Onkyo's TX-SR80X series intends to stay out of the heavyweight division

[Seth=L]

I understand you prefer using your outboard amp. I was talking about try doing it as an experiment. I also understand it is too much to ask because if I was asked I would be too lazy to swap the amp out just for an experiment and then swap it back in, all the hard work just to prove a point.

The fact is, at idling the 805 may consume 100 to 150W and probably most of that, say 80%, or 80 to 120W will end up in the form of heat that has to be dissipated. Roughly 10W will be the fixed transformer core loss (eddy current loss + hysteris loss), the remaining would be for other overheads that draws power, including the video section, indicating lights, remote receivers etc.

That is still relatively low when compared to the combined transformer copper loss of 10 to 20W (still minor) plus the loss of the amp section loss of as much as 200 to 400 watts (or more) if the amp is operating at near full load condition. On the practical side, for most 805 users the amp will likely be pumping out no more than a couple hundred watts of average power so the loss in the form of heat will in fact be roughly equal or slightly less than that during idling. Still, it would be wrong to assume the 805 will run just as hot when used as a prepro only, but it won't be much cooler either.

I will simply add, for the sake of detail, that most heat dissipated is from the transformer when the receiver is idle. A big piece of metal that constantly has amperage moving around inside of it with no where to go will produce heat (and harbor it because it's a big heavy chunk iron and copper), in the Onkyo TX-SR805's case it's a lot of heat. By reducing overall current capacity to a lower setting (in the form of 4 ohm setting for speakers) the transformer has less current being drawn into it. In practice that would definitely reduce the amount of heat dissipated, it's just science.

IMO receivers w/ preouts should have another selection for "preamplifier only" to effectively reduce the current to what is needed. I seem to recall hearing about maybe one receiver that did this, it may have been a Sherwood Newcastle AVR.

I may have misspoke regarding "lowering rail voltage", I'm not exactly sure that's what switching to the 4 ohm position does. I'm not a scientist.

 

[PENG]

I do not know enough about receivers to say if it "should" or "shouldn't", but what I do know is that it "does". As Seth has already said, the rail voltage should drop considerably.

I am curious about this too. In theory the rail voltage would probably drop by about 30% in order to limit the output to about the same as the 8 ohm rating instead of "doubling down" to a 4 ohm load.

Regardless, if the amp sections are only idling that rail voltage drop will have little effect on heat losses.

Transformers are typically highly efficient, around the 95 to 98.5% range. When idling, transformer losses will be mostly the core losses due to eddy currents and hysteris effects and that would typically amount to 0.5 to 1% of its full load rating. Assuming the 805 has a 1.5 kVA transformer, the no load/or idling loss would be about 15 watts maximum.

So if you notice a double digit temperature (F) decrease by setting to the 4 ohm position when working the 805's amp hard I can understand why but and am not surprised. If you get double digit temperature decrease with the amp idling then I would have to think harder to find the reasons.

 

[PENG]

I will simply add, for the sake of detail, that most heat dissipated is from the transformer when the receiver is idle. A big piece of metal that constantly has amperage moving around inside of it with no where to go will produce heat (and harbor it because it's a big heavy chunk iron and copper

Seth, you are totally wrong on this. You second paragrah is science but not your first (in the quote). You know I seldom use this kind of language. Tranformer no load losses are very low, typically 0.5 to 1% of its full load rating. During idling it does deliver current to the overheads aside from the amps but the current is low. For example, the AVR354's power consumption during idling is 118 watts. The transformer's no load (a fixed loss due to eddy currents and hysteris) loss in that case would be around 10 watts so the other 108 watts power the overheads.

If the 805 runs hot during idling then I would guess it has a lot of overheads that need power. It may also has a transformer that has low efficiency, even then i cannot imagine any such transformer would have any more than 2% fixed loss under very light load conditions.

 

[Seth=L]

Seth, you are totally wrong on this. You second paragrah is science but not your first (in the quote). You know I seldom use this kind of language. Tranformer no load losses are very low, typically 0.5 to 1% of its full load rating. During idling it does deliver current to the overheads aside from the amps but the current is low. For example, the AVR354's power consumption during idling is 118 watts. The transformer's no load (a fixed loss due to eddy currents and hysteris) loss in that case would be around 10 watts so the other 108 watts power the overheads.

If the 805 runs hot during idling then I would guess it has a lot of overheads that need power. It may also has a transformer that has low efficiency, even then i cannot imagine any such transformer would have any more than 2% fixed loss under very light load conditions.

