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Author Topic: AD-20 w/ AT-822 mic... unbalanced?  (Read 3668 times)

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Offline edwardo_machino

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AD-20 w/ AT-822 mic... unbalanced?
« on: April 07, 2007, 07:43:24 PM »
Ok, forgive my lack of understanding on this matter but I do not quite understand the difference between a balanced and unbalanced setup, save that I think it has to do with an extra ground...but anyway, I have a Microtrack 24/96 and just purchased an AD-20.  Looking at an Audio Technica 822 for the mic, as it is battery powered and this works for me.

Noticed, however, that the AD accepts balanced XLR inputs.  So, the AT-822 outputs an unbalanced signal - what should I do to make this work?  What would be the harm in plugging it up as is?  But better yet, what would be the best way to wire up a balanced output from the AT-822? 

According to http://www.micsupply.com/ad20.htm, "In order to connect unbalanced mics to the AD-20 you should use a cable that will properly balance the signal (usually this involves a small resistor/pad between ground and the 2nd leg of the balanced input that isn't being used)."  Could some of you explain this to me?

Thanks.

Offline ArchivalAudio

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #1 on: May 01, 2007, 12:26:40 AM »
I think the AT-822 is balanced
Balenced just means 3 conductor in XLR its a + and - and a common (not really ground, but it could be thought of that way)
on 1/4 plugs it also called TRS (Tip Ring Sleeve) thats also balanced you would notice 3 conductors as opposed to unbalanced TS (or Tip Sleeve)

but to go into the AD-20 you need the in's to be a Left + Right XLR-M plugs
since the 822 is battery powered there is no need for phantom power
which if you needed it it could be the Denecke PS-2
the AT 822
looks like it comes with this cable:
Includes a 1.7 ft. cable (XLRF-type to stereo 3.5mm mini-plug); and a 10 ft. (3 m) cable (XLRF-type to 2 mono 3.5mm mini-plugs)

but you would want a 5-pin XLR -F(from the back of the mic to 2 XLR-M a Left & Right
I think the next model up comes with this one
I know you can find such cables out there

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Offline goodcooker

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #2 on: May 02, 2007, 09:34:49 PM »
the AT822 is terminated in a mini plug and would need to be adapted to 2xXLR for the AD20.
The AT825 comes with a 5 pin xlr to 2x3pin xlr cable....it also operates off of battery or phantom...822 batt only. Be forwarned that the AT822/5 cannot handle extremely high rock concert SPLs... IME
for your use get an 825....maybe I'll sell you mine....
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Offline edwardo_machino

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #3 on: May 03, 2007, 11:56:41 AM »
Ok, I got all the gear - tenesejedd sold me an excellent quality AT-822.

Problem: slight hiss.  My setup is AT-822 > AD-20 > Microtrack.  I have the levels on the Microtrack bottomed out and only use the AD-20 levels to adjust.  Could the hiss be caused by the 822's unbalanced output? 
 
To connect the microphone I am using the cables that came with it - XLR to 1/8th inch male which plugs into a cable with a female 1/8th inch on one end and two male XLR connectors on the other, which plug in to the AD-20.

Any ideas?

Offline Church-Audio

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #4 on: May 03, 2007, 12:20:11 PM »
Ok, I got all the gear - tenesejedd sold me an excellent quality AT-822.

Problem: slight hiss.  My setup is AT-822 > AD-20 > Microtrack.  I have the levels on the Microtrack bottomed out and only use the AD-20 levels to adjust.  Could the hiss be caused by the 822's unbalanced output? 
 
To connect the microphone I am using the cables that came with it - XLR to 1/8th inch male which plugs into a cable with a female 1/8th inch on one end and two male XLR connectors on the other, which plug in to the AD-20.

Any ideas?

Here is my first idea.. DONT USE PHANTOM POWER WITH THE AT-822 MIC..

If you have the AT-825 that is a phantom powered microphone with true balanced outputs you can use phantom with this mic..

Warning: The AT822 is designed for battery operation only. Do not attempt to use when phantom power is present. Possible damage to the microphone may result.

This mic must be used UNBALANCED into a preamp if your preamp has phantom disable it.. You should connect pin 1/3 together as ground use pin 2 as signal on the XLR going to the preamp input. This is a low impedance microphone so you must use a XLR input but you must unbalance it by doing the wiring as I suggested. You need a good preamp to drive this mic..

Chris
« Last Edit: May 03, 2007, 12:24:34 PM by Church-Audio »
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Offline edwardo_machino

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #5 on: May 03, 2007, 02:53:30 PM »
The AD-20 supplies no phantom voltage.  I am aware the AT-822 is battery only, in fact, that is why I chose it.

