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Author Topic: Crest Pro 8200 amps  (Read 36862 times)

TJ (Tom) Cornish

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Re: Crest Pro 8200 amps
« Reply #20 on: July 22, 2010, 08:38:38 PM »

Alan Sledzieski wrote on Thu, 22 July 2010 17:35

Bob Lee (QSC) wrote on Thu, 22 July 2010 18:07

Alan Sledzieski wrote on Thu, 22 July 2010 14:31


As voltage drops, current goes up.


Only if you use one of those voltage regulators that the pros here have advised you not to use on power amps.

Quote:

If voltage is low would a amp tend to run hotter because of increased current?


No, because the current will decrease.




Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?

Still confused why someone would want to run at 100 v when you could run them at 120 fairly cheap for a small system like mine.

In the case of most unregulated amps: The input voltage charges the voltage rails of the amp.  If the input voltage of the amp is lower, there is less voltage in the amp's power supply to create output voltage.  Less output voltage into an unchanging load impedance equals less current.  Amps running on lower mains voltages produce less waste heat too for the same reason - there is less spare power to be dissipated in the output stage.

There are a few models of amps (Itechs, Powersoft I believe, and probably a couple of others that have internal regulation and can produce full rated output at voltages as low as 90 or 100 volts, which do indeed work the way you expect.  Your Crests do not fall into this category.

As far as your question about why not use a voltage regulator - first of all you haven't really defined if your 100 volt spec is an "unloaded" voltage, or if this is what you are imagining the circuit does when the amp pulls a bit of power.  Any branch circuit that has lost 20 volts by the time it gets where you are using it is going to be so spongey that even if you prop it up to 120 volts using a regulator, you're going to knock it down a whole bunch more when you ask for 50 amps of instantaneous current, which is not untypical for a non power factor corrected amp of the sizes we are discussing.

For those peak hits, they happen faster than your regulator can switch taps, so you're not really even catching them, short of permanently setting up your VR as a boost transformer.

A power factor corrected amp is able to draw current over the entire waveform, which reduces peak demand, softens hits on the supply circuit, and just plain lets you get more usable power out of a limited supply.

In one of your other replies you said you can't damage a circuit due to heating because the breaker is protecting it - I would beg to differ.  The same resistances that cause low voltage create heat.  I have melted more than a couple extension cord plugs in my time.  In my home breaker panel, the previous owners hadn't re-torqued the breakers probably ever, and the line to the washing machine got loose.  The wire got so hot that the insulation melted about an inch and a half from the breaker.

There are two good solutions to the problems you have:

1.  Figure out how to get better power - rent a generator, use a distro, find better circuits, and/or reduce your load.

2. Get more efficient amps that can better deal with the power you have to work with.
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Alan Sledzieski

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Re: Crest Pro 8200 amps
« Reply #21 on: July 22, 2010, 09:08:34 PM »

TJ (Tom) Cornish wrote on Thu, 22 July 2010 20:38

Alan Sledzieski wrote on Thu, 22 July 2010 17:35

Bob Lee (QSC) wrote on Thu, 22 July 2010 18:07

Alan Sledzieski wrote on Thu, 22 July 2010 14:31


As voltage drops, current goes up.


Only if you use one of those voltage regulators that the pros here have advised you not to use on power amps.

Quote:

If voltage is low would a amp tend to run hotter because of increased current?


No, because the current will decrease.




Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?

Still confused why someone would want to run at 100 v when you could run them at 120 fairly cheap for a small system like mine.

In the case of most unregulated amps: The input voltage charges the voltage rails of the amp.  If the input voltage of the amp is lower, there is less voltage in the amp's power supply to create output voltage.  Less output voltage into an unchanging load impedance equals less current.  Amps running on lower mains voltages produce less waste heat too for the same reason - there is less spare power to be dissipated in the output stage.

There are a few models of amps (Itechs, Powersoft I believe, and probably a couple of others that have internal regulation and can produce full rated output at voltages as low as 90 or 100 volts, which do indeed work the way you expect.  Your Crests do not fall into this category.

As far as your question about why not use a voltage regulator - first of all you haven't really defined if your 100 volt spec is an "unloaded" voltage, or if this is what you are imagining the circuit does when the amp pulls a bit of power.  Any branch circuit that has lost 20 volts by the time it gets where you are using it is going to be so spongey that even if you prop it up to 120 volts using a regulator, you're going to knock it down a whole bunch more when you ask for 50 amps of instantaneous current, which is not untypical for a non power factor corrected amp of the sizes we are discussing.

For those peak hits, they happen faster than your regulator can switch taps, so you're not really even catching them, short of permanently setting up your VR as a boost transformer.

A power factor corrected amp is able to draw current over the entire waveform, which reduces peak demand, softens hits on the supply circuit, and just plain lets you get more usable power out of a limited supply.

