Capsule swapping

[dgatwood]

I have this bizarre urge to rip a mic apart and hack in a new capsule, say a Peluso CEK-89. Does the capsule in most phantom powered mics typically run at 48v? Is there any trick to doing such a substitution, or is it largely just a matter of swapping the wires (assuming the original capsule isn't running at too high a voltage, of course)?

The mod I'm considering doing is installing it into the case and guts of an AT2020, just to be able to say that I owned a microphone that no one else in the world owned (or would ever assemble in their right minds). It seems like a perfectly reasonable body, and the electronics seem pretty clean, so.... (That, and it's the mic that I'd be the least sad about losing if I screw something up, since it was a freebie in a package deal.)

Thoughts?

 

[crazydoc]

I switched out the capsules of an Oktava MK219 with MXL990. The 219 capsule in the 990 housing/electronics sounds pretty nice. I've meant to take off the HF boost discs, but due to lots of life changes have never got around to it. All my stuff is in a storage shed in Reno now, but hopefully I'll be able to break it out later this year.

Check out this thread and the links there - lots of interesting info.
https://homerecording.com/bbs/showthread.php?t=143092

 

[PhilGood]

The AT2020 uses an electret, or 'fixed charged' capsule, meaning the capsule itself is permanently charged. The peluso wouldn't work. You'd have to replace it with another electret element.

 

[northsiderap]

Capsule Swap

The Peluso might work, but you have to make sure there is a polarization voltage on one half of the Peluso capsule. Usually 40-70 Volts.

You also want to make sure there's a roughly .01 capacitor between the capsule and the gate of the FET or tube.

The polarizing resistor matters too.

Each capsule has its own capacitance, and the polarizing resistor (usually @ 680meg to 1 gig) forms a 'RC Filter' with the capsule to determine your low end cutoff frequency. You probablly therefore want to test your capsule capacitance and determine the size of the resistor to use for a low end cutoff of @ 25 Hz.

 

[PhilGood]

The Peluso might work, but you have to make sure there is a polarization voltage on one half of the Peluso capsule. Usually 40-70 Volts.

You also want to make sure there's a roughly .01 capacitor between the capsule and the gate of the FET or tube.

The polarizing resistor matters too.

Each capsule has its own capacitance, and the polarizing resistor (usually @ 680meg to 1 gig) forms a 'RC Filter' with the capsule to determine your low end cutoff frequency. You probablly therefore want to test your capsule capacitance and determine the size of the resistor to use for a low end cutoff of @ 25 Hz.

That's pretty advanced for someone wanting to do their first mod.

 

[kidvybes]

The Peluso might work, but you have to make sure there is a polarization voltage on one half of the Peluso capsule. Usually 40-70 Volts.

You also want to make sure there's a roughly .01 capacitor between the capsule and the gate of the FET or tube.

The polarizing resistor matters too.

Each capsule has its own capacitance, and the polarizing resistor (usually @ 680meg to 1 gig) forms a 'RC Filter' with the capsule to determine your low end cutoff frequency. You probablly therefore want to test your capsule capacitance and determine the size of the resistor to use for a low end cutoff of @ 25 Hz.

...I knew that ...

 

[dgatwood]

The Peluso might work, but you have to make sure there is a polarization voltage on one half of the Peluso capsule. Usually 40-70 Volts.

You also want to make sure there's a roughly .01 capacitor between the capsule and the gate of the FET or tube.

A DC block to keep the V+ out of the FET, I assume? I'd imagine there would have to be one no matter what capsule it uses, wouldn't there? Or am I missing something?

The polarizing resistor matters too.

Each capsule has its own capacitance, and the polarizing resistor (usually @ 680meg to 1 gig) forms a 'RC Filter' with the capsule to determine your low end cutoff frequency. You probablly therefore want to test your capsule capacitance and determine the size of the resistor to use for a low end cutoff of @ 25 Hz.

I get the impression the board on this thing is all surface mount, so raising the resistance to ground might be problematic if needed, though I could easily lower it if needed by adding a resistor to ground right off the back of the capsule in parallel....

