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Thread: trying to bi-amp...crossover adding too much hiss

  1. #1
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    trying to bi-amp...crossover adding too much hiss

    Hi guys,

    Maybe you guys can help me with bi-amping my front JBL 4675's & 4670.
    Pre/pro=Denon 2807
    HF amp= L/C/R channels of an Outlaw 7700
    LF amp=Monster MPA-3250

    Signal from Denon is unbalanced.

    I've tried several different prosound x-overs including a behringer dcx2496 digital, an analog dbx, an analog behringer, and I currently have a bbe ds48 digital. All of them have caused too much hiss.

    Thinking maybe the hiss is due to trying to run a balanced pro sound x-over with an unbalanced signal I even tried my old Audio Control caraudio x-over and it hissed badly also.

    Everything I've tried results in WAY too much hiss coming from the horns.

    I tried various level settings such as boosting the input signal and cutting the hf outputs on the x-overs but it really didn't help. Basically with all trims on the x-over at their minimum I still hear a lot of hiss.

    If i just run the signal straight from Denon right into the Outlaw(hf amp) then there's barely any hiss at all.

    Both the Outlaw and the Monster have the balanced input option so would getting something like a rane balance buddy to get a balanced signal help hiss?

    Thanks in advance for the help,
    Ken

  2. #2
    JBL 4645
    Guest
    The cinema setting is usual 500Hz 24db down at the LF end that is you know at the top of the range, the HF horn is crossed off at 24db where it starts off at, if you what to cross off the LF at the lower end to prevent excursion with lower filter setting that’s up to you, personally the JBL 4675-A THX is bitching loudspeaker that kicks ass BIG TIME!

    Add some EQ filtering to you know fitter out the hiss, that should compensate, and besides you don’t need the whole sonic range to rip you’re ears off in home, you’ve got those JBL 2360-A horns haven’t? those beasts are very sensitive, so set the microphone to the RTA if you have one and just set them for a lower level in the room they have a wonderful dynamic range handling that needs less in the home, so have ago with that idea if it helps.

    85db in the cinema so try aiming for 75db rather than 85db set the levels up high on the Behringer DCX2496 and reduce the amplifier power keep going at it and don’t give up, I noticed this yesterday when I decided to boost the level outputs on the DCX2496 all I did was turned down the amplifier levels and besides I’m running far smaller JBL loudspeakers than you, only wished I had a set of JBL 4675-A three!

  3. #3
    JBL 4645
    Guest
    Look at the size of that thing!



    I gather youíve add a third JBL 4675-A since last year then, yeah set the amplifier levels at a differently I was speaking to one of the UKís top cinema installers a last month and I canít remember what the guy said as I had a dozen questions about the THX set-up at the Empire, where different mixtures of crossover filters are used a combination of (Bessel and Linkwitz-Riley).

    Amplifier levels as far as I can remember he said where set at different levels, I could chase this up for you in the morning UK time and get a little feedback.

  4. #4
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    Hi jbl 4645,

    Yah that's an older pic of my front stage. I've since changed the center channel a bit where each woofers in their own cabinent and the horn is between them. I did this cause I'm running a larger 133" screen now and I needed to drop the horn down below the screen.

    I've also sold the maggies.

    I'm now running four 2242's for subs.

    I want to keep the 500hz x-over point. The Outlaw and the Monster don't have adjustable level controls. I have been using QSC amps and I could run the gains down on them to get the hiss bareable but I was having to crank up the denon to the point where it started adding some unpleasantries. I would like to keep the "hifi" amps in the system for now if possible as the lack of fan noise is nice plus from what little I've run them I like the sound of them paired with the JBL's.

    Now matter how I calibrate the hiss is present even at idle. It doesn't go up with volume...just a steady loud hiss.

    I wonder what are the x-overs doing to the signal to add so much hiss?
    I could understand if I had the x-over gains cranked wide open but even at their lowest settings the hiss is far too loud.

  5. #5
    JBL 4645
    Guest
    KenWH

    I looked around and remembered thereís the JBL cinema handbook or cinema manual, it might come in handy with most of the pro JBL that youíre using there.
    Donít leave home without it.

    http://www.jblpro.com/pub/cinema/cinedsgn.pdf

  6. #6
    JBL 4645
    Guest
    How about then a simple routable voltage control volume pot that can brought from any electronics store and just apply several in-between the line outputs to the amplifiers, solder up the cables, starting to get the picture now! This should cost no more than $15.00 US dollars for six, with cable and a few RCA phone plugs to be attached on one end or it might cost over $15.00 if you amps have XLR, this is the easiest approach I can think of at the moment.


    In fact I donít know why I didnít think of this before, I think Iíll use the same approach, Iíll need to pop down to (DJ electronics) the week after next. Iíll need a plastic box to fit the volume pots in, and attach the necessary RCA phone inputs and outputs on the back of the box, otherwise LOL it would be a load of dangling wires everywhere.

  7. #7
    JBL 4645
    Guest
    This got me thinking for a moment while I have this weeks top region 2 film playing, I muted all the channels turned up the volume on my Marantz 1050 which are driving the JBL control 1 as a mid and high end, I know that sounds confusing no matter, I then adjusted the crossover on the HF while reducing the high end from 20KHz down to 1KHz the hiss became lesser and lesser.

    I notched the hiss is more on the right output channel with my DCX2496 and after a little toying around I activated an EQ filter and reduced the level and widened the Q and the hiss dropped down considerably. Have a go with that solution and see if this adds any remedy for the hiss issue.

