Installs Amplifier Setup!

[techietim]

Hey guys!

Possibility of replacing amplifier at my church venue with one of the following two Behringer amps (just looking at these two at the moment!)
My question is regarding the set up and wiring of the amplifier.

• We have one, mono, output from the mixing console
• The amplifier will need to run all 4 of our speakers (either two pairs or individually)

Is it possible/how would I, set up the two following amplifiers so that it would take the single, mono XLR input from the desk output and provide the same, amplified output on all the amplifier output channels.

Behringer amp links:
Quad channel amp - EPQ304
Stereo channel amp - EPQ900

Your help is very much appreciated!
NB: As we are not ordering yet, please could you not suggest alternative models or makes! It is not possible to take two XLR outputs from the desk with our current set up.

 

[lakota651]

Hi Tim,

Those amps have a Mono, Stereo, Mono-Bridged selector switch on the back. Set it to Mono, and the first input will feed both outputs. For the 4 channel amp, it is treated as two pairs, so you will want to set both to Mono, then use an XLR 'Y' adapter to split your signal to inputs 1 and 3. There are some nice diagrams in the brochure that might help you out too.

http://www.behringer.com/assets/EPQ2000_EPQ1200_EPQ900_EPQ450_EPQ304_WebBrochure.pdf

Cheers!

 

[FMEng]

What speakers are you driving with this? Their impedance is a big factor in this.

 

[cmckeeman]

Hi Tim,

Those amps have a Mono, Stereo, Mono-Bridged selector switch on the back. Set it to Mono, and the first input will feed both outputs. For the 4 channel amp, it is treated as two pairs, so you will want to set both to Mono, then use an XLR 'Y' adapter to split your signal to inputs 1 and 3. There are some nice diagrams in the brochure that might help you out too.

http://www.behringer.com/assets/EPQ2000_EPQ1200_EPQ900_EPQ450_EPQ304_WebBrochure.pdf

Cheers!

If you are set on those amps this will be one of the best options.

 

[techietim]

Hi Tim,

Those amps have a Mono, Stereo, Mono-Bridged selector switch on the back. Set it to Mono, and the first input will feed both outputs. For the 4 channel amp, it is treated as two pairs, so you will want to set both to Mono, then use an XLR 'Y' adapter to split your signal to inputs 1 and 3. There are some nice diagrams in the brochure that might help you out too.

http://www.behringer.com/assets/EPQ2000_EPQ1200_EPQ900_EPQ450_EPQ304_WebBrochure.pdf

Cheers!

Good call lakota651, that adaptor is the wrong genders but I know what you mean (plus I need one from the UK ideally - easy enough to get/make)! So I'll take it Mono is better than Mono-Bridged?

What speakers are you driving with this? Their impedance is a big factor in this.

Sorry - don't have this information on file at present - trying to get it noted down so that I can do posts on here. Does the impedance affect the set up then? I'm not particularly worried about the power of the amplifier yet - need to check that the wiring is feasible and that the finance team agree to getting a new one!

If you are set on those amps this will be one of the best options.

Thanks cmckeeman.

Also does anyone have any preference over the two or four channeled amplifiers? (If you want to guess the power that you think would be needed to, go ahead but without knowing the impedance and specific speaker models (JBL), I guess that's almost impossible...)
Image below shows speaker placement, two rear ones just off camera left and right.

 

[lakota651]

With the two channel amp, selecting Mono will still leave each output channel independent. Mono-Bridged effectively makes the amp into a single channel, allowing you to use the the power of both channels to drive a single speaker (fyi, you do have to wire the connector differently too). The down side to this though is that you really only want to drive a cabinet with an impedance of 4ohms or greater, where as running it in dual channels you can theoretically go as low as 2ohms.

Do you have lines to each speaker currently at the amp rack, or are they daisy chained?

 

[Footer]

You have a delay currently? If you have two more speakers farther back in the sanctuary you really should go with the 4 channel amp and delay the back set. That's what your description sounds like...

