Testing audio amplifiers

It is important to know how to test an electric guitar amplifier before you buy one to ensure that it meets your needs. When choosing an amp, you need to take several things into consideration, such as tone, distortion, features, and budget.

testing audio amplifiers

Before you buy it, you should plug in the amp and give it a try. You should inform the salesperson at your local music store that you intend to try the amp before you buy it.

He or she may even make preparations for the impending noisiness. Many music stores have a separate room for just such high-volume noise-making. Outlet issues can sometimes be an obstacle in places where the outlets are controlled with a switch. Remember that some amps have more than one volume knob, and they might have a lot of other knobs besides. Midway is generally at about if you picture the dial as a clock.

This ensures that you get a neutral, uncolored sound from the amp. Play a few licks on different parts of the guitar, and at different volumes and tone levels.

Listen for unwanted or desired? Many amps have a light that shows that the amp is on. About the Book Author Jon Chappell is a multistyle guitarist, arranger, and author. Jon has also contributed numerous musical pieces to TV and film.This is a simple DIY Speaker dummy load that was put together very quickly. So rather than test with unsecured hot resistors, it was necessary to build a properly enclosed speaker dummy load that would not be a fire hazard.

Rather than just using a load resistor across the output of an amplifier, it is often nice to also be able to hear output during testing.

The schematic below shows two dummy loads, built into one enclosure. With a speaker connected, the amplifier will see either a 4. You can check the net load for yourself by following the basic electronics formulas. With a simple setup like this you can test at high power without risking damaging speakers, going deaf or driving other people crazy. If a speaker is not connected to the dummy load, the amplifier will see either a 4.

To help promote cooling, I mounted the 50W resistors to heat sinks that had been salvaged from dead computer power supplies. The 4. The aluminum enclosure also helps dissipate some heat from the resistors. Since the resistors are cooled somewhat, it is ok to apply more than 50W of power for a very SHORT period of time, but don't get carried away.

I used binding posts to allow for easy connection to and from the dummy load. The binding posts also make it easy to add a small capacitor or inductor if you want to try different load scenarios when testing an amplifier. The dummy speaker load box is configurable for 2-ohm, 4-ohms, 6-ohm, 8-ohm, ohm and ohm loads. Last update 7 April Created 10 December Giovanni Militano.The Web This site. Record your results in Part 3 of the Amplifier Design Record sheets.

Visually double check the circuit, especially the capacitor connections see warning in Part 2. Switch on and re-check the transistor voltages to make sure the circuit is operating as predicted. Gain can be measured using the set up shown in Fig 2. The generator is set to a mid-band frequency of 1kHz and a small amplitude sine wave signal applied to the amplifier input. With the oscilloscope attached to the output terminals, the input signal is adjusted to give a large amplitude output signal that still has an undistorted waveform.

The peak-to-peak amplitude of the output signal is measured and then the oscilloscope probes are transferred to measure the input. Since the input of the amplifier will be mainly resistive at frequencies around or below 1kHz the input impedance Zin can be represented in the diagram of the amplifier Fig. To find the value of Z in at 1kHz a variable resistor of about 10K ohms a larger value than the amplifier input impedance is expected to beor a decade resistance box can be connected between the generator and the amplifier input as shown in Fig.

Initially the variable resistor is set to zero ohms and the generator is adjusted to give a large undistorted display on the oscilloscope. The amplitude of the display on the oscilloscope should be adjusted to fit exactly between an even number of the horizontal graticule markings.

The variable resistor is now adjusted until the peak-to-peak of the output wave is exactly half its original value.

Disconnect the variable resistor taking care not to disturb the slider position, and measure its resistance value with the multi-meter. The output of the amplifier is developed across the load resistor R L so this resistor is effectively the output resistance and approximately the output impedance Z out at 1kHz of the amplifier.

Analog Engineering Associates

The output coupling capacitor C2 see Fig. Checking the bandwidth of the amplifier requires the same equipment set up as in Fig. Initially set the generator frequency to 1kHz and adjust the generator amplitude and the oscilloscope controls to view a large, undistorted waveform, adjust the amplitude of the waveform to fit exactly between an even number of horizontal graticule lines on the oscilloscope display. Without altering the generator amplitude, reduce the frequency of the input wave and observe its V PP amplitude on the oscilloscope.

