Topic: pfa, plug-in power questions for different mics

[weroflu]

sorry, i'm sure this has been answered before, but i'm still unclear on some issues...

i'm unclear on some of the terminology used ever since i built these ke4 capsule mics.

from naiant site

<In standard configuration, the PFA supplies +9V across 5.6KΩ resistors to each microphone channel.>

-does this have anything to do with input impedance  or is it specific to the plug-in power circuit?
-do all battery boxes provide the same 5.6k load?
-on the ke4 datasheet it says that the capsule wants 5.6k at voltages between 2.5 and 5v, but at 9v it wants 18k,
so is the ke4 an exception?
-is the 5.6k resistor the same thing as a source resistor?

not sure what load the oscartech or 4060 mics want to see

so i'm gathering that there is no standard for plug-in power and loads. on average i'm guessing that 5.6k through 9v works well, but
this is possibly not optimal for every mic?

to optimize each of these mics then is it best to use a preamp designed specifically for them? or does the load not play too big a part in the sound. i know that for ribbon mics the loading makes a big difference in sound. when i emailed oscartech they recommended one particular mic based on the impedance of the pcm-m10, so i'm inclined to think that impedance does matter from mic to mic.


when people are running balanced high ouput outboard preamps, what is the best way to unbalance the signal to connect with consumer recorders without loss of quality? or is it best to mate balanced outboard pres with balanced recorders.

[Church-Audio]

sorry, i'm sure this has been answered before, but i'm still unclear on some issues...

i'm unclear on some of the terminology used ever since i built these ke4 capsule mics.

from naiant site

<In standard configuration, the PFA supplies +9V across 5.6KΩ resistors to each microphone channel.>

-does this have anything to do with input impedance  or is it specific to the plug-in power circuit?
-do all battery boxes provide the same 5.6k load?
-on the ke4 datasheet it says that the capsule wants 5.6k at voltages between 2.5 and 5v, but at 9v it wants 18k,
so is the ke4 an exception?
-is the 5.6k resistor the same thing as a source resistor?

not sure what load the oscartech or 4060 mics want to see

so i'm gathering that there is no standard for plug-in power and loads. on average i'm guessing that 5.6k through 9v works well, but
this is possibly not optimal for every mic?

to optimize each of these mics then is it best to use a preamp designed specifically for them? or does the load not play too big a part in the sound. i know that for ribbon mics the loading makes a big difference in sound. when i emailed oscartech they recommended one particular mic based on the impedance of the pcm-m10, so i'm inclined to think that impedance does matter from mic to mic.


when people are running balanced high ouput outboard preamps, what is the best way to unbalance the signal to connect with consumer recorders without loss of quality? or is it best to mate balanced outboard pres with balanced recorders.

Both mics will work well with my preamp. The performance of each mic will be fine with a 4.7k resistor for the plug in power supply.

Chris

[weroflu]

i noticed that your mics worked perfectly with the ugly preamp, that's what got me started on this line of thought. (only the second charitable act of my lifetime was giving them away to a destitute friend who is a talented songwriter)  i wish i still had the ugly preamp.

but i'm really interested in understanding a bit of the reasons why  -- like impedance matching. also i mentioned three mics and you said that 'both' mics work well with your preamp. i'm guessing you meant the oscar and the 4060.

[Church-Audio]

i noticed that your mics worked perfectly with the ugly preamp, that's what got me started on this line of thought. (only the second charitable act of my lifetime was giving them away to a destitute friend who is a talented songwriter)  i wish i still had the ugly preamp.

but i'm really interested in understanding a bit of the reasons why  -- like impedance matching. also i mentioned three mics and you said that 'both' mics work well with your preamp. i'm guessing you meant the oscar and the 4060.

Gross impedance matches can effect frequency response but generally speaking its not a huge issue. The way I set a resistor is simple I look at reducing distortion, first voltage second. I dont really care about voltage if the distortion is very low and the output is very high. With the ability I have to measure distortion both via computer and via my Keithley 2015 meter. I have the ability to test different resistors and voltages to get it right for most mics. Phantom powered mics are whole different ball game. But plug in power mics generally speaking all work with my preamp. I have to do some modifications to some mics to reduce distortion, but not to the preamp it self.

Chris

[Church-Audio]

Dynamic mics (like ribbons) are a mechanical system where the load is part of the damping of the system.  This is a larger effect in moving-coil mics than ribbons though, the ribbon loading effect is due to loss of level and also maybe the complex impedance of the output transformer.

In a condenser mic the mechanical system is isolated from the load by the capsule FET, which is essentially a resistive source (does not change output impedance at audio frequencies).  So it is usually just a function of gain and distortion.  As you increase supply voltage for a given supply resistance (technically the drain resistor, not the source resistor), you will increase headroom to a point, then it makes no difference until you go too high and toast the FET! (>20V typically).

Usually you design the other way around; you have a given supply voltage which indicates a maximum possible circuit gain given the current draw of the FET (which is typically a current source; that is, a fixed current).  If you use too high of a resistor value or too low of a supply voltage, then the capsule FET drops below its designed current and you start to lose headroom (distortion increases).

Different capsules have different current draws, which is why changing circuit values can optimize results.

Well said Jon!