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Denon 3700 and 4700 have the same amplifier boards

mike7877

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The 3700 and 4700 have the same amplifier boards.

I will convince you:

The 2 channel 4 ohm measurement of the 3700 is 168 watts, and the 2 channel 4 ohm measurement of the 4700 is 173 watts. These are the numbers from the graphs which are both taken at the point at which distortion starts to sharply rise for both receivers, (~-85db).

The power vs distortion charts (the ones plotting distortion at different frequencies) are basically identical for the two receivers (the 3700's 5khz distortion rise begins at 7 watts, the 4700's 5khz distortion rise, at 7 watts. All other trends align too.

You don't get both an identical current limited peak power output (170w), and a matching distortion curve (5khz @ 7w), unless the amplifiers are the same.

Further evidence: Denon put a full top down view of the 3700's internals on their site, and just a small piece of the 4700's internals - a couple inches of the amp board can be seen in the shot of the transformer. Upon inspection you'll see: the amps have the same layout, same capacitor size/type/make (do I see some Panasonic FM/FC?), same resistors, same variable resistors, and the same unused pins on the corner. I think it may have been a deliberate move to do this - if the 3700's amp looked exactly the same as the 4700s (because it is) and one costs $500 more, who would buy the 4700? Answer: less people would buy the 4700, especially the ones buying it for a better amplifier section.

So you think the amps are different because the 4700 makes 10 more watts into 8 ohms before distortion starts to rise when driving 2 channels?

Those 10 watts come from the 4700 using a different transformer, one with slightly higher voltage taps for the power amp section. The 10 watt into 8 ohm increase implies a 5% higher supply voltage. A more in depth analysis follows - I've simplified it to what's necessary and my teaching ability.
One thing you need to know to follow is: Power (Wattage) is Potential (Voltage) multiplied by Current (Amperage).
Ok:

Increasing the supplied voltage to an amplifier circuit will result in a higher possible output voltage before clipping begins. This higher output voltage results in a higher output power. Caveats: only within voltage limits and if the additional current required is available. And if this current doesn't exceed the current limits implied by the design of the amplifier.

All electronic components have a maximum current handling capacity - the point at which they conduct less well than is required for desired operation. If it's exceeded, parts can get hot or damaged, or cause damage to other components (from heat or their improper operation during overload). Most commonly, associated components will be caused to operate improperly. Exactly how an amplifier is affected by one or more of its components being in an overcurrent situation depends on the overloaded component, its status, and the degree to which it is overloaded. A safe bet, though, is distortion will begin to rise.

If you design a class AB amplifier to provide 114 watts into 8 ohms, the components in its output stage must remain reasonably linear up to an output of at least 6 amps. The average power of a 114 watt sine wave into 8 ohms is 3.75A. Instantaneous current required for this is higher: 5.25A. The "at least 6 amps" comes from adding the current dissipated as heat by the transistor: a result of the transistor's operating voltage requirement: it needs 5-10% more supply voltage than the maximum desired output. A sine wave needs its peak to be 42 volts into an 8 ohm load for the power to be 114 watts.

Choosing to not use parallel transistors (for fidelity's sake), you pick a 100 volt transistor rated for 12 amps continuous, 20 amps peak. It seems like overkill at first, but it gets de-rated. Taking into account its projected operating temperature and supply voltage (60 deg C, 50V), it is capable of 9 amps peak, 6.5 amps continuous. Since you want the thing to actually be able to drive real speakers with the impedance dips they have in the bass/midbass octaves, this transistor's 9 amps juuuust makes the cut. You surround a pair of them with the components to operate them in class AB (one + direction, one -) and linearize their output with feedback (you make the amplifier). You ensure all the high current components and paths supporting them through 9 amps are adequately sized and properly arranged on the board to ensure distortion does not rise prematurely. In doing this, amplifier potential is maximized, cost, minimized.

