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

[JBL 4645]

Just thought I’d mention, this the DCX2496 does have slight humming sound emission when the output gain is raised to +15db. Also I noticed last night when selecting anyone of the buttons on the left hand side channel 1 2 or 3 you’ll hear a sound that is in-sync with the flashing LED’s? It’s a very faint sound but it is there.

[Baron030]

Hi Ken

I have been following this thread for a while. And I am not really sure that I can help you or not. Personally, I have never had any problems with hiss. In my own system, I run unbalanced lines from the preamp into an electronic crossover network. And then I use balanced line XLR cables between the crossover and an array of 5 amplifiers. So, I really don’t think cables are the source of the hiss.

I know most people set all of the amplifiers input controls to their maximum gain setting and then adjust each of the output levels on the electronic crossover network to achieve a system balance. But, because the HF drivers are so much more efficient then LF drivers, I have found that it is better to first set the all of level controls on the electronic crossover network to a common neutral gain setting. And then adjust the input levels on each of the amplifiers to bring the system into a coarse level of balance. After, all of the amplifiers input levels have been adjusted, I then go back and make only fine adjustments to the crossover network’s output levels to finally bring the system into balance. I know this may contradict what others have said on the subject. But, I have found that this method has given me the quietest noise floor in my own system.

For example, I run my Crown D75a HF amplifiers with their input levels set all the way down to -26db for the 2446 drivers and -22db for the 2405 drivers. While, my Crown K series, LF amplifiers are set to their maximum (-0db) input setting.

Since, your Outlaw 7700 amplifiers do not have any input level controls, it might be possible add some attenuators between the electronic crossover and the HF amplifier inputs to help balance the gain levels and hopefully reduce the hiss. I would suggest trying a -20db T or H Pad. The T-Pad can be thought of as a symmetrical variation of the L-Pad and it is for use with unbalanced line inputs, while the H-Pad is for use with balanced line inputs.

Assuming that the Outlaw 7700 has about the same input impedance as a Crown D75a (20K balanced/10K unbalanced), a -20db T or H Pad could be made using 1/8 watt 1% metal film resistors following one of the schematics pictured below. Since, physically these resistors are really small, it might be possible to build the H-Pad directly inside the XLR connector's housing that plugs into the HF amplifier’s input. This would put the attenuation right at the amplifier's input, which should reduce any noise to a minimum.

Here is a link to a T or H pad attenuator calculator program should you need to calculate different attenuator values: http://www.icycolors.com/nu9n/tpad-calculator.html

And here is a link to a good source for the resistors: http://www.mouser.com/xicon/

Well, I hope you find a solution to your hiss problem.

Best of luck,
Baron030

[Zilch]

I know this may contradict what others have said on the subject. But, I have found that this method has given me the quietest noise floor in my own system.

Nope, no contradiction here. It's a major reason amps have input attenuators.

Amp doesn't have them, you add them as required for the desired system gain structuire....

[KenWH]

Wow...sorry for not posting lately...for some reason the site stopped emailing me new reply notices...I thought this thread was dead.

I've been in contact with Outlaw Audio and they seem to think the problem is the rca to xlr connections at the xover.

Since the xover only has balanced xlr in/out they suggested using a di box to get a signal the xover likes. So I've got an Aphex 228 rca to balanced xlr interface/converter box on the way. The 228 will be in tommorow and I'll install it asap and report back.

Btw...the Outlaw tech also advised me against using a diy level control at the amp as it could possibly increase noise potential.

edit:
As for using level controls on the amps...before the Outlaw/Monster combo I've been using pro-amps in my system for a few years and set them up pretty much just as Baron does. I ended up with the horn channels levels on the amps nearly turned completely off in order to get the hiss down to acceptable levels. Again though I was still trying to run the unbalanced signal thru the balanced xlr x-overs so hopefully the Aphex will help.

edit#2:

Thanks for the help/suggestions everyone!!!!

[hjames]

Interesting - I run (preamp-level) RCA out from my Harman Kardon AVR-335 receiver over to the JBL M552 crossover, then run Balanced XLR out for Low and High to a terminal strip on a pair of JBL amps.
No problem like that with my gear. Opimax will vouch that it sounds ok ...

