The background noise is really quiet. It was not expected to offer any special merit in performance. This appears to arise and be particularly associated with transistor power amplifiers because most of these are easily able to deliver large amounts of power at supersonic frequencies, which the speakers in a high quality system will endeavour to present to the listener. Also, I want to notice, for example, the sound of the felt hammer of a piano hit the string, followed not only by the sound of the string vibrating but also the more subtle reflected and attenuated sounds of the hammer and its mechanism as these reverberate between the walls of the recording venue.
Each one has produced a very noticeable improvement and, in particular, the capacitor and the MJ transistor changes must be singled out as making a larger improvement than I had expected. However, some of these designs are now rendered obsolescent by changes in the availability of n, and others datashfet intended to provide levels of power output which are in excess of the requirements of a normal living room.
My main interest was in music, not in circuitry, so I thought it would be prudent to ask my ears what they thought of the alternatives, before I started to replace my hardware. This is because of the following conflicting demands: If an equivalent resistive dummy load is connected for bench-testing, all should be found to be well. The rectifier diodes specified are International Rectifier potted bridge types. Page 7 of 8 Electronics World, September Fig.
Whilst it should not be difficult to obtain fixed resistors with the required power rating, the preset potentiometer could be more of a problem since dtasheet more common ones are datasehet rated at 0. Regulated power supply for the Class-A amplifier uses boosters around the three-terminal regulators. It is interesting to compare the sound of the Iq ccs circuit with that of the bootstrap which shared many of the attributes of the ccs but had a lumpy and coloured, slightly congested characteristic which I found unpleasant.
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Minor text changes A Simple Voltage Regulator The following diagram is provided for anyone who would like to include a voltage regulator but who does not want to use one of the ic versions as in the updated, regulated supply for the design. It took me several weeks to find out that the sound of the amplifier changed just because of this removal of the resistor.
This results in instability and oscillation, which requires additional compensation such as a dominant pole capacitor. Scheme for 30W class-A system. I was immediately intrigued by the man and his ideas. One channel of the enhanced 15W Class-A design incorporating — amongst other things — direct loudspeaker coupling. Page 4 of 9 Wireless World, April Transistor protection circuit The current which flows in the output transistor chain Tr1, Tr2 is determined by the potential across Tr2, the values of R1 and R2, and the current gain and collector-base leakage current of Tr2.
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When I first switched on this prototype now it really was a prototype, I did not know if and how it would work there was a terrible hum. R10 has been retained to provide an easy means of measuring the quiescent current. I had received reports that the circuit modified to dual supply rails sounded better than the version, but I could not be sure that there were no other variables involved.
Both amplifiers stay way ahead of any transistor competition that I know of. Later, when everything worked properly, I could easily bypass this resistor with a few inches of thick wire. A number of interesting designs were offered. This sounded logical, it had no use after all. A simple modification which takes advantage of this effect is the use of a Darlington transistor such as an MJ for Tr1.
To minimise quiescent current and dc offset drift due to temperature rise, resistor R10 0R33 should be a 7W or 10W type or 3 x 1R0 3W in parallel. R10, the short-circuit current drawn from Tr1 and Tr2 will also be limited. Notes to Table 1: The amplifier now sounds far more powerful than many watt amplifiers that I have heard and owned but has a warmth, purity, delicacy and speed that has eluded them all.
This amplifier did not sound like a transistor amplifier at all, it sounded so round and full and gave an immense depth into the music. Fig 3 — The Higher Power Circuit When used with conventional speakers, this circuit can deliver over 40W provided the supply rail voltage and quiescent current are selected to suit a specific load impedance.
A much greater improvement was obtained when separate regulators were provided for each dayasheet, whilst retaining a common transformer, rectifier bridges and reservoir capacitors. Chapter 13 gives plenty of useful information on these topics and the rest of the book is worth reading as well. It should be emphasized that the differences observed in these experiments are small, and unlikely to be noticed except in direct side-by-side comparison.
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