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Audiophile help please - Ohms and power

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Siwastaja:
There is no specific %. The more accurately you want to understand the amplifier, the more details you need to fill in.

Exact maximum voltage swing you get out of amplifier depends on the engineering details. For example, very low-resistance MOSFETs can go just millivolts away from the rails, and assuming the rails are produced with regulated supply (say switch mode, for example) to a stable value, you get practically +/- 20V swing from +/-20V rails.

On the other hand, if the rails are non-regulated and have the rectified mains ripple (100Hz or 120Hz) riding on the top, say, the rails ride between 18V and 20V at full load, then if you try to go any further than +/-18V, you periodically run out of voltage, but at other times get higher; meaning, the mains ripple goes through to the speakers. So you need to limit the swing to the lowest voltage available to avoid this.

Or, a certain power stage might use Darlington transistors with large saturation voltage drop, say over 1V. Then your 20V supply with 2V ripple only gets you up to 17V.

Maybe the final stage is a voltage follower (voltage gain = 1), and even if the transistors could get closer to the rails, the previous stage cannot.

This is just the tip of the iceberg. It's always case-by-case and requires understanding of the actual circuit used.

DW1961:

--- Quote from: Siwastaja on August 01, 2020, 09:12:05 pm ---There is no specific %. The more accurately you want to understand the amplifier, the more details you need to fill in.

Exact maximum voltage swing you get out of amplifier depends on the engineering details. For example, very low-resistance MOSFETs can go just millivolts away from the rails, and assuming the rails are produced with regulated supply (say switch mode, for example) to a stable value, you get practically +/- 20V swing from +/-20V rails.

On the other hand, if the rails are non-regulated and have the rectified mains ripple (100Hz or 120Hz) riding on the top, say, the rails ride between 18V and 20V at full load, then if you try to go any further than +/-18V, you periodically run out of voltage, but at other times get higher; meaning, the mains ripple goes through to the speakers. So you need to limit the swing to the lowest voltage available to avoid this.

Or, a certain power stage might use Darlington transistors with large saturation voltage drop, say over 1V. Then your 20V supply with 2V ripple only gets you up to 17V.

Maybe the final stage is a voltage follower (voltage gain = 1), and even if the transistors could get closer to the rails, the previous stage cannot.

This is just the tip of the iceberg. It's always case-by-case and requires understanding of the actual circuit used.

--- End quote ---

I'm talking speicficallya bout teh amp chip I posted above:

    2 × 50 W Into a 4-Ω BTL Load at 21 V (TPA3116D2)
    2 × 30 W Into a 8-Ω BTL Load at 24 V (TPA3118D2)
    2 × 15 W Into a 8-Ω BTL Load at 15 V (TPA3130D2)

No other variables. How would I calculate power for 19V?

retrolefty:
 Just to bring another perspective to the topic of maximum audio output power, I thought I would share my experiences with vintage 1970s audio systems (a golden era) that I started collecting in the 1990s via thrift store finds and some ebay purchases. I would snap up anything near top of the line in Japanese stereo that I could find as people were dumping their gear for 5 channel stuff in the 90s. I would repair anything broken and either keep it if it was 'better' then I had and or sell it off on ebay. I went though maybe a dozen receivers and preamp/amp separates.

  I worked all the way up to a Kenwood SX-1980 working into some English 12" 3 way speakers. That receiver was  rated at 270 RMS watts per channel back when the FTC regulations required much more rigorous and truthful ratings compared to the nonsense of peak/music power ratings many advertise today. I mostly like classic rock and like to feel the music as well as hear it, but I would get plenty of complaints from SWMBO any time the wattage scale on the receiver was peaking above just 2 watts no matter wherever in the house she might be!

 It is mostly a marketing thing, like never too thin, too light, never to much horsepower, never too much audio output power that sells regardless of any actual practical need. Unless one is building large PA systems or concert setups, one rarely needs more then say 20 wpc when driving normal speakers in normal homes. There are some speaker designs (seal enclosures) that have much lower SPL ratings that could require more  power but they are not very popular these days.

 What are others thoughts and experiences on audio setups they have enjoyed? How much output wattage is too little or too much?


 

DW1961:

--- Quote from: retrolefty on August 01, 2020, 11:42:19 pm --- Just to bring another perspective to the topic of maximum audio output power, I thought I would share my experiences with vintage 1970s audio systems (a golden era) that I started collecting in the 1990s via thrift store finds and some ebay purchases. I would snap up anything near top of the line in Japanese stereo that I could find as people were dumping their gear for 5 channel stuff in the 90s. I would repair anything broken and either keep it if it was 'better' then I had and or sell it off on ebay. I went though maybe a dozen receivers and preamp/amp separates.

  I worked all the way up to a Kenwood SX-1980 working into some English 12" 3 way speakers. That receiver was  rated at 270 RMS watts per channel back when the FTC regulations required much more rigorous and truthful ratings compared to the nonsense of peak/music power ratings many advertise today. I mostly like classic rock and like to feel the music as well as hear it, but I would get plenty of complaints from SWMBO any time the wattage scale on the receiver was peaking above just 2 watts no matter wherever in the house she might be!

 It is mostly a marketing thing, like never too thin, too light, never to much horsepower, never too much audio output power that sells regardless of any actual practical need. Unless one is building large PA systems or concert setups, one rarely needs more then say 20 wpc when driving normal speakers in normal homes. There are some speaker designs (seal enclosures) that have much lower SPL ratings that could require more  power but they are not very popular these days.

 What are others thoughts and experiences on audio setups they have enjoyed? How much output wattage is too little or too much?

--- End quote ---

You should start a new thread for that. Would be fun.

This was my 1980s receiver. Damn it would drive those 70 watts RMS Cerwin Vega HED 12" woofer speakers I had. Had the neighbor come down one Saturday night when we were partying to say he could hear my music 10 houses down, inside his bedroom. https://www.hifiengine.com/manual_library/yamaha/r-900.shtml

Even by today's standards, it was a nice looking piece.




But that was nothing compared my friends brother in law and sister who bought a pair of BOSE 901s in 1972. OMG you could hear those things a mile a away. (Yes, literally)

Siwastaja:

--- Quote from: DW1961 on August 01, 2020, 11:05:46 pm ---I'm talking speicficallya bout teh amp chip I posted above:

    2 × 50 W Into a 4-Ω BTL Load at 21 V (TPA3116D2)
    2 × 30 W Into a 8-Ω BTL Load at 24 V (TPA3118D2)
    2 × 15 W Into a 8-Ω BTL Load at 15 V (TPA3130D2)

No other variables. How would I calculate power for 19V?

--- End quote ---

Opening up the datasheet, Figure 13 on page 10 shows the output power at any input voltage. Yes I know; no calculation involved, you were given the answer directly.

They calculated, simulated or measured it, because no one else can know all the internal details of the chip that affect the exact value. Do still note this is just a single figure for a single part, there will always be unit-to-unit variation so even when this graphs says 22W at 19V at 1% THD to 8 ohm load, if you measure that on your system, it might be 21W or 23W. Also your external filter network components affect the power, for example, if you have more resistance than TI did in their test system, you are losing part of the power there.

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