Wow...sorry for not posting lately...for some reason the site stopped emailing me new reply notices...I thought this thread was dead.

I've been in contact with Outlaw Audio and they seem to think the problem is the rca to xlr connections at the xover.

Since the xover only has balanced xlr in/out they suggested using a di box to get a signal the xover likes. So I've got an Aphex 228 rca to balanced xlr interface/converter box on the way. The 228 will be in tommorow and I'll install it asap and report back.

Btw...the Outlaw tech also advised me against using a diy level control at the amp as it could possibly increase noise potential.

edit:
As for using level controls on the amps...before the Outlaw/Monster combo I've been using pro-amps in my system for a few years and set them up pretty much just as Baron does. I ended up with the horn channels levels on the amps nearly turned completely off in order to get the hiss down to acceptable levels. Again though I was still trying to run the unbalanced signal thru the balanced xlr x-overs so hopefully the Aphex will help.

edit#2:

Thanks for the help/suggestions everyone!!!!

[JBL 4645]

I agree with what timc said to me on MSN messenger the DCX2496 does inherit a “noisy ground floor” that is quite distracting for a professional product. He said all pro gear is noisy and I hope with his “modification” he might turn up with a few easy solutions.

I hiss is more easy to detect and humming, well you might partly blame the amplifier. Well I’ve discounted the RCA phones that go to the amplifies from the DCX2496 and when raising the gain level output there’s a slow steady increase in noise.

It gets worse when the amplifiers are turned up to there fullness, hiss and humming, where does the fault lead to and how simple, for one to make alterations to the fault to improve on the function of the DCX2496.

I have second active crossover which I’ll check-out later to see if that model is noisy both in hiss or humming.

[hjames]

imc said all pro gear is noisy and I hope with his “modification” he might turn up with a few easy solutions.
I hiss

I think Bo and a few others might chime in here about that line - I doubt that all Pro gear is noisy, i would think the correct phrase is Cheap pro gear is noisy. Did anyone ever confirm if the hiss was the problem we've already read about here in other threads with poor solder joints and grounds in that model of device?

Good troubleshooting technique would be to substitute it with another similar device and isolate the problem ... (You can get a used JBL 552 for about $120 on "the bay" for testing - you can always resell it later for the same price if you don't like it).

It also sounded like Zilch and a few other had a good idea - get the signal level down to a reasonable level and the crossover and Amps will no doubt play much better. Hit your device with too hot a signal and you are outside the point of linear behaviour and into distortions and noise.

For "4645" - One issue with hiss may be cascading device after device - extended strings of EQs, expanders, Active crossovers and such have a real potential for noising up the signal. Simplify the signal chain while troubleshooting and listen for improvements.

[KenWH]

Interesting comments on the low quality=noise issue.

I've used several different pro crossovers in my system including the Behringer dcx2496(digital), DBX 224xl(analog), Behringer cx3400(analog), and now the BBE ds48(digital) and their use has caused similar levels of hiss. Again though I was not running them balanced so the Aphex unit will finally settle the signal issue one way or the other and I'll go from there.

[KenWH]

Good news...got the Aphex in about 10min ago and now I can only hear a faint hiss if I'm within 2 or 3 feet of the horns. Even with all the xover levels set flat the hiss is not really noticeable.


So far so good...

[boputnam]

...would getting something like a rane balance buddy to get a balanced signal help hiss?

Hi, Ken..

I need to read all this thread closely, but my grab is: "No" the Rane Balanced Buddy would do nothing for this - it is intended to avert ground loops )"GL", i.e., Pin1 problems). "Hiss", is not a Pin1 problem.

[boputnam]

...I can only hear a faint hiss if I'm within 2 or 3 feet of the horns. Even with all the xover levels set flat the hiss is not really noticeable.

Bullshit. There should be no hiss.

The hiss is only noticable (audible) in the HF, but my grab is there is noise throughout your signal path - you have a very high noise floor. You talk of trialing all manner of xovers and no change. My guess is the noise originates BEFORE the xover insertion point.

QSC's are not the problem. Stay with the pro amps.

