Yamaha RX-A8A RCA (pre) Output Voltage

[jcmccorm]

I didn't want to pollute the A8A review thread with this but felt it was interesting enough to post about and I'd like some confirmation if possible.

So I replaced my Behringer subwoofer amps with CVRs and I lost some output. My sub trim was already at +2.0db so I didn't want to go further for fear of clipping the AVR output. I have a miniDSP 2x4 HD in the subwoofer signal path and it has a strict 2Vrms limit for both it's input and output as well. In short, I needed to look at my signals and see if I had some headroom anywhere to get some gain back.

It was during that pursuit that I had a 'scope hooked up to the SUB1 output of the Yamaha and thought, I wonder where this thing clips? Well, it wasn't where I thought.

I had to feed it a 0dbFS signal and turn the MV up to +16.5db before I saw clipping. (mind you this is with REW feeding the center channel with bass management on, not feeding the LFE channel. So no 10db reduction in the AVR).

I backed the MV down by 1db and came out of clipping.

So 7Vrms out of a Yamaha RCA preamp output? I like it, but it seems unusual. Has anyone else taken these kind of measurements? I checked the probe level with the 'scope's internal 5V square-wave output and it matches so I feel confident that the 'scope is correct. I just haven't ever heard of anyone getting that kind of signal out of a Yamaha RCA.

 

[jcmccorm]

Well I guess I can answer my own question. Google AI says that Yamaha can output up to 6.5Vrms on the subwoofer output, not the main preamp outputs. Makes sense, and my measurement is not unusual after all.

 

[peng]

View attachment 528588


I backed the MV down by 1db and came out of clipping.

View attachment 528589


So 7Vrms out of a Yamaha RCA preamp output? I like it, but it seems unusual. Has anyone else taken these kind of measurements? I checked the probe level with the 'scope's internal 5V square-wave output and it matches so I feel confident that the 'scope is correct. I just haven't ever heard of anyone getting that kind of signal out of a Yamaha RCA.

I have no idea why your oscilloscope shows 7.09 Vrms, to me that seems technically impossible. Again, I can see it in you posted photo, obviously..

I have seen some Yamaha RX-A AVRs and the CX-A5200 service manuals, also Gene's reviews with bench measurements on them, such as the following two:

https://www.audioholics.com/av-receiver-reviews/yamaha-rx-a6a, and Gene noted:

RX-A6A:​

Gene noted:
"And now the not so great news. With the RX-A6A engaged in “Pure Direct”, and HDMI input being fed a test signal from my APx585, I did a 1kHz sweep of multi-ch preouts (FL, C, FR, SurL, SurR, SBL, SBR) vs distortion. As you can see the Yamaha was able to output 4Vrms for all channels unclipped. However, I identified the C, Sur L and Sur R channels produced higher distortion than the rest of the channels tested once the output level exceeded 650Vrms. Please note, the distortion never went above 0.05% THD+N and likely inaudible, however."

The RX-A8A has the same preout/DAC signal chain so the results should be very similar.

or even the AVP, CX-A5200 could only do 4 Vrms, 8 Vrms balanced.

Yamaha AVENTAGE 5200 Series 11CH Processor/Amplifier Review

Yamaha is on their 3rd generation of separates in the Aventage line with their new 11-channel CX-A5200 AV Processor and MX-A5200 amplifier. Read our review to find out if they are a worthy successor.

www.audioholics.com

Well I guess I can answer my own question. Google AI says that Yamaha can output up to 6.5Vrms on the subwoofer output, not the main preamp outputs. Makes sense, and my measurement is not unusual after all.

The funny thing with Google AI is, if I go and ask the same question, it would likely tell me the same 6.5 Vrms answer because it would likely reference your post right here on ASR, that is a very popular audio forum that AI, not only Google Gemini, would reference.

 

[jcmccorm]

I was surprised as well. But that's what I measured. I did *not* know that the subwoofer RCA outputs are handled differently than the other preamp outputs. I guess they are trying to support diffetent sub amplifier sensitivities.

I wonder if, when Gene said "all channels", if he was including the subwoofer outputs in that group.

 

[peng]

I was surprised as well. But that's what I measured. I did *not* know that the subwoofer RCA outputs are handled differently than the other preamp outputs. I guess they are trying to support diffetent sub amplifier sensitivities.

I wonder if, when Gene said "all channels", if he was including the subwoofer outputs in that group.

The subout is only dealt with differently on the digital input side, and only relatively.

