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Thread: DBX Driverack PA

  1. #46
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by Tim Rinkerman View Post
    ...now you are quoting techspertise from RANE!!!? The poor man's Behringer?! There are very few "pro" devices of any sort than can corrupt the signal chain merely by pushing the "in" button without actually using the device's features...Rane makes most of them....
    +1.

    Quote Originally Posted by 1audiohack View Post
    The statement that Rane is the poor mans Berhinger is just bullshit.
    Golly, you're right too! They're both all that - and less! Never met a piece of either I wouldn't bypass - physically!

    Quote Originally Posted by Tim Rinkerman View Post
    ...you've dragged this piece of crap Driverack out to ad nauseum...
    +100...

  2. #47
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by Steve71 View Post
    Did I make a mistake with my ... calculation?
    Uh, yeah, it would seem so.

    Quote Originally Posted by Steve71 View Post
    I'm more than willing to eat my words, but I'll need some facts please, not just a 'because I said so'.
    OK.

    Quote Originally Posted by Steve71 View Post
    The outputs on the dbx (+4dbu) will overdrive the inputs on a consumer amp (-10dbu).
    See, that there is wrong - you've blurred the units. It is +4 dBu relative to -10 dBV. You are changing reference levels (units), the former to 0.775 volts the latter to 1.0 volts. Remember, we only have conventions so we can change them!

    Quote Originally Posted by Steve71 View Post
    To overcome this your only option ... is to use the dbx's digital gain controls. Now you've just reduced your s/n ratio by 14db.
    When adjusting for units, the gain difference is 12 dB.


  3. #48
    Senior Member Eaulive's Avatar
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    Quote Originally Posted by Steve71 View Post
    Sure you can, but since it's done in the digital domain, it's unless for setting up correct gain structure (unless you already happen to be in the ball park). IE it does nothing to reduce the noise the DRPA adds to the chain.
    Words of wisdom.

    In some installations I had to set the levels on the PAs to prevent a bozo from cranking them up because he wanted more volume, effectively using very little output from the driverack but that's not the way to go.

    If you use a sensitive amp (like a consumer amp or a pro amp with the levels set to max) and reduce the output on the driverack, you are NOT reducing the noise caused by the D/A converter!
    The right way would be to use the processor up to its full output or let's say 12dB down, and to reduce the gain on the amp or with a attenuator or a pad.

  4. #49
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    Quote Originally Posted by boputnam View Post
    Uh, yeah, it would seem so.

    OK.

    See, that there is wrong - you've blurred the units. It is +4 dBu relative to -10 dBV. You are changing reference levels (units), the former to 0.775 volts the latter to 1.0 volts. Remember, we only have conventions so we can change them!

    When adjusting for units, the gain difference is 12 dB.

    Red herring! JR's Krell amp has XLR inputs so the voltage difference (between the dbx and amp) was an incorrect assumption on my part (this was discussed earlier in this thread).

    However this (as already discussed) does not alter the fact that the input led's on the dbx did not get above -30dbu, which of course tells us the DRPA was not setup correctly (by a wide margin) for whatever reason.

    This is a really open and shut case of user error and no amount of wishful thinking can alter that.

  5. #50
    Senior Member jerry_rig's Avatar
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    Quote Originally Posted by Steve71 View Post
    Red herring! JR's Krell amp has XLR inputs so the voltage difference (between the dbx and amp) was an incorrect assumption on my part (this was discussed earlier in this thread).

    However this (as already discussed) does not alter the fact that the input led's on the dbx did not get above -30dbu, which of course tells us the DRPA was not setup correctly (by a wide margin) for whatever reason.

    This is a really open and shut case of user error and no amount of wishful thinking can alter that.
    Not that I have to defend myself to you on this forum, but I never said that in my installation the dbx did not get above -30db. Please do not be so quick to assume "user error." It will not make you many friends here.

    Peace.

  6. #51
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    Quote Originally Posted by jerry_rig View Post
    Not that I have to defend myself to you on this forum, but I never said that in my installation the dbx did not get above -30db. Please do not be so quick to assume "user error." It will not make you many friends here.

    Peace.
    From post # 22

    Quote Originally Posted by jerry_rig View Post
    Please don't take my comments as a bonafide review of the DriveRack. I was simply noting what I perceived as cleaner deep bass from the Ashly. All lights on the dbx indicated very low operating levels. As I recall only the first level was lit up. Note that the crossover is being used to match a pair of 2235s to my other speakers. All are driven from the same pre-amp and the low-end power amp does not have attenuation, so I don't have much flexibility to push (or limit) signal strength at the crossover. It is what it is...
    The first level is -30db (see pic below)

    I come here to learn and, on rare occasion to debate something I see is in error. I try to do that in a somewhat diplomatic manner and to let the facts speak. I do not wish to offend you, but If the truth offends you, then so be it. From the facts you presented here the dbx was not set up correctly. And if you don't consider throwing away a potential 45db of s/n ratio as user error, I'd hate to see what you do consider user error.

    To be fair to you though, you were just using what equipment you had on hand. And you have stated many times that you're not presenting your impressions as the be all end all. I would be interested to know (1) if your pre-amp has XLR outputs and if so did you use them? And (2) if your pre-amp doesn't have XLR outputs, did you use the +4dbu/-10dbu sensitivity switch on the back on the unit? It's entirely possible that you did the best with what you had to worth with, but it's also entirely possible that you could have improved the s/n ratio a bit. However without an amp with gain controls, you're behind the 8 ball to start with.
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    Senior Member jerry_rig's Avatar
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    Quote Originally Posted by Steve71 View Post
    I would be interested to know (1) if your pre-amp has XLR outputs and if so did you use them? And (2) if your pre-amp doesn't have XLR outputs, did you use the +4dbu/-10dbu sensitivity switch on the back on the unit?
    My preamp is a Pass Labs XP-20 and I used the balanced XLR outputs to drive the crossover (and XLRs to the Krell). My recall as to the level readings should not be taken as gospel. I'm certain it was working properly. Now let's move on, please. Thank you.