Sent from my Nexus 7 using Tapatalk

 

[techietim]

With the two channel amp, selecting Mono will still leave each output channel independent. Mono-Bridged effectively makes the amp into a single channel, allowing you to use the the power of both channels to drive a single speaker (fyi, you do have to wire the connector differently too). The down side to this though is that you really only want to drive a cabinet with an impedance of 4ohms or greater, where as running it in dual channels you can theoretically go as low as 2ohms.

Do you have lines to each speaker currently at the amp rack, or are they daisy chained?

So Mono means that you can have much more flexibility and spread out power usage across the speakers?
The lines run to each speaker individually from the amp.

You have a delay currently? If you have two more speakers farther back in the sanctuary you really should go with the 4 channel amp and delay the back set. That's what your description sounds like...

Sent from my Nexus 7 using Tapatalk

We do not use a delay unit though I guess having the 4 channel amp would allow the flexibility to include something like this in the future..? Is this what you meant?
I guess it would also mean that if our band wanted to rehearse with the FoH sound on (don't ask!) then they could a specific speaker and turn the rest off?

 

[FMEng]

Bridge mode is for 8 ohm loads only with those amps, so that would require two or four amplifier chassis. They are also not rated for 2 ohm loads.

If the speakers are 8 ohms, I would parallel two of them onto each output of the EPQ900. If they are 4 ohms, then it's one speaker per output, since the amp isn't rated for 2 ohm loads.

The theory behind this is that when you parallel the speakers, the load impedance drops by half every time the number of speakers doubles.

 

[JD]

Think about Kyle's comment about the delay. We currently have three delays in our church sound system to keep everything in sync.

Be aware that when you switch in to mono mode, your one channel is inverted in output on most amps. As long as you are setting up your bridge between the + phase outputs, no problem, but if you were to use the convention output posts, Channel A and B would be 180 out of phase with each other.

Also, are you sold on Behringer ?
I would use the QSC amps. They may look identical, but when you take the covers off, the build is quite different. (Different model, but you get the idea.) Picture credit bitcore.org

 

[FMEng]

Be aware that when you switch in to mono mode, your one channel is inverted in output on most amps. As long as you are setting up your bridge between the + phase outputs, no problem, but if you were to use the convention output posts, Channel A and B would be 180 out of phase with each other.

Be careful with the correct definitions here. Mono mode is not the same as bridging mode. The Behringer amps have all three modes. In stereo mode, each output is driven by its own input. In mono mode, one input drives two outputs identically.

In bridging mode two outputs drive a single load, from a single input, with roughly double the power. If the two outputs were, incorrectly, used independently in bridging mode, then there would be a polarity inversion.

 

[Footer]

We do not use a delay unit though I guess having the 4 channel amp would allow the flexibility to include something like this in the future..? Is this what you meant?
I guess it would also mean that if our band wanted to rehearse with the FoH sound on (don't ask!) then they could a specific speaker and turn the rest off?

How are you speakers deployed right now? If you have two more speakers on the walls outside of that shot, I assume they are about 20'/30' away from the alter where the speakers upfront are 5' to 10' away from the alter?

 

[JD]

It really helps! We have speakers up front, then 20, 40, 60 feet back on progressive delays and things are clear as a bell in the back. Had a problem once tracking down a noise, and I pulled the delay as part of the process of elimination. Short story, the old oxide on a connector was the problem, but with the delay pulled the system sounded horrible! All the clarity was gone, so words blurred. I am sure with only two sets things aren't too bad, but if you get a chance to incorporate a DL, you will be surprised at how it cleans up the consonants in the verbage. (ps- Another reason I like equipment with spade lugs for signal connection in installations where the equipment may reside for 10 or 20 years.)

 

[cmckeeman]

Also does anyone have any preference over the two or four channeled amplifiers? (If you want to guess the power that you think would be needed to, go ahead but without knowing the impedance and specific speaker models (JBL), I guess that's almost impossible...)

Are you going to buy only one amp regardless?