In one of your other replies you said you can't damage a circuit due to heating because the breaker is protecting it - I would beg to differ.  The same resistances that cause low voltage create heat.  I have melted more than a couple extension cord plugs in my time.  In my home breaker panel, the previous owners hadn't re-torqued the breakers probably ever, and the line to the washing machine got loose.  The wire got so hot that the insulation melted about an inch and a half from the breaker.

There are two good solutions to the problems you have:

1.  Figure out how to get better power - rent a generator, use a distro, find better circuits, and/or reduce your load.

2. Get more efficient amps that can better deal with the power you have to work with.



I'm talking about unloaded voltage, usually 110 to 113, with load they do drop. I'm using 100 for a example as you said amps can run to 80 -90 volts.

The reason for melting your breaker or plug is a high resistance path the breaker does not see.  Its a bad conection making the heat.  It actually starts to act like a fuse.  You could run 400 amps on 4 ott copper, put a piece of 6 wire a foot long in the circuit, then go back to 4 ott cu.  The breaker will never trip, but the 6 wire will melt.

I've been to many a house that smell the smoke of a electrical burning smell.  Seen what you have said a hundred times.  A hot extension cord plug, or burned up end does not mean high current flow at the breaker.  It means your tring to draw as few as a couple amps through a connection the size of dental floss, thus the heat.


As far as more efficient amps, others may have said they sound good, but I need a comparison.  What are they comparing the class d amp to.  Are they of equal output?

As far as class d, I have never heard one of equal wattage, come close to having the punch or headroom of a class ab, or h. Pro sound, home entertainment, car audio.

It really depends what you compare a d amp to.  I really doubt a 5 kw d amp is going to sound as good as a macro 5000 watt or old 9001's, even ca series amps.  Now if you compare a d amp to a mackie or the likes, it may sound ok.
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TJ (Tom) Cornish

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Re: Crest Pro 8200 amps
« Reply #22 on: July 22, 2010, 09:21:58 PM »

Alan Sledzieski wrote on Thu, 22 July 2010 20:08

I'm talking about unloaded voltage, usually 110 to 113, with load they do drop. I'm using 100 for a example as you said amps can run to 80 -90 volts.

Then as I mentioned above, your VR is missing most of the transient voltage drop since you're starting at the neutral tap.  Your VR goes to boost, but the amp's peak current has already passed.  You click back down to the neutral tap, rinse, repeat.

Alan Sledzieski wrote on Thu, 22 July 2010 20:08

The reason for melting your breaker or plug is a high resistance path the breaker does not see.  Its a bad conection making the heat.  It actually starts to act like a fuse.  You could run 400 amps on 4 ott copper, put a piece of 6 wire a foot long in the circuit, then go back to 4 ott cu.  The breaker will never trip, but the 6 wire will melt.

I've been to many a house that smell the smoke of a electrical burning smell.  Seen what you have said a hundred times.  A hot extension cord plug, or burned up end does not mean high current flow at the breaker.  It means your tring to draw as few as a couple amps through a connection the size of dental floss, thus the heat.


Much of your resistive load causing the voltage drop is after the breaker.  The breaker sees it just fine - the load is just less than the trip current. 2400 watts is plenty to start a fire.
Alan Sledzieski wrote on Thu, 22 July 2010 20:08

As far as more efficient amps, others may have said they sound good, but I need a comparison.  What are they comparing the class d amp to.  Are they of equal output?

As far as class d, I have never heard one of equal wattage, come close to having the punch or headroom of a class ab, or h. Pro sound, home entertainment, car audio.

It really depends what you compare a d amp to.  I really doubt a 5 kw d amp is going to sound as good as a macro 5000 watt or old 9001's, even ca series amps.  Now if you compare a d amp to a mackie or the likes, it may sound ok.


Then you have never heard any of the amps I've mentioned.  Listen before you dismiss them.  The world is moving on to class D and there will be no going back - even on the low end of the price scale.

Alan - I'm sure you're a very smart guy, and I can pretty much guarantee that you know certain things about electricity that I don't.  That being said you need to decide if you believe the entire rest of the industry is stupid/wrong for not using voltage regulators like you are proposing.  There are a few of us who have done this before.  What works gets done again in the future.  If it doesn't work well or a higher cost option fails to produce a benefit worth the cost, then the practice is dropped.
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Alan Sledzieski

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Re: Crest Pro 8200 amps
« Reply #23 on: July 22, 2010, 09:57:23 PM »

Tom,

At 110 t0 113 the ar is in regulation at all times.  I measured input and output voltage.  Its not in the neu. tap at these voltages, its boosting.  I loaded the ar with a 1800 watt hairdrier and watched voltage, line and load side.

The breaker does not see a bad connection, a bad connection is like a small piece of wire tring to pass to much current.  Trust me, a load of a 5 amps will burn your house down at a bad connection and the breaker will never see it.   That's how house fires start.  People use 16 gauge extension cords on space heaters, the breaker never trips, its seeing 1800 watts, the wire can't take the current, fire.  Run your 1850 watt hairdrier for 5 min.  The cord will be warm, the wall circuit and breaker will not be. Its like breathing through a straw.