Keep reducing the frequency until the amplitude of the output wave falls to 0. Increase the frequency past 1kHz until the output V PP again falls to 0. It is quite probable that the tests will show that the amplifier bandwidth will not conform to a nice 20Hz to 20kHz specification, or that there may be variations in maximum gain over the frequency range. This is not the ideal situation for a good audio amplifier, so the design may need improving as described in Amplifiers module 2.

Hons All rights reserved.The results of such tests are published in journals, magazines, whitepapers, websites, and in other media. Those who test and evaluate equipment can be roughly divided into two groups: " Objectivists ", who believe that all perceivable differences in audio equipment can be explained scientifically through measurement and double-blind listening tests ; and the " Subjectivists ", who believe that the human ear is capable of hearing details and differences that cannot be directly measured.

Objectivists believe that audio components and systems must pass rigorously conducted double-blind tests and meet specified performance requirements in order to validate the claims made by their proponents. British audio equipment designer Peter Baxandallwho is often considered an objectivist, has written, "I Subjectivist Harry Pearsonlong-time editor of the audiophile magazine The Absolute Sound has stated: [6].

Some audiophile equipment designers and consumers are obsessed over seemingly irrelevant details. Many components, for instance, are able to reproduce frequencies higher than the limit of human hearing—20 kHz. Subjectivists claim that experienced listeners can be relied upon for valid advice on how equipment sounds.

British Hi-fi critic, Martin Colloms, writes that "the ability to assess sound quality is not a gift, nor is it the feature of a hyperactive imagination; it is simply a learned skill", which can be acquired by example, education and practice. The most significant difference between the two groups is that subjectivists claim there is a limit to what can be tested using objective measurements, while objectivists believe that since blind testing is the gold standard of all science, perceived sound quality should not be exempt from objective measurements.

Objectivists tend to see the subjectivists as irrational and prone to gullibility, while subjectivists often dismiss objectivists as simple "meter men" who lack a nuanced appreciation of sound. Although the debate can be heated in certain quarters, both groups seek optimal listening experiences, and in some cases, the findings of one group has informed the other.

Objectivists argue that vacuum-tube amplifiers often exhibit lower-fidelity than solid-state designs, and that in addition to their substantially higher total harmonic distortion level, they require rebiasing, tend to be less reliable, less powerful, generate more heat, and are usually more expensive. Subjectivists are often argue that while tube electronics are less linear than solid-state electronics at high-signal levels, they are much more linear at low-signal levels less than one watt and that many musical signals spend much of their time at these low levels.

However, in cases where the subjectivists' claims can be verified by objective measure, it could not be considered a strictly "subjective" position. A more literally subjectivist argument is that listeners may be able to discern pleasurable benefits from tube equipment that would escape any attempt at objective measurement.

Objectivists claim that digital sound can have higher fidelity than analog sound because it lacks clicks, pops, wowflutteraudio feedbackdegradation, generational loss, and rumblehas a higher signal-to-noise ratiohas a wider dynamic rangehas less total harmonic distortionand has a flatter and more extended frequency response.

Subjectivists have argued that the process of converting a bit-stream to an analog waveform requires heavy filtering to remove spurious high-frequency information and that it should be expected that such filtering should involve some signal degradation and a large amount of phase shift in the passband.

They point out that commonly used consumer-grade digital-to-analog converters DACs exhibit poor linearity at low levels. Both of these problems have since been verified by objective measure, and were then addressed by such solutions as digital filteringoversamplingand the use of DACs operating at bit or higher resolution. Today, many objectivists and subjectivists may agree that a preference for analog formats is often rooted in pleasing and familiar distortions and artifacts.

At the same time, members of both camps might also agree that the best historical analog formats have often displayed great levels of audio fidelity as well. Musician Neil Young is a harsh critic of the sound of the original CD format, but has expressed approval for the sound of higher definition formats such as SACDwhich he believes has a greater safety margin between its ideal behavior and the theoretical limits of human hearing.

