Underpowered receiver

[PENG]

Guys, please realize that a 2.5A slow blow fuse 'may' take forever to blow if the rms current averages only slightly above 2.5A. Fuses just don't blow quickly otherwise every other time you turn on one of those entry level amps as the light dims the fuses would blow. Even if you double it to 5A it will not blow right away. You need to obtain the time/current curve from the fuse manufacturer in order to know what the fuse characteristics are. I suggest you get a decent clamp on ammeter and measure the actual current that flows when you crank the volume up to get say 102 dB. You will find out how low the rms current you may be seeing.

I am not saying it is for sure but do not rule out the possibility that your amp may in fact be clipping, resulting in momentary high peak current high enough to blow the 2.5A fuses instantaneously. If you are curious enough, go get that big amp first, try it out and if it still blows the fuses then get rid of them. Or regardless of the result, get rid of the fuses. The difference is then you will have learnt more about what might have been taking place.

 

[PENG]

Yes, Peng that is absolutely correct, a generator, or UPS, what ever device you are using for supply, must be rated the KVA requirement AND the true power in watts of the anticipated load.

However the fuse is in the connecting cable, so the only factor of concern is the current between the source and the load. As far as a load is concerned, (let it be a speaker) then the only thing that will generate heat in the load is the true power.

You have to define 'true power' in the case of a loudspeaker. A loudspeaker is meant to produce sound not heat. A generator is designed to deliver power for all sorts of things, not just heat.

That's why for clarity I prefer to based the heat produced on the actual current flow so I do not have to worry about true or apparent. If you still don't buy in please think about your own generator. I can assure you if you hook it up to a big inductor that has negligible resistance and very low inductance it will still trip on overload or even instantaneous overcurrent. My point is simply that it does not matter what the power factor is, it is CURRENT that cause damages to equipment in the form of heat and/or movements resulted from high magnetic field created by the high current, or excessive voltage that cause insulation failure. True power vs apparent power is a different topic (example:efficiency/losses considerations) altogether.

 

[TLS Guy]

You have to define 'true power' in the case of a loudspeaker. A loudspeaker is meant to produce sound not heat. A generator is designed to deliver power for all sorts of things, not just heat.

That's why for clarity I prefer to based the heat produced on the actual current flow so I do not have to worry about true or apparent. If you still don't buy in please think about your own generator. I can assure you if you hook it up to a big inductor that has negligible resistance and very low inductance it will still trip on overload or even instantaneous overcurrent. My point is simply that it does not matter what the power factor is, it is CURRENT that cause damages to equipment in the form of heat and/or movements resulted from high magnetic field created by the high current, or excessive voltage that cause insulation failure. True power vs apparent power is a different topic (example:efficiency/losses considerations) altogether.

99% or more of the power consumed by a speaker is converted to heat. In an inductive load, only the true power is dissipated as heat. The source must be able to handle the current for the apparent power. So yes, of course my generator cutout would trip because the load would exceed the generators VA rating. Heat dissipated in the load is always the power in watts and not related to the apparent power. The reason the load you describe would not heat but the breaker trip, is that with those extreme phase angles, the source would see the load as very low impedance while current was high.

Just like an amplifier driving a difficult speaker load.

 

[3db]

You have to define 'true power' in the case of a loudspeaker. A loudspeaker is meant to produce sound not heat. A generator is designed to deliver power for all sorts of things, not just heat.

That's why for clarity I prefer to based the heat produced on the actual current flow so I do not have to worry about true or apparent. If you still don't buy in please think about your own generator. I can assure you if you hook it up to a big inductor that has negligible resistance and very low inductance it will still trip on overload or even instantaneous overcurrent. My point is simply that it does not matter what the power factor is, it is CURRENT that cause damages to equipment in the form of heat and/or movements resulted from high magnetic field created by the high current, or excessive voltage that cause insulation failure. True power vs apparent power is a different topic (example:efficiency/losses considerations) altogether.

