Hi all!

After a lot of reading, I see for short cables (less than 2 meters) the Simple P48 circuit is enough for a good quality build.

My question here is: I see a lot of people talk about taking care of polarity on the Electrolytic Aluminum Capacitor, and I was thinking about using a Bipolar like this:

or this one:


Does it make any difference? As far I know using a Bipolar Capacitor you don't have to pay attention to this and I don't know if using a Bipolar Capacitor will produce the same good results as a normal Capacitor

I've used both polar and bipolar in the signal lines in microphones. It doesn't make much difference so long as the capacitor value is sufficiently high to pass the low frequencies.

A bipolar electrolytic capacitor is simply the same as two polar electrolytic capacitors back-to-back (with their negative leads tied together or positive leads tied together). If you do put two in series like this, remember that their total capacitance will be half of each capacitor's value.

The Nichicon bipolar caps are excellent. Just make sure they are rated for at least 50V DC if using on Phantom Power (your one here is 35V). I tend to overspec the capacitor capacity so I don't lose low frequencies should whatever I'm sending the mic signal to have feeble input impedance, so I'd typically go for 10?F or above. Capacitor tolerances are often +/- 20% so at 4.7?F you could be as low as 3.7?F in reality, which could start blocking low frequencies if you connect it to a shoddy mixer with a low input impedance.

You would only actually need a bipolar if you're thinking of having switchable power (internal battery vs phantom). Otherwise a polar electrolytic with positive to the XLR side is fine.

Thanks for the explanation Michael,

the point about tolerance is really good. My plan is to connect that Mic's via XLR to a new Zoom F3, but better for a capacitor rated for at least 50V like this one:

https://www.mouser.es/ProductDetail/Nichicon/UKW1H4R7MDD1TA?qs=WJSLByB5Mu28FaeGBvn6BQ%3D%3D

About low frecuencies:
Reading this: ?he says?

?The capacitor can be 1uF to 4.7uF without noticeable change in sound. I am using 3.3uF

What do you think about this?

Cheers

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The other issue is size of the capacitor. ?I’m the 3.3uF 63V guy. ?They work great and physically allow you to build the SimpleP48 into the XLR connector. ?I use this with my ZoomF6. ?

We are probably worrying about nothing TBH. Jules @ Sound Sleuth designs excellent circuits, if he says it's good, it'll likely be good.

I can only see a problem if you're intending on capturing low frequencies (e.g. 30Hz) and feeding it into a mixer with low input impedance on its mic channel (e.g. <1000 ohms). If your mixer / sound card mic input is decent it'll have >1500 Ohm on its input and so you won't see a problem.

An aluminum electrolytic capacitor consists of two Al foil electrodes separated by a conductive electrolyte. Al forms an oxide coating on the surface on contact with air or water, and the oxide coating is the dielectric of the capacitor. So an Al electrolytic consists of two caps in series, one at the anode and one at the cathode. The anode is formed with the thicker oxide, is high voltage and lesser capacitance. The cathode is low voltage, a volt or two, and very high capacitance. The over all result is two caps in series, of which the anode primarily determines the voltage and capacity. It turns out the cathode contributes most of the tiny distortion to any signal passing through.

This is where it gets interesting. Bipolar electrolytics are NOT made as two polar caps in series. Bipolar caps have two anodes and no cathodes. Bipolar caps exhibit much less distortion than polar caps in audio coupling circuits. So to answer the OP question, bipolar caps are fine. They are actually preferred if they can be had in the desired voltage and capacity. They exhibit more than an order of magnitude less distortion. They are physically larger, because the two anodes in series have to be larger to reach the same capacity, but otherwise they are better, even in circuits where the polarity applied never changes.

Let me add that capacitor distortion is likely to be the least contributor to the sound of a mic, but still . . .

Understood. That last explanation about Bipolar was really refreshing from the old days, thanks!

Why people don't use? 10uf? 63V, or even 10uf 100V?

Is it only for the space it takes physically inside the XLR connector or there is something related that can affect the frequency response??

Cheers

Unless there is a need for a high pass filter, using a larger coupling cap won't hurt. Something that's often forgotten is the series reactance of a cap is a noise source, just like a series resistance. So if your coupling cap is 3dB down at 50Hz working into , say, 1K ohm, it has a noise contribution at 50HZ same as a 1K resistor. Even at 500Hz, it contributes as much noise as a 100 ohm resistor. In a mic, there is a tradeoff between noise and the need to high pass filter thumps and plosives.

The noise audibility is reduced by the Fletcher-Munson effect, but it's still there on spectral plots of many mics. I use larger caps than most engineers, because I think I can hear that LF noise.

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Unless there is a need for a high pass filter, using a larger coupling cap won't hurt.

Yes.

Something that's often forgotten is the series reactance of a cap is a noise source, just like a series resistance.

Only resistances are a source of brownian noise. Reactances are not.

So if your coupling cap is 3dB down at 50Hz working into , say, 1K ohm, it has a noise contribution at 50HZ same as a 1K resistor.

This is where it takes some discussion.
I take it as a 3.2uF capacitor, that has a reactance of 1Kohm at 50Hz. Its brownian noise contribution is zero.

But the noise current of the active device (FET, BJT, vacuum tube...) developped across the capacitor will contribute to noise as much as a 1k resistor at 50Hz, as much as a 10k resistor at 5Hz, as much as a 100R resistor at 500Hz.

Even at 500Hz, it contributes as much noise as a 100 ohm resistor.

That's partly correct. the contribution of real resistor is brownian noise + In.Z

The contribution of a reactance is only In.Z. In addition it is phase-shifted by 90°, so it combines quadratically, not algebraically. If it is small (<1/10th), it is negligible.

In a mic, there is a tradeoff between noise and the need to high pass filter thumps and plosives.

Yes.

The noise audibility is reduced by the Fletcher-Munson effect, but it's still there on spectral plots of many mics.

Not only the physiological hearing but mainly the spectral distribution will make it less perceptible. White noise has less energy at LF than HF.

I use larger caps than most engineers, because I think I can hear that LF noise.

I won't debate over teh internet what anybody hears or not. ?