However, many independent listening tests and mathematical studies have shown that Young's assertions are basically untrue. Objectivists and Subjectivist were once at odds about the importance of total harmonic distortion. Both groups now seem to agree that the distribution of harmonic distortion can be important in perceived sound quality.As reviewers, we rely on lab tests to evaluate gear, but we lean a lot more on our collection of stereo test tracks, which have been accumulated, augmented, and pruned through years of testing experience.

These songs are the kind that we can play through speakers or headphones to assess how well or not a product sounds. Any audio enthusiast should put together a selection of tunes like this. It's convenient for checking pairs of headphones in stores, a friend's new stereo speakers, or the audio systems you might encounter at Hi-Fi shows.

You can even edit the songs if you like, cutting straight to the parts you want to hear just for testing purposes. To get the best possible fidelity from songs, be sure to buy the CD or digitize vinyl LPs to create lossless digital music files. Or, at the very least, download the highest-quality MP3 tracks available—recommended kbps or better.

Although your audio-test tracklist evolves over time, keep several staple tracks that you know well and do not change.

The 10 Best Tracks for Evaluating Audio Equipment

The folks at Harman Research, who easily rank among the top audio researchers in the world, have been using Tracy Chapman's "Fast Car" and Steely Dan's "Cousin Dupree" for over 20 years now. Scoff if you will at Toto's album, Toto IVbut this track's dense mix truly spans the audio spectrum. This is usually the quickest test we've found for judging the accuracy of an audio product's tonal balance—the relative level of bass to midrange to treble.

testing audio amplifiers

Just 30 seconds of "Rosanna" will tell you whether a product is on the good or bad side of things. We purchased Cole's album Temptation when it was released in This song starts with some intensely deep bass notes, which can easily push lesser speakers and subwoofers towards distorting the lows. The tinkly percussion that dances across the front of the sound stage is a great test of high-frequency performance and stereo imaging.

If your tweeter can cleanly and clearly reproduce the super high-pitched chime, struck right after Cole sings the line, "…never, never, never ring a bell," then you've got a good one.

Use the studio recording instead of the live version. Feelgood uses so much dynamic compression that the readout on your sound pressure level meter or the needle on your amp's output meter will barely move. And that's a good thing because the steady level lets one judge the maximum output capabilities for products like Bluetooth speakers and soundbars. But listen for the way your system reproduces the bass and kick drum during this song; the groove should sound punchy, not loose, bloated, or boomy.

Sadly, many headphones make this tune sound boomy, and that is just plain wrong. The Coryellsthe eponymous album featuring jazz guitarist Larry Coryell and his hyper-talented sons Julian and Murali, is one of the best that Chesky Records has ever done—and that's saying a lot. This particular song is a favorite for judging sound stage depth. If the instruments sound like they're coming from 20 or 30 feet behind the guitars, and if you can hear them echoing off the walls and ceiling of the large church where this recording was made, then your system is doing a fine job.

Each of the group's four saxophones—all four of which play nonstop through the entire tune—is positioned at a certain place within the stereo soundstage. You'll want to be able to pick out each saxophone individually and point to it yes, in the air.

If you can do that, then you've got a fantastic system. If not, don't worry too much, because this particular listening test is pretty hard! If you want one of the best bass tests in existence, go for Olive's Extra Virgin.

How To Test and Measure Audio Amplifiers

We often use the song "Falling" when testing for the best subwoofer placement. The synthesizer bass line is powerful and punchy, dropping way down to a deep note, one that tends to nearly disappear when played over mini speakers or bad headphones. Know that this is a harsh-sounding recording if you're listening to the mids and treble. So it might be worth making a custom version with the treble rolled off -6 dB at 20 kHz. Headphones can sometimes be marketed as a "hip-hop thing," with many popular models designed specifically with hip-hop in mind.

In our opinion, most hip-hop mixes are too elemental to tell you much about an audio product. Both of these men have smooth voices that shouldn't sound rough on any good system. But the best part of this track is the background vocals repeating the phrase, "Keep giving me love.

You should feel some tingles along the spine or prickles on the skin. If not, a new set of headphones might be in order. We don't mean the booming, headache-inducing hip-hop or heavy rock brand of bass.The content you have requested is available only to registered visitors.