It would be the instantaneous current that would cause the trip but the heat generated would be the dc resistance only seen by teh current flowing through the device.

 

[TLS Guy]

It would be the instantaneous current that would cause the trip but the heat generated would be the dc resistance only seen by teh current flowing through the device.

This is a good review.

 

[3db]

This is a good review.

I have a degree in Electrical and am well versed in this.

 

[TLS Guy]

I have a degree in Electrical and am well versed in this.

I just posted that so there are graphics. We are both agreed in any event that it is the true power consumed by the load that generates the heat, and the current be it for the true or apparent power that trips the breaker (fuse).

 

[M Code]

Guys, please realize that a 2.5A slow blow fuse 'may' take forever to blow if the rms current averages only slightly above 2.5A. Fuses just don't blow quickly otherwise every other time you turn on one of those entry level amps as the light dims the fuses would blow. Even if you double it to 5A it will not blow right away. You need to obtain the time/current curve from the fuse manufacturer in order to know what the fuse characteristics are. I suggest you get a decent clamp on ammeter and measure the actual current that flows when you crank the volume up to get say 102 dB. You will find out how low the rms current you may be seeing.

I am not saying it is for sure but do not rule out the possibility that your amp may in fact be clipping, resulting in momentary high peak current high enough to blow the 2.5A fuses instantaneously. If you are curious enough, go get that big amp first, try it out and if it still blows the fuses then get rid of them. Or regardless of the result, get rid of the fuses. The difference is then you will have learnt more about what might have been taking place.

A slo-blo fuse is inadequate to protect a loudspeaker...
Note that the slo-blo fuse requires 100% current overload for 10 seconds before opening...
Fuses in general cannot protect loudspeakers as when a power amplifier clips badly it is instantanteous and again a fuse has difficulty reacting fast enough. Thats why modern protection circuitry is internal and has a fast action, yes a fuse will be used within the power supply section but again the power supply is reacting to the exterme external conditions and is very slow..
The damage to the loudspeaker is already done..

The best protection of a system is to measure/quantify the target acoustic SPL, then use electronics and loudspeakers components designed to deliver this..

Hope that clears up any misunderstanding for this subject..

Just my $0.01...

 

[bnairb]

However much I appreciate all of your input (you guys are very smart), I'm afraid your technicality is leaving me in the dust and still with blown fuses. Where am I now? The general consensus earlier was the 2.5 amp fuses would never allow the watts the speakers are rated at or as much as the 2700 is capable of delivering. Then Peng said to not rule out that the 2700 is clipping. If I short out or up the amperage on the fuses and the amp IS clipping, won't I surely blow the speakers? Peng mentioned testing with an ammeter. Will this tell me for certain if clipping is occuring? If so, what are the steps to perform the test? As a reminder, CV tech support said the RE-38's carried ferro fluid. What should I do next? And again, I can't thank you all enough for your participation. I just wish I understood most of what you were saying.

 

[TLS Guy]

However much I appreciate all of your input (you guys are very smart), I'm afraid your technicality is leaving me in the dust and still with blown fuses. Where am I now? The general consensus earlier was the 2.5 amp fuses would never allow the watts the speakers are rated at or as much as the 2700 is capable of delivering. Then Peng said to not rule out that the 2700 is clipping. If I short out or up the amperage on the fuses and the amp IS clipping, won't I surely blow the speakers? Peng mentioned testing with an ammeter. Will this tell me for certain if clipping is occuring? If so, what are the steps to perform the test? As a reminder, CV tech support said the RE-38's carried ferro fluid. What should I do next? And again, I can't thank you all enough for your participation. I just wish I understood most of what you were saying.

Get rid of the fuses, and you will be fine. If you have ferro fluid in the tweeters you will be fine. Either jump the fuses best, or put in 20 amp fuses.

