'오디오'에 해당되는 글 3건

  1. 2010.06.22 1969년식 JLH 의 온전한 구현
  2. 2010.06.22 여러가지의 JLH 버전들 (2)
  3. 2010.02.08 오디오 ) 에르노보벨리
2010.06.22 02:32

1969년식 JLH 의 온전한 구현

오디오 DIY 맨으로 JLH를 몇개 만들었지만 아주 온전하다고는 볼 수 없었는데 
출력석을 내 마음대로 썼기 때문이다. 

얼마 전 김형섭님이 완전한 JLH 의 워킹카피를 만드셨는데 전원부까지 완전 복원된 셈이다. 
방열기가 작지만 케이스에 넣을 때 큰 것으로 넣으면 되니 별 문제는 없다. 

아주 좋은 소리를 내는 DIY 오디오의 중요한 앰프하나가 완전 복원된 셈이다. 
케이스에 들어가면 아주 좋을 것 같다는 생각이 든다. 
긴 세월동안 들을 수 있는 얼마 안되는 앰프중에 하나다, 거하지도 않으며 10와트 정도의 출력으로
잘 조정되면 소리는 정말 최고다. 클래스 A의 성배같은 앰프중 하나다, 
나머지는 알레프와 F5 , hiraga 같은 앰프다. 물론 크렐 ksa-50이나 다른 상업용 앰프들도 중요하다.
그러나 10와트 언더에서는 오리지널과 양전원 버전은 정말 최고다. 

많은 앰프를 들어보았어도 변함은 없다.

회로는 오리지널 그대로 .. 

많은 사람들이 만들어 보았으면 하는 앰프이기도 하다. 
벤치마크 앰프로 수많은  영감을 낳게한 회로로 40년 이상 사람들의 사랑을 받고 있다. 
어느 정도 많은 사람들이 만들어 보면 음질과 회로에 대해 토론이 될 것 같기도 하다. 



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2010.06.22 02:31

여러가지의 JLH 버전들

이상하게도 이 글은 비공개로 되어 있었다. 
별 내용은 아니지만 무언가 더 끄적거리고 공개로 바꿀 예정이었던 것 같다.

1.  DOZ를 제외한 버전으로 제작에 참고한 것은 Nob라는 일본 사람의 글이다.
半導体アンプの7台目です。

JLH Class-A Ampを作成してみました。
このampは1969年にJohn Linsley HoodさんがWireless World という雑誌の4月号に発表した回路を基にしています。
その後1996年にupdateが発表され、1996年versionとして海外では数多く作られているようです。
さらに2003年にupdateが発表されています。
今回はこの2003年版を基に作成しました。

Circuit

回路はこのようになりました。

Parts

  • 出力段には2SC5200を採用しました。(千石で300円と安かったので)
  • ドライバ(と言えるか)には2SC3421。(これも千石で50円と安かったので)
  • 定電流回路には2SA1538を。(2SC3421のペアでこれも50円)
  • 初段およびその他の定電流回路には2SA1015。(秋月で1000円/200個)
  • 抵抗は0.33Ω5W以外、在庫があるものは金属皮膜、なければカーボンです。
  • コンデンサですが、電解はふつーのもの。カップリングのC1は結局外しました。

Making

試作したところ、やはりA級です。発熱が半端ではありません。
放熱を考えて、左右を別ケースとして、ケース自体を放熱器とすることにしました。

Adjust

半固定抵抗のVR1,2,3は中点にしておきます。
電源ONにして出力電位をチェックします。
VR1で出力電位を0Vに調整します。調整しきれないときはVR3を調整してください。
R10(0.33)の両端の電圧を測定し、0.33で割った値が出力電流となります。
出力電流はVR2で調節します。オリジナルでは1.5Aとか流していますが、0.5Aで充分でした。
この場合0.33Ωの両端の電圧は0.15V程度です。

