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Old 26th July 2004, 06:30 PM   #1
AJ is offline AJ  United States
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Default Ribbons and active XO redux

I'm looking for solutions to the big "thump" that occurs when using an active XO during a power outage. I'm pretty careful to turn off my amps before turning off the XO so that's not a problem, but when a brown out or complete outage occurs, my speakers let out a pop that sounds like a gun shot. It dosn't seem to bother the drivers I have now in the system, but I'm going to add some ribbon tweeters and I just don't know if they'll be able to take it.

So I had a thought...suppose I plug the XO into a UPS that's good for say 15 minutes. That would keep the XO powered at least until the amps discharged. Does that sound like a possible solution?

Anyone else here with experience with the active XO/ribbon tweeter issues?

thanks again,
Allan
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Old 26th July 2004, 07:06 PM   #2
tiroth is offline tiroth  United States
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Add more capacitance to your active XO supply. Uness it is high-current you should be able to keep the XO powered longer than the amp.
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Old 26th July 2004, 07:19 PM   #3
usekgb is offline usekgb  United States
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I think that adding a UPS is an excellent solution. They will often have some surge suppression built in to them as well. Any time you use digital equipment, I think it is a good idea to have a UPS back-up, as brownouts can cause serious damage to some digital gear.

Cheers,
Zach
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Old 27th July 2004, 07:51 AM   #4
AJ is offline AJ  United States
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hey Zach,

The UPS works like a charm. I bought a beefy one (45 minutes of backup @ 450 watt/800Va) and plugged my preamp and the XO into it.

For a trial run, I connected the preamp and the XO to the UPS, and then the UPS along with the amp to a power strip with an on/off switch so I could cut the power to all three at once. With a great deal of wincing trepidation, I flipped it off and it was quiet as a mouse. That would've normally caused a huge pop from the drivers, but there was nothing but silence as the amp powered down and the XO and preamp kept on running. Very cool!
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Old 27th July 2004, 08:01 AM   #5
Previously: Kuei Yang Wang
 
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Default Re: Ribbons and active XO redux

Konnichiwa,

Quote:
Originally posted by AJ
I'm looking for solutions to the big "thump" that occurs when using an active XO during a power outage.
I am not sure that I follow. Your Active X-Over gives big thump noises when switched off? Then you need to have it fixed (or fix it yourself). No well designed piece of kit does that sort of thing. What sort of X-Over is it?

Sayonara
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Old 27th July 2004, 08:11 AM   #6
AJ is offline AJ  United States
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It only thumps when it's turned off before turning off the amp; eg. during a power outage or when I'm not thinking. My current XO are Marchand XM1's (2-way) but I've got an Ashly XR2001 (3-way) coming shortly. I talked to Ashly today and they said it would do the same thing and I've heard the same stories about Behringer CX3400's - it's the nature of the beasts evidently. If they're turned off in the correct sequence, there's no problem.

I don't know about other models of active XO's, maybe the Behringer digital XO's don't have the same issues - not sure.

Allan
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Old 27th July 2004, 09:54 AM   #7
Mark25 is offline Mark25  United Kingdom
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Default Re: Ribbons and active XO redux

Quote:
Originally posted by AJ
Anyone else here with experience with the active XO/ribbon tweeter issues?
Hi AJ,
I prefer to use a large value cap to protect my tweeters (not ribbons) when driving them actively. This then also protects them from power amp turn on/off thumps, power amp dc offset, power amp faults and inadvertent missconnection (i experiment a lot!)

There is a sound quality penalty associted with this approach though.
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Old 27th July 2004, 10:26 AM   #8
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Konnichiwa,

Quote:
Originally posted by AJ
My current XO are Marchand XM1's (2-way) but I've got an Ashly XR2001 (3-way) coming shortly. I talked to Ashly today and they said it would do the same thing and I've heard the same stories about Behringer CX3400's - it's the nature of the beasts evidently.
This suggests the absence of muting circuitry. Very naughty.

Best build/fit your own. All you need is to hunt down on the net a suitable circuit with a 555 that gets re-triggered with every mains cycle (I had to design my own discrete circuit back in Eastern Europe when I build PA Amp's and X-Overs).

If more than a pre-set number of mains cycles (eg set time constant to 60mS for 3 mains cycles cut out or are below trigger (brown out) level the muting (shunt) relais (which "hard" mute the outputs) are immediatly released. You need relais that release quickly, normally closed (NC) contact type.

You may even find that muting circutry is in place but has no triggering for brown/black out and you could add this on. I know the older Behringer Digital EQ muted quickly before it started to kake farting noises etc, so the same MAY apply to Behringer Digi X-Over, in which case there would be a lot of relais on the Output PCB.

Sayonara
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Old 27th July 2004, 10:36 AM   #9
Mark25 is offline Mark25  United Kingdom
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the Audio Analogue Bellini has a line level mutting circuit which incorperates DC offset protection and startup delay (a few secs).
The circuit itself is in zipped poscript format.
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Old 27th July 2004, 02:22 PM   #10
paulb is offline paulb  Canada
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Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,



This suggests the absence of muting circuitry. Very naughty.

Best build/fit your own. All you need is to hunt down on the net a suitable circuit with a 555 that gets re-triggered with every mains cycle (I had to design my own discrete circuit back in Eastern Europe when I build PA Amp's and X-Overs).
...

Sayonara
I don't recommend the 555. Here's an appropriate circuit from the renowned Rod Elliot:
http://sound.westhost.com/project104.htm
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