 

[PENG]

99% or more of the power consumed by a speaker is converted to heat. In an inductive load, only the true power is dissipated as heat. The source must be able to handle the current for the apparent power. So yes, of course my generator cutout would trip because the load would exceed the generators VA rating. Heat dissipated in the load is always the power in watts and not related to the apparent power. The reason the load you describe would not heat but the breaker trip, is that with those extreme phase angles, the source would see the load as very low impedance while current was high.

Just like an amplifier driving a difficult speaker load.

Let me emphasis for once that there is no disagreement here except the true power thing that you have been talking about. Are you saying that true power of a speaker is the square of the current X the resistance (part of the impedance) of the voice coil? I sure hope not! Or you are referring only to the heat produced by the current that passes throuogh the d.c. resistance (not impedance) of the voice coil, or both?

Take an example, what is the true power of an electromagnetic coil? I think a more acceptable answer would be, the power due to the attractive force it develops with a current that lags the voltage by a huge angle (almost 90 degrees), than to say its true (more like wast in fact) power is the heat developed in the coil due to the inherent low resistance of the winding. If you were to stick with current, resistance, reactance then there would have been no confusion. It is when you say only the true power blow the speaker then it begs the question what exactly do you mean by "true power".

For argument sake, consider a scenario when you push a box on your carpeted and level floor by applying your line of force horizontally and you have to apply 100 lbf. Now you do the same but push it with the applied line of force at an angle of 45 degrees, you are going to have to apply much more than 100 lbf, at least > 100Xcos45=1414 lbf (how much > depends on the coefficient of friction) due to the phase angle as well as the additional frictional force to overcome. Now you can argue that the true power is the part (>100 lbf) resulted from moving the box. Well, the fact is, the person still must deal with the full power resulting from having to exert greater than 1414 lbf whether that power is useful, "true" or "apparent". So it will be wrong to say it is only the 100 lbf push that "blows/ or injures" the person. It is easy to define "heat dissipation" due to the resistance of a load, but much harder to define "true power" unless you stick to the formula Power in watts=I^2*R or I^2*Z*CosΦ where Φ is the phase angle between the current and voltage.

Back to the OP, in your case it is the current that causes the damage regardless of what the heck "true power" means. You pump enough current into the thing it will blow, no need to complicate things.

 

[PENG]

It would be the instantaneous current that would cause the trip but the heat generated would be the dc resistance only seen by teh current flowing through the device.

Yes, isn't that simple? But no, Dr. TLS has to call that "true power", when it is simply P=I²R=power dissipated as heat in the d.c. resistance; and who care if it is true, waste, useful or whatever. In my example it is an inductor coil so what the any resistance is just inherent, not intended, nothing "true" about it. If I have to give it a name I would call it wasted power.

 

[PENG]

I have a degree in Electrical and am well versed in this.

Good to know. Now you know why whenever the Dr. talk about speaker design I do not make comment and I admire his talent. When he threw electrical theories and terminologies around I always felt compelled to help clarify any confusion and misconception. In this debate so far it has been mostly confusion with a little misconception.

 

[PENG]

However much I appreciate all of your input (you guys are very smart), I'm afraid your technicality is leaving me in the dust and still with blown fuses. Where am I now? The general consensus earlier was the 2.5 amp fuses would never allow the watts the speakers are rated at or as much as the 2700 is capable of delivering. Then Peng said to not rule out that the 2700 is clipping. If I short out or up the amperage on the fuses and the amp IS clipping, won't I surely blow the speakers? Peng mentioned testing with an ammeter. Will this tell me for certain if clipping is occuring? If so, what are the steps to perform the test? As a reminder, CV tech support said the RE-38's carried ferro fluid. What should I do next? And again, I can't thank you all enough for your participation. I just wish I understood most of what you were saying.

My $3000 a pair speaker had its tweeter blown once when driven by a 200WPC amp and the amp's clipping indicating light never even came on. How old are your RE-38? Apparently the ferro fluid can dry up.... I don't know about speakers like TLS Guy does but I also don't believe in line fuses for speakers. So I would also say get rid of them but I won't guarantee your 2700 won't clip based on what you have told us.