Physically, it is still limited to output about 4Vrms because the parts and circuitry are the same, the rail voltage is still 7V and the volume control IC cannot ouput more than about 4vrms unclipped. So, if I were you I would be interested in solving the 7Vrms mystery as displayed by the scope.

 

[jcmccorm]

Will do. I'll try a multimeter. I have a good fluke that measures RMS. Backup would be a better scope that I borrow from work.

One thing. The purpose of my measurements was to analyze the gain structure of my subwoofer path. I have a miniDSP 2x4 HD in the chain. I was able to clip its output. MiniDSP claims that their output is good to 2vrms and that's exactly where it clipped, giving me some confidence in the scope. I'll definitely try another tool though.

 

[peng]

Will do. I'll try a multimeter. I have a good fluke that measures RMS. Backup would be a better scope that I borrow from work.

One thing. The purpose of my measurements was to analyze the gain structure of my subwoofer path. I have a miniDSP 2x4 HD in the chain. I was able to clip its output. MiniDSP claims that their output is good to 2vrms and that's exactly where it clipped, giving me some confidence in the scope. I'll definitely try another tool though.

Also, you can take a look of the schematics in the service manuals of the CX-A5200, or RX-A3060 that are available online (probably hifiengine.com) and will see that the sub and front L,R,C, and other channels are virtually identical You will get higher voltage out of the sub out with digital contents such as movies but to get 10 dB hotter you still don't need more than 2 V, if 1 to 1.2 V will get you 105 dB peak after auto setup/calibration. Still, I do hope to learn something new, so please do come back with an update of your findings.

 

[jcmccorm]

I got a chance to spend a few minutes with this at lunch today.

Here's the subwoofer output, clipped.

Here's where I backed off a bit, getting to where it appeared to be not clipped.

Here's the Fluke looking at the same signal.

Just for fun, here's the center channel preamp output clipped.

Here's the doodad I use to connect the scope probe to the preamp signals.

Here's a snip from the Yamaha A8A manual.

They got the sub output right, but they are saying 2V for the Center but I'm getting 4V. No explanation for that.

Can anyone confirm these numbers for an A8A?

 

[jcmccorm]

Ah, I found this on Audioholics. Apparently they measured the A6A preamp outputs to 4Vrms before clipping. So I think my measurement is ok.

 

[peng]

Ah, I found this on Audioholics. Apparently they measured the A6A preamp outputs to 4Vrms before clipping. So I think my measurement is ok.

That's strange, I did link you to Gene's review and even quoted me saying that the A6A output 4 V, all channels, guess you missed that but good that you found it yourself anyway.

View attachment 528977

No question about 4 V, it is the 7 V that you measured could not be explained. If you keep cranking the volume, ignore the distortions, you potentially could approach the rail voltage but 7V? If you could really get 7 Vrms from the RCA outputs, you would get 14 V from the XLR output and that would far exceed the rail voltage, not electrically possible!

However, your Fluke shows that the scope's 7 V is not far off so I search for the service manual myself and found that as you alluded to before, and the manual also indicated the same, the Yamaha did provide additional headroom for the subwoofer output. That would be helpful I guess, for those who use very long subwoofer cables.

Based on the schematics, it would appear that the 6.9 V you measured is as you said " ok ". Though your "ok" remark if perfect, as the THD at that point would likely be around 1% or higher, and if you push further, the output will clip badly soon and the unit might even shutdown.

Anyway, great find, that this flagship Yamaha AVR has nice feature, that allows subwoofer outputs to have significantly higher headroom.

 

[peng]

I got a chance to spend a few minutes with this at lunch today.

Here's the subwoofer output, clipped.
View attachment 528944


Here's where I backed off a bit, getting to where it appeared to be not clipped.
View attachment 528945


Here's the Fluke looking at the same signal.
View attachment 528946


Just for fun, here's the center channel preamp output clipped.
View attachment 528947


Here's the doodad I use to connect the scope probe to the preamp signals.
View attachment 528948


Here's a snip from the Yamaha A8A manual.
View attachment 528949

They got the sub output right, but they are saying 2V for the Center but I'm getting 4V. No explanation for that.

Can anyone confirm these numbers for an A8A?

I don't have an A8A, but I have now seen the schematics for the A6A, and based on what I saw, the Front L/R and other main channels should be able to do 4 V unbalanced for sure, as verified by Gene in his review on the A6A, and your own measurements.