The power supplies used in class AB AVRs, are almost always unregulated. Unregulated power supplies consist of a transformer, a bridge rectifier, and capacitors. Voltage is determined during design and cannot be adjusted. Output voltage is proportional to the input voltage. Any load on the output causes a voltage drop which is not compensated for. This is "unregulated". The amount of voltage drop is determined by the transformer's power rating and the size of capacitors used for filtering (capacitors turning pulsed DC from the transformer/rectifier into smooth DC for the transistors). The smaller the allowable voltage drop is, the bigger the transformer and capacitors have to be.

A balance must be struck: you need to limit the supply voltage to the transistor (amplifier) so to not de-rate its current capability too much, and you have to limit the amount of voltage drop under load so that it doesn't fall too far, leaving you with inadequate voltage for 9 amps at lower impedances (where hitting 9 amps is possible). Denon did this with the 3700. The tiny bit of extra voltage on the 4700 is effectively, useless.

Anyway, if you want your 3700 to be like the 4700 and have an undetectable 0.34db more headroom in 2 channel mode while driving your imaginary 8 ohm speakers with flat impedances, you can save $500 and get yourself a variable transformer from the internet for $50 and turn it up to 126v. Then it'll be the same as the 4700 and you'll have $450 extra in your pocket. When you're done driving your imaginary ideal speakers 0.34db louder, you can turn the regulator down to 108 volts (Denon designed all of its receivers to work on 108-126 volts). A 108 volt supply will lower your 3700's power consumption to 75 watts from 100 (2160kwh in 10yrs) while avoiding the crap caused by ECO mode (if that crap affects you). If it doesn't affect you, you can still turn it down to 108 volts and power consumption will drop down to 45 watts in eco mode! (instead of 60) This saves 1296kwh in 10yrs.

A 10% reduction and 5% increase in residential power is acceptable for power delivery over the long term. It's accounted for during the design of everything, not just Denon's receivers.

Like a scientist I like to experiment and you get to benefit from knowing my 3700 shuts off at 97 volts. It likely won't cause damage to run your 3700 on a bit less than 108 volts, but power consumption doesn't go down much more under 108, and the thing isn't specifically designed for it, so you might as well just set it to 108, making sure that during peak load times (eg 5-7pm when voltage is lowest) it doesn't fall to below 106.

If you're considering running your 3700 above 126, you need to know that very likely, the further you go above 128 volts, the faster your capacitors will fail. Capacitors are good up to their rated voltage, but above that, the relationship time to failure is exponential. If you give it 150 volts, you could have only hours (possibly less) until the caps leak and/or blow up. 126 only!
 

peng

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I don't know about the 3700 vs the 4700. I can tell you the 4500, SR6014, SR7012 all have the same schematics, same rail voltages, even bias voltages. So yes it is highly possible that the 3700 and 4700 have the same power amp boards.

The power supplies are definitely different, at least the storage caps are different, 15,000 uf for the 4500 and 7012, 12,000 uf for the 6014.
I doubt the transformers have different input voltage taps because they have the same (6014 vs 4500) rail voltages. I think the 4000/7000 series have a slightly larger (VA rating) transformers and that would be the main reason for them to be 2 to 3 lbs heavier. The combinations of a marginally larger transformer and storage caps would explain the higher output specs, and measurements.
 
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mike7877

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I don't know about the 3700 vs the 4700. I can tell you the 4500, SR6014, SR7012 all have the same schematics, same rail voltages, even bias voltages. So yes it is highly possible that the 3700 and 4700 have the same power amp boards.

The power supplies are definitely different, at least the storage caps are different, 15,000 uf for the 4500 and 7012, 12,000 uf for the 6014.
I doubt the transformers have different input voltage taps because they have the same (6014 vs 4500) rail voltages. I think the 4000/7000 series have a slightly larger (VA rating) transformers and that would be the main reason for them to be 2 to 3 lbs heavier. The combinations of a marginally larger transformer and storage caps would explain the higher output specs, and measurements.