 

[museav]

Sorry - don't have this information on file at present - trying to get it noted down so that I can do posts on here. Does the impedance affect the set up then? I'm not particularly worried about the power of the amplifier yet - need to check that the wiring is feasible and that the finance team agree to getting a new one!

It's not clear why you are considering replacing the existing amplifier but I can think of few situations where you would be replacing an amplifier and the power rating of the replacement would not be an important factor. If the replacement amp(s) either won't allow the system to get loud enough or could potentially damage the speakers with their output capability then what is the point of purchasing it/them? And the power rating could definitely affect the budget. If you can identify the existing amplifier and its power ratings are available then that information along with how the system is currently wired might provide some starting point, be it in trying to get the same output or some change in potential output with the new amp(s).

As far as how the two models listed compare, the four channel EPQ304 is rated at 40W ito 8 Ohms in stereo mode while the two channel EPQ900 is rated at 175W per channel into 8 Ohms in stereo mode. Assuming your speakers could handle either then that's a 6.4dB difference in the potential output of your system, which is definitely a noticeable difference. So a single EPQ304 might be less cost than two EPQ900s, but at the trradeoff of a readily noticeable difference in maximum output for the system.

The impedance is important, especially for those amps. As noted, bridge mode effectively 'bridges' two channels to provide a single channel with greater power, however in this case both amps are only rated for an 8 Ohm load in bridge mode, so a bridged EPQ900 could likely only safely drive a single speaker and while since the EPQ304 has two channel pairs it could probably drive two speakers, one speaker per channel pair, in bridge mode. That probably makes bridge mode likely less applicable in your situation.

The 4 Ohm, stereo mode power ratings for both amps being less than twice the 8 Ohm, stereo ratings also suggests the amps are current limited even with a 4 Ohm load. That's getting a bit technical but it has two important impacts. One is that two 8 Ohm speakers wired in parallel to a single amplifier channel will result in less power per speaker than will one speaker connected to that channel (although the difference would result in only about 1dB less output per speaker). The other is that it means you might want to be rather wary of operating the amps at lower impedances than those specified.

 

[techietim]

How are you speakers deployed right now? If you have two more speakers on the walls outside of that shot, I assume they are about 20'/30' away from the alter where the speakers upfront are 5' to 10' away from the alter?

That's right!

It really helps! We have speakers up front, then 20, 40, 60 feet back on progressive delays and things are clear as a bell in the back. Had a problem once tracking down a noise, and I pulled the delay as part of the process of elimination. Short story, the old oxide on a connector was the problem, but with the delay pulled the system sounded horrible! All the clarity was gone, so words blurred. I am sure with only two sets things aren't too bad, but if you get a chance to incorporate a DL, you will be surprised at how it cleans up the consonants in the verbage. (ps- Another reason I like equipment with spade lugs for signal connection in installations where the equipment may reside for 10 or 20 years.)

The building is not all that large. Words are pretty clean already, a lot better since I set up the new desk and put 3KHz boosts on radio mics!

Are you going to buy only one amp regardless?

Suppose we could actually have 2 (ideally 1U) stereo amplifiers and use an XLR splitter - this may be the best option. Further details to follow.

 

[techietim]

It's not clear why you are considering replacing the existing amplifier but I can think of few situations where you would be replacing an amplifier and the power rating of the replacement would not be an important factor. If the replacement amp(s) either won't allow the system to get loud enough or could potentially damage the speakers with their output capability then what is the point of purchasing it/them? And the power rating could definitely affect the budget. If you can identify the existing amplifier and its power ratings are available then that information along with how the system is currently wired might provide some starting point, be it in trying to get the same output or some change in potential output with the new amp(s).

As far as how the two models listed compare, the four channel EPQ304 is rated at 40W ito 8 Ohms in stereo mode while the two channel EPQ900 is rated at 175W per channel into 8 Ohms in stereo mode. Assuming your speakers could handle either then that's a 6.4dB difference in the potential output of your system, which is definitely a noticeable difference. So a single EPQ304 might be less cost than two EPQ900s, but at the trradeoff of a readily noticeable difference in maximum output for the system.

