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Author Topic: AC wall switch for Power Amps?  (Read 3624 times)

Corey Willis

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AC wall switch for Power Amps?
« on: July 27, 2005, 04:16:12 PM »

Hey everyone. My church is getting ready to purchase and install some new sound equipment in our fellowship hall. Here's the question. The electrician in the church wants to install an AC wall switch (light switch) so the power amps can easily switched on and off. This would be nice to have considering the placement of the power amps, but I'm concerned about power surges during power up and power down. We're getting Carvin amps (DCM1500, DCM2000, and DCM2500). Any advice here will be welcomed, as I definitely do not want them to ruin new equipment.

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Ivan Beaver

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Re: AC wall switch for Power Amps?
« Reply #1 on: July 27, 2005, 07:08:22 PM »

What we do is to use a single turn on switch at the mix position and have that trigger a remote turn on AC switch, such as Lowell RPC's that are just looking for a contact closure to turn the outlets on.  

The turn on "thumps" will be minimized if your gain structure is setup properly.  Many people like to use sequencers, and those will stop thumps-if timed properly.  I just think of them as an extra unneeded expense with another failure possible point.  I just set the gain structure properly using pads between the processors and amplifiers.
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Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.

George Linkenhoker

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Re: AC wall switch for Power Amps?
« Reply #2 on: July 27, 2005, 08:13:16 PM »

Quote:

The turn on "thumps" will be minimized if your gain structure is setup properly.


I'm not sure how that works when "thumps" are caused by upstream equipment being powered up or turned off when the amps are on.  Thumps can be prevented through proper power up and power down sequence.  Amplifiers are turned on last and turned off first.

I could not find specific power needs for those amplifiers, but I did see their output power.  From their output power, I'm not sure that all three will fit on one 20 amp circuit and be able to power on at once.  They will have a large in-rush of current at power on and then variable drain based on output levels.  

One of the churches that I work with has used the light switch method to turn on/off the amplifier rack for 15+ years now (think install was in '88 with modifications and upkeep as needed).  I am not sure if it causes any issues.  The one thing I would caution is to make sure that if you go with this that you make sure that you have a switch that is rated to handle 20 amps.

My personal choice, would be to purchase a power conditioner unit that sits in the rack with the amplifiers.  You can then use the switch on the front of the power conditioner to turn the whole rack on/off and the conditioner will give surge protection and power filtering.

-George
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Greg Hertfelder

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Re: AC wall switch for Power Amps?
« Reply #3 on: July 27, 2005, 10:46:10 PM »

You have well-founded concerns, and this is the window of opportunity to get it right.

While I have to admire your electrician's enthusiasm, I recommend one of two alternatives in lieu of a wall-mounted light switch. Alternative one is to install rack-mounted power strips with big fat illuminated switches (Furman comes to mind). While powering on the amps with this switch is still a manual process and subject to order error, this switch is better than something that could be confused for a room light switch.

Alternative two (recommended) is that you take the consultant path and install a power sequencing system. To do this, the electrician needs to wire an adequate quantity of AC circuits direct to a sequencing power system, spread out in the power amp and mixing console racks. Just write down all the current requirements of your power amps and spread the load out over several AC circuits so as to not exceed the capacity of the circuit breaker.

When the operator presses the System On button (or turn of a key) on a sequencer, the sequencer closes the relay for each power circuit. Each circuit is turned on serially (click...click...click....click) and with a delay between, so that no two circuits power on simultaneously (to prevent overloading), and that the correct order is observed (mixing console/effects power on first, then power amps; off in the opposite order). This order prevents annoying and potentially costly amplifier thumps that could damage loudspeakers.

In the church environment, we work with various levels of expertise, and any time we can automate processes so that the least technical volunteer can press a button to make it happen with confidence is a good thing. We don't want volunteers to be thinking "Now was it power amps that I power on first, or the mixing console?".

Manufacturers of power sequencers that I have worked with in the past are Lyntec and Atlas/Soundolier. Other manufacturers now in the market are JuiceGoose, Furman and Lowell. (Incidentally, GE made or makes a really fast power sequencer intended for lighting circuits; do not use this sequencer if offered by an electrician. This sequencer fires too fast to prevent amplifier thump.)

I have never met a client, with volunteer or paid sound techs, that regretted installing a power sequencing system.
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Corey Willis

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Re: AC wall switch for Power Amps?
« Reply #4 on: July 28, 2005, 02:05:30 PM »

Hey everyone...  thanks for the input! I would definitely like some more info on the power sequencing system (primarily price, because I think we've about tapped our budget for the time being with everything else.)

A little more info though...

1. I believe the electrician was going to run a separate circuit for each amp- if they do this, should they be 15 amp or 20 amp circuits if only one amp in powered on each?