Impression

これはもう、作ってみるしかないです。
低音の響きの豊かさは、これまで聞いていたものはいったいなんだったの、、、状態です。
特にウッドベースの音にはしびれます。

2N3055 version

その後、秋月で1つ150円で売っていた2N3055を使って、もう1セット作ってみました。
10個購入し、hFEを測定してpairをとりました。
hFEは、かなりバラツキがあるんで、面倒でもpairをとったほうがよいです。
2N3055はTO-3型なので、後面にTO-3用のheat sinkを付けるようにしました。
上からみた配置です。すかすかです。
後ろから見た図です。中心が電源。右に入力、左に出力。下側に2N3055が実装されています。
基板表面。
基板裏面。

2.  그런데 이 앰프는 본질적으로 2003 업데이트의 일본판이다,

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, recent ill health has meant that I have been unable to spend much time sitting at my pc so, rather than incur yet more delay in publishing the results, I have decided to write a short summary instead. I am very pleased that Tim has taken the time to supplement this with his own comments. At the end of the page is a brief update on the higher power ‘JLH for ESL’ circuit.

 

Tim is a professional musician (a classical concert pianist) and so I trust his subjective judgement when it comes to assessing the accuracy and realism of sound reproduction. Before Tim first contacted me, he had built a kit version of the 1996 design, which he had subsequently upgraded with higher quality components. Though Tim was happy with the results, he was keen to see if further improvements could be made to the sound quality and I was pleased to be able to suggest various circuit modifications, the majority of which subsequently proved to be very worthwhile. Each of the modifications was carried out separately so that the results could be evaluated on an individual basis.

 

Rather than show schematics for each stage, I will start off with the penultimate circuit and include some appropriate comments.

 

 

Fig 1 – The Penultimate Circuit

 

Transistor substitutions

 

One of the first modifications was to try alternative output transistors. The MJL3281A gave an audible indication of oscillation and was quickly rejected. The MJ21194 sounded significantly better than the 2N3055 but, in Tim’s layout, introduced a low-level hum. The MJ15003 gave a similar improvement to the MJ21194, but without the hum, and so was retained for future use. At a later stage, the BC212 and 2N1711 (Q4 and Q3) were replaced with the 2SA970 and 2SC3421.

 

Output dc offset control

 

The standard dc offset control circuitry (7815 and associated components) was replaced with a two transistor constant current source (Q5/Q6). I had various reasons for suggesting this change. Firstly, three terminal regulators are not renown for their quietness and so it did not seem like a good idea to inject the noisy output from one directly into the feedback loop. Also, I had received reports that certain 7815s oscillated due to the low current conditions under which they were being operated.

 

However, one of the main benefits of the ccs is that the output dc offset variation as the amp warms up is greatly reduced. This is because the temperature coefficient of the ccs acts in the opposite direction to that of the input transistor (Q4) and negates the effect of temperature changes in Q4 (assuming that the temperature of Q5 follows that of Q4). This cancellation of temperature coefficient effects can be put to further good use as will be seen later.

 

Quiescent current control

 

I first suggested that Tim try the 1969 bootstrap Iq control circuit, partly because the simulated distortion figures were half those for the 1996 version but mainly because I wanted to know how the two methods of Iq control compared in the same amplifier. I had received reports that the 1969 circuit (modified to dual supply rails) sounded better than the 1996 version, but I could not be sure that there were no other variables involved. As it turned out, the bootstrap circuit was a retrograde step and Tim immediately reverted to the original 1996 arrangement.

 

I still had some nagging doubts about the 1996 Iq control circuit and so I suggested introducing another constant current source (Q7/Q8). As with the bootstrap circuit, the simulated distortion figures were still half those for the 1996 version but with the added advantage that the distortion did not increase at low frequencies due to a reduction in capacitor effectiveness. A further advantage was an increase in amplifier efficiency (or maximum output). The maximum output voltage swing with the ccs is greater than that for the standard 1996 circuit and the maximum output current increases from around 1.35 to about 1.5 times the quiescent current.

 

When carrying out this modification, Tim reused the existing MJE371 for Q8. R10 has been retained to provide an easy means of measuring the quiescent current. To my relief, Tim found the second ccs to be worthwhile improvement.

