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Onkyo shuts off with Forte II speakers


Defacto
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I bought a pair of Forte II speakers last weekend.  I've been loving them!

But, I cranked the volume to 80 and the Onkyo TX NR656 receiver shut down. (45-50 is more common for me.)

Upon restarting it, error check speaker wires comes up.  All is fine again until I crank to 80.

I see no issues with the cables. 

 

Could this be a speaker problem?  

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It's rated 160 watts into 6 ohms

 

That's 31Vrms into 6 ohms and a little over 5 amps of current

 

If you have dips down below 6 ohms (most likely you do) and the amp can only deliver 5 amps, the protection will trip before reaching the 31v output into a tougher load like 4 ohms. Delivering 5 amps into a 4 ohm load is 20Vrms.

 

As you can see lower load impedances require more current, the amp will try and reach the rail voltage into the load but if the load is too low it may exceed the output stage current delivery capability and either blow up or go into protection mode.

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10 minutes ago, ODS123 said:

Make sure you don't have a strand or two of speaker wire crossing speaker jacks..  Has the speaker ever been modified?  If so, maybe possible one of the crossovers has a small short.

 

This is good advice. The higher power output to the speaker could make a bad connection short out and trip the protection of the amp.

 

17 minutes ago, Defacto said:

I'm not sure what you suggest captainbeefheart?

 

It wasn't so much of a suggestion, looking at the specs they say nothing about being able to drive 4 ohm loads. They specify the output power into 8 and 6 ohm loads which tells me it won't be happy with anything lower than 6 ohms when cranking it.

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I now see that your model does not have a speaker ohm selection that is available on my Onkyo. I should have read your owners manual before answering. So, I defer to the other advice that has been posted above.

 

A couple questions. What speakers did you have connected before and how high could they play? Have you performed the AccuEQ set-up process?

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I have checked and rechecked for wire issues.

 

I reconnected the Klipsch R26F,am listening to them at 80 

and all is fine.

 

The ex-owner did replace tweeters and caps himself.

Perhaps he never plaid them loud and this could cause the issue?

Edited by Defacto
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35 minutes ago, Defacto said:

I have checked and rechecked for wire issues.

 

I reconnected the Klipsch R26F,am listening to them at 80 

and all is fine.

 

The ex-owner did replace tweeters and caps himself.

Perhaps he never plaid them loud and this could cause the issue?

 

I cannot find a frequency vs impedance plot for the R26F.

 

Looking at R28F it drops to about 3.8 ohms at ~150Hz

 

Forte II looks about the same, just below 4 ohms at same frequency.

 

This kinda leads me to think there is something wrong with your Forte II speakers. Either something is shorting during higher excursions, have a look at the woofer wiring and tinsel wire for frays that may cause a short. Make sure crossovers are okay as well.

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If you have a multimeter you can put it in continuity mode or lowest scale of resistance and connect the test leads to the input jacks of the speaker. Then wiggle things around and see if it changes to a short circuit or very low resistance.

 

You can also gently move the drivers in and out while doing the same test to see if it's shorting out in the voice coil area during excursions. Put your thumb on the face of the cone and a couple fingers through the basket to the back side of the cone, once you have the cone gently 'pinched' between thumb and fingers gently move it in and out, the voice coil should move freely through the magnet.

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5 hours ago, Khornukopia said:

Go to your Onkyo set up menu, enter Speaker Settings, enter Impedance. You should have a choice of 6 ohms or 4 ohms. Select 4 ohms.

Bearer of bad news, but this is very bad advice, and it should not be repeated. Some days we come here and learn new things. Today is one of those. I totally understand how this setting can be misunderstood though. Here are the facts.

 

This setting has got nothing to do with the nominal impedance of your speakers. In short, what a lower impedance setting of a consumer AVR generally does is engage a circuit that significantly limits the output voltage of the AVR. This is solely for the purposes of continuous multichannel high power heat dissipation testing by the electrical product certifiers. In other words, it's actual purpose has nothing to do with real-world usage. This setting is there so the manufacture can get a certifiate, nothing more. 

 

The Onkyo (and other AVR's) impedance setting should never be used, and only be kept at the default setting.

The Low Z mode effectively limits the current available to the speakers, but greatly increases the risk of clipping the amps due to the severely curtailed output. Amplifier clipping is a highly undesirable outcome.

 

Read everything you ever wanted to know on the subject in one 3 page article. I provided the link to it below.

https://www.audioholics.com/audio-amplifier/impedance-selector-switch-1

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26 minutes ago, 314carpenter said:

Bearer of bad news, but this is very bad advice, and it should not be repeated. Some days we come here and learn new things. Today is one of those. I totally understand how this setting can be misunderstood though. Here are the facts.

 

This setting has got nothing to do with the nominal impedance of your speakers. In short, what a lower impedance setting of a consumer AVR generally does is engage a circuit that significantly limits the output voltage of the AVR. This is solely for the purposes of continuous multichannel high power heat dissipation testing by the electrical product certifiers. In other words, it's actual purpose has nothing to do with real-world usage. This setting is there so the manufacture can get a certifiate, nothing more. 

 

The Onkyo (and other AVR's) impedance setting should never be used, and only be kept at the default setting.

The Low Z mode effectively limits the current available to the speakers, but greatly increases the risk of clipping the amps due to the severely curtailed output. Amplifier clipping is a highly undesirable outcome.

