Amp outputting low bass?

[Finemoves]

Hi guys,
First time posting. Just wondering if amplifiers are meant to output the same power at different frequencies? I recently purchased a Yamaha RN803, and it sounded amazing for about a week, then it seemed like the bass went lower, empty.. kinda hollow. So I took the amp to a service center and they ran it through a digital oscilloscope to check power output at different frequencies. It was definitely lower on the 2nd frequency test. Here's a video I took of the testing.

My amp shouldn't be doing this right?

 

[everettT]

That's really not enough info to give an opinion about. What speakers are you using and do you have them crossed over to a sub? Amplifiers are load dependant, it's just to what degree.

 

[fmw]

Review everything. For example be sure you haven't connected the speakers out of phase. The problem may not be in the amp.

 

[TLS Guy]

Hi guys,
First time posting. Just wondering if amplifiers are meant to output the same power at different frequencies? I recently purchased a Yamaha RN803, and it sounded amazing for about a week, then it seemed like the bass went lower, empty.. kinda hollow. So I took the amp to a service center and they ran it through a digital oscilloscope to check power output at different frequencies. It was definitely lower on the 2nd frequency test. Here's a video I took of the testing.

My amp shouldn't be doing this right?

Hard to know. First of all, was the receiver set to pass through with bass management disengaged? If the bass management is engaged that is what you would see.

The other issue is, did the tech change voltage sensitivity on the scope, when changing the frequency range?

If the answer is NO and NO, then yes your unit is defective.

 

[Old School]

Most modern surround sound receiver/amplifiers are filled FULL of microprocessor crap inside of them that can act squirrely once in awhile. That's one of the big MINUSES about 'em, they can be full of all kinds of intermittent craziness! You can try the 'Pure Direct mode'and see if that helps. Also, your Tech guy really Acts like he knows his stuff. Did He mention bypassing the processor nitty-gritty and see what happens? This unit was made in Malaysia, (which isn't as good compared to Japan but, much better than something made in China), and just the complexity of the circuitry can be a service person's Nightmare! So iF your woe's can't be remedied pretty quick you might be ahead to Swap it out for a different one. Good luck to you

 

[everettT]

Most modern surround sound receiver/amplifiers are filled FULL of microprocessor crap inside of them that can act squirrely once in awhile. That's one of the big MINUSES about 'em, they can be full of all kinds of intermittent craziness! You can try the 'Pure Direct mode'and see if that helps. Also, your Tech guy really Acts like he knows his stuff. Did He mention bypassing the processor nitty-gritty and see what happens? This unit was made in Malaysia, (which isn't as good compared to Japan but, much better than something made in China), and just the complexity of the circuitry can be a service person's Nightmare! So iF your woe's can't be remedied pretty quick you might be ahead to Swap it out for a different one. Good luck to you

None of these products should act squirrelly unless failing. That's not to say some updates haven't caused issues for some over the years, but this is Yamaha not Arcam, they're not niche and their products are either working or not, rarely do you find bugs.

Seeing how we have such limited information and that this is not a new receiver on the market from them, I'm guessing that it's likely not an manufacturers error, but a setting or speaker issue. An amplifier doesn't have bass, speakers do.

 

[lovinthehd]

It should be good for the stated spec, go to Yamaha's page for such and I see this for frequency response: 0 ± 0.5 dB / 0 ± 1.0 dB.....lol, so who knows?

The manual says for power bandwidth 0.06%THD 40.0 W, 8Ω) ..................................... 10 Hz to 50 kHz

Then again maybe something failed in the unit. I couldn't tell much specific from that video, tho. What frequencies were outputting at a lower level, by what dB?

 

[Finemoves]

That's really not enough info to give an opinion about. What speakers are you using and do you have them crossed over to a sub? Amplifiers are load dependant, it's just to what degree.

The speakers are 2 x Tower cabinets, 8ohm, custom built. Each cabinet has 2 x 6.5inch woofers & 1 tweeter. I'm not using a sub as these speakers are full range and have plenty of bass. The test in the video provided was running the amp at maxiumum load. He wound up the volume to where it was clipping then brought it back a little to get a clean signal. It was outputting at 28v at maximum at 1khz. Then only 16.5v when he changed the frequency to 10khz.

 

[Finemoves]

Review everything. For example be sure you haven't connected the speakers out of phase. The problem may not be in the amp.

Yeah, checked all that. Disconnected everything, checked & reconnected.

 

[Finemoves]

Hard to know. First of all, was the receiver set to pass through with bass management disengaged? If the bass management is engaged that is what you would see.

The other issue is, did the tech change voltage sensitivity on the scope, when changing the frequency range?