 

Power supply

 

Whilst making the other alterations, Tim also took the opportunity to upgrade his power supply, initially by fitting larger bridge rectifiers and snubber capacitors and then by replacing the LM338s with ‘follower’ type discrete regulators, in line with my desire to remove unnecessary feedback loops from the overall circuit. The ‘follower’ regulators, basically a capacitance multiplier circuit with a fixed voltage reference (derived from a resistor fed by a ccs), gave a small improvement. A much greater improvement was obtained when separate regulators were provided for each amplifier, whilst retaining a common transformer, rectifier bridges and reservoir capacitors.

 

 

Fig 2 – The Final Circuit

 

Removal of the feedback capacitor

 

I had received emails from a couple of constructors reporting on the beneficial effects of removing the feedback capacitor (C4). I passed these comments on to Tim and he decided to try this modification for himself.

 

This modification should be treated with caution. I would not recommend trying it unless the dc offset ccs (Q5/Q6) modification has been done first because otherwise the output dc offset variation during the warm-up period is likely to be in the order of several hundred millivolts. In Tim’s case, with the dc offset ccs fitted, the output dc offset variation with the feedback capacitor removed was only slightly higher than that which he had previously with the standard 1996 circuit.

 

I believed that the offset variation could be reduced further by utilising the temperature coefficient of the Q5/Q6 ccs. I therefore suggested that R11 be made adjustable so that the temperature rise of Q5 could be varied. In this way, the output dc offset variation due to temperature changes in all stages of the amplifier could be compensated for, though this requires a lengthy, iterative process. With the amp at its normal operating temperature, the offset is adjusted to near zero using VR1. The offset when the amp is cold is then measured. VR3 is adjusted slightly, the amp is allowed to warm up and the offset is re-zeroed using VR1. The offset is then rechecked when the amp is cold and the process repeated until the minimum offset variation has been obtained. Tim has been able to achieve an output dc offset variation between switch-on and normal operating temperature of less than 50mV.

 


 

15/03/2003 Addendum

 

It has been brought to my attention (thanks Mietek and Rudy) that removing the feedback capacitor increases the hum level at the amplifier output, which is particularly noticeable with high sensitivity speakers and if a simple rectifier/capacitor power supply is used. I had not anticipated this, but some quick simulations soon indicated that removal of the feedback capacitor reduces the PSRR of the amp by a factor of about 3, causing any supply rail ripple to become more audible.

 

Fortunately, the cure for this problem is relatively simple. The PSRR of the input stage ccs can be improved by the addition of a single capacitor, connected between the junction of VR3/R11 (Fig 2) and the +ve supply rail. Doug Self’s ‘Audio Power Amplifier Design Handbook’ indicates that this modification will improve the PSRR of the ccs by about 10dB. A capacitor value of 47uF will suffice, but higher values (within reason) can be used.

 

The higher power (‘JLH for ESL’) circuit can be similarly modified by splitting R11 (Fig 3) into two 4k7 resistors in series and connecting the capacitor from the mid-point of these resistors to the +ve supply rail.

 

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.

 

 


 

17/08/2003 Addendum

 

Several constructors have found that adding the 47uF capacitor to the input stage ccs after having removed the dc blocking capacitor from the feedback network has caused the ccs to become unstable. This has manifest itself by relatively large output dc offset variations when taking voltage readings around the input circuit or when a hand is moved near to the ccs components.

 

In Tim’s case, a successful solution to this problem has been to replace Q5 and Q6 with ‘slower’ transistors. The MPSA56 appears to work well in the ccs. Alternatively, the 47uF capacitor could be removed and the PSRR of the ccs improved by omitting VR3 and replacing R11 with a 1mA constant current diode (or an FET wired as a ccs to give a similar current).

 

Adding base resistors (100R to 1k) to Q5 and Q6 and/or a 1k resistor between Q6c and Q4e should also help to improve stability.

 


 

Tim’s comments on the modifications (Updated 17/08/2003)

 

A few years ago I built the 1996 version JLH Class-A amplifier. 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. In its standard 1996 form, which I built from a kit using cheap components, my first impressions of its sound were of smoothness coupled with a relaxed liquid musical flow which I found far preferable to anything else which I had previously heard. In the context of my system with speaker efficiency somewhere around 87dB/W and with volume set correctly such as is appropriate for the perspective as recorded, or in other words "at a realistic level", its limited power output has never been a problem. The amplifier and its power supply have since been subject to extensive component substitutions and substantial circuit modifications.

