ADK ST mic MOD?

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mica

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Apr 20, 2010
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134
Location
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I just got one of these throw at me: http://www.adkmic.com/specs/ST.html

I was wondering if there's a mod for it? I got a C12 style capsule lying around that i could put in, but if anyone experienced has some ideas i would very much appreciate it. Never done a mod before, only full kit builds..

 

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How does it sound already? ADK have a decent reputation, it depends what you want to achieve. But there's always a mod!

Looks like a standard Fet followed by a transistor stage driving a low-turns ratio transformer.

Most obvious place to start would be caps in the signal path. Look for a small cap after the capsule, maybe just after the pattern switch - probably 1000pF. It may be on the switch pcb, or on the back of the main board. Upgrade it to a polystyrene or a decent film type if it's not already.

That orange tantalum C4 is another candidate assuming it connects to the emitter. It's probably around 4.7uF. It'll be hard to find a film cap small enough to fit(!), but you could try a decent (eg Nichicon) audio grade non-polar type. Increase its value if you want, anything higher will be fine.

Those are the best bang for your buck.

And swap the capsule if you like - see how it sounds. Experiment...
 
Thanks! I was just wondering if the insides was similar to the MXL ones that some people mod in one way or the other.. I will try switching capsule for sure.. just for fun! The mic sounds decent enough, but the project here was to do some sort of mod, just to try it out..Don't know if that makes sense... :eek:  Im not skilled enough to invent my own mod, sadly..
 
The basic circuit: capsule -> fet -> bjt -> low ratio transformer, is similar to various MXL designs (2001, V67 etc) and many others that are basically rebadged versions probably made in the same factory. Yours has a dc converter and a polar pattern switch which complicates the circuit a bit, but the main circuit is essentially the same.

Basic mod would be to do what I said, basically improve what's there.

There's a more advanced mod originally done for the MXL 2001 which reconfigures the output to look more like a U87 (just search for the mod). This replaces the output transistor and the transformer which starts to get expensive because you need a decent transformer eg Cinemag 2480. The overall tone of this type of mic is basically determined by the capsule and the transformer. And if you're going to replace both of those then it may be better to just replace the entire thing. That's why the best mod for these is often just to upgrade the obvious signal path components - basically the caps I mentioned.

Hope that helps.

Edit: There's also a mod that some people do on the V67 that involves adding a 510k resistor to the transistor base. You'd need to trace your circuit to see if it applied to your design.
 
It seems this is a very common (Chinese?) circuit.
The capsules were not too bad in the ones I had here.
Personally I have modified a couple of those microphones.
You could increase the value of the capacitor between the FET and the transistor to get a better LF response.
Also I have changed the transistors, because they were rather noisy.
And while you are doing that, it might be a good idea to check the bias of those transistors too, it is just a matter of changing one resistor...
 
You are problably right about doing a complete makeover to a U87 would be easier :) I've done two of the U87's from poctop, and the body seems to fit ok. I really like the headbasket on this one though. Very U47ish :-D

NB!
Maybe its a stupid question but here goes: I have a brand new extra C12 style capsule, could i use that in a poctop U87 mic build?
 
I have a brand new extra C12 style capsule, could i use that in a poctop U87 mic build?

The C12-style capsule is made for a flat circuit.
The U87 has a de-emphasis circuit, so it needs a capsule with a deliberate and ample treble rise (pre-emphasis), starting before the air region.
Of course, one could mod to make it work, sort of, but that would seem like missing the point of the design.
 
Micaddict's right, but it's something that I've been wondering about too. There's something very 'pure' about the original U87 design that I really like - in essence it's just capsule -> FET -> transformer (plus some feedback elements).

If you've built a poctop U87 already then try the C12 capsule and see what it sounds like - you can only connect the front diaphragm and the backplate to FD and FBK, so it will be cardioid only. It'll probably sound much better with C6 removed.

I suspect there are better things you could do with a C12 style capsule (like a Schoeps or a tube build/mod).
 
I have posted a set of adjustments for MXLV67 2001 etc microphones N channel JFET and PNP keeping most of the stock parts

I have not traced the ADK microphones
I do like that it looks to have a +- capsule voltage 2nd DC to DC converter board
What don't you like about the microphone?

 

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