SARA-amplificator de inalta performanta

[hpavictor]

Cred ca problema provine din alta parte ...tine de modul cum ai definit sursa de alimentare , condesatorii de decuplare a alimentarii etc . Poate nu strica un filtru pe intrare RC trece jos ( sub 80 kHz ) pentru o proba .

[Sharky]

Cat de apropiate erau frecventele si cum le-ai aplicat pe intrare?

[hpavictor]

Aici avem explicatiile despre masurarea distorsiunilor de la firma RANE , sper ca cineva priceput la limba engleza sa ne traduca si sa adapteze textul in limba romana :

 

Audio Distortion

 

By its name you know it is a measure of unwanted signals.

Distortion is the name given to anything that alters a pure input signal in any way other than changing its magnitude.

The most common forms of distortion are unwanted components or artifacts added to the original signal, including random and hum-related noise.

A spectral analysis of the output shows these unwanted components.

If a piece of gear is perfect the spectrum of the output shows only the original signal -- nothing else -- no added components, no added noise -- nothing but the original signal.

The following tests are designed to measure different forms of audio distortion.

 

THD. Total Harmonic Distortion

 

What is tested?

A form of nonlinearity that causes unwanted signals to be added to the input signal that are harmonically related to it.

The spectrum of the output shows added frequency components at 2x the original signal, 3x, 4x, 5x, and so on, but no components at, say, 2.6x the original, or any fractional multiplier, only whole number multipliers.

 

How is it measured?

This technique excites the unit with a single high purity sine wave and then examines the output for evidence of any frequencies other than the one applied.

Performing a spectral analysis on this signal (using a spectrum, or FFT analyzer) shows that in addition to the original input sine wave, there are components at harmonic intervals of the input frequency.

Total harmonic distortion (THD) is then defined as the ratio of the rms voltage of the harmonics to that of the fundamental component.

This is accomplished by using a spectrum analyzer to obtain the level of each harmonic and performing an rms summation.

The level is then divided by the fundamental level, and cited as the total harmonic distortion (expressed in percent).

Measuring individual harmonics with precision is difficult, tedious, and not commonly done; consequently, THD+N (see below) is the more common test. Caveat Emptor: THD+N is always going to be a larger number than just plain THD.

For this reason, unscrupulous (or clever, depending on your viewpoint) manufacturers choose to spec just THD, instead of the more meaningful and easily compared THD+N.

 

Required Conditions.

Since individual harmonic amplitudes are measured, the manufacturer must state the test signal frequency, its level, and the gain conditions set on the tested unit, as well as the number of harmonics measured.

Hopefully, it's obvious to the reader that the THD of a 10 kHz signal at a +20 dBu level using maximum gain, is apt to differ from the THD of a 1 kHz signal at a -10 dBV level and unity gain.

And more different yet, if one manufacturer measures two harmonics while another measures five.

 

Full disclosure specs will test harmonic distortion over the entire 20 Hz to 20 kHz audio range (this is done easily by sweeping and plotting the results), at the pro audio level of +4 dBu.

For all signal processing equipment, except mic preamps, the preferred gain setting is unity.

For mic pre amps, the standard practice is to use maximum gain.

Too often THD is spec'd only at 1 kHz, or worst, with no mention of frequency at all, and nothing about level or gain settings, let alone harmonic count.

 

Correct: THD (5th-order) less than 0.01%, +4 dBu, 20-20 kHz, unity gain

 

Wrong: THD less than 0.01%

 

THD+N. Total Harmonic Distortion + Noise

 

What is tested?

Similar to the THD test above, except instead of measuring individual harmonics this tests measures everything added to the input signal.

This is a wonderful test since everything that comes out of the unit that isn't the pure test signal is measured and included -- harmonics, hum, noise, RFI, buzz ... everything.

 

How is it measured?

THD+N is the rms summation of all signal components (excluding the fundamental) over some prescribed bandwidth.

Distortion analyzers make this measurement by removing the fundamental (using a deep and narrow notch filter) and measuring what's left using a bandwidth filter (typically 22 kHz, 30 kHz or 80 kHz).

The remainder contains harmonics as well as random noise and other artifacts.

 

Weighting filters are rarely used.