So the heat comes from final output stage then? The heat dissipation from the TX-SR805 definitely has a substantiated amount rising from the front half of the unit.

 

[PENG]

So the heat comes from final output stage then? The heat dissipation from the TX-SR805 definitely has a substantiated amount rising from the front half of the unit.

I would guessimate 10 to 20W (for a poor transformer so it is unlikely) come from the transformer, 100 to 130W from the overheads including the prepro sections but not the final output stage. Is the preamp section in the front half?

The final output stage heat dissipation depends largely on how hare you drive the amps. At rated output the heat will be significant because class A/B has a notoriously low efficiency, around 45 to 60% so you can do the math if you assume most of the lost will be in the form of heat that needs to get out. It can be as much as 20O to 400 watts in the form of additional heat if you push the 805 to its limit.

That being said, I am sure you will agree with me that most of the time your amp would not be outputting any more than 20 watts per channel of average power. Surely there will be triple digit peaks but only for split seconds. So once again you can do that math and draw your own conclusion.

 

[Seth=L]

I would guessimate 10 to 20W (for a poor transformer so it is unlikely) come from the transformer, 100 to 130W from the overheads including the prepro sections but not the final output stage. Is the preamp section in the front half?

The final output stage heat dissipation depends largely on how hare you drive the amps. At rated output the heat will be significant because class A/B has a notoriously low efficiency, around 45 to 60% so you can do the math if you assume most of the lost will be in the form of heat that needs to get out. It can be as much as 20O to 400 watts in the form of additional heat if you push the 805 to its limit.

That being said, I am sure you will agree with me that most of the time your amp would not be outputting any more than 20 watts per channel of average power. Surely there will be triple digit peaks but only for split seconds. So once again you can do that math and draw your own conclusion.

It's half and half, half heatsink/transformer/fans and half preamp, output devices, switching and all other manor of electronic bits. Considering how much heat comes from the front in idle it would seem something in the front would be involved in the creation of that heat.

 

[PENG]

It's half and half, half heatsink/transformer/fans and half preamp, output devices, switching and all other manor of electronic bits. Considering how much heat comes from the front in idle it would seem something in the front would be involved in the creation of that heat.

This is better than a thousand words. It could be that the heat sinks gather up all the heat from the prepro and when it rises up via radiation and natural convection it got somehow deflected toward the front of the top. I really don't know what the answer is. If I had one I would open it up and find out what's going on in a hurry. May be time to email Onkyo?

 

[MatthewB.]

Actually I have to disagree with you Peng and Jostenmeat on this. About a year ago I discussed this very issue with an Onkyo engineer regarding the heat issue and using the 805 as a preamp. He said that when used as a preamp it bypasses the amp section altogether, so the impendence selector switch could be on 4 or 6 (he even said if there was a 2 it could be set there) doesnt matter, since the amp section is bypassed altogether. And the Voltage rail is not needed since the amp isnt driving any load and is being bypassed to the outboard amp which is driving the speaker.

I use mine strictly as preamp and have my cooling fan (one fan blows in while the other blows out) at the back right corner directly over the video chips and everytime I turn off my gear I place my hand on top of the reciever to make sure the fan is doing it's job and the front section is very cool to the touch, in fact like it was barely on. The area above the video chips is also cool due to the fans and the only section that is slightly warm is the left back corner and just behind the heat sink (towards the back).

There have been many many articles published about proper impendence selectors and most will say to use the 8ohm setting (the Onkyo engineer said to keep it at 6ohm even if running 4 ohm speakers) but if that's not enough here is an article from Audioholics own site regarding setting impendence and voltage rail effects by selecting a lower impendence and how by setting it to 4ohm you are giving up dynamics and cutting the amperage.

http://www.audioholics.com/buying-guides/how-to-shop/av-receivers-buying-guide

Audioholics - "What Doesn't Matter?

Impedance Selector Switches
This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation"

So I would rather place a small fan and keep one of the benefits of this reciever (high current) and increased sound dynamics, rather than limit this receiver in any way. So I leave it at 6ohms and have my tiny fan control the heat issue.

 

[PENG]

Actually I have to disagree with you Peng

What are you disagreeing with? I thought we were in agreement. Would you like to re-read my post?

Thanks

 

[MatthewB.]

Sorry Peng, it's been a long day at work. My apologies and respect.

 

[Lordoftherings]

Thanks Seth=L for that excellent picture.

* I just love both my 805 & 876.

