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Power amp question

Dimitrov

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Hi everyone,

Hoping there are some EEs in the house that can help me understand this. Let's say I have an AVR and decide to add a power amp to it. I do nothing else, other than adding the power amp to the AVR via the preouts.

When I say do nothing else, I mean I keep my master volume and all other settings the same as I did before adding the power amp. My question is ... would adding a power amp in this situation change the volume levels? The reason I ask is because I'm trying to understand and figure out why people often claim that adding a power amp improves the sound, almost immediately.

My theory and I could be completely wrong on this, is that maybe the volume levels change and people perceive this level change as a sound quality change. I just need to have my facts straight on this.

Any advice would be appreciated.
 
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Dimitrov

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Just to add ... I understand the reason why power amps are sometimes necessary over using the built-in AVR amps. But the claim is almost always that the sound has improved and I simply don't believe every single person is clipping the sh*t out of their AVR's.

I could be wrong and there is more to this than I realise, but for right now I suspect volumes changing is the culprit. Am I crazy or do I have a point?
 

restorer-john

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An AVR is a compromise. Multiple channels in one box, all pulling from a common power supply, often with power amplifier stages of limited capability.

Taking a line out into a dedicated high power amplifier may offer anything from barely noticeable to significant improvements. Bear in mind, the signal you are sending to an outboard power amplifier will be limited by the capability of the front end stage of your AVR.

If you are more interested in 2 channel (stereo) audio reproduction, I would suggest you scrap the AVR front end altogether and start with a pure 2ch feed- a high quality D/A converter and a good line stage.

PS. Welcome Dimitrov. :)
 
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Dimitrov

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An AVR is a compromise. Multiple channels in one box, all pulling from a common power supply, often with power amplifier stages of limited capability.

Taking a line out into a dedicated high power amplifier may offer anything from barely noticeable to significant improvements. Bear in mind, the signal you are sending to an outboard power amplifier will be limited by the capability of the front end stage of your AVR.

If you are more interested in 2 channel (stereo) audio reproduction, I would suggest you scrap the AVR front end altogether and start with a pure 2ch feed- a high quality D/A converter and a good line stage.

PS. Welcome Dimitrov. :)

Hi Restorer-John. Thanks for the welcome, I've been here for a little while. :)

As I said earlier, I understand the need for external power amps and I have no doubt that they can improve sound quality. But I'm not referring to clipping or distortion here.

I'm saying, just take a power amp, connect it up to an AVR ... and use some random master volume setting. Will adding the power amp change the volume levels, yes or no? Because if it does, without changing anything else, that would bolster the claim that a level difference can be interpreted as a sound quality change/improvement.

It could mean that folks that buy power amps are not necessarily experiencing improvements due to the added power/current delivery, but simply due to a level mismatch are experiencing that level difference as an improvement.

I stand to be corrected here, I'm not an EE, this is just a theory of mine.
 

andreasmaaan

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I'm saying, just take a power amp, connect it up to an AVR ... and use some random master volume setting. Will adding the power amp change the volume levels, yes or no?

It depends on which amps were used. In most cases, yes, but it’s conceivable that a power amp could have the same gain as the amp section of an AVR from which it receives signal.

Expectation bias would also have to be considered a potential factor here (and of course the possibility that the power amp section of the AVR was audibly deficient in the first place).
 
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March Audio

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It depends on the gain of the external amifier compared to the internal amp. However being an avr if you use its calibration routine it will set gains accordingly to suit
 

solderdude

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connecting a power amp to the pre-outs will not change volume on the AVR.
It will also not change SQ of the AVR.

But as Restorer-John already explained the 'improved SQ' would come from the better quality poweramp in that case (assuming main speakers will be powered by extra amp).
Also this means that there is more power available for rear channels etc and this may improve SQ.
I suppose that is what some people find.
I don't think merely connecting an amp to pre-outs and not connecting anything to that amp will change anything about the the SQ of the AVR.

I assume this is the background of your question.
 

March Audio

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Most integrated AVRs I have seen have their main channel power outputs degrade significantly when running the rest at high power. Really need a power amp with separate psu per channel to avoid this.
 
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Dimitrov

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connecting a power amp to the pre-outs will not change volume on the AVR.
It will also not change SQ of the AVR.