 

Read everything you ever wanted to know on the subject in one 3 page article. I provided the link to it below.

https://www.audioholics.com/audio-amplifier/impedance-selector-switch-1

 

Yup exactly.

 

If the rails is say 35v and its rated to deliver current into a specific load, if you change the impedance setting lower it will not allow the outputs to swing up to their rail potential, it will limit them to where the maximum output current is. My example above for 160 watts into 6 ohms is 31v, this is about 5 amps of current and most likely the most the output is allowed to deliver into any load. So for a 4 ohm load if say lowered by the setting it will limit the output voltage to 20v instead of the 31v it's capable of in order to keep the current at 5 amps.

 

Now 5 amps at 20v is 100 watts, you have now reduced your output power by 60 watts. They won't increase current through the output devices because it increases the temperature over rated amount.

 

Note: They don't change the rail voltage, instead they usually use a limiter/compressor circuit to reduce output signal to keep output current within rating. The amp in question doesn't do this, it is just rated for a 4 ohm load at 160 watts. I have not looked at the schematic but it most likely will have a thermistor on the heatsink and if too much current passes through the output devices for too long increasing the temperature it will open the relays at the output and go into protection mode. It also may have direct current sensing from the output which will open the relay also if it exceeds a specific current amount.

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2 hours ago, Defacto said:

I have checked and rechecked for wire issues.

 

I reconnected the Klipsch R26F,am listening to them at 80 

and all is fine.

 

The ex-owner did replace tweeters and caps himself.

Perhaps he never plaid them loud and this could cause the issue?

 

My hunch is that while replacing the caps he either replaced them with something not suitable OR wasn't sufficiently careful and caused a short.  

 

Fortes present an easy load to amplifiers  As such I would definitely suspect the modified FII's as the cause before I'd suspect the unmodified Onkyo.  ..If it were me, I'd go back to stock tweeters and cross-overs..  I don't mean to sound negative - I do empathize.

 

If there's a lesson to be learned, perhaps it's that people should trust Kiipsch engineers and quit modifying their speakers.

 

If it's not too late, I'd probably return the speakers to the seller.  ..It's highly improbable that the problem lies with your receiver.

 

 

 

 

 

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4 hours ago, 314carpenter said:

Bearer of bad news, but this is very bad advice, and it should not be repeated. Some days we come here and learn new things. Today is one of those. I totally understand how this setting can be misunderstood though. Here are the facts.

 

This setting has got nothing to do with the nominal impedance of your speakers. In short, what a lower impedance setting of a consumer AVR generally does is engage a circuit that significantly limits the output voltage of the AVR. This is solely for the purposes of continuous multichannel high power heat dissipation testing by the electrical product certifiers. In other words, it's actual purpose has nothing to do with real-world usage. This setting is there so the manufacture can get a certifiate, nothing more. 

 

The Onkyo (and other AVR's) impedance setting should never be used, and only be kept at the default setting.

The Low Z mode effectively limits the current available to the speakers, but greatly increases the risk of clipping the amps due to the severely curtailed output. Amplifier clipping is a highly undesirable outcome.

 

Read everything you ever wanted to know on the subject in one 3 page article. I provided the link to it below.

https://www.audioholics.com/audio-amplifier/impedance-selector-switch-1

 

4 hours ago, captainbeefheart said:

 

Yup exactly.

 

If the rails is say 35v and its rated to deliver current into a specific load, if you change the impedance setting lower it will not allow the outputs to swing up to their rail potential, it will limit them to where the maximum output current is. My example above for 160 watts into 6 ohms is 31v, this is about 5 amps of current and most likely the most the output is allowed to deliver into any load. So for a 4 ohm load if say lowered by the setting it will limit the output voltage to 20v instead of the 31v it's capable of in order to keep the current at 5 amps.

 

Now 5 amps at 20v is 100 watts, you have now reduced your output power by 60 watts. They won't increase current through the output devices because it increases the temperature over rated amount.

 

Note: They don't change the rail voltage, instead they usually use a limiter/compressor circuit to reduce output signal to keep output current within rating. The amp in question doesn't do this, it is just rated for a 4 ohm load at 160 watts. I have not looked at the schematic but it most likely will have a thermistor on the heatsink and if too much current passes through the output devices for too long increasing the temperature it will open the relays at the output and go into protection mode. It also may have direct current sensing from the output which will open the relay also if it exceeds a specific current amount.

 

Interesting info. Good to learn those facts about the selection option. 

 

The owners manual just states, "If the impedance of any speaker is 4 ohms or more but less than 6, set the minimum speaker impedance to 4 ohms".

 

Fortunately, my highly efficient Klipsch speakers never even needed half the available power to play loud, so the amp never clipped, but I will switch the AVR back to the High Z setting and experience full power! Thanks for the education.

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16 hours ago, captainbeefheart said:

If you have a multimeter you can put it in continuity mode or lowest scale of resistance and connect the test leads to the input jacks of the speaker. Then wiggle things around and see if it changes to a short circuit or very low resistance.

 

***One speaker shows 0.4 ohm resistance; the other shows 4 ohm.  I want to take a look inside before trying the wiggling.  I guess the 0.4 ohm speaker should be first.***

 

***EDIT:  My Bad.    Both speakers show about 7 ohms resistance.

 

Thank you all for your time and advice!  I'll take some pics of internals later today.

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