Author Topic: connecting speaker drivers to amplifers  (Read 606 times)

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Offline Adhith

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connecting speaker drivers to amplifers
« on: January 06, 2019, 07:01:19 pm »
Hello everyone,
While reading articles and post related to audio amplifiers and speakers, I often read this note." Connect the speakers drivers first at the output before powering the amplifier".  So what is the purpose of doing it?? does leaving a speaker not connected at the output cause any damage to the amplifier circuit??
 also some suggests to use a power resistor at one of the audio outputs (rather than leaving it floating) for DIY projects using only one speaker driver.

Could anyone help me understand whats the reason for it??

 

Online Zero999

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Re: connecting speaker drivers to amplifers
« Reply #1 on: January 06, 2019, 07:37:47 pm »
I don't think there's any chance of damage from operating an audio amplifier unloaded, but it's possible it might not work properly. Most modern class AB designs should be fine, but there could be problems with EMI on a class D amplifier, as the filter won't be optimised for operation without a load.
 
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Offline Johnboy

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Re: connecting speaker drivers to amplifers
« Reply #2 on: January 06, 2019, 07:40:46 pm »
It's a good rule of thumb to have a load already in place for the power section to lessen the chances of overheating. In some cases a design will incorporate a "safety" for this, but if the project you're working on already suggests placing a power resistor on one of the outputs, I'm not surprised that it also specifies that you should connect a load (like the speaker) to the other as well before lighting things up.
 
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Online Benta

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Re: connecting speaker drivers to amplifers
« Reply #3 on: January 06, 2019, 07:46:34 pm »
It's a relict from the tube amplifier days, where an unloaded output transformer could cause problems. In "solid state" or rather semiconductor amplifiers it has no place at all.
I've never seen a bipolar or MOSFET power amplifier where this could be an issue.
 
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Offline pwlps

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Re: connecting speaker drivers to amplifers
« Reply #4 on: January 06, 2019, 08:49:10 pm »
It's a relict from the tube amplifier days, where an unloaded output transformer could cause problems. In "solid state" or rather semiconductor amplifiers it has no place at all.
I've never seen a bipolar or MOSFET power amplifier where this could be an issue.

I don't know for the audio domain amps but in RF it is a known issue at high power, even with solid state (power MOSFET) devices: without a matched load the power is reflected back to the output stages causing an overvoltage.  Usually there is a protection supposed to monitor the overvoltage, yet I have seen several NMR/MRI RF power amps damaged after having been used without a proper load.   I don't have any experience with audio amps but I'm curious to understand why similar overvoltage problems couldn't happen there. 
 
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Online Zero999

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Re: connecting speaker drivers to amplifers
« Reply #5 on: January 06, 2019, 08:51:28 pm »
It's a relict from the tube amplifier days, where an unloaded output transformer could cause problems. In "solid state" or rather semiconductor amplifiers it has no place at all.
I've never seen a bipolar or MOSFET power amplifier where this could be an issue.

I don't know for the audio domain amps but in RF it is a known issue at high power, even with solid state (power MOSFET) devices: without a matched load the power is reflected back to the output stages causing an overvoltage.  Usually there is a protection supposed to monitor the overvoltage, yet I have seen several NMR/MRI RF power amps damaged after having been used without a proper load.   I don't have any experience with audio amps but I'm curious to understand why similar overvoltage problems couldn't happen there.
Yes that's true, but this thread is about audio amplifiers, not RF.
 

Offline Adhith

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Re: connecting speaker drivers to amplifers
« Reply #6 on: January 08, 2019, 04:01:21 pm »
Thank you guys for the replies.
 

Offline lutkeveld

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Re: connecting speaker drivers to amplifers
« Reply #7 on: January 08, 2019, 04:10:09 pm »
Also the risk of blowing up the output capacitors. Class-D output filters can start to ring without load. They should be operated with a load in place.
 

Online Zero999

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Re: connecting speaker drivers to amplifers
« Reply #8 on: January 08, 2019, 04:42:28 pm »
Also the risk of blowing up the output capacitors. Class-D output filters can start to ring without load. They should be operated with a load in place.
That's plausible, but I would hope that a decent amplifier would be adequately protected against that.
 


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