If the answer is NO and NO, then yes your unit is defective.

There are no bass management options in the Yamaha RN803. There's no option to set a crossover frequency when a sub is connected, even though I don't have a sub connected. Doesn't look like he changed the voltage sensitivity, only the frequency. Voltage was reading 28v output at 1khz, then only 16.5 when he changed the frequency to 10khz.

 

[Finemoves]

Most modern surround sound receiver/amplifiers are filled FULL of microprocessor crap inside of them that can act squirrely once in awhile. That's one of the big MINUSES about 'em, they can be full of all kinds of intermittent craziness! You can try the 'Pure Direct mode'and see if that helps. Also, your Tech guy really Acts like he knows his stuff. Did He mention bypassing the processor nitty-gritty and see what happens? This unit was made in Malaysia, (which isn't as good compared to Japan but, much better than something made in China), and just the complexity of the circuitry can be a service person's Nightmare! So iF your woe's can't be remedied pretty quick you might be ahead to Swap it out for a different one. Good luck to you

Yeah thanks, i'm already in the process of getting a replacement sent through. I was just curious about the readings. I was always under the impression that power output should be the same at different frequencies. Yeah I'm not sure if the tech guy used 'pure direct'. He did have all the EQ set to flat though.

 

[lovinthehd]

There are no bass management options in the Yamaha RN803. There's no option to set a crossover frequency when a sub is connected, even though I don't have a sub connected. Doesn't look like he changed the voltage sensitivity, only the frequency. Voltage was reading 28v output at 1khz, then only 16.5 when he changed the frequency to 10khz.

That would mean it's dropping off at a higher frequency...or do you mean 10Hz?

 

[Finemoves]

It should be good for the stated spec, go to Yamaha's page for such and I see this for frequency response: 0 ± 0.5 dB / 0 ± 1.0 dB.....lol, so who knows?

The manual says for power bandwidth 0.06%THD 40.0 W, 8Ω) ..................................... 10 Hz to 50 kHz

Then again maybe something failed in the unit. I couldn't tell much specific from that video, tho. What frequencies were outputting at a lower level, by what dB?

I only recorded the last part of his test. I think he tested the low frequency first. The one in the video is 1khz & 10khz test.

"power bandwidth 0.06%THD 40.0 W, 8Ω) ..................................... 10 Hz to 50 kHz"
I assume the 0.06% means the variance in power output between the 10Hz to 50kHz? We definitely see more than 0.06% variance in the video. 28v down to 16.5v when switching from 1kHz to 10kHz.

 

[fmw]

Yeah, checked all that. Disconnected everything, checked & reconnected.

Perhaps time to visit the repair shop or the AV website.

 

[lovinthehd]

I assume the 0.06% means the variance in power output between the 10Hz to 50kHz? We definitely see more than 0.06% variance in the video. 28v down to 16.5v when switching from 1kHz to 10kHz.

No, .that particular spec doesn't indicate the variance, which is generally expressed with +/- dB parameters. 06% is THD-total harmonic distortion. The variance in frequency isn't included in any of the specs I see in the manual....but is likely within the .5 to 1dB range I found originally on the product sheet on their website....

 

[TLS Guy]

The speakers are 2 x Tower cabinets, 8ohm, custom built. Each cabinet has 2 x 6.5inch woofers & 1 tweeter. I'm not using a sub as these speakers are full range and have plenty of bass. The test in the video provided was running the amp at maxiumum load. He wound up the volume to where it was clipping then brought it back a little to get a clean signal. It was outputting at 28v at maximum at 1khz. Then only 16.5v when he changed the frequency to 10khz.

Well, that tells us nothing about the bass output. We have no where near enough information about your receiver. My hunch is there is nothing wrong with your receiver.
We have no idea of the acoustic data of those speakers. Two 6.5" woofers will not give a speaker plenty of bass.

To test your receiver, you need to run it into an 8 ohm load. It does not need to be full power or anywhere near that. Then measure the output voltage at 1 KHz, 100 Hz, 80 Hz, 60 Hz, 40 Hz and 20 Hz. If they are all close to the same number, then your receiver is fine, as long as bass managements is off.

Are you sure you have set sub to none, in your speaker set up menu? If not, then that is your problem.

 

[everettT]

There are no bass management options in the Yamaha RN803. There's no option to set a crossover frequency when a sub is connected, even though I don't have a sub connected. Doesn't look like he changed the voltage sensitivity, only the frequency. Voltage was reading 28v output at 1khz, then only 16.5 when he changed the frequency to 10khz.

Just a note: your reciever does have bass management and a version of YPAO (the app is easiest to view and make changes). Did you run the auto setup? Also, what 6.5" drivers were used on the build?