 

[Lordoftherings]

Actually I have to disagree with you Jostenmeat on this. About a year ago I discussed this very issue with an Onkyo engineer regarding the heat issue and using the 805 as a preamp. He said that when used as a preamp it bypasses the amp section altogether, so the impendence selector switch could be on 4 or 6 (he even said if there was a 2 it could be set there) doesnt matter, since the amp section is bypassed altogether. And the Voltage rail is not needed since the amp isnt driving any load and is being bypassed to the outboard amp which is driving the speaker.

I use mine strictly as preamp and have my cooling fan (one fan blows in while the other blows out) at the back right corner directly over the video chips and everytime I turn off my gear I place my hand on top of the reciever to make sure the fan is doing it's job and the front section is very cool to the touch, in fact like it was barely on. The area above the video chips is also cool due to the fans and the only section that is slightly warm is the left back corner and just behind the heat sink (towards the back).

There have been many many articles published about proper impendence selectors and most will say to use the 8ohm setting (the Onkyo engineer said to keep it at 6ohm even if running 4 ohm speakers) but if that's not enough here is an article from Audioholics own site regarding setting impendence and voltage rail effects by selecting a lower impendence and how by setting it to 4ohm you are giving up dynamics and cutting the amperage.

http://www.audioholics.com/buying-guides/how-to-shop/av-receivers-buying-guide

Audioholics - "What Doesn't Matter?

Impedance Selector Switches
This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation"

So I would rather place a small fan and keep one of the benefits of this reciever (high current) and increased sound dynamics, rather than limit this receiver in any way. So I leave it at 6ohms and have my tiny fan control the heat issue.

Great post, Thanks Matthew.

 

[Lordoftherings]

What are you disagreeing with? I thought we were in agreement. Would you like to re-read my post?

Thanks

Hi Peng,

You, I, and Matthew, we are all pretty much on the same page.
No wonder, we're all Canadians.

And people like you guys, are nice to know, and are on my "best buddy's" list.

* Seth=L too.

 

[MatthewB.]

Actually LOTR, I live in Arizona, but thanks anyway.

 

[Lordoftherings]

Actually LOTR, I live in Arizona, but thanks anyway.

My best buddy also live in Arizona, his name is Robert. He is about 80 years old, a very nice guy, true Arizonian guy that loves horses, cowboy hats, cowboy boots and tequila. Oh, and he also loves women and turquoise; you know the type of rock that people wears as necklaces and bracelets, and rings...

He is very Canadian spirited too, meaning very friendly and peaceful, with strong convictions about the world we live in.

Have a great day Matthew from Arizona, where the snakes from the desert are making lines in the sand, and where the temperature goes to both extreme of the thermometer.

Bobby

 

[MatthewB.]

Actually we only have two temps, Hot and OHMYGODI'MMELTING!!!!!!

 

[lsiberian]

Actually we only have two temps, Hot and OHMYGODI'MMELTING!!!!!!

The location on your profile told me Arizona. But I guess some folks don't notice that sort of thing.

 

[Lordoftherings]

Actually we only have two temps, Hot and OHMYGODI'MMELTING!!!!!!

The location on your profile told me Arizona. But I guess some folks don't notice that sort of thing.

Now, both of you guys got me completely lost.

I thought Arizona gets super hot in daytime, and then super cold at night time?
I guess that it's in the deep canyon of the desert, that it gets cold?

* Sounds almost like Onkyo 805 (HOT) receiver vs. Pioneer Elite SC-07 with ICE.

~~~ And lsiberian, how did you guess from his profile that he is from Arizona?

 

[lsiberian]

Now, both of you guys got me completely lost.

I thought Arizona gets super hot in daytime, and then super cold at night time?
I guess that it's in the deep canyon of the desert, that it gets cold?

* Sounds almost like Onkyo 805 (HOT) receiver vs. Pioneer Elite SC-07 with ICE.

~~~ And lsiberian, how did you guess from his profile that he is from Arizona?

Oh dear Lord,

http://www.weather.com/outlook/homeandgarden/home/wxclimatology/monthly/graph/USAZ0166?from=homealmanac

There is Phoenix's average high and low's Throughout the year.

As always the average state is actually the mean and an average temperature is actually a range of the 1st standard deviation from the mean.

http://www.weather.com/outlook/travel/businesstraveler/wxclimatology/monthly/graph/CAXX0518?from=homealmanac

I believe that's your town.

You can see that Arizona is significantly hotter than where you live

The temperature is hotter at night than it gets during the day in vancouver.

 

[MatthewB.]

Great chart, but doesnt take into account the high humidity we now have which makes it feel way hotter. It's no longer a dry heat.