Please complete the short form below all fields are required. Email :. First Name :. Last Name :. Company :. No - I don't want to receive the latest audio test information by email. Specifically designed for the audio test market, it incorporates several features unique to the needs of audio test and measurement, and unnecessary features found in regular audio amplifiers have been eliminated to keep production line operation simple and error-proof.

Specifically designed for the making audio measurements, it incorporates several features unique to the needs of loudspeaker testing, and unnecessary features found in regular audio amplifiers have been eliminated to keep production line operation simple and error-proof. Fixed gain eliminates calibration errors as there is no gain knob to be accidentally knocked or tweaked whenit is in use. It supports the application of a DC voltage offset to the AC signal for testing transducers under adverse conditions.

This simple front panel keeps operation easy and error-proof as there is no possibility of knobs or buttons being accidentally changed.

SC Amp can accept balanced or single ended audio inputs from the audio interface.

DIY Audio Projects - DIY Hi-Fi for Audiophiles

Download PDF data sheet. Physical Dimensions: 4. Part Registration required The content you have requested is available only to registered visitors. SCAmp — Front Left. Features Rugged and rack mountable Simple to use Fixed gain eliminates calibration errors Low distortion and low noise floor Supports the application of a DC voltage offset Integrated impedance measurement Download PDF data sheet.Do-It-Yourself DIY Audio Projects - projects for audiophiles, hi-fi enthusiasts, music lovers, electronic hobbyists, woodworkers and those who like to learn, build and listen to music.

testing audio amplifiers

This site exists to promote the hobby of DIY Audio. There is nothing for sale here. All project documentation presented on this site is free for personal non-commercial use. Questions about a specific projects can be sent to the project author noted at the top of the project page.

Last update: 10 November These are some of our featured DIY audio projects. For more DIY projects, use the navigation menu on the left hand side of the page. Last updated 10 November The schematic is similar to the PoddWatt design and able to use a huge variety of tubes. The circuit is biased into Class-A, ultra-linear operation and output power will be dependent on the tubes utilized. At full output the amp produces a clean 1. This amplifier did a little better than this having a -3dB bandwidth from about 46Hz to about 30kHz.

The 6CY7 stereo amp uses a 6CA4 tube rectified power supply with excellent channel separation. Matt reports: This is quickly becoming my favorite amp. I highly recommend that anyone looking for a little iPod or computer amp give this one a try. The builder will need to provide a VDC power supply, an enclosure and miscellaneous hardware like connectors and switches. Mark uses 9V batteries for the power supply and is very pleased with the results. The single-ended 6EM7 amplifier is housed in a vertical wooden chassis that has been styled after early vacuum tube equipment of the s.

Matt reports that the 6EM7 amplifier sounds wonderful! The bass is well articulated without being boomy, mid-tones are clear and even, and the highs are crystal clear. The speaker cabinet plans are from the FEEn driver datasheet. The horn loudspeaker cabinets are made from 21 mm thick pine plywood and use a single FEEn fullrange driver and no crossover.

Australian beeswax is used on the outside of the horn cabinet and heavy cedar oil was applied to the mouth of the horn. Mark reports that the horn speakers can draw an extremely accurate soundstage, sound excellent and have lead to a whole new listening experience with Paris, a 2.

This is a complete amp kit that includes all the necessary parts and enclosure to build a stereo amplifier. The LM amp kit comes with audio-grade capacitors and toroidal transformer. The Gobo amplifier kit is easy to build, looks and sounds great. The amplifier kit is well suited to first time amp builders. As a thank you for the B amplifier schematics, Stamou has shared his implementation of the B single-ended tube amplifier schematic by J.

The power supply filtering sections have been duplicated for each channel for this B triode amplifier and premium parts are used throughout. The audio output transformers are Lundahl LL You can change the tube type to vary the sound and gain considerably. The preamp uses a 6CA4 tube rectified power supply which is very quiet.

The Universal preamp is fun as it allows tube rolling to compare various tubes in your stash. This is a great simple preamplifier unit to bring out the most in your power amps. The enclosure is a 6.

The loudspeakers use a single Fostex FEEn fullrange driver with no crossover circuit.


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