 

[northsiderap]

Stuff

A DC block to keep the V+ out of the FET, I assume? I'd imagine there would have to be one no matter what capsule it uses, wouldn't there? Or am I missing something?

There isn't ALWAYS a capacitor between the capsule and the FET. I've seen designs where the backplate is polarized and the front plate goes directly to the FET gate terminal.

I get the impression the board on this thing is all surface mount, so raising the resistance to ground might be problematic if needed, though I could easily lower it if needed by adding a resistor to ground right off the back of the capsule in parallel....

Or, find the appropriate biasing resistor... Then cut the path between the resistor and the capsule. Solder the new resistor in to rejoin the bias supply and the capsule. You are leaving the old resistor in, but it 'dead ends.'

 

[Marik]

Each capsule has its own capacitance, and the polarizing resistor (usually @ 680meg to 1 gig) forms a 'RC Filter' with the capsule to determine your low end cutoff frequency. You probablly therefore want to test your capsule capacitance and determine the size of the resistor to use for a low end cutoff of @ 25 Hz.

Most of the capsules capacitance is between 5 to 60 pf, sometimes up to 100pf. The 1gig resistor (which is a standard nowdays) will work just fine with any of those. Another reason for the resistor value that high (in fact, 2 gig would not hurt, either) is a lower noise.

 

[PhilGood]

Most of the capsules capacitance is between 5 to 60 pf, sometimes up to 100pf. The 1gig resistor (which is a standard nowdays) will work just fine with any of those. Another reason for the resistor value that high (in fact, 2 gig would not hurt, either) is a lower noise.

Mark,

WHERE THE HELL HAVE YOU BEEN????

 

[PhilGood]

I think we're missing the point that since it's an electret capsule, and he wants to install it in an AT2020 with the stock circuit board, will the board supply any voltage to the capsule, much less be able to bias it correctly?

Will it?

I'm open to the education.

 

[Marik]

Mark,

WHERE THE HELL HAVE YOU BEEN????

Oh, I thought nobody would even notice my absense.

Had lots of recording gigs and have to make 7 commercial CD (I do editing and mastering myself, as well)

 

[northsiderap]

At2020

I don't know offhand if the AT2020 is electret or not.

For any mic dissection newbs out there...

Find the capsule leads. If there is a resistor between the capsule and a capacitor then it is a 'true' polarized condenser capsule.

If the lead goes straight to a capacitor with no polarizing resistor, it is most likely an electret.

All you need to know: Electret CAPSULES do not need polarizing voltage & 'true' condenser mics do.

Do not confuse the Behringer C2 mics with 'true' condenser mics. It's something that Behringer is using in their literature to describe the electret C2 microphones.

 

[PhilGood]

Audio Technica specifically states: AT2020


ELEMENT Fixed-charge back plate, permanently polarized condenser
POLAR PATTERN Cardioid
FREQUENCY RESPONSE 20-20,000 Hz
OPEN CIRCUIT SENSITIVITY –37 dB (14.1 mV) re 1V at 1 Pa
IMPEDANCE 100 ohms
MAXIMUM INPUT SOUND LEVEL 144 dB SPL, 1 kHz at 1% T.H.D.
NOISE 20 dB SPL
DYNAMIC RANGE (typical) 124 dB, 1 kHz at Max SPL
SIGNAL-TO-NOISE RATIO 74 dB, 1 kHz at 1 Pa
PHANTOM POWER REQUIREMENTS 48V DC, 2 mA typical
WEIGHT 12.1 oz (345 g)
DIMENSIONS 6.38" (162.0 mm) long,
2.05" (52.0 mm) maximum body diameter
OUTPUT CONNECTOR Integral 3-pin XLRM-type
ACCESSORIES FURNISHED Stand mount for 5/8"-27 threaded stands; 5/8"-27 to 3/8"-16 threaded adapter; soft protective pouch
AUDIO-TECHNICA CASE STYLE R7


Hey, if you get it to work, let me know! I'm always willing to fight the good fight, & mod the good mod!