 

[lsiberian]

I can't wait for the discussion on pointers or some other software topic. These electrical engineers and their big words overwhelm my mind. Of course this is Turkey day.

 

[PENG]

This is a good review.

It is a simple a basic review. Try this one too:

http://en.wikipedia.org/wiki/AC_power#Real.2C_reactive.2C_and_apparent_power

In the 2nd paragraph:

"Engineers care about this because even though the current associated with reactive power does no work at the load, it heats wires. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work."

That's what I meant by stick with the current and the resistive part of the load. That is what produces heat. If you are going to google electrical theory related topics, Wikipedia generally does a good job. Otherwise I typically go back to my text books or pay a visit to the library.

 

[PENG]

I can't wait for the discussion on pointers or some other software topic. These electrical engineers and their big words overwhelm my mind. Of course this is Turkey day.

Sorry but we are dealing with someone who likes to get technical. In my first response I used nothing much more than "current is current blablabla" simple enough?

 

[PENG]

I just posted that so there are graphics. We are both agreed in any event that it is the true power consumed by the load that generates the heat, and the current be it for the true or apparent power that trips the breaker (fuse).

You are still making such confusing general statement. However, I just thought of something. May be you are confused between a passive R,L,C circuits with active loads such as a d.c. or a.c. electric motors or loudspeakers. An active load such as a motor surely has winding resistance that results in losses in the form of heat, but a 5 kW motor is not the same as a 5 kW electric base board heater heater. In the case of the 5kW electric resistance heater I would agree totally the heat is produced is the true power, conversely like you say it is the true power that produces the heat. In the case of a 5 kW motor (same power rating but an active load), the true power would be the power developed from electromagnetic force that get translated into rotary torque and that in turn drives a load (e.g. he drive shaft of an electric car, lawn motor, propeller etc.) thereby producing mechanical power. The relatively smaller part of the power consumed due to the winding resistance is hardly "true power", more appropriate termed "winding resistance losses" along with other losses such as eddy current losses.

Sometimes you just cannot google everything. Try googling the Britannica you will have to pay before they let you in deeper. Text books and reference books in unversity libraries are still indispensable.

 

[TLS Guy]

Let me emphasis for once that there is no disagreement here except the true power thing that you have been talking about. Are you saying that true power of a speaker is the square of the current X the resistance (part of the impedance) of the voice coil? I sure hope not! Or you are referring only to the heat produced by the current that passes throuogh the d.c. resistance (not impedance) of the voice coil, or both?

Take an example, what is the true power of an electromagnetic coil? I think a more acceptable answer would be, the power due to the attractive force it develops with a current that lags the voltage by a huge angle (almost 90 degrees), than to say its true (more like wast in fact) power is the heat developed in the coil due to the inherent low resistance of the winding. If you were to stick with current, resistance, reactance then there would have been no confusion. It is when you say only the true power blow the speaker then it begs the question what exactly do you mean by "true power".

For argument sake, consider a scenario when you push a box on your carpeted and level floor by applying your line of force horizontally and you have to apply 100 lbf. Now you do the same but push it with the applied line of force at an angle of 45 degrees, you are going to have to apply much more than 100 lbf, at least > 100Xcos45=1414 lbf (how much > depends on the coefficient of friction) due to the phase angle as well as the additional frictional force to overcome. Now you can argue that the true power is the part (>100 lbf) resulted from moving the box. Well, the fact is, the person still must deal with the full power resulting from having to exert greater than 1414 lbf whether that power is useful, "true" or "apparent". So it will be wrong to say it is only the 100 lbf push that "blows/ or injures" the person. It is easy to define "heat dissipation" due to the resistance of a load, but much harder to define "true power" unless you stick to the formula Power in watts=I^2*R or I^2*Z*CosΦ where Φ is the phase angle between the current and voltage.