The impedance is important, especially for those amps. As noted, bridge mode effectively 'bridges' two channels to provide a single channel with greater power, however in this case both amps are only rated for an 8 Ohm load in bridge mode, so a bridged EPQ900 could likely only safely drive a single speaker and while since the EPQ304 has two channel pairs it could probably drive two speakers, one speaker per channel pair, in bridge mode. That probably makes bridge mode likely less applicable in your situation.

The 4 Ohm, stereo mode power ratings for both amps being less than twice the 8 Ohm, stereo ratings also suggests the amps are current limited even with a 4 Ohm load. That's getting a bit technical but it has two important impacts. One is that two 8 Ohm speakers wired in parallel to a single amplifier channel will result in less power per speaker than will one speaker connected to that channel (although the difference would result in only about 1dB less output per speaker). The other is that it means you might want to be rather wary of operating the amps at lower impedances than those specified.

Thank you for all that museav! Very interesting.

Here is what the guy who did the existing install told me;
"Amp; QSC RMX 2450, 500w channel at 8 ohm, or 1300w in Bridged mode
Speakers; JBL Control 28, 175w"
The amp is supposedly bridged (haven't looked myself but takes on input and has the four speakers across the two outputs (front and back).

Personally I think that amplifier is too powerful and, surely it could lead to massive damage to the speakers if someone hit the amp by mistake?

The amp is currently running at about 30-45% of it's total. Massively under driven, not a bad thing...?

So my thoughts as of now:
A) A single EPQ304 (or similar) amp in mono mode with a single XLR input from the desk to all four outputs.
Could someone work out roughly how different this would be? By the sounds of things, it sounds like it could be too quiet.

B) Two stereo EPQ900 (or similar/less powerful [slightly]) amps in mono mode with XLR input into each with the output on each pair on both amps.

Which options, from the above, would you go with.


PS - the amp is only possibly being changed due to some problems with the current one. May post on here!
Again - this is a big IF we have the money to replace.

Thanks to all of you for all of your help so far! very much appreciated.

 

[JD]

If you are running a mono mix, you could limit the output of the current amp simply by wiring your speakers in series. (Ex- front 16 ohm, rear 16 ohm.) This will quarter the wattage going into any given speaker.
Generally, the QSC amps are real long-term work horses. After about 20 years they need some touch up solder work on the output transistors because of age related ring cracks, but that's about it.
If you're only worried about an accidental blast, you could always use the Fuse & light-bulb trick to protect your speakers.

 

[techietim]

If you are running a mono mix, you could limit the output of the current amp simply by wiring your speakers in series. (Ex- front 16 ohm, rear 16 ohm.) This will quarter the wattage going into any given speaker.
Generally, the QSC amps are real long-term work horses. After about 20 years they need some touch up solder work on the output transistors because of age related ring cracks, but that's about it.
If you're only worried about an accidental blast, you could always use the Fuse & light-bulb trick to protect your speakers.

Could indeed do that, though that's very interesting what you've said about the QSC amp - always thought it was good.

Don't suppose you could show on a photo exactly where the output transistors are (I know roughly what I'm looking for) as I'll check them!
Would a problem with them potentially cause the amp to "shut down"?

I think from your info, it may be a repair job, so mightn't be getting a new amp after all but useful to know if we do in the future. Sure I will come back here again!

Thanks for the info about the speaker protection trick!

Thank you!

 

[JD]

Don't know how old the one you have is, but on the older QSC amps, the output transistors are the round silver things near the top of this picture. The problem is on the reverse side of the board where the leads come through. They look fine at first, but when you look real close, you will see that the leads have actually cracked free of the solder on the pad. I have run into them where almost every transistor had this and that will shut it down. Obviously, there's a lot of other things that can go wrong with an amp, but because the board, transistor, and solder all expand and contract at slightly different rates, given enough years of use, the all have some! (Picture credit DIYaudio.com)

Below is a wiki picture of typical ring cracks. I find on the QSC they are almost on the shaft of the lead itself.