    Jerry

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    Quote Originally Posted by jerry_rig View Post
    My preamp is a Pass Labs XP-20 and I used the balanced XLR outputs to drive the crossover (and XLRs to the Krell). My recall as to the level readings should not be taken as gospel. I'm certain it was working properly. Now let's move on, please. Thank you.

    Jerry
    I'm sorry you've lost me. How can you be certain that it was working properly, but also be uncertain as to the levels? The latter determines the former.

  9. #54
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    Quote Originally Posted by Steve71 View Post
    I'm sorry you've lost me. How can you be certain that it was working properly, but also be uncertain as to the levels? The latter determines the former.
    If you were using a preamp to drive the DBX, the input LEDs would probably not all be lit unless the preamp was turned up quite a bit-ie a very loud listening situation. If you set the inputs to be all lit up at a normal listening level, the inputs would clip if you ever wanted to crank it up via the preamp.

    It seem plausible that he could have it set up correctly and have only the lower LED lit if the preamp wasn't cranked up to 11.

  10. #55
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    Quote Originally Posted by JeffW View Post
    If you were using a preamp to drive the DBX, the input LEDs would probably not all be lit unless the preamp was turned up quite a bit-ie a very loud listening situation. If you set the inputs to be all lit up at a normal listening level, the inputs would clip if you ever wanted to crank it up via the preamp.

    It seem plausible that he could have it set up correctly and have only the lower LED lit if the preamp wasn't cranked up to 11.
    I have mine setup such that it doesn't clip when cranked, but at 55db (background levels) it still lights up the -30dbu lights. And it's only with fine gain controls on all the amps that I can get the volume range where it needs to be while keeping the input/output leds where they need to be.

    Ideally you'd keep your pre-amp fixed and adjust for volume after the dbx with a multichannel volume control. However these are expensive and hard to come by.

    Let's be clear though, there is a big difference in s/n ratio between a setup that lights up the -30dbu lights at high volume and one that does it at 55db. I've had my system setup both ways (before I bought the right amps for the job) and there is without a doubt a difference in sound quality.

    Actually, if your amp doesn't have gain controls you can get around it by building custom XLR cables (between the dbx and power amps) with a simple voltage divider circuit to reduce the output after the dbx. I did this for a while but in the end gain controls offer more control.

  11. #56
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by Steve71 View Post
    This is a really open and shut case of user error and no amount of wishful thinking can alter that.
    Ouch! A spanking! Odd...

    Quote Originally Posted by jerry_rig View Post
    Please do not be so quick to assume "user error." It will not make you many friends here.
    Boy-howdy to that. Agreed. There are ways, and then there are better ways.

    If one loses their inquiring students, they are no longer teaching as no-one is listening...

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    Quote Originally Posted by boputnam View Post
    There are ways, and then there are better ways.
    And there are wrong ways, and mostly wrong ways and partly, sometimes wrongs ways... ad nauseam.

    Call it what you will, it is what it is - A system with a poor gain structure such that the s/n ratio off by a potential 45db or more depending on where the volume control is. Shall I email dbx's tech support and see if they think a max signal of -30dbu is acceptable?

    From the dbx manual - second to last page of the appendix - link

    http://www.proliveaudio.co.uk/Web%20...k%20Manual.pdf

    One thing that is critical to system setup is maximizing gain structure. Gain structure refers to
    aligning the gain of each device so that they all clip at the same point, and the noise floor of
    the entire system is at its absolute minimum. Quite often PA systems are setup with the amplifier
    input controls turned all the way up in the incorrect assumption that this is the only way
    to get the maximum output level.
    Note that the Krell amp in JR's system does not have gain controls and as such falls into the incorrect 'input controls turned all the way up' category.

    Notice too how they said, "Critical" and "maximizing gain structure" in the same sentence.

    Quote Originally Posted by boputnam View Post
    If one loses their inquiring students, they are no longer teaching as no-one is listening...
    Regardless, the truth is the truth. If people want to stick their fingers in their ears, it's their loss, not mine.

  13. #58
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    The last time I used one of these in a SR situation, I was having problems with trying to get the vocals to come through. I found myself pushing the hell out of 800 - 1400 on the desk. I asked the in house guy about the crossover frquencies he was using and he gell fully replied 200hz and 1600hz. The system consisted 2240's 2225's and 2445's. I was having doubts about the performance of his driverack and then it all became clear. I asked why he chose 1600 as a crossover point and he commented that it was the optimum for the gear he was using. He then asked what I would use and proceeded to roll around on the floor when I replied 800hz......he started rambling about feedback and blowing drivers.....oh well. each to thier own........
    Many people confuse poor performance with poor setup. The driverack stuff is great when used as intended but as with most things, can sound like bum if the setup is poor.

    Allan.

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    1600hz to go from a 2225 into a 2445, not so bad'ish! 800hz to go from a 2240 into a 2225 WAY off!!!!!!

  15. #60
    Senior Member Eaulive's Avatar
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    Quote Originally Posted by Mike Caldwell View Post
    1600hz to go from a 2225 into a 2445, not so bad'ish! 800hz to go from a 2240 into a 2225 WAY off!!!!!!
    I had the same reaction when I read this post, but after re-checking I think he meant 800 instead of 1600 from the 2225 to the 2445, keeping the 200Hz point between the 2240 to the 2225.

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