But as Restorer-John already explained the 'improved SQ' would come from the better quality poweramp in that case (assuming main speakers will be powered by extra amp).
Also this means that there is more power available for rear channels etc and this may improve SQ.
I suppose that is what some people find.
I don't think merely connecting an amp to pre-outs and not connecting anything to that amp will change anything about the the SQ of the AVR.

I assume this is the background of your question.

Okay, so you are saying that it won't have any effect on the volume, but March Audio is saying that it depends on the gain of the amplifier. I mean wouldn't the input sensitivity have any effect here?

I'm confused now.
 

Sangram

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The gain of the amplifier, if different from the one inside the AVR, will affect the volume level at a given position - however this is temporary. This is also a little obvious. Both answers are correct. If the gain is the same there is no change. If they aren't you will hear a difference.

Movies may have peak power levels up to 25-30dB above the mean listening level (which for THX calibrated systems is 85dB at listening seat). An AVR may or may not, depending on its design and power supply - and the sensitivity of the speaker, be able to adequately provide the needed level of power.

The truth is that what you perceive as the final sound is a combination of multiple factors and most AVRs are severely power-limited because of cost constraints. As a result manufacturers take to tricks like quoting maximum single channel burst power instead of multiple channels driven, which leads to 100W receivers being unable to deliver even a fifth of that in real life.

That's why you add amplifiers - so you can be sure of always having the power you need on tap, on every channel, and all at the same time.
 

PierreV

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I'd guess it is a bit of everything

- dedicated amps on each line out will all other things being equal perform better than a single amp/psu.
- gain may not be identical
- expectation bias

Ran in an opposite situation where the sound quality/power quality sounded catastrophically worse (on XLR): turned out the outputs had selectable sensitivity. :facepalm: Well deserved for not RTFM...

But usually, as soon as you start driving bigger or more difficult speakers with your AVR, you quickly notice the amp section is somewhat limited.
 
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Dimitrov

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The gain of the amplifier, if different from the one inside the AVR, will affect the volume level at a given position - however this is temporary. This is also a little obvious. Both answers are correct. If the gain is the same there is no change. If they aren't you will hear a difference.

Movies may have peak power levels up to 25-30dB above the mean listening level (which for THX calibrated systems is 85dB at listening seat). An AVR may or may not, depending on its design and power supply - and the sensitivity of the speaker, be able to adequately provide the needed level of power.

The truth is that what you perceive as the final sound is a combination of multiple factors and most AVRs are severely power-limited because of cost constraints. As a result manufacturers take to tricks like quoting maximum single channel burst power instead of multiple channels driven, which leads to 100W receivers being unable to deliver even a fifth of that in real life.

That's why you add amplifiers - so you can be sure of always having the power you need on tap, on every channel, and all at the same time.

Excellent points. What do you mean by "this is temporary"? What is the likelihood that the gain will be the same?

The reason I bring this up is because I've encountered LOTS of folks who ... after purchasing a power amp, immediately notice sonic improvement. Not because they drove their speakers past the receivers limits. But from the get-go. If you peruse most audio forums you'll find this ... all over.

So in my mind the easy explanation for an improvement is that the volumes changed. I have no doubt quality will improve if you exceed the AVR's power capabilities and use a power amp, but not everyone does that and subjectively the impressions remain.
 

solderdude

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Okay, so you are saying that it won't have any effect on the volume, but March Audio is saying that it depends on the gain of the amplifier. I mean wouldn't the input sensitivity have any effect here?

I'm confused now.

You mention whether an amp connected to the pre-out will affect volume.

There are 2 different things here.
1: When you connect something to the pre-out of the AVR everything that comes out of the AVR remains exactly the same.
The connected amplifier has NO influence on the AVR when all remains the same (so main speakers still connected to the AVR and nothoing connected to the extra amplifier.

For the above situation nothing changes.

2: The extra amp is connected to the AVR and the main speakers are disconnected from the AVR and connected to the extra amp.

From this last condition things are very different.
A: the output power of the connected amp can be higher or lower.
B: the output of the connected amp can be better suited for low impedance speakers (or not)
C: the connected amp has a higher gain in which case the main speakers are louder than the rest
D: the connected amp has a lower gain in which case the main speakers are softer than the rest.
E: the connected amp has a volume control and is adjusted so it plays equally loud as the AVR would.

in case of A: dynamics can be improved as it can play louder via the main speakers. This can be perceived as 'better'.

