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Math on power amplifier selection

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#21
I nave been wondering the same thing. I use primarily large DIY bookshelf speakers like Classix II, Sambas, will be ordering Helix Dome MTs soon.

I wanted to order an amp from Buckeye amps, but lowest power one he makes is the NC252MP and I feared it would be too much for my use case.

The Classix II are 8 ohm, the others are 4 ohm. If I use something like the Topping E30 in preamp mode will I have to make sure I keep the volume sufficiently low in order not to blow out my speakers?
 

NTK

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#22
I nave been wondering the same thing. I use primarily large DIY bookshelf speakers like Classix II, Sambas, will be ordering Helix Dome MTs soon.

I wanted to order an amp from Buckeye amps, but lowest power one he makes is the NC252MP and I feared it would be too much for my use case.

The Classix II are 8 ohm, the others are 4 ohm. If I use something like the Topping E30 in preamp mode will I have to make sure I keep the volume sufficiently low in order not to blow out my speakers?
There really is no serious downside for having more than sufficient power. It may cost more, bigger, heavier, consume more electricity, generate more heat, etc. But that's about it.

If you want an amplifier that under no circumstance will overload and damage your speakers, it will invariably have insufficient power to give you satisfactory listening enjoyment. It will not be enough to handle the music dynamics.

Your ears should (or you should train your ears to) tell you when it is too loud and your speakers are struggling. If your speakers are struggling and it is not loud enough for you, you need bigger speakers.
 
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Thread Starter #23
I nave been wondering the same thing. I use primarily large DIY bookshelf speakers like Classix II, Sambas, will be ordering Helix Dome MTs soon.

I wanted to order an amp from Buckeye amps, but lowest power one he makes is the NC252MP and I feared it would be too much for my use case.

The Classix II are 8 ohm, the others are 4 ohm. If I use something like the Topping E30 in preamp mode will I have to make sure I keep the volume sufficiently low in order not to blow out my speakers?
After read the input from everyone and I googled more information, my understand is NC122MP and NC252MP will have same SPL before the input voltage from DAC (after amplified) reached the NC122MP output voltage limit which probably should be quite loud already. Any larger input voltage will clip in NC122MP and louder in NC252MP before it reach its output voltage limit. I think the key is the 2 amplifier have same gain, higher power one just have higher limit. Hope my understand is correct.
 

NTK

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#24
After read the input from everyone and I googled more information, my understand is NC122MP and NC252MP will have same SPL before the input voltage from DAC (after amplified) reached the NC122MP output voltage limit which probably should be quite loud already. Any larger input voltage will clip in NC122MP and louder in NC252MP before it reach its output voltage limit. I think the key is the 2 amplifier have same gain, higher power one just have higher limit. Hope my understand is correct.
Yes. You are correct. Below are from the Hypex NC122 and NC252 data sheets.

In the examples Hypex gave, the NC122 has a gain of 25.6 dB, and an input of 1.17 Vrms will drive it to its full rated output of 125 W with a 4 Ω load.

NC122MP.JPG


The NC252 also has a gain of 25.6 dB, and requires a higher input of 1.66 Vrms to drive it to its full rated output of 250 W with a 4 Ω load.

NC252MP.JPG


Because gains are the same, both amps will drive the same speaker to the same loudness with the same input level (e.g. you can drive your left speaker with a NC122 and your right speaker with a NC252 and the volume will match, to the tolerance of unit-to-unit variation).
 
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Thread Starter #25
Yes. You are correct. Below are from the Hypex NC122 and NC252 data sheets.

In the examples Hypex gave, the NC122 has a gain of 25.6 dB, and an input of 1.17 Vrms will drive it to its full rated output of 125 W with a 4 Ω load.

View attachment 108426

The NC252 also has a gain of 25.6 dB, and requires a higher input of 1.66 Vrms to drive it to its full rated output of 250 W with a 4 Ω load.

View attachment 108427

Because gains are the same, both amps will drive the same speaker to the same loudness with the same input level (e.g. you can drive your left speaker with a NC122 and your right speaker with a NC252 and the volume will match, to the tolerance of unit-to-unit variation).
Thanks a lot! Learn quite a lot from this forum.
 
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#26
Welcome to ASR!

The rated output of a DAC is its maximum ouput. It is a level which you should never (or very rarely) reach during normal operation. It just happens that signal-to-noise ratio is usually the best when the DAC is at its maximum output. The reason is that noise is usually constant, and does not change with the signal output level. Therefore, the higher the output, the better the signal-to-noise ratio.
Are you conflating "DAC" with "pre-amp"? A pure DAC doesn't have any volume control (attenuation) and would give you an analog output whose level is in proportion to the digital stream. You run that through your pre-amp or volume control and then you can manage your level(s), usually via passive attenuation, going into your amp(s).

Having said that, quite often (maybe even "most times") a DAC will come with a digital volume control built-in. Just wanted to make it clear that a DAC doesn't necessarily include that function, though. Full disclosure: I am being pedantic here :)

Examples:

- Khadas Tone Board
- a PC sound card (sort of - if you exclude the Windows volume control)
- ... can't really find any other ones, save for DAC modules that you have to build around yourself (like this)

Yeah, you know what, for what the OP is asking, just disregard this post... lol
 
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OP
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Thread Starter #27
Are you conflating "DAC" with "pre-amp"? A pure DAC doesn't have any volume control (attenuation) and would give you an analog output whose level is in proportion to the digital stream. You run that through your pre-amp or volume control and then you can manage your level(s), usually via passive attenuation, going into your amp(s).

Having said that, quite often (maybe even "most times") a DAC will come with a digital volume control built-in. Just wanted to make it clear that a DAC doesn't necessarily include that function, though. Full disclosure: I am being pedantic here :)

Examples:

- Khadas Tone Board
- a PC sound card (sort of - if you exclude the Windows volume control)
- ... can't really find any other ones, save for DAC modules that you have to build around yourself (like this)

Yeah, you know what, for what the OP is asking, just disregard this post... lol
Sorry that I didn't mentioned clear enough! I planning to buy a Topping D70s which can be uaed as DAC+pre-amp.
 

bigguyca

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#28
Yes, I googled it and found no real reason why they would deflate the power rating with a quoted imaginary RMS value.
Yo yo yo @restorer-john have you any idea why manufacturers use a fake Prms value of (Vpeak*0.707)^2/Rload instead of a straight up Vpeak^2/Rload calculation. What purpose does power RMS rating serve to them? It seems counter-intutive because they deflate the power rating by multiplying by 0.707
All very creative, but amazingly wrong.

For sinewaves driving a resistance:

Vrms = Vpeak x .707

Ave power

Ave power (watt) = Vrms^2/R = Irms^2 x R does not equal Prms

Prms can be calculated, but is meaningless. Calculated power rms of a power sinewave, where power is calculated as above, is higher than Ave power not lower

Peak Power

Amir uses the standard: CEA-2006/490 for peak power.

CEA-2006/490 is the power produced during 20 cycles of a 1kHz sinewave, with 20 cycles into 4ohms at 1% distortion, then 480 cycles at -20dB relative the previous power, then back again to 20 cycles at into 4ohms at 1% distortion, then 480 cycles at -20dB, rinse and repeat.
 
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