Back to the OP, in your case it is the current that causes the damage regardless of what the heck "true power" means. You pump enough current into the thing it will blow, no need to complicate things.

What I'm saying is this. It is the power actually delivered to the load that will blow it. In other words blow a speaker.

Now in a speaker we both know that you can't calculate the current from power/V. At times the current will be higher depending on the phase angle. Now that excess current is going to the load, but also back to the source and the power given back over time. Now that peak current has to be allowed for in the source and the supply lines. However only the power converted into heat and sound will be supplied by the source over time.

In practice what this means for the OP if his speaker is pretty typical, is that you would think his amp could provide 25 watts into his four ohm speakers over time, and only blow the fuse if this was exceeded. However if his speakers are typical, you could actually only deliver about 17 watts to them over time without blowing the fuse.

We got into this discussion, because I was trying to point out that a speaker line fuse will blow at a lower power level than calculated from the usual DC formulas, we ran for the OP earlier in the thread.

 

[TLS Guy]

You are still making such confusing general statement. However, I just thought of something. May be you are confused between a passive R,L,C circuits with active loads such as a d.c. or a.c. electric motors or loudspeakers. An active load such as a motor surely has winding resistance that results in losses in the form of heat, but a 5 kW motor is not the same as a 5 kW electric base board heater heater. In the case of the 5kW electric resistance heater I would agree totally the heat is produced is the true power, conversely like you say it is the true power that produces the heat. In the case of a 5 kW motor (same power rating but an active load), the true power would be the power developed from electromagnetic force that get translated into rotary torque and that in turn drives a load (e.g. he drive shaft of an electric car, lawn motor, propeller etc.) thereby producing mechanical power. The relatively smaller part of the power consumed due to the winding resistance is hardly "true power", more appropriate termed "winding resistance losses" along with other losses such as eddy current losses.

Sometimes you just cannot google everything. Try googling the Britannica you will have to pay before they let you in deeper. Text books and reference books in unversity libraries are still indispensable.

I'm not confusing anything and regard the source resistances as part of the supply chain resistance which it is. In the real world you and I know there is always source resistance. I'm defining true power as the power consumed by the load and converted into heat, sound, mechanical energy or what ever. That is the total (true) power consumed in watts. However in an AC inductive circuit, the current measured will at points in the cycle be higher than required to produce that power. The current is real, and the energy is stored in the load and given back to the source according to the point in the cycle. And yes, there will be losses from that current in the supply chain, and those peak currents have to be allowed for in the source and supply chain.

I have studied the loudspeaker amplifier interface extensively and it is much worse than you think, because of these problems. The performance of receivers and amplifiers is studied with resistive loads, that I have found has remarkably little significance for the real world.

An amplifier really does have to provide significantly more current into a speaker than a four ohm resistor and if it can't it clips. I have not examined the receivers talked about extensively in these forums. However I suspect most of them can provide no more current into an 4 ohm load than a 8 ohm one, even if they don't blow up. My best guess is that these receivers actually deliver less than 50 % of their rated power into most speakers. Most speakers are four ohm loads and even less in the frequency range were most of the power is drawn form the amp. So because of their inability to provide adequate current, voltage will be limited. So I think if these receivers were looked at critically you would find many of the receivers rated at 100 watts into 8 ohms probably actually clip at about 35 watts into most speakers.

I can tell you for certain that was so before the advent of high current solid state output devices. I studied amps of the early generations extensively and that is exactly how they performed. Since manufacturers of most receivers just state they are four ohm stable (ie don't blow up) but don't specify the power they do deliver into a four ohm load I have a strong hunch that the clip point is at a much lower power point than is generally imagined.

For the above reasons I don't discount your assertion that the OPs amps may clip and that he could need more power. However I doubt they are clipping at the point his 2.5 amp fuses are limiting his current and power.