Problem with driving LFE with pro amplifier

Discussion in 'Speakers' started by Jeffrey Stanton, Jul 18, 2003.

  1. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Hi Guys:


    I need some help with figuring out how to run a passive subwoofer with a pro amplifier off of the LFE output of my DSP-A1. I bought a Mackie 1400i amp to power my passive sub. I ran the LFE of my Yamaha DSPA1 to the pro amp and got almost no sound at all from the subwoofer. If you put your ear to the driver you could barely hear it.

    So I hooked the LFE to a Pioneer C-60 pre-amp and then to the pro amp. Got some sound. This was much better but had to turn the gains up ALL the way on both the pro amplifier and the pre-amp and the amp was still nowhere near it's maximum output, as the signal level lights on the amplifier were off most of the time, and only the bottom two would come on when the source material got loud. It's a 1400 watt amp, and the driver is rated for a maximum of 700 watts.

    The reason I think the amp isn't being driven to full-output is that with 1400 watts applied to it, I believe my AV-15 would have shot across the living room and clobbered the cat. Is there just not enough voltage (even WITH the pre-amp) from the LFE output to drive the pro amp? If that's the problem, how do I get the voltage up to specs (so the pro amp can get driven properly?

    What's your take on what might be going on here?

    Thanks,

    Jeffrey Stanton
     
  2. Ned

    Ned Supporting Actor

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    Just a note, the amp gain should always be set to max. It's not a "volume" control.
     
  3. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    It was up all the way. So was the volume control on the pre-amp.
     
  4. Edward J M

    Edward J M Cinematographer

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  5. Walt N

    Walt N Second Unit

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    I use a Mackie M1400i from the LFE output on a Denon AVR with no problem at all. With my Denon's LFE set at +4, the subs are getting enough power to blow me across the room if the master volume is high enough.

    I think something is amiss with how it's set up. The amp should work fine and I can't imagine there being a huge difference in the LFE output voltage between a DSP-A1 vs. a Denon AVR.

    Couple of troubleshooting questions:

    How far up is the LFE/sub volume on the Yamaha set?

    Are you using a 1/4" Tip/Sleeve(TS) adaptor plug on your sub cable from the Yamaha? Make sure the tip looks like the TS plug in the Mackie manual.

    Are you getting a solid connection on that adaptor? This has been a problem for some, so you might need to use some pliers to crimp the end of sub cable down a bit.

    Where are the "low cut filter" settings? If they're too high you'll get nothing out of it.

    Not to overlook the obvious, do you have the amp mode switch set to "bridge" and the sub's speaker wires connected to the two red output terminals on the Mackie?

    Good luck. You'll have that driver bottoming out in no time. [​IMG]

    Let me know if you need to make that fan quiet. I have a quick, cheap, easy, and very effective fix if it's bothering you.
     
  6. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Hey There Walt:


    "I use a Mackie M1400i from the LFE output on a Denon AVR with no problem at all.

    -No kidding? Hmmmm.....


    "How far up is the LFE/sub volume on the Yamaha set?"

    -Unless using DD/DTS, DSP-A1 LFE output is fixed, unadjustable.


    "Are you using a 1/4" Tip/Sleeve(TS) adaptor plug on your sub cable from the Yamaha?" Make sure the tip looks like the TS plug in the Mackie manual.

    -I went to Rat Shack and asked for their stock 1/4" to RCA adaptors. Think that might be the problem right there??


    Lowcut settings are ok, I experimented with them to make sure that was not the problem...also it's bridged properly
    [​IMG]

    Let me know how to quiet the fan, it is a tad on the loud side...

    I'm trying to contact Mackie as we speak but tech support is not answering their phone. And Yamaha to determine input/output characteristics of the units to see if there's a mismatch there.

    But what about those stock Rat Shack 1/4" plug to RCA connectors I'm using to go from LFE to the Mackie? I'm starting to get suspicious....


    Thanks, will get back to you tomorrow or Monday...

    Jeff S.
     
