Topic: AT822 into balanced preamp how? (plus, any way to mod it balanced? or phantom?)

[spaceboy_psy]

So I plumped for a lovely AT822, many thanks to DSatz et al. convincing me to do the honourable thing!

It's coming with the XLR->3.5stereoplug cable, and an XLR->2x 3.5monoplug cable, with 1/4" adaptors.

I've got a Microtrack II, and I've read that for going straight into that it'll be better to use the 1/8" than 1/4" as the mic's unbalanced and the MTII doesn't like that.

What about if/when I get a balanced input preamp? (thinking about the UA-2) Here - http://taperssection.com/index.php/topic,82553.0.html - Mr Church seems to imply that it's best to short the inputs of the device itself, but is there not a way to do it with a cable...?

OOOORRRRRR, how hard would it be to mod the AT822 and make it balanced?? Google didn't throw anything up, is it impossible? Surely you just need something that will reverse the phase of the signal? And I wondered about phantom power - if you could mod the AT822 to use phantom power, would it improve the sound at all? Sensitivity, signal to noise, anything? If so a balanced/phantom-powered AT822 would be perfect to run with both the UA-2 -> MTII and also straight into the MTII's TRS ins, and make a pretty wholesome setup...

Cheers in advance, I really can't wait to hear your thoughts!

[Roving Sign]

I wouldnt stress too much about the balanced aspect...unless you plan on running 100 feet of cable... - just not much to gain there.

Just use this mic as-is...

If so a balanced/phantom-powered AT822 would be perfect...

Also known as an 825

Not sure what the issues might be with the microtrack...I'd make specific post about that..."AT822 > Microtrack II: HOW?"

[spaceboy_psy]

Ah, I just had a likely-obvious thought! (yay me): doing everything balanced would get rid of noise picked up in the cable and hardware, yes? though that can be easily limited by using the shortest cables possible... BUT, can it reduce noise coming from the actual Mic? ie. improve signal/noise ratio?? I was kind of half thinking it might, but now I actually use a couple more synapses on it, I realise it probably wouldn't! Can anyone confirm this?

Yup yup yup, an 825 would be nice, but considering I got the 822 for better than half the price of an 825, I'm willing to work this mess out 

[spaceboy_psy]

Cool ^_^ cheers

Balanced AT822 mod anyone..?

[DSatz]

roving_sign, the AT825 has other differences from the AT822 in addition to balanced outputs; though the same capsules are used in both microphones, the high frequency response of the AT825 is considerably smoother. A couple of years ago I asked some of the company's chief engineers about this difference at the AES convention, and it turned out that they weren't very familiar with either model because both were designed before almost anyone who works there now had been hired. Both these mikes have been in their catalog for a very long time, and I'm glad to see that they've recently introduced some more up-to-date stereo recording microphones.

Just in general--I haven't had time yet to read this thread so someone else may well have said this already--when connecting an unbalanced, self-powered (or non-powered) microphone to a balanced input, the ideal approach is to balance the connection at the microphone output by connecting the unbalanced output to one modulation lead and imitating the microphone's output impedance as precisely as possible and connecting that impedance between ground and the other modulation lead. It isn't necessary to use a transformer or active circuitry at the microphone end to create balance; all that's needed is for the impedance to ground to be equal between the two legs of the circuit.

--best regards

[illconditioned]

roving_sign, the AT825 has other differences from the AT822 in addition to balanced outputs; though the same capsules are used in both microphones, the high frequency response of the AT825 is considerably smoother. A couple of years ago I asked some of the company's chief engineers about this difference at the AES convention, and it turned out that they weren't very familiar with either model because both were designed before almost anyone who works there now had been hired. Both these mikes have been in their catalog for a very long time, and I'm glad to see that they've recently introduced some more up-to-date stereo recording microphones.