  8. #8
    JBL 4645
    Guest
    This need some basic looking into so I powered up the Behringer MIC 100 hooked up the ECM8000 and placed it near to the JBL control 1 mid high end and looked at the RTA to see what range of the hiss was at, the Technics SH-8055 gave me a broad range from 8KHz to 16KHz! So it looks like the hiss covers from 8KHz though the high range up to 16KHz kind like wideband pink noise being filtered or something like that.

    Here’s a little picture show of what I did within the last 15 minutes. I had to turn the CRT off because the ECM8000 picks up the high frequency transmission from the TV.

    If you look close to where the RTA is, you can make out a display I know you can’t see it in greater detail, but that’s 8 and 16KHz being displayed on the RTA.
    Attached Images Attached Images   

  9. #9
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    When I was running Yamaha 31 band eqs between my preamp and power amp sections, I was also really bothered by the hiss it added.

    Rather than using pots, I simply soldered a series resistor right on the hot lead inside the 1/4" phone jack. Worked like a charm. I tried a couple until I found a value that substantially cut the hiss (a little over 10 dB), but left plenty of volume to play with.

  10. #10
    pelly3s
    Guest
    i tell my customers this all the time proper gain structure is everything. make sure if you have a -10db output the input it goes to is a -10db input. I would suggest trying a balancing box like the Rane you mentioned. if your gain structure is right then you will have no issues (well shouldnt)

  11. #11
    JBL 4645
    Guest
    Quote Originally Posted by toddalin View Post
    When I was running Yamaha 31 band eqs between my preamp and power amp sections, I was also really bothered by the hiss it added.

    Rather than using pots, I simply soldered a series resistor right on the hot lead inside the 1/4" phone jack. Worked like a charm. I tried a couple until I found a value that substantially cut the hiss (a little over 10 dB), but left plenty of volume to play with.
    toddalin

    Yes, yes someone mentioned that before. What value are the resistors that you used that might turn out to be an even more affordable solution, resistors don’t cost much.

    But from what I noticed last night the hiss was on the right channel MORE and much lesser on the left and centre can anyone confirm this.

  12. #12
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    Thanks for the help guys.

    I was hoping the consumer amps would have been easier to intergrate...I might just send the Outlaw back and reinstall my pro-amps. At least they had quality level/gain controls.

    I am in contact with Marchand about their XM46 passive single ended line level x-over which is supposed to be very quiet so I'll see what he has to say before sending the Outlaw back.

    I also suppose I could "Y" the l/c/r signal coming from my pre/pro. Then I could run one end of the "Y" directly to the HF amp then use my JBL speaker level x-overs as a high-pass filter and run the the other end of the "Y" through the active line-level x-over to get the lows...in theory that'd keep the noisy active x-over away from my horns.

    -Ken




    Quote Originally Posted by JBL 4645 View Post
    toddalin

    Yes, yes someone mentioned that before. What value are the resistors that you used that might turn out to be an even more affordable solution, resistors don’t cost much.

    But from what I noticed last night the hiss was on the right channel MORE and much lesser on the left and centre can anyone confirm this.
    Last year when I tried the dcx2496 I ended having to send it back as one channel had a lot more noise on it than the others reguardless of how it was configured. I ended up with a BBE ds48...not as many features as the dcx but it's a decent unit none the less.

  13. #13
    JBL 4645
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    Quote Originally Posted by KenWH View Post
    Thanks for the help guys.

    Last year when I tried the dcx2496 I ended having to send it back as one channel had a lot more noise on it than the others reguardless of how it was configured. I ended up with a BBE ds48...not as many features as the dcx but it's a decent unit none the less.
    Afternoon there, are you winning?

    Well I can live with the issue that Iíve noticed Iíll just work around that problem, with resistors volume trimming pots even the kitchen sink if the situation called for it.

    I wonder what the dbx 4800 sound like giving the cost £2000.00 I mean whoís got 2 grand for several of those, unless you win the lottery.

  14. #14
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    Quote Originally Posted by JBL 4645 View Post
    Afternoon there, are you winning?
    I don't know exactly what your asking here but:
    I'm not winning anything as this hiss is driving me nuts.
    Not whinning (complaining) about the DCX either.

    The sound mine was making was not something I don't think anyone should have to live with...it wasn't just a slight hiss. I recall many other DCX users back then having a similar issue and I believe it ended up being solder joints on the pc board were grounding out on the chassis. As it was a brand new unit I decided to send it back rather than voiding the warranty by attempting to fix it myself. I liked the DCX alot...it had a much better user interface than the BBE for sure.

    If your DCX is an older unit and out of warranty you might open it up and put some kind of nonconductive material(electrical tape,etc.) on the chassis in the area's where it could come in contact with the board. You could search the web for more info as it was a fairly common problem with the DCX2496's back then.

    I assume Behringer made some changes to correct the issue as I've not heard much about that problem in awhile.

    -Ken

  15. #15
    JBL 4645
    Guest
    Well it canít be any worse then ďtinnitusĒ thatís, noise and half to depress me for days on end. Iím sure thereís an easy solution thatís eluding us, it just hasnít been found yet.

    Iíve just got back and I need to rest for a few hours and then Iím going to patch the HF outputs of more rather test each output with each output plugged into my (Technics SH-8055) turn the levels up on the unit and on the DCX2496 and get another view of this (hiss issue), I find it most fascinating.

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