Your last paragraph is interesting.  You are saying I should make a cable that connects pins 1 and 3 together and uses 2 for ground?  I'm afraid I don't quite understand.  Could you elaborate?  I'm still a little fuzzy on the concept of balanced VS unbalanced.

Offline Church-Audio

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #6 on: May 03, 2007, 03:10:08 PM »
The AD-20 supplies no phantom voltage.  I am aware the AT-822 is battery only, in fact, that is why I chose it.

Your last paragraph is interesting.  You are saying I should make a cable that connects pins 1 and 3 together and uses 2 for ground?  I'm afraid I don't quite understand.  Could you elaborate?  I'm still a little fuzzy on the concept of balanced VS unbalanced.

Not a problem..

You have an ad-20 that has balanced inputs. If you are using them. You must "unbalance" the input by connecting pin 1=ground to pin 3= Signal negative to each other.. This unbalances the input of the AD-20 and allows you to use your unbalanced microphone with this preamp. If you do not connect pin 3 to anything its floating and it can pick up stray RF signals and inject them into your recording because pin3 must be terminated by a microphone or by grounding it out. If you were plugging in a balanced microphone to this input there would be no modifications necessary.

Balanced vs Unbalanced..

Unbalanced signals are very common for electret microphones. Like the ones you have. The issue with running unbalanced line for a microphone is your are really limited to about 10 feet max before you might run into problems.
With an unbalanced microphone you only have two wires..
A Shield wire this is to prevent stray RF signals from getting into the center wire or Signal wire.
The signal wire carries the signal to the destination with the aid of the ground or shield wire.

In a balanced system you have three wires..

A Shield wire - for ground and RF rejection
A Signal positive wire. This is the in phase representation of the signal
A Signal negative wire. This is the out of phase representation of the signal

When you combine the out of phase with the in phase you get whats called phase cancellation. So what this system does is cancel out interference that is inducted into the audio chain. The output then becomes clean and free of most inducted noises. The main advantage with balanced over unbalanced is better common mode rejection of inducted signals or just "less noise" there are limits to how fare you can run a balanced cable before it needs a buffer amp but we are talking distances of more then 1000 feet. With unbalanced you have less rejection of noise so the longer your unbalanced cable run is the more likely inducted noise will occur.

Here is a simple picture I stole from a web site that illustrates what I just said.


Now because the input impedance is 200 ohms on your mic and your preamp is designed for anything from 150 to 2k if its built properly you can simply just unbalance the preamps input.

If however you were connecting a high impedance microphone to a low impedance mic preamp you would need one of two things. An impedance converter like the ones found for the AT-853 microphones... Or a Transformer that has a Hi impedance primary with a low impedance secondary.. This allows the proper impedance matching of a microphone that is high impedance to a mic preamp that is low impedance.


« Last Edit: May 03, 2007, 03:18:37 PM by Church-Audio »
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Offline edwardo_machino

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #7 on: May 06, 2007, 10:08:49 PM »
So if I do not short pins one and three on the AD-20, I might get some signal interference?  How might this manifest?  I have noticed a very, very slight hissing in the background while listening to sounds I have recorded with this setup so far.

Also, what would be the best way to apply this modification to the AD-20?  Open it up, short from there or can a cable be fabricated for this purpose?

I appreciate all of your replies.

Offline spaceboy_psy

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #8 on: May 20, 2009, 06:04:49 PM »
Hi there, sorry to revive this old thing, but blastradys's last question wasn't answered! And I need to know the answer! Best to do this inside the box or in a cable?

Cheers!

Offline Church-Audio

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #9 on: May 20, 2009, 08:41:00 PM »
So if I do not short pins one and three on the AD-20, I might get some signal interference?  How might this manifest?  I have noticed a very, very slight hissing in the background while listening to sounds I have recorded with this setup so far.

Also, what would be the best way to apply this modification to the AD-20?  Open it up, short from there or can a cable be fabricated for this purpose?

I appreciate all of your replies.
When you unbalance an input its always best to terminate the unused signal path the - path to ground this prevents anything from getting inducted into the open ended input circuit.
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Offline spaceboy_psy

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Re: AD-20 w/ AT-822 mic... unbalanced?
« Reply #10 on: May 20, 2009, 08:52:44 PM »
Hi there, cheers for the swift reply! (this board is amazingly swift!)

I was referring to the question of "can a cable be fabricated for this purpose?", so that I wouldn't have to go soldering around my preamp if I wanted to use a balanced source...

Doing it in the box isn't too big a deal for my present purposes and I may well go that route, but just curious if there is a cable/external option.

 

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