Daisy Chain is a no go

Discussion in 'Archived Threads 2001-2004' started by Chris Tsutsui, Oct 8, 2002.

  1. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Test: 2 identical tempest adire alignments powered by two identical 250W plate amps. link
    2nd plate amp daisy chained to another resulted in a noticeable loss in decibels and loss in SQ.
    The Parts Express 300-974 amp manual says "full range" mono pre amp out, but in small parenthesis it says (20-20khz). Therefore during 15-20hz test tones the 2nd sub receives barely anything at all while the 1st sub shines with authority.
    Not to mention the sound quality of the 2nd daisy chained sub is noticeable worse when the crossover setting is adjusted high, I couldn't imagine anyone else running their plate amps daisy chained. The sound from the 2nd amp has more highs than the first sub and sounds muffled while lacking deep bass. Both amp settings are identical and location is mirrored in rectangular room, and I swapped the amps and messed with 3 different subwoofer interconnects and had the same conclusions.
    I guess I'm going to have to go Y-splitter because of the pre amp outs on the amps. Unless of course someone can explain what's going on.
    When I first fired up the subs I was like "What's going on! are these amps different?" The bass stage actually shifted to side of the 2nd sub as it appeared to play more muffled upper bass than the first sub therefore drawing attention to itself. Of course to the average ear the subs would be OK as I had to concentrate a bit to figure things out. [​IMG]
    I wonder if others, maybe even the AVA250 has a similar problem with pre-outs? Anyone see if their pre-outs are full range by seeing if a 15hz test tone will pass through or playing full range signals through their subwoofers and focusing on vocals like I did?
    Oh well, I hope a Y-splitter will solve the problem and not degrade SQ. Guess it's off the the rat shack tomorrow.
     
  2. ColinM

    ColinM Cinematographer

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    Identical #26 and #27 resistors I assume? Factory intact 300-794's?
     
  3. Patrick Sun

    Patrick Sun Moderator
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    Don't sweat the Y-connector to power two amps. It's done all the time.
     
  4. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Chris,

    The explanation is simple really. The preamp outputs on those amps are high-pass filtered. There was apparently some mis(non)communication between the engineering and marketing depts at the amp's manufacturer. Can't blame PE (or any other vendor), as they're simply going by what was given to them in the 'features' sheet. I suspect the Adire model has the same feature, unless it's another thing that they've chosen to modify.

    FWIW, the filter is identical to the 'rumble' filter, with different resistor values of course. It's easy to modify if you wish. I believe it presently has an Fc of 140Hz, Q=1. It's nice to have if you were in a position to utilize it properly (main preout/main in loop). The smaller amp (300-792) also has filtered preamp outputs, though they are filtered passively. IOW, the filter characteristics of that amp will depend on the input impedance of the amp that they're feeding.

    Hope this helps.
     
  5. Geoff L

    Geoff L Screenwriter

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    Chris
    The same thing happened on my end when I tried to daisey my two DIY PE~300-794 DIY powerd subs.
    I freaked too!
    What the #$@%^..!![​IMG] Something is defitnitly wrong here, so I did the Y-split off the LFE no problem!
    Just add a little more gain on the amp pots after you do the split..Even split 3 way once with no problems.
    Also feed the inputs on the PE amps with a Y and you pick up a db or so of gain over the single feed. Summed mono I know, but try it and you will hear the slight volume increase as soon as you plug the other rca in off the Y...
     
  6. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Both amps have no boost, both identical with same part number and purchased months apart from parts express.
    (300-974)
    Actually Baldemar, the 300-974 line level pre-amps outs arn't high pass filtered but are designed for mono sub outs. What I believe is happening is the signal is passing through TWO rumble filters as well as an additional subwoofer IC which degrades the signal and cuts off low frequencies (20-30hz range) from the 2nd sub.
    Here's what the manual says:
    Line out: This line level RCA output provides a full range (20-20kHz) output and is used to connect "daisy chain" the line level signal to other amplifiers. Note: Line out is only active when a signal is present at the line-in input.
    I think the problems I've encountered should be addressed with the amp makers so perhaps they can fix it or explain what's going on. I just find it odd to have pre-amp outs that call themselves full range yet alter the sound quality and filter out a few decibels and LF bands?
    Anyways:
    If you saw pics of my room you'll notice the subwoofers are positioned with one in the left front corner, one in right front corner...
    Here's what I forgot to mention..
    When daisy chaining it affects the timing the bass hits the seating position. I noticed an immediate unbalance in bass that hit my ears due to the phase cancellation occuring right at my seating position. I whipped out the SPL meter and sure enough there was definite cancellation of bass due to the lag in signal through the two 12 foot subwoofer cables and a pre-amp pass through.
    I had to change one of the amps to 180 degrees while the other amp remained at 0 deg phase in order to maximize bass at the seating location. If I set both amps to 0 degrees or both to 180 sure enough there's a loss of over 3 decibels and LOTS of noticeable bass "phase cancellation" noise. You know the real annoying bass that sounds like its pushing in one ear and pulling in the other.
    Anyways this still didn't resolve the sonic differences and response between the two subwoofers so I went to radio shack and spent $4 on a Gold series Y-splitter.
    Click, I set it all up, and what do I get? Bass cancellation at the listening position yet again... Oops, forgot to change the second amp back to 0 degrees to match the first amp...
    Bingo, both amps are now set to 0 degrees and the SPL is maximized as there's no cancellation. I feel much better now that the bass is crisp in the soundstage, and both subs have now become acoustically invisible. [​IMG]
    The Y-splitter has been the best bang per buck upgrade in my system. So, for those who will ever ask the question: To Y, or not to Y... I have the following reasons NOT to daisy chain (connect one sub amp to another amp):
    1. Signal obviously hits one sub first and then to the other which needs a phase tuning.
    2. The 2nd sub gets a signal that has to pass through a pre-amp out that could affect sound. (Despite that the amp may say full range pre-amp out)
    3. You'll need to use longer subwoofer interconnects if you separate the subwoofers to L/R since the signal has to go to one side of the room, then the other. (instead of Y splitting and both going half the distance of the room to each sub)
    Now, the question I'll have to answer next is: Does tuning 2 subs with mode cancellation work for equalization? And then: How many decibels do I gain from putting 2 subs in one corner rather than separating them, and what are the sonic differences regarding position?
     
  7. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Chris,
    I guess maybe you'll believe this guy, if not me [​IMG] He knows his stuff, and even measures it!
    http://www.geocities.com/kreskovs/PE300-794.html
    The manual has ALWAYS claimed what you've read, and unless PE has forced the manufacturer to change the active filter feeding the line outs (which would raise the cost of the amp IMO), the high-pass filter is still in place. Search the web, the schematic can be found and clearly shows the circuitry in question. You'll have to check with PE to make sure.
    Good luck.
     

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