Using the same amplifier boards, you need a 5% higher supply voltage for the 10 more watts into 8 ohms that the 4700 measures doing, so I am pretty sure the 3700's amps are run at a lower voltage than the ones in the 4700. Also, the 4700s larger transformer doesn't help increase the clean power into 4 ohms (both the 3700 and 4700 top out at ~170 watts before distortion rise), demonstrating that it is the amplifier, not the transformer, which is current limited. The slightly larger transformer in the 4700 can not and does not improve power output. Which leads to more of the points that follow in the OP - why it's not wise to buy the 4700 for extra power, how most 8 ohm speakers are actually much closer to 4 ohms in the bass/midbass, so the extra 10 watts into 2 channels the 4700 is rated to provide to 8 ohm loads isn't applicable to real world speaker setups. It's interesting, you should read it. I made it to read and enjoy and reply to.

The Marantz models may have the same rail voltages (output voltage taps), but it's not a given that Denon's will too. Denon and Marantz often do different things, and for different reasons. Maybe Denon planned to use the same rail voltages in the 3700 and 4700 and had some transformer stock on hand. When they tried to order more, they found voltage options provided to them before had changed due to a tooling change, so to avoid a really expensive custom order they chose the transformer with a slightly higher voltage because the one that was lower was too low, and they could put the higher voltage in the higher model. Giving an extra 3 volts to the amp doesn't require any modification (situational). Maybe (and this is more likely) Denon needed the 4700 to measure higher into 8 ohms for product differentiation (marketing). Whatever the cause, that's what they accomplished - a higher 8 ohm power rating. Since most people's speakers dip down near 4 ohms in the midbass, and both the 3700/4700 both begin distorting at 170 watts at 4 ohms, this 8 ohm rating is N/A.

Onto additional information about Denon receiver power supplies in general.

I did a test of a couple Denon AVRs. The average power they permit themselves to draw from the wall before enabling what I'll call "hidden eco mode" is exactly one half the number of the wattage printed on the back. After a couple minutes over this, a relay clicks inside, and
BAM
you're in Eco mode
without being notified!

If you're listening to music with peaks higher/lower than +-25v at the time, you get clipping. Denon's power consumption detection device is quite exact, too: drawing 325 watts at the wall, the relay will never click. But 335? Without fail, in just minutes. The 750h has 400 watts tattooed on its a** - same thing with it at more than 200 wall watts. Hidden eco mode turns on (to lower power consumption, which lowers a lot), and clipping. Fortunately, this never happens to everyone everywhere. Never. Probably due to the extremely transient nature of movie and TV sound making this scenario very unlikely to happen outside of a test. With normal content you'd be way into clipping first. You might be surprised to learn that the 3700 only takes 5 speakers drawing like 10 watts each to pull 330 watts from the wall. But it's OK! Maybe more surprising: 10 watts RMS is all you can really put into a speaker with an amp rated for 100 watts if you don't want clipping (yes, even harder to believe, and maybe more so because it's coming from me!) And no, I'm not talking Tchaikovski. Pop/Rock music. Everything but extremely bass heavy music.

Back on task: I presume this switch to lower rail voltages is for thermal reasons. Not for the amplifiers, they have fans. For the transformers. They aren't exactly large for 660/700 watts. I wouldn't think they were rated for that much continuously, indefinitely. Maybe if they weighed as much as the entire AV units. Fortunately, transformers are nice and can provide way more than their ratings. They're rated at 100% load, 24/7 operation. Can it do 200% for 20 minutes? No problem. 400% for 3? Oh yeah! The Denon's 3700 allows itself to draw over 1000 watts easily from the wall with its relatively small 330 watt (continuous) transformer.

From a warm start, after drawing 325 watts from the wall with my 3700 for a couple hours, I measured the transformer with my IR thermometer - over 70 degrees Celsius! I can imagine how hot it'd be with 660 (you can too, look up transformer temperature rise + loading). It's not sustainable. Anyway, the point isn't these receivers can't do their jobs, they can. The point is that during use, the 3700 does just as well as the 4700. While running cooler and taking less power with its ~5% lower voltage rails.
 
