How to measure and calculate output power of power amplifier

How to measure and calculate output power of power amplifier

There are three output powers commonly used, rated output power, maximum output power and music power. Here is tube amplifier as an example.

1.    Rated output power (RMS): When power amplifier frequency characteristic and harmonic distortion coefficient can reach the specified technical specifications (generally tube power amplifier distortion should be less than 1%), power amplifier can work continuously for a long time safe continuous sinusoidal signal power.

2.    Maximum output power (PM): it can meet the basic parameters that Maximum output power of the power amplifier at the rated load resistance.

3.    Music Power (MPO): the instantaneous power value that power amplifier can output when Input a large dynamic music signal and keeping that there is not voltage drop of amplifier power supply. This MPO power is typically 4 or 6 times RMS power.

The output power of tube power amplifier is measured by output a 1 kHz sine wave signal from audio signal generator to input to power amplifier to be measured through the attenuator, and send to input end of the measured channel is placed at the maximum position, and other channels are placed at the minimum position, and its tone control is placed at normal position as shown. Then connect a distortion measuring instrument to output terminal of rated load, increase input signal voltage, make the harmonic distortion coefficient of output voltage reach the corresponding specified value, and finally measure the output power under normal operation and continuous signal.

How to measure and calculate output power of power amplifier

Output power measurement method block diagram

The output power is calculated as: P=U²/RL.

If the power amplifier is placed under an 8 ohm load and its output signal voltage is 20v and the distortion factor is 1%, so its rated output power (RMS) of the amplifier is

P= U²/ RL =20²/8=50W

In addition, in order to simplify the method of output power of tube power amplifier measurement, we can use the method shown in the figure below to make measurements. The specific method is, placing the measured work in a normal working state, the volume potentiometer is placed at the maximum position, and the music signal output form CD player or the record player or the signal of 1 kHz signal generator self-made is input to the input end of the measured power amplifier, is connected to an 8 ohm speaker or an 8 ohm load resistor at output end of tube power amplifier, and the dynamic voltage across the load is measured by an AC voltmeter or a multimeter AC 20V gear. The average of measured value is its output voltage.

If a tube power amplifier is placed at both ends of the speaker load and the output AC voltage is measured as 10v, the estimated power of its power amplifier is

P= U²/ RL = 102/8=12w

IWISTAO Mono FU50 Tube Amplifier Singal-ended Small 300B with dual 6J4P Preamplifier

IWISTAO Mono FU50 Tube Amplifier Singal-ended Small 300B with dual 6J4P Preamplifier  

The unit used the power tube stage FU-50 (or rY-50), it is an original high-frequency emission control, her sister possession of the same series is famous 805 (FU-5), 807 (FU-7), 845 (FU-45), 813 (FU-13) and so on. After it is transplanted to Hi-Fi stereo, its middle and high frequency is transparent bright, airy, grainy good. When connected to a triode connection output, frequency response curve is closer to the famous king tube 300B, so called "small 300B". Suitable for the performance of the human voice, strings and so on. This tube looks simple, but was called extraordinary refined, is also being used in multiple tube amp manufacturers product.

This mono FU50 tube amplifier is positioned as a desktop sound system, which adopt a power adapter as power supply to save the space and reduce the weight to compare the traditional tube amplifier.  

Whole casing of the power amplifier adopted aluminum alloy chassis and wooden panel, large gold-plated output and input terminals; mono design with class A single-ended output, the sound is bright and warm. And its preamplifier used 2pcs 6J4P that can be replaced by tube 6H4C, 6AC7.

The actual listening experience, sound neat, vivid and elegant, thick warm quality! High frequency delicate and elegant, quite expensive! Midrange sweet round, warm, aura! Low-frequency strong, dive deep, Tri-band balance, have strong tube taste, reduce grinding most of the digital sound, so that the sound more rounded and it don’t tire to listen sound.

More details, please visit https://www.iwistao.com/products/iwistao-1pc-mono-tube-amplifier-fu50-power-stage-class-a-signal-ended-small-300b-12w-preamplifier-2-x-6j4p-hifi-audio?variant=42938228748

IWISTAO Mono FU50 Tube Amplifier Singal-ended Small 300B with dual 6J4P Preamplifier  

Two FU50 tube amplifier + HIFI Bookshelf Speaker + CD Player 

Another option for music playing -- HIFI Digital Player Turntable

Another option for music playing -- HIFI  Digital Player Turntable 

Except CD player, you have another option for music playing. That is, a HIFI  Digital Player Turntable, you can storage those songs with  MP3, WAV, FLAC, APE format to USB disk or SD card which can  storage high volume songs. It is a turntable when it plays.

