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As a result of this publication, I suddenly found myself to be a vatasheet guru …………… Fig. A high frequency roll-off can then be obtained, if necessary, by connecting a small capacitor between the gate of the f.

The perceived stage width is not obviously any wider than before, although I couldn’t fault it before, on a good recording the stage width was almost limitless, on a bad recording it had definite limits. I must stress that the circuit diagram Figure 3. The 2NA is just about adequate with a good heatsink, but a larger power device such as the 2N is preferable.

Daasheet up-dated, I mean using more modern components and delivering a bit more power output. I acquired the newer version of the JLH on loan from a friend. Second voltage equation added JLH Class-A Update I had originally intended that this page would be a step-by-step record of the modifications carried out during the past year by one constructor — Tim Andrew.

However, some of these designs are now rendered obsolescent by changes in the availability of components, and others are intended to provide levels of power output which are in excess of the requirements of a normal living room. Where an unsmoothed h.

2N – Trans GP BJT NPN 40V 3-Pin TO-5

A friend of mine sent me the article that appeared in Electronics World. In this respect, and that of transient response, the class-A design is probably better than any circuit so far datashwet.

No blurring of image or loss of depth on loud moments. The rectifier diodes specified are International Rectifier potted bridge types.


Somehow it seems that you can hear two different capacitors. Most of the components needed I had somewhere lying around the house. At that time, there were audiophiles who decried the use of push-pull output stage layouts. From feedback I have received, higher quiescent currents tend to sound better so you may wish to bias the compromise between voltage and current accordingly whilst keeping the power dissipation in the output transistors at a safe level.


Original 10W Class-A design is still valid, but the power devices are now obsolete. However, this still left the output transformer — however well made — as a major source of transfer and frequency response non-linearities.

Since the main problem in the design of valve audio amplifiers lies in the difficulty in obtaining adequate performance from the output transformer, and since modern transistor circuit techniques allow the design of power amplifiers without output transformers, it seemed feasible to aim at a somewhat higher standard, 0. The supply rail voltages assume a regulated supply, with the consequential volt drop, and the quiescent current has been calculated from either the maximum current into 4ohm or, in the case of the 25 and 30Vrms secondary, the transistor power dissipation limit.

The focus or image position is better with the JLH. To minimise quiescent current and dc offset dataeheet due to temperature rise, resistor R10 0R33 should be a 7W or 10W type or 3 x 1R0 3W in parallel. The negative end of C4 should be connected to the 0V earth point and not the —22V supply rail as shown.

The amplifier gave a somewhat coloured overall view I guess, like many fine-sounding tubeamplifiers dwtasheet the s. Actually, he did not hear any significant differences between the ’69 and ’96 versions, good is good.

Simple Class A Amplifier transistor amplifiers

Also, as before, it fades away into the general noise background of the measurement system as the output power is reduced. This time, a substantial improvement over the 2Ns. At 1kHZ, this reduces the distortion level at just below the onset of clipping from about 0. It should be noted that either all of these components should be added or none at all, they are not alternatives.

This seemed to be beneficial with more smoothness and an improved “woody” quality with woodwind. You really have to bring in a normal commercial transistor amplifier to be able to hear the special qualities of the JLH again.

The little 10W JLH worked well with the ESL57s, albeit with some occasional clipping on louder passages, and Nick felt that a higher current version would best meet his needs. This was replaced with a 2SC Constructors of this amplifier have commented about its smooth sound, with many favourable comments and comparisons against valve designs and a few not so favourable comments with regard to its limited power output. This modification can also be carried out even if the feedback capacitor is not removed, and will give an improvement in PSRR with the corresponding reduction in hum.


To be fair, the differences between any of these were not very great — but they were audible. The necessary value of resistors R5 and R6 to give an entirely adequate accuracy in the mid-point voltage setting can be predicted, and the suggested amended values are shown.

I am very pleased that Tim has taken the time to supplement this with his own comments. Geoff gave me some extra advice, remove the 0. The transparency was all right though. This is because the base-emitter potential of this transistor controls the operating current, which in turn, affects the output dc offset.

For minimum distortion, Tr1 and Tr2 should be a matched pair. Relative 2nn697 straight single ended circuits, push-pull stages would give greater output power for a given distortion level. When the power supply, with or without an amplifier, is to be used with an r. Regulated power supply for the Class-A amplifier uses boosters around the three-terminal regulators. I previously suggested by-passing all electrolytic capacitors with a nF polypropylene capacitor in parallel with the electrolytic.

These requirements have combined to increase the complexity of the circuit 2697, and a well designed low-distortion class B power amplifier is no longer a simple or inexpensive thing to construct. Even so, the inclusion of a 3A fuse in the loudspeaker output line would seem prudent.

So, as a final thought, if any of you want to find out how datasheft top quality valve amplifier like the Williamson sounds, you can find out at a tenth of the cost of building one by making up this Class-A design. Various amplifier designs incorporating local negative feedback had been proposed. Improved smoothness and texture, with a more fluid sound. The offset is then rechecked when the amp is cold and the process repeated until the minimum offset variation has been obtained.