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peng

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Using the same amplifier boards, you need a 5% higher supply voltage for the 10 more watts into 8 ohms that the 4700 measures doing, so I am pretty sure the 3700's amps are run at a lower voltage than the ones in the 4700. Also, the 4700s larger transformer doesn't help increase the clean power into 4 ohms (both the 3700 and 4700 top out at ~170 watts before distortion rise), demonstrating clearly that it is the amplifier, not the transformer, which is current limited - the slightly larger transformer in the 4700 can't and doesn't improve power output. Which leads to more of the points that follow in the OP - why it's not wise to buy the 4700 for extra power, how most 8 ohm speakers are actually much closer to 4 ohms in the bass/midbass, so the extra 10 watts into 2 channels the 4700 is rated to provide to 8 ohm loads isn't applicable to real world speaker setups. It's interesting, you should read it. I made it to read and enjoy and reply to.

The Marantz models may have the same rail voltages (output voltage taps), but it's not a given that Denon's will too. Denon and Marantz often do different things, and for different reasons. Maybe Denon planned to use the same rail voltages in the 3700 and 4700 and had some transformer stock on hand. When they tried to order more, they found voltage options provided to them before had changed due to a tooling change, so to avoid a really expensive custom order they chose the transformer with a slightly higher voltage because the one that was lower was too low, and they could put the higher voltage in the higher model. Giving an extra 3 volts to the amp doesn't require any modification (situational). Maybe (and this is more likely) Denon needed the 4700 to measure higher into 8 ohms for product differentiation (marketing). Whatever the cause, that's what they accomplished - a higher 8 ohm power rating. Since most people's speakers dip down near 4 ohms in the midbass, and both the 3700/4700 both begin distorting at 170 watts at 4 ohms, this 8 ohm rating is N/A.

Onto additional information about Denon receiver power supplies in general.

I did a test of a couple Denon AVRs. The average power they permit themselves to draw from the wall before enabling what I'll call "hidden eco mode" is exactly one half the number of the wattage printed on the back. After a couple minutes over this, a relay clicks inside, and
BAM
you're in Eco mode
without being notified!

If you're listening to music with peaks higher/lower than +-25v at the time, you get clipping. Denon's power consumption detection device is quite exact, too: drawing 325 watts at the wall, the relay will never click. But 335? Without fail, in just minutes. The 750h has 400 watts tattooed on its a** - same thing with it at more than 200 wall watts. Hidden eco mode turns on (to lower power consumption, which lowers a lot), and clipping. Fortunately, this never happens to everyone everywhere. Never. Probably due to the extremely transient nature of movie and TV sound making this scenario very unlikely to happen outside of a test. With normal content you'd be way into clipping first. You might be surprised to learn that the 3700 only takes 5 speakers drawing like 10 watts each to pull 330 watts from the wall. But it's OK! Maybe more surprising: 10 watts RMS is all you can really put into a speaker with an amp rated for 100 watts if you don't want clipping (yes, even harder to believe, and maybe more so because it's coming from me!) And no, I'm not talking Tchaikovski. Pop/Rock music. Everything but extremely bass heavy music.

Back on task: I presume this switch to lower rail voltages is for thermal reasons. Not for the amplifiers, they have fans. For the transformers. They aren't exactly large for 660/700 watts. I wouldn't think they were rated for that much continuously, indefinitely. Maybe if they weighed as much as the entire AV units do. Fortunately, transformers are nice and can provide way more than their ratings. They're rated at 100% load, 24/7 operation. Can it do 200% for 20 minutes? No problem. 400% for 3? Oh yeah! The Denon's 3700 allows itself to draw over 1000 watts easily from the wall with its relatively small 330 watt (continuous) transformer.

From a warm start, after drawing 325 watts from the wall with my 3700 for a couple hours, I measured the transformer with my IR thermometer - over 70 degrees Celsius! I can imagine how hot it'd be with 660 (you can too, look up transformer temperature rise + loading). It's not sustainable. Anyway, the point isn't these receivers can't do their jobs, they can. The point is the 3700 does just as well as the 4700. Probably runs cooler and is more efficient too, with its 5% lower voltage rails (more than 5% cooler and efficient)

I was only talking about the 4500, 4400, sr6014 and sr7012 based on what I have seen in the service manuals, that they have the same schematics, parts, and voltages for the power amp section. My comments on their power supply differences are based on specs to some extent, plus a little bit of educated guess of my own.