  7. Walt N

    Walt N Second Unit

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    The adapter you want is Rat Shack Cat # 274-884 or the equivelant. Just your basic phono to mono 1/4" plug adapter. The Rat Shack adapters can be a loose fit with some sub cables, so do crimp that phone plug on your sub cable a bit if you have anything less than a nice and tight fit there.

    "-Unless using DD/DTS, DSP-A1 LFE output is fixed, unadjustable."

    There's no subwoofer volume level adjustment for listening to music and whatnot? You might double check the speaker level setting calibration menu as I can hardly believe they'd do that to you.

    To quiet the fan, remove the outer case on the Mackie and cut one of the wires to the fan. (Doesn't matter which one.) Stay clear of the capacitors! Solder into the fan circuit a 10v 100ohm wirewound resistor from Rat Shack (Cat # 271-135) then tape up or heat shink the solder joints in the wire. Attach the resistor to the bottom of the amp case with a small dab of high temp RTV and you're done.

    I did this many years ago and now the fan is nice and quiet, but the amp still runs very cool. The fan in the Mackie is a two-speed model, yet I've never heard the fan go to the higher speed despite being run hard at times with dual SVS subs. Just make sure the exhaust ports on the sides of the amp are clear and you should have no problems at all.

    BTW I called Mackie about this years ago when I bought it, and they said they'd still honor the warranty even with the fan mod, as long as the damage was not heat related.
     
  8. Walt N

    Walt N Second Unit

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    BTW I just checked the sub-out voltage on a Yamaha and a Denon AVR in some old S&V bench tests. Both were lower models than what we have, but both tested between 7 and 8 volts max unclipped. Looks like the Yamaha isn't the problem there.
     
  9. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Hey Walt:

    Thanks for the info. I talked to tech support at Mackie and I told them what was happening and they said that I would need to get some sort of amplification of the LFE in order to drive a sub with the 1400i. They suggested a $99 TAPCO mixing board (which they make/sell) in order to get the gain I need for the Mackie to handle. I was in a hurry Friday so I couldn't get into a whole lot of detail with him (like why your Denon works eith no extra gain and why mine doesn't).

    I guess there are a few options to achieve this line level amplification of the LFE, but they said that would be one of them.


    My DSP-A1 LFE set-up must be weird. I've been through and through the bass management menus & owner's manual. For DD, default gain is 0, adjustable downwards ONLY. For DTS, LFE gain is default = 0, will go up to +10, and I think it is adjustable way down also. For non 5.1 material, there is no adjustment. It's fixed. This was their "flagship" receiver about 3 years back, don't know why it would be set up like that. Might e-mail tech support at Yamaha and see what they say. May have to keep you posted on this one in case things don't go well from here...

    Thanks,

    Jeffrey Stanton
     
  10. Walt N

    Walt N Second Unit

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    Jeffrey, when you go into the speaker level calibration menu (the menu you use to calibrate your speaker levels with an SPL meter) there will be a setting for "subwoofer". What level is that set to? If you're not seeing an adjustment for "subwoofer level", make sure your sub output is enabled in the speaker configuration menu.

    *If all the connectors are of the appropriate type and working correctly*, this should fix your problem. Turning up the sub level via this menu will increase the voltage to the LFE.

    I'm pretty darned sure you won't need an LFE amplification device. That just doesn't make sense at all given the voltage range your Yamaha puts out on the LFE compared to mine. Add to that, there have been many people on various forums using Mackie amps for subs (including Tom Vodhanel at one time) and I've never seen another mention of anyone having this problem.

    Please let me know what you come up with on the subwoofer level setting, and verification that your RCA adapter is the same as pictured in the Mackie manual or the one from the Rat Shack catalog I mentioned earlier. I fairly sure you'll find your problem with one of these items.
     
  11. Walt N

    Walt N Second Unit

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    BTW Jeffrey, I checked the Mackie manual and the input sensitivity requirement for the Mackie is only 1.23 volts for the amp to put out full rated power into 4 ohms. Your Yamaha is capable of at least 6 or 7 times that, so I'd say it's 100% certain that no signal amplification device will be needed.
     

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