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Another gain structure question!

Kev ParkerKev Parker Posts: 4
edited August 2017 in PA General Discussion
Hi all,

I’m a newbie to the board and would really like some help. After years in the game I am trying to increase my knowledge and set my system up better. I’m sorry that this question is on gain structure and promise that I have read all the guides plus tonnes of information from the web but I have some statements / questions I would like the experts to confirm/answer if you don’t mind �

My setup – Yamaha 01v96 V2, Driverack PA in to EV P3000 (top cabs) and a (new) Crest Pro Lite 7.5 subs. I have already set the X-over positions correct but with flat gain.


1st - I understand all the principles around the gain structure but still am struggling a little as my desk is digital and I’m not sure where to set the levels. So, I put pink noise through a channel and bring it until just under clipping on the trim, now, do I put channel up to 0? How about the master channel – what level? I think I am getting confused with dbu and dbfs. As I understand it ~-16 dbfs on the desk will be about 0 dbu = 0.775v output so should I just work on the master output meter and aim for no more the ~-12 dBfs??

2nd- once I know where I am with the above I can go through to the Drive Rack. Some questions – what output from the 01v96 will clip the DriveRack? I bring the level up (master) on the desk until the Drive Rack inputs are just under clipping then move to the power amps with no speakers connected

3rd – Increase the level on the power amps until the clip light just comes on then back off a notch. Mark the position. Now I know there is a lot of discussion around this but my amps have completely different input sensitivities – the EV quotes in the manual 0dBu/0.775V 6dBu/1.55V and Crest 2.20 V @ 2 ohms (I will be running at 2.67 ohms). For my system, this is the wrong way round as the EV is for tops so if I have to back off the input on the EV to compensate for the fact the Crest needs 2.20V and also back it off because tops normally need less power, then the EV might hardly be turned on! Is that OK or should I boost the level in the X-over for the Crest to make them “equal� at the point where the signals go in?

4th - as soon as all that is sorted go to the limiters and follow the well set out instructions.

I think my main issue is around having a digital desk and what the definition of unity is on the desk and how to deal with the mismatch in my power amp sensitivity's.

Sorry – I am sure you experts are sick of answering questions like this but I promise I have read a lot about this – I must just be a little stupid!

Thank you

Comments

  • DraDra Posts: 3,844
    Lets start with this. YOU must have self control, because however you set up the mixer / driverack / amp, YOU can drive at least one component into clipping if you don't
    Clipping at the amp: degrades the overall sound from not much to pretty bad and risks damage to the speakers.
    Clipping at the Driverack: DO NOT EVEN GO THERE. Meter levels should max (typ) at +10, with the very worst an occasion bump at +15. Horrible (actual) sound when clipped.
    Clipping at the mixer: Same as above and more critical to never clip. Meter levels should max (typ) at -9 or lower.

    1) Send pink noise to a channel and get it into the main bus (that is the only goal here). Monitor the channel level PFL on the main output meter and adjust gain until it is maybe -9, with fader down.
    2) Turn off PFL to monitor the main bus with the main meters and set main fader to unity (-0-).
    3) Increase the Pink channel fader until the main meter reaches -9.
    4) Check the DRPA input meters. Hopefully they are +10 or lower.
    5) With speakers unplugged, increase the amp's attenuators until the inputs are lightly clipping. At this point there is no more to give.
    6) Set the limiters in the DRPA for the amps. Remember that if you boost the gain of a x-over band that you may push the signal into clipping on the output side. If this is the case you must return the band level to not clip and REDUCE the gain of the other output band. You might also set the limiter in the mixer to keep the DRPA from receiving to much signal.
    7) If all has set up as planned, -9 on the mixer is your "Don't go past this point under any circumstances!" The amps are out of gas. If you need more volume, you need more rig.

    Hope this helped. You can creep closer to 0 on the mixer but there are risks (big ones). Make sure to adjust everything downstream to match up.
    DRA
  • DraDra Posts: 3,844
    Amp sensitivity problem.

    You simply will set each amp to it's max (non-clipping) attenuation level. From there you decrease the band that is too loud (never turn up the weaker because you are already at the clip point). This is either done at the amp or in the DRPA x-over gain for that amp. Some like to turn all amps up to max and do all gain structuring and band reduction (balancing) in the DRPA x-over section.

    So if you play music and you say "I need more sub output.", no... that is wrong. You should say "I need less mid/hi output.", because you have no more sub to give.

    DRA
  • Thanks for both replies - I really appreciate it!

    Just a couple more questions.

    If everything in the DRPA is "flat" i.e. no boosts/EQ etc, should, say, +10 on the input translate to +10 on the output?
    There is definitely no harm running both the P3000 and the Pro-Lte 7.5 with no load?

    Thank you!

    Kev
  • DraDra Posts: 3,844
    +10 in = +10 out?
    Generally, no. At least if the signal is divided by the x-over, because each side of the separation has removed signal. To gain signal back, you'd have to raise the gain for that band in the x-over, but usually that is not necessary.

    No, modern transistor amps won't be damaged. My understanding is that old tube amps would be if there was no load.

    DRA
  • Interetsing - and it makes sense. I guess the output will be determined by the nature of the incoming source (drum and bass v's opera!) and where the cross-overs are set. But if there is no crossover and you are running full range +10 in means +10 out......

    Thanks for all your help - appreciated very much!

    Cheers

    Kev
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