 

As this section is about my impressions of the modifications that have been made to the circuit, a brief word on what I consider to be an "improvement" might be in order. I want to hear, with ease, the ambient signature of the recording venue, with a distinct impression of the space between its walls. 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. This is sometimes more noticeable in larger venues where the reflected sound arrives later, albeit weaker. Those delicate piano harmonics must be reproduced with the greatest accuracy, enabling subtle shadings of timbre to be noticed, again with ease. As a pianist, I want to hear the "pitch" of the note as it decays through to its quietest moment as acutely as possible, but I want no hint of hardness or roughness. With orchestral strings for example, where there are many instruments playing together, I don't want to hear one homogeneous group, and I want transparency, not brightness.

 

Professionally, I have a very close affinity with the piano. A difficult instrument to reproduce, it is perhaps more revealing of faults in the reproduction chain than can be the case with other instruments although the human voice is also very useful, for obvious reasons. It is my view that any modification that produces a more realistic rendition of the complex sound of this instrument, and the very subtle structure of its over-tones, will also represent an improvement in the accuracy of the amplifier overall. This has been the case during all my listening trials. It is worth mentioning that any modification which leads to an apparent decrease, for example in the level of the treble, will not necessarily be deemed to be an improvement, even if the new treble level is a welcome one, unless it is accompanied by an improvement elsewhere, improved detail or portrayal of nuance for example. From this, you will gather that I am not in the habit of 'voicing' the system, adjusting one thing to correct for another, but that I prefer to address the transparency of the system as a whole, with the aim of neutrality. Only then will I look at altering the balance, perhaps with a slight adjustment to the treble. It is through this approach (transparency first, followed by tonal balance) that I am now able to enjoy the vast majority of recordings in my collection, previously I had found many of these to be deficient in one way or another. Almost without exception, each modification has improved "difficult" recordings, whilst further improving others, often revealing a warmth and atmosphere, the previous lack of which had been wrongly attributed to the recording.

 

Though considerable time has been expended on both the amplifier and its power supply, I find it sobering to say the least that improvements made to power supply, specifically to the method of its delivery into various parts of the amplifier circuit have been so rewarding. The following is a list of the modifications that, with considerable help from Geoff, I have been able to carry out on the 1996 version of the JLH. Also included are my opinions of the results of these. Each substitution has been carried out individually, this has enabled subsequent and hopefully accurate (but not always positive!) evaluation. !

 

The Amplifier

 

Input capacitor.

The cheap polycarbonate(?) 1uF input capacitor was replaced with a  470nF Mcap "Audiophile" polypropylene type.  This led to an improvement in both bass firmness and in detail, treble sounded less bright. Later, I replaced the Mcap 470nF with Audio Note paper-in-oil 470nF. This sounds very different, smooth, warm and open with much more textural detail and firmness in the bass. There is some loss of focus when compared with the better plastic types and the positioning of instruments within the stage is not as precise as it could be, however none of the plastic types I have tried has approached the naturalness and openness of the paper-in-oil, particularly in the treble, and any shortcomings are easily forgiven in light of considerable improvements elsewhere.  This simple modification has since proved to be one of the most effective. I have also tried a polystyrene type (333nF) which sounds more detailed and focussed than anything else tried previously, though there is a tendency to sound a little "squeaky" on occasions (placing a small paper-in-oil capacitor across it improves this considerably), nevertheless I prefer this to most polypropylene types, many of which sound hard and slightly blurred to me. 

 

Resistors.

All standard grade metal film resistors in both critical and semi-critical parts of the circuit were replaced with tantalum film types.

Improved smoothness and texture, with a more fluid sound. A slight "mumbling" quality has been removed.

 

Output transistors.

The 2N3055s were replaced with MJ21194. In comparison with these the 2N3055s sound grey and rather diffused with less sense of authority, less detail and a more prominent treble quality. In contrast, the MJ21194s have a noticeably firmer sound with more ambience in the treble and greater detail. More natural generally. Reluctantly, they were removed from the circuit due to a faint hum which was not present with the 2N3055s.

Wanting to try something else, and now with the strong impression that the 2N3055s were less than ideal, I tried some MJ15003s.