2. IF, and I do say IF, they decide to go with wall switches, personally I would think those keyed switches (like I used to see in schools) would be the only way I would concur, so that the amps don't mistakenly get turned on or off.

So, in summary, I REALLY like the idea of the power sequencer, but I'm not sure if they can afford it right now. In lieu of that, do you think any damage would be done to the amps if they were all on separate circuits with properly rated keyed switches (20 amp I'm assuming), with a power conditioner/surge suppressor on each amp? Thanks again for all the input!!!
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Greg Hertfelder

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Re: AC wall switch for Power Amps?
« Reply #5 on: July 29, 2005, 12:13:44 AM »

Quote:

1. I believe the electrician was going to run a separate circuit for each amp- if they do this, should they be 15 amp or 20 amp circuits if only one amp in powered on each?

2. IF, and I do say IF, they decide to go with wall switches, personally I would think those keyed switches (like I used to see in schools) would be the only way I would concur, so that the amps don't mistakenly get turned on or off


Basically, you need to first research the Line Current requirements from the spec sheet of each amplifier model. Current, or amps (short for "amperage", not "amplifier") is indicated by a number, followed by capital "A" for "amps". The nomenclature of "2A" means "2 amps". Carvin's spec sheet on the web is a little lean with this information, and the nearest I can find are conflicting markings about internal fuses. But a visit to the Crown Audio web site reveals some insightful figures.

For instance, looking at the Crown CTs-1200 power amplifier operating in 120VAC (VAC=Volts, Alternating Current) mode, for reference, the CTs-1200 amplifier puts out 600 watts per channel (stereo), or 1200 watts bridged (mono) with an 8-ohm load, resulting in a Line Current requirement of 7.6amps to 10amps (according to thier Power/Current Draw and Thermal Dissipation chart). In this example, you could use the P/E=I formula of bridged mono output (1200 watts) divided by operating voltage (120VAC), resulting in a current requirement of 10amps, and limiting the quantity of this amplifier to two per 20A breaker, or one amplifier per 15A breaker. In this case, I would err on the side of safety / reliability, and put one amplifier on a 15A or 20A circuit breaker.

Using these figures as a guideline, and information I was able to glean from the Carvin web site, the DCM1500, DCM2000, and DCM2500 amplifiers put out 1000, 1400, and 1700 watts, (bridged mono mode, 8 ohm load) respectively, resulting in Line Current requirements of 8.3A, 11.6A, and 14.16A, respectively. So you could put two DCM1500 amplifiers (2 x 8.3=16.6) on one 20A circuit breaker, but the other Carvin amplifier models, DCM2000 (11.6A) and DCM2500 (14.16A), should be on one dedicated 20A breaker each.

Incidentally, if the amp were configured at the factory for 240 VAC, the current requirements would be half. There is something to be said for configuring amplifiers for 240VAC operation, but wiring can get a little more complex, too.

In the end, I think you will find that it will be less expensive and speedier to use off-the-shelf hardware configured for power switching and sequencing (Lyntec, Atlas/Soundolier, Furman, Lowell, JuiceGoose, etc.) than putting your electrician through the paces of fabricating work-arounds with switches from the hardware store. In addition, the above-mentioned manufacturers already offer configurations that include key switches, and other useful features.

Going over budget feels like failure, but is really just a momentary blip on the radar, and then its forgotten. Your pastor or board of elders/deacons understand that it is hard for one to think of everything, and once you explain the options to them  and that you are simplifying operation to help dummy-proof the system, I think they will see fit to approve the budget for a sequencing system. And you will leave a good legacy for those following in your footsteps.
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Scott Raymond (Scott R)

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Re: AC wall switch for Power Amps?
« Reply #6 on: July 30, 2005, 12:55:17 AM »

We just went through an upgrade at church last fall.  After discussing it with the company doing the install they went ahead and installed three switches controling four circuits.  The top of the boxes is labled "ON with 1, 2 and 3.  The bottom is labeled "OFF with 3, 2 and 1.  Switch 1 is wired to the board and FOH rack.  Switch 2 and 3 control 2 circuits each. (double pole switches) These turn on amps and equipment in the main rack.  Simple, easy to understand and has been working well.

Adam Kane

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Re: AC wall switch for Power Amps?
« Reply #7 on: July 30, 2005, 08:36:59 AM »

The Furman PS8R can be found for less than $300/ea and is linkable with other PS8R's and other Furman stuff.  Delay times are adjustable.  One button on the front panel of any PS8R in the chain turns the system on/off.  You can also hook up remote switches to trigger them.  I believe they have 30A relays for handling power amps.

They also have a high current version of the PS8R (I believe it's called the "Series II") that may hold up better w/ power amps.  Haven't used that one though.

adam
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Adam "Drumrkane"

ProSoundWeb Community

Re: AC wall switch for Power Amps?
« Reply #7 on: July 30, 2005, 08:36:59 AM »


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