JBL 4312As & New Power Amp

Discussion in 'Monitoring' started by Gary Gidak, Feb 10, 2003.

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  1. Gary Gidak

    Gary Gidak Active Member

    Apr 25, 2002
    Hi Folks,

    Got a minor dilemma I'm hoping you guys can help with. I've been mixing with a set of JBL 4312As for the last 10 years, and I really like the tone. Call me crazy! Anyway, the amp I was using was an old Denon (home stereo - multi input - dual speaker channel out) amplifier. I got totally used to mixing with the "Loud" button depressed (I thoroughly expect a tongue lashing from Fats), because of the increased bass at lower mixing levels. Anyway, the amp finally blew up last week in a hail of smoke and fire, and I bought a new Alesis RA300 to replace it. Now, that lovely bass I was used to hearing at low levels is GONE. The Alesis sounds beautiful by the way - clean, clear, with a nice shimmer on the high end, but not the bass response I'm used to. So, I placed a sub woofer (JBL Control SB-5) on a separate channel of my speaker switcher in order to get somewhere close to what I'm used to hearing. I do get an increase in the bass freq's, but not near what I think it should be. Should I - a) retune my ears to the existing acoustics? b) get a separate amp and do the bi-amp thing? or c) get some totally helpful advice from you folks. I'm hoping for "C". What do you guys think?
  2. audiowkstation

    audiowkstation Active Member

    Jun 29, 2001
    Two bad deals...

    First, the RA is a power amp. It is accustomed to being used with a line amplifier (like your mixing console) but make sure the impedance of your inputs on the amp matches what the output of your mixer has.

    Do balanced with balanced, unbalanced with unbalanced ONLY!

    Most of the time, using main out to an amp is better than control room out.

    On the note, the gains on the amp should be setr "all the way up" at all times. When you cut them, you are attenuating the input (and changing the input impedance some as well) Make sure they are against the stops. If one of them accidently gets turned down a tad, your mix will lean.

    Raw deal 2.

    By loading one channel of that amp with a sub and a JBL and the other with just the JBL, you are creating an impedance mix match (even with a speaker selector) that will cause L/R balance to be skewed.

    Either use 2 subs R/L or no sub at all.

    Unless you are summing the L/R to the sub, it will not be balanced. I never recommend a mono sub for these reasons... I only rec. 2 subs:

    1. Cone cannot be in 2 different places at the same time. Their are phase cues present in stereo that dictate stereo subs for proper translation

    2. Thre above impedance situation.

    Loose the speaker selector. It has resistors in it that ruin the dampning factor that you paid good money for in your amp.

    I would loose the sub, go main out and if you havce to insert a stereo EQ to get your house balance where you want it..you can..but EQ's shift phase as well so I would just get use to it without one.
  3. Gary Gidak

    Gary Gidak Active Member

    Apr 25, 2002
    Hi Bill,

    Thanks for the reply. To answer a couple of questions - I have an unbalanced out (digi 001) to an unbalanced in on the amp. The amp is only 2 channel out (L & R), and I have 3 sets of speakers: near fields, a stereo sub woofer, and the 4312As. That's why I went with the speaker switch to begin with, so I could select the speakers I monitor with.

    I will try running without the switch this evening, and see how that works.
  4. Gary Gidak

    Gary Gidak Active Member

    Apr 25, 2002
    Hey Bill,

    Just wanted to say, "thanks" one more time. You've been very helpful to me in my many cunundrums, and I truly appreciate your efforts. I tried the set-up without the switch, and it made no discernable difference. Straight out of the amp into the 4312s was the same as using the switch in-line. One tip that did help was cranking up the amp volume to MAX. That did the trick! It's amazing how simple some fixes can be. I now have a great, full sound, with nice low end. Thanks again.
  5. themidiroom

    themidiroom Active Member

    Apr 20, 2002
    St Louis
    I have a similar situation with my monitoring setup. I use my RA-300 to drive either my NS10s or a homemade set of nearfields with Vifa drivers. Any suggestions on more suitable speaker selectors? I'm using one I picked up from Radioshack. No frills spring loaded push button switches with gold plated contacts.

  6. Gary Gidak

    Gary Gidak Active Member

    Apr 25, 2002
    I got mine from Best Buy, although it's probably sold elsewhere. It's made by Monster Cable, and the model number is SS-4. They have a 4 speaker, and six speaker (pairs that is) version, and the output is 8 ohm impedence matching, so you can run more than one pair at a time without overpowering your amp. Check out monstercable.com, and you can find a picture of it with a little searching. Good Luck.
  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

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