Can you trial another player and preamp unit, like Heather suggested? I mean hell, I've used all manner of consumer gear but the thing that totally ruined me was a lame Onkyo consumer-grade preamp. That said, all it had was a poorly grounded (designed) power supply, but there was no hiss.

I'd start at the beginning of the signal path. I think your problem is rigth there, and not related to a GL (balanced vs unbalanced).

[KenWH]

Bullshit. There should be no hiss.

The hiss is only noticable (audible) in the HF, but my grab is there is noise throughout your signal path - you have a very high noise floor. You talk of trialing all manner of xovers and no change. My guess is the noise originates BEFORE the xover insertion point.

QSC's are not the problem. Stay with the pro amps.

Can you trial another player and preamp unit, like Heather suggested? I mean hell, I've used all manner of consumer gear but the thing that totally ruined me was a lame Onkyo consumer-grade preamp. That said, all it had was a poorly grounded (designed) power supply, but there was no hiss.

I'd start at the beginning of the signal path. I think your problem is rigth there, and not related to a GL (balanced vs unbalanced).

Your right in that balancing didn't help hiss. The Aphex is going back. In my first post about the Aphex I didn't realize the tiny gain knobs where at full min when I hooked it up. I barely turned the gain knobs...HISS.

The crossovers appear to be the problem as if I remove them the horns are dead silent. I've also been using passive speaker level crossovers and they are dead silent also...so active line level xovers=loud(hear from 20+feet away) hiss for me.

So at least I finally know it's not a really a signal balance/unbalance thing either. It appears that whatever the active x-overs do to the HF the process just adds a lot of noise/hiss.

I'm going back and staying with the passive speaker level JBL 3160 x-overs for now. Yes the bass section performance will suffer a bit but at least it's quiet. The only other thing I know to try would be a passive line level x-over like the Marchand xm46...but at $750 for a custom 3ch. unit, that's not something i want to do without some certainty it will work...quietly.

Thanks for the help guys,
Ken

[Zilch]

Do what Baron030 suggested at #32.

This is virtually a no-brainer. Transistors hiss. IC and circuit designers work to minimize the impact and maximize the signal-to-noise ratio.

BUT, if you crank the signal down and then amplify it by 20+ dB, your S/N ratio has turned to crap. You're amplifying the hiss, mostly, is what, and despite what the amp rep says, you need attenuation at the amp input so that everything before it can be outputting SIGNAL, primarily, not noise.

THEN, if there's any hiss remaining, it's coming from the amp, which is too friggin' big to begin with....

[Baron030]

Hi KenWH
I am still scratching my head on this one.
Last night, I played around with my own system, trying to make it HISS.
I turned up all 3 of my CrownD-75a to their maximum input levels (-0 db).
That’s one Crown D-75A feeding a pair of 2405s with up to 40 watts per channel and two Bridged-Mono Crown D-75As feeding a pair of 2446H drivers with up to 110 watts per channel.

It’s definitely a system that Zilch would call, "too friggin' big to begin with".
But, I just happen to like it that way. Loud transients are reproduced so effortlessly.

I performed a full system test with the CD player set on "pause", the pre-amp was set to a insanely loud dial setting of 6, and I then placed my ear just one inch way from each of the drivers.
And I could not hear any HISS at all.
I know if someone had pressed the "play" button, with my ear placed that close to a driver.
It would have blown out an ear drum. (>140db @ 1 inch).
So, I think it was a viable HISS test.

Ok, for the record, my system was not completely silent, there was very faint hum coming out of the 2226H drivers.
But, at normal listening distances this hum is not noticeable.

I have looked at your Outlaw 7700 amplifier specs and they appear to have a good signal to noise ratio.
So, I really don’t think they are at fault. But, I then again, I could be wrong.

Since, you have tried several different crossover networks and they all hissed.
Then, maybe it’s time to start looking at the pre-amp or the CD player as the source.

But, if you do find that the source of the HISS to be the crossover network, then try Ashly crossover.
I am really happy with my Ashly XR-4001.

But, I still think the source of the HISS is coming from somewhere before the crossover network.

Baron030

[grumpy]

if you use a 100-600 ohm resistor as your "signal source" (nearly shorting the
input to the active crossover), does the hiss go away? or if the input really is
shorted, is there still hiss?