B: depends on speakers and amp.

In case of C: the amp is slightly louder and people perceive it as improved.
The amp is much louder and the balance between the surround channels differs.

In case of D: the amp is slightly softer and you get relatively more sound from the surround speakers which some may prefer.

in case of E: there are a few possibilities:
1: placebo (lots of different reasons here)
2: the SQ of the amp is better
3: the amp has more power available.
4: the other channels have more power available as the power from the main speakers (which is highest) is now coming from another amp. and the AVR has more power available for the surround speakers

So... it depends on the situation.
 
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Dimitrov

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Sorry solderdude, I need to amend my opening post ... because I wasn't clear enough. Of course the speakers will be connected to the power amp using the preouts on the AVR. In order for my post to make any sense it HAS to connect to the power amp.

What I'm saying is that nothing else changes beyond that - the master volume remains the same before the power amp was inserted into the system.
 

solderdude

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In that case A, B, C, D and E could all be causing the various perceived differences which usually are always an improvement to those that invested.
Not saying A is the root cause though.

So impossible to say which one is responsible. One would have to measure and know more about the used gear/speakers/circumstances to be able to say what is going on.
 

PierreV

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A lot of home theater installations sound quite well with small speakers and a subwoofer. I ran mine on a 5.1 Soundblaster game setup for a while and it was surprisingly acceptable (I still use those speakers in my gym after 20 years!). But when people move up to a bigger AVR, they have a tendency to move up in terms of speakers as well - that's exactly the "trap" I fell into btw. It feels like the bulky mighty AVR will drive them with ease, but that isn't the case in practice.

On top of that, one usually uses a higher volume on movies than on music - that's at least what I do. When you want go for the movie experience, you wish to be immersed in it and feel it. You want to hear whispered conversations clearly but also want to feel that helicopter attack. See the post about DR in movies by @March Audio in another thread. Usually, you will also want more energy hungry bass (especially if you don't have independent subs).

Now, on my big stereo speakers in a relatively large room, I am guessing I use around 5-10 watts average per channel (on 250W rated amplifiers, assuming 0dB is correct at the rated 80 volume). Assuming I am doing the same with my 9 channels AVR on the big speakers I bought to improve the sound (+2 outs for subs but those don't count) I am already pushing the poor AVR _very_ hard.

AVRs sold as 9x105 watts (for example) are often just integrated amplifiers that would otherwise be rated at 2x125W at 10% THD 2x105W 1% in other circumstances.

So after I put my supposedly nicer speakers in my HT and was disappointed I went external amplifiers for a while and SA improved dramatically, but wires, power cables and shelf load/real estate were driving me crazy. The next step, which solved 80% of my SQ my problem and 100% of my encumbrance problem was to use high-efficiency speakers (Klipsch Reference line) even if I don't particularly like them for music vs the stereo installs.
Today, I would definitely go active speakers I guess even if power lines would be an issue.

So, yes AVR are generally so-so amplifiers if all channels are driven, the difference is audible to very audible compared to dedicated amp.
 
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Dimitrov

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So, yes AVR are generally so-so amplifiers if all channels are driven, the difference is audible to very audible compared to dedicated amp.

Sure, but AVR's are also rarely required to output max power into all channels at the same time. I don't think there is any content available that requires AVR's to output power into all channels simultaneously.
 
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Dimitrov

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Because you will adjust the volume eventually to get back to your reference level.

Preferably using a multimeter before and after otherwise you won't have any reference.
 

Sangram

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Not not necessary. For example, my receiver has an auto-calibrate mode that sets the levels correctly after attaching new equipment.

Also since it is estimated that most people can not tell 1dB difference in volume levels apart, as long as your AVR has a dB output display, you will be pretty close to your normal level. Then, all source material is different so it's not about loud enough, it's about good enough. Of course you could use a measurement but it's almost impossible to take a meaningful acoustic measurement with a high-amplitude sinusoid wave of a real speaker in a real room. You would destroy your hearing, and probably the tweeter. Some estimation and extrapolation is required.

In most cases I find that as distortion reduces (which is the primary benefit of better amplification) normal listening level tends to go down as there is less muck in the output.
 
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