Yamaha rated them 2.0 V, since they don't clearly state the conditions, we can just do our own educated guess, it could simply be that they based on THD less than say 0.08%, but for the subwoofers they probably would based on 1% . As we all know, output levels are typically higher if you push the devices to higher distortion levels.

 

[jcmccorm]

Thanks @peng. I read Gene's whole review thread and only saw another poster say to keep the preamp outputs under 1.6V and 2V will clip. I'll go look again as I must have missed Gene showing 4V for the preamp outputs.

There are no XLR outputs for the subwoofers so 7V is still viable (no need for 14V).

And I am curious about the distortion. That little TEK scope I have doesn't have much in the way of measurements besides the basics so I am curious what the distortion is as the subwoofer ramps up. Just because it *looks* like it's not clipping doesn't mean that the THD isn't way over 1% still.

As for distortion on the preamp outputs (non-sub), that Audioholics review did show a sharp increase in distortion at 1.6V and above for the Center, SR, and SL. Odd.

 

[peng]

Thanks @peng. I read Gene's whole review thread and only saw another poster say to keep the preamp outputs under 1.6V and 2V will clip. I'll go look again as I must have missed Gene showing 4V for the preamp outputs.

May be you were reading a little too fast, it's on the front page of the review lol..

There are no XLR outputs for the subwoofers so 7V is still viable (no need for 14V).

True.

And I am curious about the distortion. That little TEK scope I have doesn't have much in the way of measurements besides the basics so I am curious what the distortion is as the subwoofer ramps up. Just because it *looks* like it's not clipping doesn't mean that the THD isn't way over 1% still.

Also true, but look can be deceiving, 1% THD might be hard to see by the naked eyes.

Out of curiosity, I just copy/pasted your scope captures image:

The image you provided shows a waveform that has clearly visible distortion, which is definitely much higher than 1% THD. for Google AI to look, and it responded as follow:

That might confirm my suspicious that there was distortions, just hard to quantify it by eyeballing it.

As for distortion on the preamp outputs (non-sub), that Audioholics review did show a sharp increase in distortion at 1.6V and above for the Center, SR, and SL. Odd.

Yes, but not 1.6 V, it was about 650 mV, or 0.65 V, Gene could not explained that anomaly, but it only reached 0.05% and did not rise again until it reached pass 3.5 V so no big deal there. Regardless, if I remember right, Gene found a similar anomaly on the CX-A5200, that is, some higher distortion rise in some channels though the issue wasn't exactly the same as what he found on the RX-A6A, if I remember right, he reported it (about the CX-A5200) to Yamaha who acknowledged it, so hopefully they will have fixed that issue by the time they launch the successor of the really nice CX-A AV controllers. Interestingly, the CX-5000 and CX-5100 apparently did not have such issues.

 

[jcmccorm]

Thanks again @peng!

Sigh. Yes there it is, 4Vrms from Gene. *And* you quoted it in your first reply. I've got to work on my reading comprehension

I never thought to feed that image to AI to discover THD from it. Great idea! It confirms what we both were thinking; yes, the waveform is not visibly clipped, but it's not exactly a sine wave either.

And 'yes' on the 650mv, reading comprehension again. I was confusing it with the other poster who suggested not going over 1.6Vrms.

 

[peng]

Thanks again @peng!

Sigh. Yes there it is, 4Vrms from Gene. *And* you quoted it in your first reply. I've got to work on my reading comprehension

I never thought to feed that image to AI to discover THD from it. Great idea! It confirms what we both were thinking; yes, the waveform is not visibly clipped, but it's not exactly a sine wave either.

Not sure if you downloaded the service manual, below is the page where it shows the subwoofer pre out is boosted by 4.62 dB.

Using formula V2=V1*10^(dBgain/20 = 4*10^(4.62/20) = 4*1.7 = 6.8 V, that's pretty close to the specs of 6.5 V and your measured 6.9 V.

Here's the block diagram:

And 'yes' on the 650mv, reading comprehension again. I was confusing it with the other poster who suggested not going over 1.6Vrms.

Actually Gene's graph showed about 650 mV, but in the text, he did say 650V, obviously a typo. He's human too lol..

 

[jcmccorm]

Link to schemos?

 

[peng]

Link to schemos?

I could not find one for the RX-A8A but the A6A should have the same information you need.

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.

elektrotanya.com

you can buy it here:

YAMAHA RX-A8A Service Manual

www.service-manual.pro

 

[jcmccorm]

Awesome! Thank you!