Just in general--I haven't had time yet to read this thread so someone else may well have said this already--when connecting an unbalanced, self-powered (or non-powered) microphone to a balanced input, the ideal approach is to balance the connection at the microphone output by connecting the unbalanced output to one modulation lead and imitating the microphone's output impedance as precisely as possible and connecting that impedance between ground and the other modulation lead. It isn't necessary to use a transformer or active circuitry at the microphone end to create balance; all that's needed is for the impedance to ground to be equal between the two legs of the circuit.

--best regards

Thanks for the in-depth knowledge.

By the way, do you have an opinion on the capsules in the AT822/825?  How do you think they compare to the newer single-point stereo mics AT is producing?  From the pictures, it looks like AT is using something different, perhaps the ones in the 4033 model?

Oh yeah, to all you hackers out there, it is quite easy to rip the head off the AT822/825 mic, add a 4.7k resistor to each capsule and power it with plug-in-power, from something like an Edirol R09.  I've got three of these mics, two AT822 were chopped, and the third, an AT825, was left for phantom powering.  To my ear, these mics are OK, but I prefer other mics now.  Hmm.  So why do I keep these?  Well, two of the three are loaned out...

  Richard

[spaceboy_psy]

when connecting an unbalanced, self-powered (or non-powered) microphone to a balanced input, the ideal approach is to balance the connection at the microphone output by connecting the unbalanced output to one modulation lead and imitating the microphone's output impedance as precisely as possible and connecting that impedance between ground and the other modulation lead. It isn't necessary to use a transformer or active circuitry at the microphone end to create balance; all that's needed is for the impedance to ground to be equal between the two legs of the circuit.

Wow, right, let me try and get my head around this!

Just read the wikipedia Balanced Audio article - should have done that sooner 

By the way, I just grabbed a UA-5 off ebay (whoooo!  ), so that's what we're working with, that and the microtrack.

I'm a little confused, will the UA-5/MTII will be subtracting Hot and Cold signals? so we need to reverse the polarity of one signal coming from the AT822? Is this the role of the 'modulation lead'? I couldn't find any info on what this might be. Or are you saying that it's not necessary to do any inverting, just match impedances? Where does the 200 Ohm resistor go exactly?

the signal lead is going to ground through the AT822 (200 Ohms)? And we want the shield to just run to the ground of the preamp. So we need to split the signal at some point between each capsule and the amp input, and make the cold signal go to ground through a 200 Ohm resistor at the preamp end?

That's the best I can do for now, but I'm sure I'm probably way off!    Thanks for bearing with me

it is quite easy to rip the head off the AT822/825 mic, add a 4.7k resistor to each capsule and power it with plug-in-power, from something like an Edirol R09.  I've got three of these mics, two AT822 were chopped, and the third, an AT825, was left for phantom powering.

Just so I'm clear, this is preferable to battery power because (apart from the mic being smaller of course), it's getting more voltage, ~5V rather than 1.5V, and this improves performance, like a battery box does...?

Now I think about the small voltages we're dealing with here, I suppose it must be impossible to run the AT822 on a comparatively massive 48V - would it just fry the electronics?

Wheee, this is fun, can't wait to get my AT822, and UA-5!!! whoo whoo whoo whoo 

[DSatz]

spaceboy_psy, actually it is far better to balance the signal at the source (at the microphone outputs). That allows you to use balanced cable to connect the signal to the balanced input of your preamp/mixer/recorder. That way you'll get the noise immunity across that length of cable, which is where it mostly matters.

Any differential input does the trick of sensing the moment-to-moment difference between two wires, neither of which is the signal ground. Each of those two wires (sorry, I lapsed into jargon and wrote "modulation leads" before) has some particular impedance between it and ground. A balanced circuit has a differential input that's fed by two wires, both of whose impedance is identical to each other. The function of the differential input circuit is to subtract one from the other electronically, which tends to cancel any noise that's due to interference--though in practice that also depends on the precise balance of the cable's impedance and some other factors.

