doing it preampless?

S

starsxandxslits

New member
has anone used those little inline impedance converters for mics...i have 4 xlr inputs on my board with 48v on or off for all 4...i need to run 2 condensers and 2 dynamic mics for my drums...coule i possibly get by for a while by using one of those little things...or does anyone have a better suggestion besides another preamp..i plan on buying one in the next month, but i need something to get me by until then.

thanks to all you knowlagable fellows.
 
well, this may sound dumb, but my manual states against connecting unbalaced dynamic mics to xlr inputs with phantom power on...but i am certainly not in the know about what balanced and unbalanced refers to because i'm a dummy. plz explain to ease my nerves
 
NL5 said:
phantom power won't hurt dynamics
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+1 to this... Phantom power won't hurt dynamics. :D

I think in this case balanced / unbalanced refers to whether or not the mic has a transistor (or is it transformer?) balanced output or not. (Please correct me if I'm wrong or off base here...) Condensers usually have balanced outputs due to all the circuitry involved, whereas the more simple dynamic designs do not(?). :confused: I dunno, I'm just throwin' that out there, somebody needs to fill in the gaps here big time...
 
starsxandxslits said:
well, this may sound dumb, but my manual states against connecting unbalaced dynamic mics to xlr inputs with phantom power on...but i am certainly not in the know about what balanced and unbalanced refers to because i'm a dummy. plz explain to ease my nerves
Click to expand...
Any two wire (center and shield) 1/4 TS would be unbalanced and one side of the phantom power would be passing through the mic to the shield, not good.
It could have an XLR an still be unbalanced- less likely but.. You need to find out what you got.
 
starsxandxslits said:
well, this may sound dumb, but my manual states against connecting unbalaced dynamic mics to xlr inputs with phantom power on...but i am certainly not in the know about what balanced and unbalanced refers to because i'm a dummy. plz explain to ease my nerves
Click to expand...

Yes. Do not hook up an unbalanced connection to a balanced input with +48V. Most low impedance dynamics are balanced and will not be harmed by +48V phantom power. Only under very rare circumstances will +48v harm a dynamic. Now, if you want to talk about a few other actual circuit problems having to do with noise induced by +48V, then that's another story.
I always shut off phantom power with dynamics.
 
I think they are referring to plugging the mic in while the phantom is "on". That's not good. Phantom can be on or off with a dynamic but the short created when plugging in the mic while phantom is "on" could damage the phantom and/or the mic.
 
OK, so phantom power is carried on pins 2 & 3 on (not across) a balanced mic cable, which means that a dynamic mic plugged into that cable will have +48 volts on both sides of the coil. Since the difference between +48 and +48 is zero, no potential exists and no dc current flows through the mic, and the mic is free to generate it's small ac voltage without interference.
With an unbalanced mic one side of the coil is ground, so if the phantom power voltage ends up on the other side of the coil. current will flow and the mic won't work, or at least won't work right. Any decent phantom power supply is current limited, so damage probably won't occur, but the operating word here is probably, which leaves maybe, so be careful.
 
Pardon my ignorance, but is there even one slightly respected mic that is unbalanced? Cause I don't know any.
 
Radio Shack mics are sometimes unbalanced...but then most of them are not respected.
 
starsxandxslits said:
has anone used those little inline impedance converters for mics...i have 4 xlr inputs on my board with 48v on or off for all 4...i need to run 2 condensers and 2 dynamic mics for my drums...coule i possibly get by for a while by using one of those little things...or does anyone have a better suggestion besides another preamp..i plan on buying one in the next month, but i need something to get me by until then.

thanks to all you knowlagable fellows.
Click to expand...

Why do you need impedence converters? Can you not use XLR cables on them all?
 
MCI2424 said:
Yes. Do not hook up an unbalanced connection to a balanced input with +48V. Most low impedance dynamics are balanced and will not be harmed by +48V phantom power. Only under very rare circumstances will +48v harm a dynamic. Now, if you want to talk about a few other actual circuit problems having to do with noise induced by +48V, then that's another story.
I always shut off phantom power with dynamics.
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yes i would like to talk about it! please enlighten me.
 
starsxandxslits said:
yes i would like to talk about it! please enlighten me.
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I just wrote a long winded post but it did not upload.

Suffice to say, a problem is that the receiving end of the diff amp also "sees" the +48vdc and being differential input, it amplifies the *difference* between the two signals. Now, if there is +48Vdc on one leg and +47.9Vdc on the other leg (due to some difference in line impedance) then the input would amplify the difference and this dc signal would show up as hum or buzz. I have had it happen and I am sure others have too.

Of interest: There is a new circuit that uses a "gnd bootstrap" methos that automatically compensates for this problem, but I guess the industry will take a long time to adopt it as it uses an additional unity gain amplifier to compensate. Another active component = more $$ in manufacturing.

I just shut off phantom Power OFF on my dynamics because I just don't need the noise buildup on multiple tracks.

But, YMMV (god, I hate that phrase, don;t you?)
 
MCI2424 said:
I just wrote a long winded post but it did not upload.

Suffice to say, a problem is that the receiving end of the diff amp also "sees" the +48vdc and being differential input, it amplifies the *difference* between the two signals. Now, if there is +48Vdc on one leg and +47.9Vdc on the other leg (due to some difference in line impedance) then the input would amplify the difference and this dc signal would show up as hum or buzz. I have had it happen and I am sure others have too.

Of interest: There is a new circuit that uses a "gnd bootstrap" methos that automatically compensates for this problem, but I guess the industry will take a long time to adopt it as it uses an additional unity gain amplifier to compensate. Another active component = more $$ in manufacturing.

I just shut off phantom Power OFF on my dynamics because I just don't need the noise buildup on multiple tracks.

But, YMMV (god, I hate that phrase, don;t you?)
Click to expand...

I don't know of a mic preamp that doesn't employ some de-coupling at the front end, usually either by input transformer, or by blocking capacitors, so the differential amplifier doesn't in fact "see" the phantom power.
 
starsxandxslits said:
well, this may sound dumb, but my manual states against connecting unbalaced dynamic mics to xlr inputs with phantom power on...but i am certainly not in the know about what balanced and unbalanced refers to because i'm a dummy. plz explain to ease my nerves
Click to expand...

No such thing as a dumb question, only dumb people.

I have a feeling you are making a mountain out of a molehill. You would be well served to name the make and model of your board and mics. If you have 4 XLR inputs where you can choose Phantom (or +48v) on or off and you have 4 mics with XLR connectors and 4 male to female XLR cables, you are OK.

Turn on the board, make sure phantom is off, plug everything in, turn on phantom on the mics that need it and hit record.

You should be good to go.

If you want to make 90% sure this is right, post your make and model numbers here. If you want to make 100% sure, drop an email to tech support at the board manufacturer.

Good luck and make some good music.

Jim

(that first line was a joke)
 
starsxandxslits said:
well, this may sound dumb, but my manual states against connecting unbalaced dynamic mics to xlr inputs with phantom power on...but i am certainly not in the know about what balanced and unbalanced refers to because i'm a dummy. plz explain to ease my nerves
Click to expand...
I think that mainly means that you shouldn't actually connect or disconnect mics while the phantom power is actually on. And that's true ...... phantom power should always be turned off before plugging or unplugging any mics ..... otherwise you can damage the preamp.
 
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