When they are used, too often it is to hide pronounced AC mains hum artifacts. An exception is the strong argument to use the ITU-R (CCIR) 468 curve because of its proven correlation to what is heard.

However, since it adds 12 dB of gain in the critical midband (the whole point) it makes THD+N measurements bigger, so marketeers prevent its widespread use.

 

[Historical Note: Many old distortion analyzers labeled "THD" actually measured THD+N.]

 

Required Conditions.

Same as THD (frequency, level & gain settings), except instead of stating the number of harmonics measured, the residual noise bandwidth is spec'd, along with whatever weighting filter was used.

The preferred value is a 20 kHz (or 22 kHz) measurement bandwidth, and "flat," i.e., no weighting filter.

 

Conflicting views exist regarding THD+N bandwidth measurements.

One argument goes: it makes no sense to measure THD at 20 kHz if your measurement bandwidth doesn't include the harmonics.

Valid point, and one supported by the IEC, which says that THD should not be tested any higher than 6 kHz, if measuring five harmonics using a 30 kHz bandwidth, or 10 kHz, if only measuring the first three harmonics.

Another argument states that since most people can't even hear the fundamental at 20 kHz, let alone the second harmonic, there is no need to measure anything beyond 20 kHz.

Fair enough.

However, the case is made that using an 80 kHz bandwidth is crucial, not because of 20 kHz harmonics, but because it reveals other artifacts that can indicate high frequency problems.

All true points, but competition being what it is, standardizing on publishing THD+N figures measured flat over 22 kHz seems justified, while still using an 80 kHz bandwidth during the design, development and manufacturing stages.

 

Correct: THD+N less than 0.01%, +4 dBu, 20-20 kHz, unity gain, 20 kHz BW

 

Wrong: THD less than 0.01%

 

IMD -- SMPTE. Intermodulation Distortion -- SMPTE Method

 

What is tested?

A more meaningful test than THD, intermodulation distortion gives a measure of distortion products not harmonically related to the pure signal.

This is important since these artifacts make music sound harsh and unpleasant.

 

Intermodulation distortion testing was first adopted in the U.S. as a practical procedure in the motion picture industry in 1939 by the Society of Motion Picture Engineers (SMPE -- no "T" [television] yet) and made into a standard in 1941.

 

How is it measured?

The test signal is a low frequency (60 Hz) and a non-harmonically related high frequency (7 kHz) tone, summed together in a 4:1 amplitude ratio.

(Other frequencies and amplitude ratios are used; for example, DIN favors 250 Hz & 8 kHz.)

This signal is applied to the unit, and the output signal is examined for modulation of the upper frequency by the low frequency tone.

As with harmonic distortion measurement, this is done with a spectrum analyzer or a dedicated intermodulation distortion analyzer.

The modulation components of the upper signal appear as sidebands spaced at multiples of the lower frequency tone.

The amplitudes of the sidebands are rms summed and expressed as a percentage of the upper frequency level.

 

[Noise has little effect on SMPTE measurements because the test uses a low pass filter that sets the measurement bandwidth, thus restricting noise components; therefore there is no need for an "IM+N" test.]

 

Required Conditions.

SMPTE specifies this test use 60 Hz and 7 kHz combined in a 12 dB ratio (4:1) and that the peak value of the signal be stated along with the results.

Strictly speaking, all that needs stating is "SMPTE IM" and the peak value used.

However, measuring the peak value is difficult.

Alternatively, a common method is to set the low frequency tone (60 Hz) for +4 dBu and then mixing the 7 kHz tone at a value of -8 dBu (12 dB less).

 

Correct: IMD (SMPTE) less than 0.01%, 60Hz/7kHz, 4:1, +4 dBu

 

Wrong: IMD less than 0.01%

 

IMD -- ITU-R (CCIF). Intermodulation Distortion -- ITU-R Method

 

What is tested?

This tests for non-harmonic nonlinearities, using two equal amplitude, closely spaced, high frequency tones, and looking for beat frequencies between them. Use of beat frequencies for distortion detection dates back to work first documented in Germany in 1929, but was not considered a standard until 1937, when the CCIF (International Telephonic Consultative Committee) recommend the test.

[This test is often mistakenly referred to as the CCIR method (as opposed to the CCIF method).

