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Post subject: 500 Pro Quiet with a Shure SM58
Posted: Sun Jun 12, 2011 12:57 am
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Ok, here's my problem...

I own a brand new Passport 500 Pro. I have a Shure SM58 microphone. The cable that I have to connect it is XLR on the microphone side and 1/4" on the input side. I have to max out the line level AND master volume dials to get any volume at all, and I'm still very easily overpowered by small guitar amplifiers. I have read all the related posts on this forum and I see nothing that relates directly to this situation specifically, so I thought I might ask... is plugging the microphone into the "line in" portion of the inputs the issue? I know that The SM58 does require phantom power. I turn this on and it only puts out mediocre power at best. Where might the problem lie? Should I purchase an XLR to XLR cable? Or perhaps a "hotter" microphone? Or should I sent my unit it for repairs? I have plugged my electric guitar into the unit as well with similar results (minus the phantom power, obviously). Considering that each speaker should be receiving 250watts, this things should be blasting my face off but it barely getts louder than a small guitar practice amp and that's if I'm screaming into the microphone. If someone could please give me a very comprehensive answer I would appreciate it. I am very tech savvy and I do not mind long explanations.


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Post subject: Re: 500 Pro Quiet with a Shure SM58
Posted: Sun Jun 12, 2011 6:35 am
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Aspiring Musician
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Joined: Wed Feb 16, 2011 7:24 am
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If the mic actually needed phantom power, the problem would be your cable. Phantom power only works with an XLR cable. It needs that third conductor to conduct the phantom power. That's why the graphics on the amp show phantom power only on the six channels that have XLR ports and not on the two stereo channels that use 1/4" or 1/8" jacks. Those jacks can't conduct phantom power.

Meanwhile, according to the online version of the owner's manual, this is a dynamic microphone, not a condenser microphone, so it should not need phantom power. It won't be damaged by it if you add it, but it shouldn't require it, and the manual doesn't mention phantom power anywhere. Do a search on "phantom". No hits.

If your mic needs phantom power and doesn't get it, that mic won't be merely quiet. It will be pretty much silent. I have a condenser mic that is quite hot with phantom power and completely dead without it.

I think that the real problem is still the cable, however. Sound amplification systems have two standard signal voltage levels: "mic" and "line". The "mic" level is the level that all dynamic microphones like yours produce. The design of the microphone is that the motion of the diaphragm drives a miniature electrical generator that produces current at this level. The physics of the microphone determined this volume level. The XLR standard cable and port were designed to handle this level of signal.

Because people patch things together in unusual ways, sometimes an XLR port also has to handle a "line" level signal. This signal has a voltage level that was more arbitrarily invented by engineers as a good signal level to run along relatively long wires without problems, and it is a "louder" signal than a mic level signal. The Pad button on your Passport was created in order to take a line level signal through the XLR ports without overwhelming the amp. It essentially steps the signal down to mic level before it goes to the power amplifier.

Meanwhile, the "Pad" button only affects the XLR jacks. The 1/4" port assumes that the "Pad" is always turned on (even if the actual "Pad" button is dark), lowering the volume level because the 1/4" port is intended for line-level instruments, like electric guitars and keyboards, and not for microphones. You can use a pre-amp to bring your mic level signal up to line level, but why bother? Just get the right cable.

Add that according to the online version of the owner's manual for that mic, it seems like it was designed for people who like to eat the mic while singing in a loud room. It's unidirectional, so it ignores sound that comes off-axis (to prevent feedback at high volume levels), and it rolls off the bass so you don't boom when your lips are within six inches of the mic (or even physically touching it). It has a fat pop filter, again, so you can use it up close without a lot of undesirable sounds. It also is built to minimize handling noise. All this minimizes the bass.

So, since this mic was designed to be yelled into at close range by someone jumping around on a stage holding the mic in his or her hand, it's probably not an extremely "hot" mic. If you put any distance between you and the mic, it won't be loud.

So, get a real XLR cable, plug it into an XLR port and not the 1/4" port, and put your sound source aimed straight at this mic at close range, and you should get the results you seek. Do anything else, and you probably have the wrong mic.


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Post subject: Re: 500 Pro Quiet with a Shure SM58
Posted: Fri Sep 09, 2011 9:35 am
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Joined: Mon Aug 30, 2010 10:53 pm
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Location: Scottsdale
@novanryder - did you get this issue resolved? As ContraCaller mentioned, if you get an XLR to XLR microphone cable and plug into the Mic input, you will get intended results. The Line channel that you have been trying to plug into has more than -20dB of gain, since as CC mentioned it is intended to accept much higher input levels than the microphone input. Additionally, CC is right - the SM58 is a dynamic microphone which does not require phantom power. I hope this helps.

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Byron A. Tanigawa
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Fender Musical Instruments Corp.


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Post subject: Re: 500 Pro Quiet with a Shure SM58
Posted: Fri Feb 10, 2012 8:55 am
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Joined: Fri Aug 22, 2008 1:08 pm
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It has to be the cable....I run an SM-58 into mine and it is quite a sensitive mic. I also run an SH-55 (the vintage looking version of the 58) and it too, is quite sensitive.


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