be swapped but I rather forget about the whole mic and go on with other mics. Happy new years!!
 
Khron said:
To tame the brightness, and since the circuit is basically a Schoeps-type one, you could give something like this a shot:

http://audioimprov.com/AudioImprov/...quote] looks interesting, I'll check it out.
 
Khron said:
To tame the brightness, and since the circuit is basically a Schoeps-type one, you could give something like this a shot:

http://audioimprov.com/AudioImprov/...ound 7 years old, the capsule is a bit dirty.
 
Don't you have any film caps of anything between 1nF and 10nF, to replace those ceramic ones with? I've seen those adding some audible noise in an sE X1, which went away after removing / replacing them.

Those 470nF caps really shouldn't affect the midrange or high-hend.

To help clear things up, you could hand-draw the schematic "in blank", and slowly add in the component designators from your mic.  I'm thinking it should be simple enough (although i've got a few extra years of reverse-engineering behind me :) ).
 
Khron said:
Don't you have any film caps of anything between 1nF and 10nF, to replace those ceramic ones with? I've seen those adding some audible noise in an sE X1, which went away after removing / replacing them.

Those 470nF caps really shouldn't affect the midrange or high-hend.

To help clear things up, you could hand-draw the schematic "in blank", and slowly add in the component designators from your mic.  I'm thinking it should be simple enough (although i've got a few extra years of reverse-engineering behind me :) ).

Let's see if I give myself time to really dig into it and draw. Might probably not be worth it. I really have to think and spend time :) Regarding the ceramics/filmcaps, perhaps you're right, but I read somewhere that there's a reason for the ceramics being there in the first place and that the film caps would be worse handling high frequencies (of which I don't know what I'm talking about :) anyway, I'd be happy to try. Ok good to know about the Wimas then. I'll be back :)
 
To tame the brightness, and since the circuit is basically a Schoeps-type one, you could give something like this a shot:

http://audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html

Should be simple enough to implement, adjust it until it sounds the way you like, and then replace it with a fixed resistor of roughly the same value :)

Be aware of the fact that the addition of the 10 K resistors between the FET and the output transistors will increase the self noise of the microphone!
 
I tried such a modification before, but I could measure a significant decrease in  signal to noise ratio when the value of the resistors between the FET and the output transistors became higher than 1 K.
But of course it is up to the modifier if this is acceptable!  :D
 
I'm reasonably sure that both those series resistors, as well as the RC can be scaled up or down in value, depending on the compromise you're after. LTspice should easily and nicely indicate the expected response :)
 
Khron said:
I'm reasonably sure that both those series resistors, as well as the RC can be scaled up or down in value, depending on the compromise you're after. LTspice should easily and nicely indicate the expected response :)

Haven't checked the thread for some days. Great info. For me to test this, I'd need to find out the placement of the transistor, looks like there are 4 of them. Should I take a picture perhaps. Did some tests with Silver Mica and mkpWima for the last stage before XLR. They both sounded more or less equal. I think I like the original EQ at this stage, but those Silver Mica and films caps sounded better than the ceramics that I put there at the last mod (at least in my imagination). I think the problem might just be a bad match with my voice and the mic in general. The esses are not nice. They distort too much. Or it's just a lousy capsule (which is an easy asumption)..
 
Like i said, i've seen (or rather heard) ceramics from XLR2/3 to ground cause noticeable noise, so... yeah, i've become quite anti-ceramic anywhere near the signal path :D

And, well, there's only so far a chinese K67 capsule can go, especially with a non-compensating circuit...
 
Khron said:
To tame the brightness, and since the circuit is basically a Schoeps-type one, you could give something like this a shot:

http://audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html

Should be simple enough to implement, adjust it until it sounds the way you like, and then replace it with a fixed resistor of roughly the same value :)

The photo of the Studio Projects C1 mod from microphone parts looks like it is the mod described in the link above. Can anyone confirm?

http://microphone-parts.com/products/c1-c3-mic-mod-service

 
There's a reasonably good possiblity, now that you mention it.

Most likely the "fatties" are the series coupling caps, the red Wimas the "low-pass" ones, series resistor... Although i'm not sure i can spot the cap that's part of the EQ-ing itself - or maybe the Wimas are it, in series or parallel? Hmm...

Either way, 190$ (minus return shipping) for 4 caps, 2 resistors a crappy little trimmer, cutting 2 traces and soldering 4 wires? Not bad... :D

(Edit: removed some nonsense :) )
 
Hmmm, google found me some pics of an older version of the mod. It was exactly like the schematic on that site, using 0.15uf caps in series and 1000pF Wima with 100K trimmer between the transistor bases.  There is no trace cutting involved, you just remove the old series caps and wire all the new stuff in their place.  I'm going to try this with some 0.22uF  Soviet PIO caps I have here, as soon as I figure out a way to mount everything inside.  This C1 is just too bright for my tastes...
 
Oh, then 190$ for those parts and even less work than i thought - an even "better" deal! :D
 

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