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Just changed amps- Do I have to re-run the "wizard"?

bandeng71bandeng71 Posts: 13
edited January 2012 in PA Configuration Wizard
I just changed power amps going from microtech 2400's to qsc pl230's. The guy I got the system from said he set the gain in the wizard @ 0.775 v for the crown microtechs. The qsc's are 1.4v or 32db gain.

Do I need to re-run the config wizard and set it to 1.4v and reset my gain structure?

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    GadgetGadget Posts: 4,915
    Since it takes almost double the voltage to achieve full output @ 1.4vrms yes.. I would think so, HOWEVER, your mixer have plenty of gain to make up for that... the problem arises when tops and subs are used... and different amps are used... If it's only tops you could just leave it, OR use any amp with 1.4Vrms input sensitivity, like the Crown CTs or Macrotech, or ... it's the VOLTAGE GAIN that matters after the fact...that is what determines the point the input attenuators (or crossover gain) end up...it matters little which way you goes in the long run...

    We delve into this a bit ,ore in the FAQ and "Start here" sections...

    Gadget
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    bandeng71bandeng71 Posts: 13
    That explains why I'm running out of headroom on the mixer then. Will I have to adjust my stored programs? or just run the wizard and set the new gains, then exit the wizard?
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    GadgetGadget Posts: 4,915
    Well, you never did say if this was a set of fullrange speakers or tops and subs? I "assume" at this point that it's a set of fullrange? If so why not just turn up the amp 50%? and leave everything the same.. If you go to reconfigure the program you will LOOSE the program.

    If you haven't done so already, you should copy down the setup, and settings..for a "rainy day" :wink:
    Gadget
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    bandeng71bandeng71 Posts: 13
    Sorry, it's full range tops and subs, mono. I've got all the settings written down so that's no problem.
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    GadgetGadget Posts: 4,915
    Ya but why mess with that when all you need to do is turn the amps up? I swear I'll NEVER understand this penchant for amp sensitivity settings.. It's all a tradeoff ESPECIALLY when tops and subs and disparate amps (not the same) are involved...

    Look, when you have tops and subs, you need 2-4 times the power for the subs minimum... If you had the same amps for both subs and tops you would be either WAY overpowered on the tops, or WAY underpowered on the subs, probably both.

    The chances of having the perfect setup, power wise, is slim...(read this EXPENSIVE) so we must make the best of what we have... this is where we make compromises... where we do whats necessary to balance the system and achieve a flat and accurate system.

    Now, there are a couple of ways we can accomplish this, we can simply CRANK the amps up and use the crossover gains to do the balancing, use the amp sensitivity (and still have to do some manipulating of the crossover gains if the amps and speaker gains are not matched perfectly)... or a combination of the two...but for this forum, where novice to newbie is the general wayfarer...we suggest the method in the START HERE thread, the gist of the gain structure follows:

    Gain Structure...

    note: the below was written PRE PA+ which is covered above... but the principles work well with the PA+ as well (I generally skip the auto balance step and use this method...

    1. Turn amplifier(s) attenuators all of the way down to zero (fully counter clockwise), disable amplifier(s) clip limiters (if used), and disconnect the speaker cables.

    2. Make sure all DriveRack dynamic processors like GEQ, Compressor, limiters, PEQ, AFS, SubSynth, etc., are disabled. We will set those things after we are roughed in...

    3. Play pink noise through one of input channels of the mixer because it's consistent dynamically...(equal energy to all frequencies with a crest factor that is consistent across the full spectrum)

    Note: Please click here to download a 20 minute pink noise track (track58.zip) by courtesy of Michael \"Bink\" Knowles... His entire test CD can be found here...
    http://binkster.net/extras.shtml#cd

    4. Set the mixer input channel fader (with pink noise) at \"unity\" (0dB). Also zero the EQ.

    5. Disable the AFL(s) (after fader listen) on the mixers master output channel(s) and enable the PFL (pre fader listen) on the mixer input channel (with pink noise). If your mixer does not have these features just make sure you have no clipping and sufficient signal to not run into signal to noise problems.

