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preamp and noise

Discussion in 'Preamps / Channel Strips' started by silentkid, Apr 18, 2005.

  1. silentkid

    silentkid Guest

    after recording for a year with just an sm58 (and no pre), i recently bought a new condenser mic. instead of just buying a phantom power adapter for it (which i initially wanted) the salesperson convinced me to get a basic preamp for a few more bucks.

    as i record mostly acoustic stuff, i'm really concerned with adding extra noise - which is why is wanted just an phantom power adapter - anyway, i was repeatedly told no, it's not really that noisy.

    my question is - how can you tell if a preamp is making noise, or if it's just doing it's job really well and the mic is super sensitive and picking up room noise?

    oh, i should add that there are moments when i can pick up radio station signals, albeit faint and staticky even with the gain turned all the way down.

    the pre is an apex model. i'm thinking of trying out the behringer ultragain pre, but i know some of their products are notoriously noisy, although in their product description they claim it has "very low noise"

    any thoughts/advice? thanks everyone.
     
  2. First question: How long is your cable run? I know that when I have cable runs totaling around 30 feet, I get local radio stations. When I go longer or shorter, I'm fine. The reason I am asking is that also occurs in balanced cables. (Also, the FM antenna in your car is actually around 30 feet from connection point on the board to tip).

    Second question: Have you checked for a grounding problem?
     
  3. Kswiss

    Kswiss Guest

    if you unplug the mic and turn the preamp gain all the way up and monitor the signal you can get a pretty good idea of how much noise the pre is adding to the chain..... it really shouldn't be much at all... If it has a bass rolloff punch that in and it should clear up a lot..... condensor mics are a lot more sensitive, so you are bound to hear things that you couldn't before..... i was doing a session yesterday and it was raining pretty good outside... i cranked the gain and recorded with almost perfect clarity the sound of the rain outside in a somewhat sound treated room.....

    K
     
  4. silentkid

    silentkid Guest

    hm... a grounding problem?

    i live in a 90 year old house, and some of older outlets are the 2-pronged variety. this means they're ungrounded, right? (which probably means the rest are ungrounded too)

    short of ripping all the wiring out of the walls and replacing it (and i assume that's how you would remedy it) is there something else i can do?

    kswiss, thanks for the tip - it never even crossed my mind!
     
  5. Call your local electrician. Really. It's worth every penny because if you make a mistake, that only asks for disaster. I used the old "if it has a conduit running to the box then just attach the ground wire from a three prong to the conduit or box" advice and eventually started a fire credited to that because my situation was a little different than the advisor's. Just ask the electrician about grounding only what you need grounded (cheaper that way). 99% of the time there won't be any wall-ripping. Ask him for the most cost-effective solution and make sure its someone who won't rape you with their price.
     
  6. dpd

    dpd Active Member

    Need to be careful here - the preamp is facing an open circuit with no mic attached. This raises the impedance at the preamp's input and raises the self-noise of the preamp to a higher amount than when the mic is attached. The mics are typically lower impedance and then the preamp works to a lower input impedance and, thus, presents a lower noise.

    Of course, now how do you know where the noise is from? One thing I have found is when you raise the preamp gain with a mic attached you will notice a point where the noise increases *significantly* as you increase the preamp gain from a slighly lower gain. IMO, that's the preamp's way of telling you 'too much gain' and the noise floor is now being set by the preamp and not the mic
     

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