HIFI Digital Player Turntable Hardware Decoding ESS Main Chip AK4495 Supports WAV APE FLAC MP3 Support 192K/24BIT Black from IWISTAO HIFI MINIMART2 on Vimeo.
This digital player adopted the latest ESS main chip by American, which is a hardware decoding for mastering digital turntable player. Supports WAV, APE, FLAC, MP3 format, its ultra-high speed core processing chip support to the 192K / 24BIT mastering format, analytical, detail restoring ability is excellent, relaxed nature, rich overtone, better than PCHIFI, its advantage of outputs are better than pure CD output. Its sound pure and details is better than similar products.

For AK4495 have decoding output, there isn’t an external decoder. which is dynamic sound, broad field, excellent extending. Also AK4495 adopted 7.5V power supply firstly with the highest voltage power supply, in order to break through dynamic limitations of traditional 5V power output for DAC. Meanwhile AK4495 also has five kinds of optional built-in digital interpolation filter. As you know, it is very important to a HIFI device that power supply. It uses LM2941 ultra-precision regulator device, it has a much lower noise performance than conventional LM317, LM7805 and other three-terminal regulator. Also, uses oxygen-free copper 50W R-type transformer for power supply, low magnetic leakage, low noise, so that background noise better player

Built-in JRC-end op amps MUS8820, full tone, voice very smooth with a tube taste, for better than OPA2604, LME4972 and others. MUSES8820 is an op amp with second circuit and J-FET input form, which is to be applied and developed for more "real voice" equipment and sound products.

It supports audio formats as below, a) WAV: 192K / 24BIT; b) APE: 96K / 24BIT; c) FLAC: 192K / 24BIT; d) MP3: 44-48K / 16BIT (MP3 is the absence of 192K / 24BIT format)

More details, you can visit 

https://www.iwistao.com/products/hifi-digital-player-turntable-hardware-decoding-ess-main-chip-ak4495-supports-wav-ape-flac-mp3-192k-24bit-black?variant=17798908379251

IWISTAO 300B Bluetooth Tube Amplifier with CSR8670

IWISTAO 300B Bluetooth Tube Amplifier with CSR8670

This is a 300B vacuum tube amplifier with Bluetooth 4.2 technology. Built-in CSR8670 module, you can connect your Bluetooth enabled devices via wireless connect, also can play stream music.

There is a demo below.

IWISTAO FU50 Small 300B 2x8W Vacuum Tube Amplifier PCBA Kit Single-ended Class A DIY Free Tuning

Vacuum tube FU50 is known as the small 300B and close to tube 300B, but the price is much lower than tube 300B, its treble is fine, extension is very good, overtone is excellent, and the vocals are very cordial. Listening to the original sound of the Dream of Red Mansions can feel that it is super strong; listening to symphony and string music is very good, violin is very delicate, more worth playing than the tube EL34. 

This kit's solution uses 6J8P for gain amplification driving, FU50 as single-ended class A output, and tube 5U4C as tube rectification. Its output power is 2x8W. Don’t underestimate its 8w output, it is a Class A state, and much better than the digital power amplifier 50WX2 output and also more powerful than the LM1875's 2x25W.

This finished board is free tuning, you need just insert the vacuum tubes, and connect output and power  transformers. Also, kindly remind to connect your speaker to avoid damaging the output transformers before power on. The kits are made of fine materials and all imported high-voltage capacitors ensure safety and stability. All the seats are gold-plated to ensure good contact. High-power resistors use Panasonic, KOA and other advanced fever resistors.

Meanwhile, we provide the scheme diagram for you information. This is a channel of amplifier part below.

And, there is a power supply part below.

Here is the tubes, FU50, 6J8P, 5U4C.

After you insert the tubes into this small 300B amplifier board, you will get it as photo showed.

Upgrade version

We upgraded the FU50 amplifier with dual modes for output 

Dual-Mode Operation: The amplifier board features a dual-mode design, allowing users to switch between modes using two toggle switches. For safety, the power must be turned off before switching.

A). Ultra linear Tube Mode: This mode offers a dynamic, powerful, and slightly faster sound, making it ideal for symphonic music.

B). Triode Mode: This mode provides a delicate and melodious sound, perfect for listening to vocals.

More detail, please find, 

https://www.iwistao.com/products/iwistao-fu50-vacuum-tube-amplifier-2x8w-single-ended-class-a-pcba-finished-board-small-300b-diy?variant=13990706020467

https://iwistao.com/products/iwistao-fu50-vacuum-tube-amplifier-2x12w-single-ended-class-a-pcba-finished-board-dual-mode-small-300b-diy