It may not apply to the 3700 vs 4700, but it may.. You can of course speculate all you want, and you may be right..
 
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mike7877

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I was only talking about the 4500, 4409, sr6014 and sr7012 based on what I have seen in the service manuals that they have the same schematics, parts, and voltages for the power amp section. My comments on their power supply differences are based on specs to some extent, plus a little bit of educated guess of my own. You can of course speculate all you want
With the same amplifier and same voltage you can't have a different maximum power output unless the power supply of one is too small and can't provide enough current. I assumed that the 7012 and 6014 and 4500 were all rated for different power. But they aren't measured with different power - that's the difference.

Got stuck in a rut.

Just found out this title should include the SR7015, and, I can't prove it but probably the 6015 too. Too bad Marantz screwed up their DAC implementation and preamp so bad... They charge so much more, too.
 

JR449

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Audiovision Germany has tested both models in bench. 1kHz Sinus test method, probably similar what the SoundAndVision site uses and what Audioholics Gene mentions as
  • 1kHz Power Sweep vs. Distortion (1kHz Psweep)—popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The problem with this test is it often masks slew-related and or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification number for consumers to argue over on the forums, so we are now incorporating this test to please the masses.


X3700H:

2channels 4ohm: 187w
5channels 4ohm: 106w
7channels 4ohm: 81w


X4700H:

2channels 4ohm: 201w
5channels 4ohm: 113w or 119w (poor resolution can`t see)
7channels 4ohm: 94w

 

peng

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With the same amplifier and same voltage you can't have a different maximum power output unless the power supply of one is too small and can't provide enough current. I assumed that the 7012 and 6014 and 4500 were all rated for different power. But they aren't measured with different power - that's the difference.

Got stuck in a rut.

Just found out this title should include the SR7015, and, I can't prove it but probably the 6015 too. Too bad Marantz screwed up their DAC implementation and preamp so bad... They charge so much more, too.

Again, I also think the amp boards of the 3700 and 4700 are the same, based on the 6014 vs 4400, 4500, 7012's being the same. I am speculating, that the Denon 4000 and Marantz 7000 series probably have a slightly larger transformers than the 3000 and 6000 series; and definitely larger storage caps. You can actually see a little more differences in the output of the 3000 vs 4000 and 6000 vs 7000 series in the "maximum power tests" that Amir also included as well as Audiovision.de's 5 and 7 channel driven test results. You seem to be saying even the power supplies of the 3700 and 4700 are the same, just a little voltage taps. If that's the case, as I said, that's what you believe/speculate and you may be right, but I don't think so. We can agree to disagree on that, no big deal..
 

peng

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Audiovision Germany has tested both models in bench. 1kHz Sinus test method, probably similar what the SoundAndVision site uses and what Audioholics Gene mentions as
  • 1kHz Power Sweep vs. Distortion (1kHz Psweep)—popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The problem with this test is it often masks slew-related and or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification number for consumers to argue over on the forums, so we are now incorporating this test to please the masses.


X3700H:

2channels 4ohm: 187w
5channels 4ohm: 106w
7channels 4ohm: 81w


X4700H:

2channels 4ohm: 201w
5channels 4ohm: 113w or 119w (poor resolution can`t see)
7channels 4ohm: 94w


I doubt you can change his mind..:)
 
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mike7877

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Again, I also think the amp boards of the 3700 and 4700 are the same, based on the 6014 vs 4400, 4500, 7012's being the same. I am speculating, that the Denon 4000 and Marantz 7000 series probably have a slightly larger transformers than the 3000 and 6000 series; and definitely larger storage caps. You can actually see a little more differences in the output of the 3000 vs 4000 and 6000 vs 7000 series in the "maximum power tests" that Amir also included as well as Audiovision.de's 5 and 7 channel driven test results. You seem to be saying even the power supplies of the 3700 and 4700 are the same, just a little voltage taps. If that's the case, as I said, that's what you believe/speculate and you may be right, but I don't think so. We can agree to disagree on that, no big deal..

I know you said you think they're the same boards.