As far as hearing the amps you talk about, I have not. I'm going from what I  consider a transistor radio compared to what you guys run for a rig.  Small venues, sound quality in mind at all times.  I've listened to many small systems. 20 kw and lower.

I can only dream of running rigs like what you guys do.  One thing I know is, I have a good set of ears that are very picky, As of now there will not be a d amp in the rig, house, or auto.

I'm just going by my ears. heck I'd love to carry a 1 space amp around that does 8 kw at 12 lbs.  They just don't sound as good to me as a ab or h.  I'm surprised the 8200 sounds as good as it does.

Like i said before, I run a small rig, I'll continue to run regs on everything. So far its been a great improvement, and just giving my findings from a weekend warrior .

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Andy Peters

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Re: Crest Pro 8200 amps
« Reply #24 on: July 23, 2010, 01:58:27 AM »

Alan Sledzieski wrote on Tue, 20 July 2010 17:36

What I need to do is make a 12'' extension cord, with the hot and neutral apart from each other, put a digital clamp on amp meter on the hot leg, or neutral, and see whats actually going on.


You really need to do this while looking at resulting waveform on an oscilloscope, as the integration time of your meter is probably long enough to ignore fast peaks, like one would see from kick-drum hits.

-a
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Bob Lee (QSC)

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Re: Crest Pro 8200 amps
« Reply #25 on: July 23, 2010, 06:27:07 PM »

Alan Sledzieski wrote on Thu, 22 July 2010 15:35


Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?

Still confused why someone would want to run at 100 v when you could run them at 120 fairly cheap for a small system like mine.


So you're saying that if you turn off the AC voltage, the amp will try to draw infinite current?

Interesting. Wink

The fallacy you're stuck on is assuming constant power consumption as the AC mains voltage varies. In amps with unregulated rails (i.e., most of them), the rail voltages will track the mains voltage somewhat--maybe not exactly proportionally, but close to it. So you lose headroom when the mains sag, and the amp will indeed draw less current than if the mains voltage holds stiff. (Of course, the I
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Alan Sledzieski

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Re: Crest Pro 8200 amps
« Reply #26 on: July 23, 2010, 07:42:39 PM »

Bob Lee (QSC) wrote on Fri, 23 July 2010 18:27

Alan Sledzieski wrote on Thu, 22 July 2010 15:35


Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?

Still confused why someone would want to run at 100 v when you could run them at 120 fairly cheap for a small system like mine.


So you're saying that if you turn off the AC voltage, the amp will try to draw infinite current?

Interesting. Wink

The fallacy you're stuck on is assuming constant power consumption as the AC mains voltage varies. In amps with unregulated rails (i.e., most of them), the rail voltages will track the mains voltage somewhat--maybe not exactly proportionally, but close to it. So you lose headroom when the mains sag, and the amp will indeed draw less current than if the mains voltage holds stiff. (Of course, the I
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Alan Sledzieski

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Re: Crest Pro 8200 amps
« Reply #27 on: July 23, 2010, 07:45:40 PM »

Bob Lee (QSC) wrote on Fri, 23 July 2010 18:27

Alan Sledzieski wrote on Thu, 22 July 2010 15:35


Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?


So you're saying that if you turn off the AC voltage, the amp will try to draw infinite current?

Interesting. Wink




Nope, I never said that, not sure I implied that?

1200 / 0 = 0
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Mac Kerr

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Re: Crest Pro 8200 amps
« Reply #28 on: July 23, 2010, 08:29:07 PM »

Alan Sledzieski wrote on Fri, 23 July 2010 19:45

Bob Lee (QSC) wrote on Fri, 23 July 2010 18:27

Alan Sledzieski wrote on Thu, 22 July 2010 15:35


Interesting.

P = V x A

1200 watts = 120 volts x 10 amps

1200 watts = 100 volts x 12 amps ?


So you're saying that if you turn off the AC voltage, the amp will try to draw infinite current?

Interesting. Wink


Nope, I never said that, not sure I implied that?

1200 / 0 = 0


What you more than implied is that as the voltage goes down the current goes up. The logical extension of that is that as the voltage approaches zero the current approaches infinity.

By the way, 1200/0 does not equal 0.

Mac
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Alan Sledzieski

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Re: Crest Pro 8200 amps
« Reply #29 on: July 23, 2010, 09:58:02 PM »

Mac Kerr wrote on Fri, 23 July 2010 20:29


What you more than implied is that as the voltage goes down the current goes up. The logical extension of that is that as the voltage approaches zero the current approaches infinity.

By the way, 1200/0 does not equal 0.

Mac




Ok, so the formula p = v x a has been wrong all these years?

So, 1200 w does not equal 1 volt X 1200 amps.

You should be logical here, you turn off the power to a given item, there will be no currant flow.  Amps will equal 0, not infinity.
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