Condensor Mic, phantom power, sound card - bad sound

Chanimal wrote on 11/25/2004, 8:27 PM

For voice over work I have been using a Radio Shack XLR (an audio engineer I know said the XLR mics are made by Shure) to 1/4 to 1/8th plug dynamic mic with a pop screen hooked directly to the Audigy2 EZ sound card mic input.

It worked fine, so long as I recorded away from the PC (8 fans).

I wanted to do better voice over work so I picked up the MXL 63m (Mogami wire) 1" condensor mic. It required Phantom Power so I use the Nady SMPS-1 which supplies the required 48v (basic XLR in and XLR out). I hooked the 25' cable into the phatom power, then hooked the 25' cable into the sound card mic input (I wanted longer cables so I could park the mic in the large hall closet, which makes a very good sound room. The sound card mic input is set for +20 db gain.

The sound through my dymanic mic sounds very good. Within Sound Forge the meters move substantially and I get a fairly clean sound (not rich like a condesor mike, but clean).

I just hooked my MXL via phantom to the mic input. The meters barely move (like 1/32nd of an inch at most during talking) and the sound is very low and unusable. It is solid noise and my voice is barely audible.

I thought I might have some noise via the Audigy2 EZ mic in, but not this (considering my good experience with the dynamic mic). It seems that something is wrong, since the meters hardly move at all.

I know the Audigy2 EZ is not the preferred sound card, but it has worked well with the dynamic mic. I don't have a pre amp or mixer to test the line in difference.

I've searched this board and read most everything within the last hour. It seems like some folks are getting their condesor mcs to work directly into their mic input (after phantom power).

Am I missing something (I want to make sure I don't have a broken mic or phantom power (both brand new))? With phantom power do I plug directly into the line level?

Also, is it possible to hook this setup into my Canon GL2 (want to ask before I make a mistake).

Advice?

P.S. Most other threads on this subject diverted quickly into different boards (and their specs) and everything else. I just need some advice on the best way to see any results from the equipment that I have.

Thanks,

Ted

Comments

Spot|DSE wrote on 11/25/2004, 9:04 PM

Well...first of course you can connect the mic to your GL2 if you have a phantom supply inserted between the two. The GL2 doesn't offer phantom, as you likely know.
Second, it may well be that the dynamic had a hotter output, although that's unlikely. However, you should be using mic input and not line input. Are you sure your phantom supply is providing power? Some condenser mics will output marginal sound without the phantom if the audio is loud enough. I don't know who builds the Mogami mics, I see them at NAMM, but have never paid attention.
The sound card's mic input should be set to =4, not +20. That's a HUGE amount of gain. Is that the only place you've got input? Is there a mic/line switch? Sure that you've got a good cable from the phantom to the card?

Chanimal wrote on 11/26/2004, 1:02 AM

I get more sound when I connect directly to the microphone than when I go through the phantom power. Looks like that's the problem. I'm going to check the power out at a music store tommorow.

I'll be replacing it with a Behringer 1202 mixer so I can get both phantom power and a pre-amp so I can use the line in versus mic in. Plus I'll be able to use the mixer for other events (i.e., when our makeshift band gets together as the backup band for the annual talent show).

farss wrote on 11/26/2004, 1:44 AM

Well first of all mics go into mic inputs not line inputs, there's a BIG difference in the gain. Adding a phantom power supply doesn't change that at all, all it does is supply the power to the mic, no gain in the unit at all.
Now your phantom power supply has two connections, one must go to the mic and the other to the mic input on your recording device. You can check this easily enough with a meter, between pins 1-2 and 1-3 you should read around 48V.
One trap though, some mics, although not many these days, only need 12V and may have a dummy spit if you feed them 48V and some phantom power supplies only supply 12 V which again most but not all mics are happy with.
Hope this helped rather than confused.
Bob.

Chanimal wrote on 11/26/2004, 9:43 PM

I brought my mic and phantom power supply into a music store and they hooked it into one of their mixers. Everything worked great.

Somehow as I go from the phatom power supply to the PC mic input (I use an XLR to 1/4 cable and then a 1/8th adapter) I am getting a feedback loop, or something.

I still want to figure this out. I saw a forum discussion elseware that said to go stereo into the mono mic plug (because of the difference in wiring). However, I have no problem using my dynamic mic, just the condensor with phantom power using the existing hookup.

I now have it working. I picked up a Behringer 1202 (supports 4 mics, has phantom power built-in, a clean pre-amp), hooked the mic directly to the mixer and took the mixer into the "line" out and it works perfectly. Plus, the mixer allows me to contol the sound on the way in (didn't think I would use this but it is really helpful to get the tone you want prior to recording anything).

Any help understanding the conflicts from the original setup are appreciated.

Blues_Jam wrote on 11/26/2004, 11:24 PM

"Any help understanding the conflicts from the original setup are appreciated.
"

I think you are better off using the pre-amp but as to your original problem the symptoms sound like a classic impedance mismatch. I haven't looked up the specs for your mics or soundcard but I suspect that your dynamic mic is Hi-Z (Z represents impedance), your condenser mic is Lo-Z, and the mic input on the sound card is Hi-Z.

If that is the case then the XLR to 1/4" cable is simply a straight wiring of the two different connectors. To make this work with the condensor mic you would need an impedance-matching transformer (Lo-Z to Hi-Z) before pluging into the sound card's mic input. I think Radio Shack still sells these. The ones I have are XLR to 1/4" phone plug but I think they come in other configurations as well.