This time, a substantial improvement over the 2N3055s. The MJ15003's bass is both tauter and more authoritative, with cleaner treble and greater textural detail.

 

DC offset control.

Replace 7815 with constant current source.

Result...Cleaner, smoother and weightier, with what can only be described as an organic flow. It was obviously all there before, but I suppose it was masked somewhat by the noise of the regulator. The volume can be increased further without sounding "loud".  A substantial improvement in all respects.

 

Iq control circuit.

The Iq control circuit was replaced with a bootstrap circuit (using an Elna "Silmic"). Less clarity was the result, with less tonal variety and focus, sounding more shut-in. The bootstrap simply doesn't sound as detailed. I assume this is due to the presence of the bootstrap capacitor connected to the signal path. Perhaps a Black Gate might improve things, but I suspect not enough to equal the MJE371 circuit which is more transparent, open, dynamic and uncoloured, the female voice sounds less "female" with the bootstrap circuit. It strengthens my theory that those who prefer the earlier version of the JLH do so because of the absence of the 7815 in the earlier circuit. I would go further and say that due to the absence of both a bootstrap capacitor, and an output capacitor, and with the ccs in place of the 7815, they might well prefer the 1996 version, all other things being equal.  My original Iq control circuit was very quickly re-instated!

 

It was not long until the original Iq control circuit was removed again, this time replaced with a constant current source and with better results this time. The initial reaction is to think that the treble detail and "air" have been diminished with a reduction of transparency. On prolonged listening things are rather different. There is actually more detail coming across, coupled with a growing sense of "rightness". Sounds are presented in a more natural light, gone is the spotlight effect with its admittedly pleasant but artificial treble detail. String harmonics are more balanced and proportioned with a sense that they now belong to the fundamental, part of the whole. The gaps between rapid piano notes are often missed by amplifiers, the JLH reproduces these well and they are even clearer now than before. Familiar recordings of woodwind and brass instruments sound remarkably smooth and natural. Differences in scale between smaller chamber music recordings and larger scale works are now more clearly conveyed. 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. Returning to the standard 1996 Iq circuit the next day was quite a relief, this time I have no plans return. I would miss the qualities that the Iq ccs circuit has brought to the amplifier. Final thought........Recommended for those who want to sit down for an evening of good music and a fine wine.

 

Feedback capacitor.

The 470uF Oscon (previously a very similar sounding 220uF Silmic) feedback capacitor was replaced with link (needing a small change in value to the DC offset ccs preset). The result of this change was a more open and natural treble with an increased sense of fluidity, depth and ease. Hot/cold offset variation are much greater without the feedback capacitor, in my circuit a variation of 150mV was observed (with the feedback capacitor it was around 65mV), this was reduced by controlling the current through the ccs in an effort to adjust the temperature compensation, but on a recent re-build of the circuit this arrangement proved ineffective and was subsequently removed.   

 

Driver transistor (2N1711).

This was replaced with a 2SC3421. As with the other transistor substitutions I have made in the JLH, the actual pitch of a note is more easily heard with the 2SC3421s. The same characteristics introduced by the Iq ccs circuit are still there but each single note now conveys more "meaning", more clearly defined in time. Timing, of course, is a musician’s greatest asset! The Iq ccs circuit introduced a smoother, rounder sound with a somewhat darker hue, the extra transparency and openness brought about by the 2SC3421s has lifted that slight darkness away whilst apparently retaining the smoothness and naturalness of the Iq ccs.

 

Input transistor.

The BC212 was replaced with 2SA970 with similar improvements to those noticed with the 2SC3421.

 

The Power supply.

 

Rectifier diodes.

Having tried snubber capacitors across the original "standard" diodes with no noticeable improvement, the originals (and snubbers) were replaced with schottky types. This seemed to be beneficial with more smoothness and an improved "woody" quality with woodwind.

 

Regulators.

The LM338K regulator circuit was replaced with a capacitance multiplier. The bass now conveys more authority and the amplifier sounds a little warmer, also with more detail. 

 

Dual regulators.

The single capacitance multiplier was replaced with a new (adapted) dual version allowing separate regulation for each channel. This warrants a detailed write-up so I shall list my observations in the order in which I noticed them and in descending order of their magnitude.