    6. Turn up the mixer input channel gain trim pot (with pink noise) until the meter bounces in the yellow at least 6dB below clipping. MAKE SURE THERE IS NO CLIPPING! (actually anything over 0 VU will be fine)

    Note: If your mixer doesn't have PFL simply set the input gain just below the point where the channel \"clip light\" barely (occasionally) bounces on.

    7. Disable the PFL on the mixer input channel and enable the AFL(s) on the mixer master output channel(s). Again if you don't have these features just make sure that your output meters are just at the clip point.

    8. Slide your mixer's master fader(s) up until meter is just barely (occasionally) bounces in the red at clipping.

    9. (DR260)With the DriveWare GUI open (DR260) the DriveRack panel meter and then one of the mixer input dialogs (click on the \"M\"). Put the master fader at “unity� (0dB). Watch the DriveRack’s panel meter and pull the input fader up or down until the output meters are bouncing in the yellow about 3dB just below clipping. Absolutely no clipping (red) on the DriveRack’s input or output panel meters!
    If you are using a DRPA you have a button on the back that sets the input sensitivity to +4db (pro level) or -10 (consumer level) if the meters on the mixer are at just clipping and your using +4 and the meters on the Driverack are anywhere above the threshold -20 area, but below the clip light your fine... there is no input mixer to adjust... If the signal is low try the -10 setting and see if that gets you to a more appropriate setting. (NOTE most pro level mixers will put out 22-28dB of gain, if your sending a signal that is close to -0- vu the input meters will read only the first 2 LED's THIS is because the -0-vu point on the Driverack is +22dB.

    10. Click on the other channel’s mixer input dialog (click on the “M�), set the master fader at “unity� and put the input fader at the very same location as the previous channel.

    In the DRPA, output levels are controlled by the crossover gain... this means that if your at 0db as we discussed earlier the output meters will be showing the output gain... as long as they show a decent signal this is fine... remember this is all in the digital domain so signal to noise is not as big a problem as in analog circuits... try adjusting the amps before you change the gain of the crossovers, if you cannot get the amps to clip, or your amp sensitivity is perceived to be too high... then adjust the crossover gains...

    11. Make sure all speakers are DISCONNECTED FROM THE AMPS..(unplug speakers as proscribed in step #1).. modern amps have open circuit protection) Turn up the amplifier gain trim pot (clockwise) until the amplifiers red clip light barely bounces on.

    12. Turn back the amplifier gain trim pot (counter clockwise) about 3dB to 4dB from the clip position. Mark this position. This position provides approximately 3 to 4dB of headroom before clipping. This is the highest the pots should ever be turned...More headroom can be achieved here by turning DOWN the control but it is NEVER to be turned up past this point!

    13. Repeat steps 11 and 12 for all amplifier(s) channels driven by the DriveRack. Return the master faders on the mixer to -0- . Plug the speakers back in.

    Now we have all the equipment talking the same language.. but we haven't balanced the system yet... it's most likely that one set of speakers will be louder than the other so we need to balance them before we move on... it's a good bet that the subs will be the quietest since they require the most power... put some good full range music on your system.. I like Steely Dan, Toto, Dread Zeppelin, ETC and set the input fader on the input channel on the design center( unity gain point) (this gives the best signal to noise in the analog domain) again press the PFL button and view the output meters and verify that the signal is well below clipping but above or about 0vu.. those lucky enough to have channel meters on each strip a yellow indication is acceptable..if only a two light LED is available turn up till red then turn down below clip point.. disable PFL. Turn master fader up till the system comes to life and if the tops are much louder than the subs... turn the tops amp down... get a good balance and turn the system up till near performance volume and assure it still sounds balanced...
    So that's my argument here.
    Gadget
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