One caveat here is that Hi-Z is intended for connecting with short cable lengths (like 15 feet or less). Lo-Z connections allow for the use of 25 foot cable lengths or longer without appreciable signal degradation. But whichever is used, output and input impedances must be matched.

Blues

John_Cline wrote on 11/27/2004, 12:22 AM

I'm certain that by unbalancing the phantom power adapter you are shorting one leg of the phantom power to ground and essentially rendering it useless. Basically, the condenser mic isn't getting any power. If the phantom power adapter output was transformer isolated, you could unbalance it by tying pins 1 & 3 of the XLR together and running that to the sleeve of the 1/8" plug and hooking pin 2 of the XLR to the tip of the 1/8" plug, it would work fine.

Also, it isn't necessarily important to match impedances unless you are dealing with transformer inputs. Otherwise, as long as the source impedance (microphone) is lower than the input impedance (sound card mic input) then there really shouldn't be an issue.

John

farss wrote on 11/27/2004, 4:21 AM

I'd sort of thought of that possibility however the good phantom power supplies dont feed volts to the mic preamp, ours cost about $500 so that might be the difference and they're clearly marked which connector goes to the mic and which goes to input.
Bob.

If that is the cause of the problem then say a 0.47uF capacitor in each leg of the mic line before the sound card but after the power supply would isolate the DC from the soundcard. If it really is a HiZ input then smaller value cap would do, just make certain they're not polarised caps.

Bob.

Chanimal wrote on 11/27/2004, 9:09 AM

The mic impedance is listed at 200 Ohms. Would this be considered Hi or Lo?

John_Cline wrote on 11/27/2004, 11:08 AM

You're right, Bob, the good ones don't feed phantom power into the mic preamp. They either have transformers or capacitors to block the voltage.

I got so hung up in my last post about why it wasn't working that I missed making the point that the mic preamps in a soundcard SUCK and running any kind of high quality mic into one isn't a good idea anyway. Actually, what he (and everyone else) needs is a "Behringer Shark DSP-110." For around $100, it is a VERY slick piece of audio hardware. I'm not usually a huge fan of Behringer stuff, but this thing is incredibly useful in a lot of situations.

Behringer Shark DSP-110

Shark Spec Sheet PDF

John

Blues_Jam wrote on 11/27/2004, 9:09 PM

Chanimal, 200 Ohms is most definately low impedance (Lo-Z).

Blues

farss wrote on 11/27/2004, 10:13 PM

I'd never noticed that the Behringer lineup before, if it's half as good as they say it is it's an absolute bargain, we spent way more than that just for a phantom power supply unit. Mind you our power supply does clip onto your belt, does have sexy blue anodizing...

Bob.

Blues_Jam wrote on 11/27/2004, 10:27 PM

Chanimal,
I just did a little investigating a found something a bit interesting. That Radio Shack mic is rated at 500 ohms impedance at + or - 30%. That means it could be as low as 350 ohms or as high as 650 ohms (more likely in your case). It is rated as low impedance but that is quite the high side of Lo-Z and probably why you were able to get descent results with it.

The Audigy card gives no specification for the mic input impedance but I would bet my hat that it is high. I very much doubt that you would find a Lo-Z mic input on any sound card except perhaps a pro-level card costing hundreds more.

So, I still think that the Lo to Hi-Z transformer is still your ticket if you wish to use the sound card's mic input. If you do buy the transformer, try it with your Radio Shack mic too. I think you will be surprised by the results.

Radio Shack does in fact still sell a XLR to 1/4" transformer and it's only $15.
Copy and paste the following URL into your browser to see it.

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=274-016

Do not underestimate the importance of matched impedances for the highest possible audio quality.

Blues

John_Cline wrote on 11/27/2004, 11:23 PM

The problem with a LoZ to HiZ matching transformer is that it increases the voltage by the same ratio as the input to output impedance ratio. So, the possibility exists that the voltage of the HiZ output of the matching transformer might be high enough to overload the mic preamp on the soundcard. It may be that there is enough level on the HiZ output side to use the line inputs on the soundcard as opposed to the mic input.

Also, the HiZ output of the Radio Shack transformer is 30k, so it will be expecting to see at least a 30k impedance input. I suspect that the input impedance of a soundcard mic input is somewhere around 5k, so the impedances won't be matched. (And they will be unmatched in the wrong direction, higher source impedance than input.)

Still, the best way to deal with this issue is either the Shark I mentioned earlier, or Behringer's lowest priced mixer with 48v phantom power, the UB802 for $59.

http://www.behringer.com/UB802/index.cfm?lang=ENG

John

farss wrote on 11/28/2004, 12:56 AM

Over the average length of mic cable running a low Z mic into a high Z load will not make a shred of difference, the other way around will at the least give you a loss of level but most likely that's about all.
Only last week I ran the instrument level O/P of an electric piano into the mic input of a 150, apart from the noisy preamp in the camera it worked, level was down a fair way which was why the noise in the mic preamp was an issue.
In the good old days with transformers in inputs and outputs yes impedance matching was a big issue. Most line drivers today have an output impedance of less than an ohm and are purely resistive. With improperly terminated transformers the inductances can do wierd things but even then you had to be at least an order of magnitude off the mark for things to really start to show. Very long cable runs (over say a mile) can be more demanding.
Bob.