A mistake compounded by the many correct audio references to the CCIR 468 weighting filter.]

Ultimately, the CCIF became the radiocommunications sector (ITU-R) of the ITU (International Telecommunications Union), therefore the test is now known as the IMD (ITU-R).

 

How is it measured?

The common test signal is a pair of equal amplitude tones spaced 1 kHz apart. Nonlinearity in the unit causes intermodulation products between the two signals.

These are found by subtracting the two tones to find the first location at 1 kHz, then subtracting the second tone from twice the first tone, and then turning around and subtracting the first tone from twice the second, and so on.

Usually only the first two or three components are measured, but for the oft-seen case of 19 kHz and 20 kHz, only the 1 kHz component is measured.

 

Required Conditions.

Many variations exist for this test.

Therefore, the manufacturer needs to clearly spell out the two frequencies used, and their level.

The ratio is understood to be 1:1.

 

Correct: IMD (ITU-R) less than 0.01%, 19 kHz/20 kHz, 1:1, +4 dBu

 

Wrong: IMD less than 0.01%

[hpavictor]

Sper ca am inteles corect metoda lui @cri cri de determinare a distorsiunilor de tip IMD !

[sk24bpo]

Au venit si cablajele . Victor o sa citesc cu atentie ce ai postat si revin cu comentarii imediat, fiind ziua mea de nastere starea de ebri-ebrea ma distrage de la lucruri serioase. icon_jook

[retrosong]

LA MULTI ANI CRI CRI

[maxente]

Au venit si cablajele . Victor o sa citesc cu atentie ce ai postat si revin cu comentarii imediat, fiind ziua mea de nastere starea de ebri-ebrea ma distrage de la lucruri serioase. icon_jook

La multi ani si multa sanatate greierasule !!! Cat a costat o pereche de cablaje facute la fabrica (banuiesc ca la noi in tara, nu)?

[capabilu]

LA MULTI ANI @greierasul2006Multa sanatate si putere de munca

[sk24bpo]

Multumesc frumos baieti, sa va lustruiti ghetutele ca sa vina Mosu :-). Legat de IMD am ales varianta CCIF cu 19 si 20khz la +20dB, nivele egale. Un cablaj a costat destul de mult, cam 70 lei bucata si e facut in Bucuresti la PCboards.

[Vizitator doktort34]

O mica contributie controlati cineva de greseli.... In aceasta schema sar putea de folosit finalii darlington? am niste Sanken originali

[Vizitator doktort34]

ce spuneti se poate de folososit acest tip de softstart?

[sk24bpo]

In baza tranzistorilor finali in acest moment exista niste rezistori de 4,7 ohm, base-resistor. Rolul lor in principal ar fi ca tranzistorii finali sa nu se transforme la frecventa inalta in oscilator. Sincer nu stiu, la acei Sanken exista asa ceva ? Cu ceva modificari cred ca-i poti folosi dar necesita ceva calcule in plus fata de schema actuala astfel incat sa nu ai niciun fel de problema. Softstarul respectiv o sa suporte curenti mult mai mari fiind pus in secundar, asta poate duca catre o fiabilitate mai scazuta in timp.

[Vizitator doktort34]

la sfirsitul pdf este echivalent circuit

mn2488.pdf

mp1620.pdf

[sk24bpo]

Cum am sesizat ca sunt cativa oameni interesati de acest proiect, am hotarat sa fiu ceva mai atent cu partea de comunicare si sa postez fiecare avansare a constructiei amplificatorului. Astazi au mai sosit cateva piese. Comenzile sunt realizate exclusiv la firme mari din domeniu cu factura si certificate de conformitate tocmai pentru a evita sabotarea proiectului de catre piese dubioase. Azi au mai venit BF423-uri, finali TTC5200 de la Toshiba , zenere, conector de power cu siguranta si contact de pornire/oprire si nu in ultimul rand conectorii de semnal mic de la Neutrik, conectori integral din metal, foarte solid lucrati.

[maxente]

Iar intervin, sper sa nu te superiCand ai timp sa faci o masuratoare (cat de simpla) sa vezi ce distanta este intre acei finali (chiar si la prefinali daca ii ai) la hFE in procente intre pnp si npn ca sunt curios, mai ales ca sunt luati de la distribuitori consacrati