[ACM investiupgradifications] All things MICROPHONE

If ther diaphragm is getting sucked then either buy a new capsule (or spare from someone who swaps theirs), or you could try lowering the B+ voltage in the supply by swapping the zener diodes.

rodabod said:

If ther diaphragm is getting sucked then either buy a new capsule (or spare from someone who swaps theirs), or you could try lowering the B+ voltage in the supply by swapping the zener diodes.

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Would that be D5 and D6 in the power supply?Any values to try to start?

Search, Google zener diode and zener diode regulator and powers supplies and things like that.  Then take some voltage and current measurements(voltage drops across known resistor values, Ohms law) in the power supply and see if you need to adjust a resistor value in the B+ RCs so not to exceed the wattage rating of the zener.

hint: do the zener part math at no load(highest current/power in the zener) and with the microphone load.

Ohms law and DC power math, sum up the ma in the microphone on the B+.  Capsule divider current and plate current and also PS pattern control current.

Crash
If you are using it with voice are you using a pop filter?  It could be dust on the capsule leaking the charge with moisture from breath if you are not using a pop screen if it is a 67/87 type capsule.

Marik, which clip is which? I'm assuming ribbon1 is the modded one...

I should add to my original post, lowering the B+ is generally a good idea (as is removing the diode which lifts the heater voltage by 0.7V). The B+ might sit nicely at 160V rather than what it is at just now which might be ~200V. Measure it.

The B+ is also the valve's supply, so it might be worth considering adjusting the polarisation voltage alone. That isn't quite so simple; you'd need to adjust the 270K/270K voltage divider which feeds the backplate, and also the vari-volatge feed which comes from the power supply similarly.

I would check for dust/dirt around the edges as Gus suggests as you may be experiencing leakage rather then sucking.

Gus said:

Crash
If you are using it with voice are you using a pop filter?  It could be dust on the capsule leaking the charge with moisture from breath if you are not using a pop screen if it is a 67/87 type capsule.

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I am using my voice and no, I am not using a pop filter. I have no idea what this capsule is... whatever comes in a  1200, it is the stock baby in there. So, are you saying that the way I am testing may be causing this and it is normal? Thanks guys, for helping me out. How does one remove dust from the capsule???

Try breathing heavily on the mic without blowing hard (to cause condensation) and see if this cause the same effect.

Or just use a pop filter and see if it stops happening!

rodabod said:

Try breathing heavily on the mic without blowing hard (to cause condensation) and see if this cause the same effect.

Or just use a pop filter and see if it stops happening!

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Yep, that causes it to die.... I have the factory issued black bulbous foamy and it improves greatly with that in place. I have to get all up on it for it to finally cut out. I would guess this means a dust issue?

Crash said:

I have to get all up on it for it to finally cut out. I would guess this means a dust issue?

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That's natural for condensers, but gets worse with dust/dirt. Sucking onto the backplate is not, but that doesn't sound like your issue.

rodabod said:

Crash said:

I have to get all up on it for it to finally cut out. I would guess this means a dust issue?

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That's natural for condensers, but gets worse with dust/dirt. Sucking onto the backplate is not, but that doesn't sound like your issue.

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Well, don't I feel like a jackass..... How does one remove dust if/when it becomes an issue?

Crash, does it affect both sides equally?

Inspect by eye for dust around the edges. If it's an issue, then search here for guidance about using a small soft brush to remove particles. Josephson gave a good introductory guide.

I'd still also try it with a good pop filter though...

rodabod said:

Crash, does it affect both sides equally?

Inspect by eye for dust around the edges. If it's an issue, then search here for guidance about using a small soft brush to remove particles. Josephson gave a good introductory guide.

I'd still also try it with a good pop filter though...

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I stumbled across the Josephson article...just in case. Interestingly, one side seems to react to moisture more than the other. What does that tell ya???

I guess I find the dust issue sort of hard to buy into, since the mic is new. But then again, it is from China and with my luck on things Chinese.

I have microphones that had the same problem out of the box.  I open the china tube microphones before I power them up to check the PCBs and I often remove the grill and check the capsule for dirt and other problems before the first power up.

Google K67 and K87 and CK12 look at the pictures.  The neumann 87/67 type have a insulating no gold deposited area at the edge.  That area is were dust and moisture can make a leakage path and discharge the charge on the capsule.  Often using a dry artist brush and light touch you can remove the dirt/dust there.

Gus said:

I have microphones that had the same problem out of the box.  I open the china tube microphones before I power them up to check the PCBs and I often remove the grill and check the capsule for dirt and other problems before the first power up.

Google K67 and K87 and CK12 look at the pictures.  The neumann 87/67 type have a insulating no gold deposited area at the edge.  That area is were dust and moisture can make a leakage path and discharge the charge on the capsule.  Often using a dry artist brush and light touch you can remove the dirt/dust there.

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In would say it is the K87 type by pics I saw by doing a Google search. The one on the right in the pic looks just like it. It is out of an Apex 460 I believe.

http://www.morphproductions.com/apexmod/IMG_6766.jpg

One thing I noticed while I had the grill and body off is that there is very small reverse dimple on the gold part of the capsule not to far from where the center wire is on the front side. That may or may not mean anything but thought worth mentioning. I also see what looks like really tiny hairs all over this thing. I love China!!! I'll try the brush technique when I get a chance.

Thanks for all the help and suggestions fella's.

Anyone know the pinout (7 pin connector) of the ACM-1200? I don't believe it is the same as the G7 at all.
I don't have it in front of me but wanted to figure out the pins for later.

Thanks in advance!

-Chuck

Search Apex 460

Matti

OK fine you made me go search the internets

Here it is

1. B+
2. Heater
3. Pattern Vari V+
4. GND
5. Out +
6. Out -
7. GND tied to pin 4

With this map you can change the G7 to use the off the shelf power supplies.

-Chuck

Ptownkid said:

Marik, which clip is which? I'm assuming ribbon1 is the modded one...

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Yes 

Ok I dropped in my own AKG C24 pcb design (see page 2 of this thread). Used wima caps MK4s and a Cinemag 2480 / 6072A combo.
I have not put in the CEK-12 yet as I wanted to test with the original capsule first. Also I removed the two inner meshes.

Here are the voltages.



I was thinking 84VDC was a little high?
Right now the mic sounds very bright and clean.
I am going to go ahead and put in the CEK-12 now.


Opinions?


-Chuck

 

Looks good to me Chuck. I agree about the high B+ though; that's going to skew your patterns a little if the variable voltage maxes at 58V. Are you sure it is leaving at 58V? I thought he Chinese supply derived the variable voltage using a divider from the B+ directly.

The stock capsule will sound bright with that circuit. The CEK12 will also be bright, but probably in a more pleasant way.