--Before I forget to mention it, occasionally someone does connect an AT822 to phantom powering, which burns out its circuitry in an instant. My wife's voice teacher did it a few years ago so I arranged the repair for him; when I called A-T to arrange the repair, it was like they'd heard the story many times before. The repair cost isn't huge but it's still a mistake worth avoiding.

--I'm assuming that the UA-5 has balanced mike-level inputs and balanced line-level outputs. If that's wrong, please let me know; I'm actually not sure what a UA-5 is. The MicroTrack recorder I know has line-level inputs and can record either balanced or unbalanced signals, but it has severe noise (internal interference) problems when unbalanced signals are used, so it's not a good idea to drive it that way.

[kirk97132]

Edirol UA-5 has balanced mic inputs(xlr/trs) with unbalanced line level outputs(rca/1/4") or digital(coax/optical).  Sorry picture isn't a little better.  kirk

[spaceboy_psy]

UA-5: http://www.core-sound.com/ua-5.html

balanced mic inputs indeed.

DSatz, thank you very much for your help, but I'm afraid I've been getting rather confused as to what you think I should actually, physically, be doing! But after some reading, I'm wondering, are you simply talking about leaving the shield disconnected at the microphone end...?

ie. illustration no. 14 here: http://www.rane.com/note110.html?

or this? ("preamp" referring to an unbalanced signal which is going to the balanced Microtrack inputs, so the same as we're talking about I think):

This is using special unbalanced to balanced adapter that takes unbalanced preamp common ground wired to TRS (-minus) ring connections, sending EACH channel's +hot signal to TRS tips, and leaves the common TRS sleeve cable ground shield connections UNCONNECTED, preferably near the preamplifier output jacks.

So this is making me imagine a setup like this:

AT822L signal -> TRS tip L -> UA-5 L
disconnected <- cable shield L <- TRS sleeve L -> UA-5 L
AT822 ground  -> TRS ring L -> UA-5 L
                    -> TRS ring R -> UA-5 R
disconnected <- cable shield R <- TRS sleeve R -> UA-5 R
AT822R signal -> TRS tip R -> UA-5 R

Is this anything like what you're talking about?? I hope I'm at least close after all that 

Perhaps I should make clear that although I've done some electronic tinkering here and there, my knowledge of theory is patchy to say the least

Oh and kirkd, nice rig! - is that a massive elastic band??? and what's the black thing? I ebayed that exact same battery last night, is it the highly regarded 'Walmart DVD battery' I've heard so much of?

[kirk97132]

Yep one big ass rubber band.  The black thing is a Beachtek SVU-1.  One of the downsides to the UA-5 is metering.  It only has a peak light which is designed to light up at about +3 .  The SVU-1 provides much easier way to set levels.  There is an SVU-1 for sale in the YS right now.  They are a discontinued item and can only be found used.  And that is one of the "Walmart DVD" batteries that a lot of people use for their gear.  A 5400mAh battery will run the UA-5 for over 6 hours no problem.  Probably much longer but I've never needed it to go longer than that. 

[spaceboy_psy]

hmm, metering, an unforeseen niggle! SVU-1 looks perfect, except I'm in the UK and don't trust international post to necessarily get here before I leave for Nepal next month. Plus possible import duties.

So the peak lights go on at +3db..? as in, louder than 0db..??

[Roving Sign]

hmm, metering, an unforeseen niggle! SVU-1 looks perfect, except I'm in the UK and don't trust international post to necessarily get here before I leave for Nepal next month. Plus possible import duties.

So the peak lights go on at +3db..? as in, louder than 0db..??

I think that should be -3db

[spaceboy_psy]

Ha, ok, so that makes things tricky. I'll have to look into this some more *dons investigative cap...*

[kirk97132]

Oops that is correct it is supposed to light at -3dB.  See that's why I use a meter   Edirol manual says "light in red at the level at which the sound begins to distort (-3dB)."  It also does state that the unit will accept an unbalenced 1/4" input along with 1/4" TRS.  Also my unit has had different knobs installed on the front