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

  1. #16
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    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 donít 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.
    I pulled the Yamahas out of the system some years back. Give me the weekend to try to go though my multitude of cords and find it.

  2. #17
    JBL 4645
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    LOL there’s a multitude of cables behind the equipment looks like "spaghetti junction" on Friday afternoon.

  3. #18
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    I found the cord. Resistors are 100K ohms (brn/blk/yel). (Actually measure about >~98K.) I think they are 1/8 watt (very small) to fit within the 1/4" phono plug.

  4. #19
    RIP 2011 Zilch's Avatar
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    I don't get what the problem is.

    Compression drivers require very little power, like one watt, in home use.

    If you have a 50W amp running them with no input attenuation, all of the noise of the crossover is being amplified, as you have to attenuate the signal ahead of the crossover, or use its inputs to do it.

    You need a gain structure which allows the active crossover to operate with a decent signal to noise ratio, which means attenuation of the amp.

    Making matters worse is the fact that you're driving consumer amps with pro level gear.

    Sticking a high-value resistor in series with the input is neither a rational nor recommended approach to accomplishing what needs to be done; all you're doing is increasing the amplifier input impedance, a bad idea. You want to use a divider there....

  5. #20
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    Quote Originally Posted by Zilch View Post
    I don't get what the problem is.

    Compression drivers require very little power, like one watt, in home use.

    If you have a 50W amp running them with no input attenuation, all of the noise of the crossover is being amplified, as you have to attenuate the signal ahead of the crossover, or use its inputs to do it.

    You need a gain structure which allows the active crossover to operate with a decent signal to noise ratio, which means attenuation of the amp.

    Making matters worse is the fact that you're driving consumer amps with pro level gear.

    Sticking a high-value resistor in series with the input is neither a rational nor recommended approach to accomplishing what needs to be done; all you're doing is increasing the amplifier input impedance, a bad idea. You want to use a divider there....
    Donít JBL 2360-A HF horns have a sensitivity of around 113db! So I agree less is more.

    http://www.jblpro.com/pages/pub/components/23606566.pdf

  6. #21
    Senior Member Ian Mackenzie's Avatar
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    Ken,

    I am not sure why you are biamping if its this much trouble?

    The problem as I see it is you have very high sensitivity horns running from a source that is inherantly noisy ie the active crossovers. The S/n is badly degrade at the active crossover, with the unbalanced leads and with the horns.

    If you insist on biamping use the JBL 5235 (bal in and out) and run it to dedicated amps with balanced inputs and attenuators. I would also have an L pad on the horn to -10 db to further enhance the final s/n.Otherwise it jsut wont work in the domestic scene. Not an issue in apub or a night club of course and they live with this issue all the time.

  7. #22
    Administrator Robh3606's Avatar
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    Does the crossover have a selectable output level so you don't have to run at the Pro levels +10?? Can you put volume pots on the inputs to the amps or use a simple voltage divider to pad it down. I run 2 set-ups and both have a mix of balanced and unbalanced equipment. I have no issues with hiss. You just need to get the gain structure right.

    Rob

  8. #23
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    Quote Originally Posted by JBL 4645 View Post
    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 don’t know why I didn’t think of this before, I think I’ll use the same approach, I’ll need to pop down to (DJ electronics) the week after next. I’ll 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.
    I've been going to do the same with a couple of Haffler 200 but I was going to add a little series resistance as I'm not sure what happens if you turn it all the way down and apply a short to your preamp or crossover output. If someone knows for sure speak up please. Of course this may be different brand to brand. Also what is a reasonable value? I'm sure there is a broad range that would work but if someone could help keep my trial and error to a few less trials and a lot less errors it would be appreciated.

    Also, any experience out there using those little 5 legged or 7 legged TO220 cased amps to run compression drivers? I know they have plenty of power for a living room setting, but I don't know about the quality.

  9. #24
    Senior Member grumpy's Avatar
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    all you're doing is increasing the amplifier input impedance, a bad idea. You want to use a divider there....
    I believe what Todd did qualifies as a divider (would guess worth 10-15dB, depending
    on the amp input impedance). No, it didn't preserve the input impedance as seen by
    the preceding device, but that's not necessarily a big deal; it's just not a universal
    solution. -grumpy

  10. #25
    JBL 4645
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    Quote Originally Posted by Ian Mackenzie View Post
    Ken,
    Quote Originally Posted by Ian Mackenzie View Post

    I am not sure why you are biamping if its this much trouble?

    The problem as I see it is you have very high sensitivity horns running from a source that is inherantly noisy ie the active crossovers. The S/n is badly degrade at the active crossover, with the unbalanced leads and with the horns.

