Topic: Phantom power adapters for electret mics (AT853a)

[lukpac]

I have a pair of AT853as that are currently terminated with a single 1/8" plug to run off of plug-in power. I'd like to start using these with phantom power, but looking through the archives, it looks like some of the recommended adapters are no longer available. Are there any these days that people either 1) think are really great or 2) think are terrible? I see the Audix APS910 is going for about $35. The Nady Audio XM-10 is about $25. Is quality much of an issue with these?

[tgakidis]

You should hit up Robb AKA "Darktrain"  http://taperssection.com/index.php?action=profile;u=17532

He seems to come accross these often and might have a set lying around or a line on them.  You can also go the PFA route from Naiant  http://www.naiant.com/naiant/inlinedevices.html

Either way you will need you mics modified back to three wire with mini xlrs to run them with phantom adapters or a PFA.

[lukpac]

You should hit up Robb AKA "Darktrain"  http://taperssection.com/index.php?action=profile;u=17532

He seems to come accross these often and might have a set lying around or a line on them.  You can also go the PFA route from Naiant  http://www.naiant.com/naiant/inlinedevices.html

Either way you will need you mics modified back to three wire with mini xlrs to run them with phantom adapters or a PFA.

Thanks. I can handle putting on new connectors, I just want to have the phantom adapters first before I go hacking things up.

I figure I'll save the 1/8" plug and put some female mini-XLRs on the stub ends in case I ever want to run plug-in in the future.

[Gutbucket]

Niant PFAs are available as two-wire on request, typically with a pair of them terminated to a single 3.5mm stereo mini jack input.  That's how Jon provided them for me.

The AT phantom adapters are called PPAs I think.   Two versions, both three-wire mini-XLR input. The smaller, older barrel shaped PPA1s are phantom powered only and can be plugged directly into a recorder's XLR inputs like the Niant PFAs.  [edit] They invert the signal polarity.  The newer box shaped PPA2s do not invert polarity and may be powered by either a AA battery or phantom, but are bulkier and require an XLR cable patch cable between them and the recorder's input.  Not certain about which invert, some ones invert polarity when used with 2-wire mics, others do not.

[lukpac]

Niant PFAs are available as two-wire on request, typically with a pair of them terminated to a single 3.5mm stereo mini jack input.  That's how Jon provided them for me.

I saw that, but I definitely want to wire them "as intended" so they can better handle higher sound levels (although, quite honestly, I haven't yet run into issues...perhaps that speaks to my taste in music).

The AT phantom adapters are called PPAs I think.   Two versions, both three-wire mini-XLR input. The smaller, older barrel shaped PPA1s are phantom powered only and can be plugged directly into a recorder's XLR inputs like the Niant PFAs.  They invert the signal polarity.  The newer box shaped PPA2s do not invert polarity and may be powered by either a AA battery or phantom, but are bulkier and require an XLR cable patch cable between them and the recorder's input.

I should really run a quick test to verify, but I *think* wiring them for plug-in power ends up reversing the polarity. It seems like I've noticed that, anyway. Why would the older adapters invert polarity?

[Gutbucket]

I should really run a quick test to verify, but I *think* wiring them for plug-in power ends up reversing the polarity. It seems like I've noticed that, anyway. Why would the older adapters invert polarity?

I think you are correct.  Really only matters when you are mixing them with other souces, and even then it's good to check by ear and easy enough to invert in software.

I've only used a couple pairs of borrowed ATs with my Niant PFAs, and both pairs were 2-wire stereo mini-jack terminated, but I can't remember if I checked polarity on them.  Jon can build the PFAs with either polarity you specify and he mentioned that many 2-wire low-voltage mics output inverted polarity so his standard build is to invert polarity to correct for that.   I use the PFAs with miniature DPAs and those mics output correct polarity, so the standard build 2-wire input PFAs I have end up inverting their output. I should have specified non-inverted but it's no big deal.  I'm aware of it and just invert as necessary in software when mixing.

[edit] I don't know why the older barrel-shaped PPA's invert 2-wire polarity and the later square box PPA2 does not (the one with the option to be powered by a AA battery).  I use the PPA2s to power a Tetramic and found the polarity information about them below on Len's page here- http://www.core-sound.com/TetraMic/6.php

November 17, 2009:We've replaced the Phantom Power Adapter (PPA) with a new model that maintains phase, instead of inverting it as the older model did. The new PPA2 will ship with all orders placed after December 1, 2009.

[lukpac]

I think you are correct.  Really only matters when you are mixing them with other souces, and even then it's good to check by ear and easy enough to invert in software.

Yeah, that's how I noticed it. For that particular recording I used an SM58 as a vocal mic and one of the AT853as as a guitar mic, and I noticed things sounded a bit odd. After flipping the polarity of the guitar track things fit a bit better.

[lukpac]

I should really run a quick test to verify, but I *think* wiring them for plug-in power ends up reversing the polarity. It seems like I've noticed that, anyway. Why would the older adapters invert polarity?

Finally got around to checking. Yes, when connected to the phantom adapters, the polarity is correct. When connected to plug-in power, the polarity is reversed.

[DSatz]

Actually, a small but significant minority of listeners can detect absolute polarity of audio signals at low frequencies. For them, inverted recordings can sound distinctly unnatural and uncomfortable to listen to, depending on what kinds of sonic events are in the recorded material (e.g. an inverted string quartet or chorus might well be no problem, but an inverted percussion ensemble or a kick drum could sound quite strange to them). It's so easy to maintain correct polarity when working with balanced microphones, etc., that I've always made a point of doing so.

I've also sometimes wondered how much this phenomenon may have skewed listening tests where it wasn't controlled for because people didn't think that it mattered, or even people's opinions of an entire medium or genre of recording. In the early days of CD, for example, ISTR that some players had outputs that were inverted from true polarity. For that matter I have no idea whether most consumer audio these days maintains correct polarity or not; some kinds of amplifier stages are inherently polarity-inverting, and as a circuit designer you have to take care about the total result; it doesn't take care of itself.

--best regards

[Gutbucket]

Interesting to hear of the audibiliy of inverted polarity at low frequencies for some listeners.  I haven't found that I'm sensitive to it, but I haven't really tested properly. I figured that if audible it would likely be on asymetrical wave forms like those sometimes seen from from brass instruments, but which aren't necessarily low in frequency.

Other than determining the polarity of an exisiting recording by zooming in and visually examining the waveforms of sharp transients to determine if their initial peak moves in the positive or negative voltage direction, is there anything one who is not sensitive to this phenomena can look for visually, learn to listen for, or in other way determine if a there is a low-frequency polarity inversion problem that may be objectionable to others?

[lukpac]

I won't claim to be able to hear a difference in absolute polarity, but people frequently mention things like bass drum hits, in terms of the direction the air is moving.

[Gutbucket]

Ahh, the room pressurization.  Okay that makes sense.

[lukpac]

I suppose that would depend on whether they are a drummer or a listener 

That's actually one thing I've wondered. I've never bothered to look too closely into it though.

[chinariderstl]

Marking thread. 

[lukpac]

Oh, just noticed this:

The AT phantom adapters are called PPAs I think.   Two versions, both three-wire mini-XLR input. The smaller, older barrel shaped PPA1s are phantom powered only and can be plugged directly into a recorder's XLR inputs like the Niant PFAs.  They invert the signal polarity.  The newer box shaped PPA2s do not invert polarity and may be powered by either a AA battery or phantom, but are bulkier and require an XLR cable patch cable between them and the recorder's input.

Not certain about the AT8538 (or the "box" versions, for that matter), but the AT8533x barrel module does *not* invert signal polarity.