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.

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

Does anyone know of source of low resistance 6?m aluminiumised Mylar? I'm not keen to go ripping apart electrolytic caps if I can get my hands on factory samples!

Fig-8.doc in my FILES directory describes a Fig-8 capsule I designed some 40+ yrs ago for Calrec.? It has sources for 5 & 10 um Aluminised Mylar and other useful info.

Excellent result -- well done! :)
I must confess I didn't think I was going to hear something quite that impressive, when I first downloaded your mp3....

If one could create a version with a capacitance of around 70 - 80pF, and with a low tension membrane, it would be fascinating to know how that would perform in an RF bias mic configuration.
(Some notes here for circuit ideas: )

The commercial RF mics from Sennheiser use a lower tensioned membrane ... feasible simply because there is only around 3 or 4 volts of? RF across the capsule, as opposed to the 60 or 70v DC in a conventional condenser configuration. Helps quite a lot with sensitivity, apparently?..
Low impedance as well --- makes worrying about screening a bit less important! :)
Just a thought...

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Excellent!!!! More microphone Instructables!

Full Instructable now available here:

Very interesting!

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On Sat, Apr 16, 2022 at 08:11 PM, <michaeljtbrooks@...> wrote:

So, single-side metalised 6?m Mylar is available in sheets of 100cm x 150cm, (folded into 10cm x ~7cm rectangles) for a few pounds each. If you don't mind edge-terminated I can't imagine a cheaper way to make condenser capsules!

where do you get this sheet?

I bet not all space blankets are the same and this thin.

I have small confession to make...

The space blanket I've been using is not 20?m thick as originally assumed. It is actually just 6?m thick! I got hold of a proper micrometer today and was able to measure it far more accurately.?

So, single-side metalised 6?m Mylar is available in sheets of 100cm x 150cm, (folded into 10cm x ~7cm rectangles) for a few pounds each. If you don't mind edge-terminated I can't imagine a cheaper way to make condenser capsules!

Brilliant!! That sounds much better than any of my home made capsules.

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I believe the only thing this circuit has in common with the subject discussed here is that they both are related to electronics.

Taking on board what has been said about the backplate mass, I've built another capsule with a double PCB backplate. I also played around with another shape: a bowed-in square.?

Thanks to having two PCB layers I was able to add some blind-ended attenuation holes too.

I did cock up the membrane a little bit - a couple of tiny spurs from the drilled holes are tenting the membrane a little. It is much better in the high frequency end, a bit lacking in the bass (I think due to the tenting), and lower signal output, but a lot less resonant. I've used the same 20?m space blanket as the diaphragm.

Here's the design, some photos and how it sounds.

Buggy whip with 56k modem, and tape backup..

I my very very humble opinion, I agree. ?Think “simpler” would have been better (again, my opinion). ?Maybe the inventor had some goals in mind that I wouldn’t have, don’t know. ?He also co-invented the “Sustainiac”, which I find to be a fun gadget.

Still think I might try it with a tiny 1.5v GOW/GOR bulb, under-driven by phantom (and buck converter or something?) modulated by a dynamic or piezo. ?Maybe make it a stand alone effect instead of “in mic effect”. ? Just a fun experiment..

I would have been very curious had I seen my dad’s Leslie speaker cabinet glow more with the reverb! ?(I LOVED the reverb, and everything else about it and the Hammonds he had - except having to move them for gigs!)

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The circuit itself pretty much already existed, as the "phantom power for Radio Shack PZM" design. Very much a stripped-down Shoeps, for electret capsules.? The "Alice" really started when we got access to the Transsounds capsules for the first time, though.? The definitive Alice is that basic circuit with a TSB-165A capsule.

Also I was listening to Tom Waits' album "Alice" quite a lot during that period. :)

-Scott

Here is the History: (And I am Sure Scott will correct me if I miss something)

Scott hand built mics with this name and a simplified circuit. He named it this because he took photos of it initially?for his ?and felt the initial?ones kinda looked like they were miniaturized and in "Wonderland". I actually added in the bias Pot and published it in my Modify a Cheap?Chinese?Mic Instructable. I coined the term "Pimped Alice". I added it to help bias the FET without hand selecting resistors. Homero designed?and laid out the PCB and was selling them on ebay. He deserves a huge amount of credit for that and the OPA Alice PCB's. Thank you Homero!? I kind of adopted?the name and asked Scott if he minded me naming?my Ambisonic DIY mic the "AmbiAlice"? and for the OPA circuit to be the "OPA-Alice"

Scott Helmke deserves credit for the initial?name. The community here helped it grow and become what it is.?

Jules

On Thu, Apr 14, 2022 at 7:02 AM Mic Scharf <micscharf@...> wrote:

I think the name Alice (in microphones) was created by Scott Helmke. If I remember correctly, it was based on 16mm capsule and a FET circuit.
Now I see "Alice" all over in the mic DIY communities.? Homero Leal calls his "Pimped Alice". Jules Ryckebusch calls his "OPA based Alice".

What defines a microphone an Alice?

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Best Regards,

Jules Ryckebusch

214 399 0931

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for everything is holy"  - Joe Henry

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