Yes, the maximum power tests show the 4700 puts out more power into 4 ohms before hitting 1% THD (here and on Audiovision), but that's never been my point.

I'm done, the thread's been made - it's online for anyone to search and see my take and the differing views. If a future reader agrees with my analysis and enjoyed the read and saves themselves a bit of money by buying the 3700, I'm satisfied
 
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Descartes

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Interesting if true! Of course Sound United will never say it’s true! Just change the model number and increase your profits!

How about the 8500?
 
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mike7877

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Interesting if true! Of course Sound United will never say it’s true! Just change the model number and increase your profits!

How about the 8500?

The 6700/8500 is a bit harder to say for sure. They do have similar frequency distortion curves... I'm busy at the moment, but I'll do some looking later!
 

peng

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Interesting if true! Of course Sound United will never say it’s true! Just change the model number and increase your profits!

How about the 8500?

Likely the same kind of deal, that the power amp modules may be the same or almost the same in terms of schematics and parts (based on the fact that the X8500H and X6500H share the same power amp module schematics), I have to highlight may be because I have not seen the schematics/block diagrams of the X6700H. The power supplies and heatsink arrangements are definitely different, the X8500H's quite a bit bigger (transformer VA and storage caps), you can even see the differences (heatsinks, transformers, storage caps) in the available photos.

Take a look of another interesting post on the comparison if you are interested:

 
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luft262

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The 3700 and 4700 have the same amplifier boards.

I will convince you:

The 2 channel 4 ohm measurement of the 3700 is 168 watts, and the 2 channel 4 ohm measurement of the 4700 is 173 watts. These are the numbers from the graphs which are both taken at the point at which distortion starts to sharply rise for both receivers, (~-85db).

The power vs distortion charts (the ones plotting distortion at different frequencies) are basically identical for the two receivers (the 3700's 5khz distortion rise begins at 7 watts, the 4700's 5khz distortion rise, at 7 watts. All other trends align too.

You don't get both an identical current limited peak power output (170w), and a matching distortion curve (5khz @ 7w), unless the amplifiers are the same.

Further evidence: Denon put a full top down view of the 3700's internals on their site, and just a small piece of the 4700's internals - a couple inches of the amp board can be seen in the shot of the transformer. Upon inspection you'll see: the amps have the same layout, same capacitor size/type/make (do I see some Panasonic FM/FC?), same resistors, same variable resistors, and the same unused pins on the corner. I think it may have been a deliberate move to do this - if the 3700's amp looked exactly the same as the 4700s (because it is) and one costs $500 more, who would buy the 4700? Answer: less people would buy the 4700, especially the ones buying it for a better amplifier section.

So you think the amps are different because the 4700 makes 10 more watts into 8 ohms before distortion starts to rise when driving 2 channels?

Those 10 watts come from the 4700 using a different transformer, one with slightly higher voltage taps for the power amp section. The 10 watt into 8 ohm increase implies a 5% higher supply voltage. A more in depth analysis follows - I've simplified it to what's necessary and my teaching ability.
One thing you need to know to follow is: Power (Wattage) is Potential (Voltage) multiplied by Current (Amperage).
Ok:

Increasing the supplied voltage to an amplifier circuit will result in a higher possible output voltage before clipping begins. This higher output voltage results in a higher output power. Caveats: only within voltage limits and if the additional current required is available. And if this current doesn't exceed the current limits implied by the design of the amplifier.

All electronic components have a maximum current handling capacity - the point at which they conduct less well than is required for desired operation. If it's exceeded, parts can get hot or damaged, or cause damage to other components (from heat or their improper operation during overload). Most commonly, associated components will be caused to operate improperly. Exactly how an amplifier is affected by one or more of its components being in an overcurrent situation depends on the overloaded component, its status, and the degree to which it is overloaded. A safe bet, though, is distortion will begin to rise.

If you design a class AB amplifier to provide 114 watts into 8 ohms, the components in its output stage must remain reasonably linear up to an output of at least 6 amps. The average power of a 114 watt sine wave into 8 ohms is 3.75A. Instantaneous current required for this is higher: 5.25A. The "at least 6 amps" comes from adding the current dissipated as heat by the transistor: a result of the transistor's operating voltage requirement: it needs 5-10% more supply voltage than the maximum desired output. A sine wave needs its peak to be 42 volts into an 8 ohm load for the power to be 114 watts.