    If you insist on biamping use the JBL 5235 (bal in and out) and run it to dedicated amps with balanced inputs and attenuators. I would also have an L pad on the horn to -10 db to further enhance the final s/n.Otherwise it jsut wont work in the domestic scene. Not an issue in apub or a night club of course and they live with this issue all the time.
    Excellent notion! L-pad there affordable and very easy to use.


    I agree with what Zinc said. Perhaps he should pop on over and give Ken a little help. I keep the levels on the mid to high frequencies down at a low amplifier volume level and have no difficulties hearing the highs, some films tend to be a little bright so I hope Ken is running those JBL 4675-A at near to cinema levels because I was seating at least 20 feet away when listening to those at the Empire years ago and I tell you it was ďJust Bloody LoudĒ and powerful.

    So Ken mate a little less get the SPL db metre out and start over again. Note set the fader volume level at 0db set the gain levels on the DCX2496 at +15 on outputs (1 2 3 4 5 and 6) Start off with the centre channel using (wideband pink noise) set the SPL db metre to C weighting and aim for a peak of 75dbc weighting, while adjusting the volume on the amplifier for that value.

    Note: mute each channel on the DCX2496 while adjusting each of the LF and HF Iíve practiced this and have found it to be speedy and easy.

    Once set move over to the HF and set the SPL db to A weighting and aim for 75dba while adjusting the amplifier volume.

    Now move over to the left and right and repeat this over again, once done play the (automatic pink noise sequencer), if you hear anything that sounds like a peak or a jump in the tone then you need to set up a microphone to an RTA and conduct the wideband noise over again while looking at the individual left centre and right this takes a few hours at best.

    Once done play the (automatic pink noise sequencer) to verify the timbre, is matching as close as possible.

    I do hope the JBL 4675-A are all at the same height level including HF horns otherwise the sound will not match up, it will be going from left then dropping down or upwards as is the case that I noticed with one cinema where the HF horns left and right where placed on the floor behind the screen!

    Once all is sounding well with pink noise play a few films that have dialogue panning a good choice is Indiana Jones and the Temple of Doom and the Last Crusade, when Donavon enters the drawing room, his voice is heard over to left and partly on the centre channel it takes a bit of skill to obtain a good clear openness with a little delay on the centre channel LF and HF.

  11. #26
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    Thom

    I get wonderfully ideas but LOL I’m not a qualified electronics expert, I know how to use a soldering iron and so does the rest of the population, if someone said use these components and in this order, then I’ll do so to make it work.

    Also I noticed the function of the DCX2496 becoming more active when adjusting the levels higher early this week, the audio limiter function was more active rather than sitting way below, the dynamic EQ was more alive and the overall barograph was lighting up like a Christmas tree a few peaks in the (amber) I’ll have to see how it goes with Lord of the Rings and a few dts laserdiscs last thing I want to see is consent clipping.

  12. #27
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    If you insist on biamping use the JBL 5235 (bal in and out)....
    5235 is UN-balanced out, potentially a trap, if one is unaware.

    Quote Originally Posted by Thom View Post
    I've been going to do the same with a couple of Haffler 200 but I was going to add a little series resistance as I'm not sure what happens if you turn it all the way down and apply a short to your preamp or crossover output. If someone knows for sure speak up please.
    NO, man, the potentiometer is connected as a voltage divider, not as a variable resistor (rheostat); it's the amp input that gets shorted to common at max attenuation.

    What value? What's the preamp or active crossover output impedance? :dont-know

  13. #28
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    Quote Originally Posted by Zilch View Post
    I don't get what the problem is.

    Sticking a high-value resistor in series with the input is neither a rational nor recommended approach to accomplishing what needs to be done; all you're doing is increasing the amplifier input impedance, a bad idea. You want to use a divider there....

    Maybe, but it certainly worked for me. I say for the $0.10 for a resistor, try it and let your ears decide. Ultimately, as long as it does no harm to the equipment (and it won't), shouldn't your ears the final judge?

  14. #29
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    Quote Originally Posted by toddalin View Post
    ....shouldn't your ears the final judge?
    Regarding arbitrarily adding 100k to the input impedance of an amp?

    I don't THINK so....

  15. #30
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    Quote Originally Posted by toddalin View Post
    Maybe, but it certainly worked for me. I say for the $0.10 for a resistor, try it and let your ears decide. Ultimately, as long as it does no harm to the equipment (and it won't), shouldn't your ears the final judge?
    Well Iím going to try it. Iíll use my ears and SPL db RTA to see the differences, 100K thatís not to costly, thou I donít think Maplin, sale them separately so packet of assorted resistors, would be fine.

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