Choosing to not use parallel transistors (for fidelity's sake), you pick a 100 volt transistor rated for 12 amps continuous, 20 amps peak. It seems like overkill at first, but it gets de-rated. Taking into account its projected operating temperature and supply voltage (60 deg C, 50V), it is capable of 9 amps peak, 6.5 amps continuous. Since you want the thing to actually be able to drive real speakers with the impedance dips they have in the bass/midbass octaves, this transistor's 9 amps juuuust makes the cut. You surround a pair of them with the components to operate them in class AB (one + direction, one -) and linearize their output with feedback (you make the amplifier). You ensure all the high current components and paths supporting them through 9 amps are adequately sized and properly arranged on the board to ensure distortion does not rise prematurely. In doing this, amplifier potential is maximized, cost, minimized.

The power supplies used in class AB AVRs, are almost always unregulated. Unregulated power supplies consist of a transformer, a bridge rectifier, and capacitors. Voltage is determined during design and cannot be adjusted. Output voltage is proportional to the input voltage. Any load on the output causes a voltage drop which is not compensated for. This is "unregulated". The amount of voltage drop is determined by the transformer's power rating and the size of capacitors used for filtering (capacitors turning pulsed DC from the transformer/rectifier into smooth DC for the transistors). The smaller the allowable voltage drop is, the bigger the transformer and capacitors have to be.

A balance must be struck: you need to limit the supply voltage to the transistor (amplifier) so to not de-rate its current capability too much, and you have to limit the amount of voltage drop under load so that it doesn't fall too far, leaving you with inadequate voltage for 9 amps at lower impedances (where hitting 9 amps is possible). Denon did this with the 3700. The tiny bit of extra voltage on the 4700 is effectively, useless.

Anyway, if you want your 3700 to be like the 4700 and have an undetectable 0.34db more headroom in 2 channel mode while driving your imaginary 8 ohm speakers with flat impedances, you can save $500 and get yourself a variable transformer from the internet for $50 and turn it up to 126v. Then it'll be the same as the 4700 and you'll have $450 extra in your pocket. When you're done driving your imaginary ideal speakers 0.34db louder, you can turn the regulator down to 108 volts (Denon designed all of its receivers to work on 108-126 volts). A 108 volt supply will lower your 3700's power consumption to 75 watts from 100 (2160kwh in 10yrs) while avoiding the crap caused by ECO mode (if that crap affects you). If it doesn't affect you, you can still turn it down to 108 volts and power consumption will drop down to 45 watts in eco mode! (instead of 60) This saves 1296kwh in 10yrs.

A 10% reduction and 5% increase in residential power is acceptable for power delivery over the long term. It's accounted for during the design of everything, not just Denon's receivers.

Like a scientist I like to experiment and you get to benefit from knowing my 3700 shuts off at 97 volts. It likely won't cause damage to run your 3700 on a bit less than 108 volts, but power consumption doesn't go down much more under 108, and the thing isn't specifically designed for it, so you might as well just set it to 108, making sure that during peak load times (eg 5-7pm when voltage is lowest) it doesn't fall to below 106.

If you're considering running your 3700 above 126, you need to know that very likely, the further you go above 128 volts, the faster your capacitors will fail. Capacitors are good up to their rated voltage, but above that, the relationship time to failure is exponential. If you give it 150 volts, you could have only hours (possibly less) until the caps leak and/or blow up. 126 only!
I have the 3700. The only real advantage I saw in the 4700 was the front-side HDMI connection. I have a long HDMI cable and just leave it plugged into the AUX port on the back and tuck the cord under the TV stand when not in use. If budget is of no concern the front side HDMI and other bennies, like the jidder reducer, might make the 4700 worth it, but if budget is no option, you'd probably opt for a larger AVR. Either way they are both phenomenal AVRs in comparison to most of the other AVRs on the market and I feel lucky to have one. Thanks for the breakdown!
 
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