It is only now that I have heard the new dual power supply, that I can identify the sonic effects of the single supply. For the first, and most important observation, I shall use a single piano note as an illustration. With the single supply, when the note is struck there is an initial transient 'bump' as the hammer hits the string, followed by the decay, which starts after the initial 'bump' has subsided. With the dual supply, this initial transient is less 'loud' (better controlled?) and it carries more weight and meaning, this is followed by the decay which not only conveys better pitch, leading to more emotion and tunefulness, but the decay starts sooner, its first moments not masked by the apparently exaggerated impact of the hammer blow introduced by the single supply. Also, due to the increased definition, the note seems to decay more slowly, incidentally this is one of the more significant differences between a small grand piano, and a large 'concert' grand where, due to the increased string length of the larger instrument, its sustaining power is much greater. A single note can therefore be followed more easily from start to finish. The tonal signature and real colour of all instruments are now better conveyed.


There is also a significant improvement in the quality of the treble where there is greater transparency. For most of the time, it is less obvious than before, and smoother, but little details previously almost un-noticed are conveyed more clearly and with improved texture. This treble improvement was unexpected and is a constant pleasure!


The third improvement I have noticed is an improvement in the positioning of individual instruments. 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. This hasn't changed, what has improved is the positioning of instruments within the limitations of the stage width imposed by the recording, with instruments on the edge of the stage more clearly conveyed in space with a better "floating" feel to the acoustic coupled with a more acute sense of the venue.

 

Filter capacitors.

Having previously bypassed the standard grade electrolytics with Elna "Silmic" 100uF with little, if any improvement, this time the original capacitors (30,000uF per rail) were replaced entirely with "Silmics" (18,000uF per rail).  A superb improvement in definition. The scale of which came as quite a surprise.

 

Conclusion.

I consider the JLH in its present form, to be a very special amplifier. Its ability to portray the acute sense of emotion and excitement contained in a fine performance, through its accuracy and with such grace, coupled with its ability to scale music's dynamic heights so convincingly, is rare. My most sincere thanks to Geoff who, through spending so much time helping others like me, has so far not had time to carry out these modifications for himself *.

 

* Unfortunately not the only reason - Geoff

 


 

Higher power circuit

 

The ‘JLH for ESL’ circuit, which can be used with conventional speakers as well as electrostatics, already has a ccs for dc offset adjustment but it would benefit from the other modifications outlined above. In particular, the use of a ccs for quiescent current adjustment obviates the need for a high power preset, which can sometimes be hard to find.

 

 

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. The supply rail voltage needs to be a couple of volts higher than the peak output voltage swing and the total quiescent current should be about 0.7 times the maximum output current. The power dissipated in each output transistor (supply rail voltage times half the quiescent current) should be limited to about 40 to 45W, assuming decent sized heatsinks are used (0.6 to 0.8degC/W per transistor).

 

The peak load voltage and current can be calculated from required power and the speaker’s impedance in the normal way using:

 

Vpk = sqrt(2*Pwr*Rload)  and  Ipk = sqrt(2*Pwr/Rload)

 

To allow for speaker impedance variations, I would suggest that current is calculated using ¾ of the speaker’s nominal impedance and voltage using 1½ times the nominal value. Of course, you are free to make your own assumptions about speaker impedance variations and to calculate the required supply rail voltage and quiescent current accordingly. 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).

 

The following table indicates the maximum power output into 8, 6 and 4ohm loads for some standard transformer secondary voltages, assuming a resistive load and without any allowance for the impedance variations mentioned above. 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.

 

Secondary

Voltage (Vrms)

Supply Rail

Voltage (V)

Quiescent

Current (A)

Power

8ohm (W)

Power

6ohm (W)

Power

4ohm (W)

18

18

2.8

16

21

32

22

23

3.7

28

37

56

25

28

3.2

42

56

42

30

33

2.7

60

45

30

 

3.  http://www.tinholt.eu/jlhevolution.htm 이것은 아직 분석을 안했다.

Schematic amp
4. 그런데 정말 재미있는 분석은 정작 pass 가 만든 부분이다.   (내용은 첨부 화일 참조)

The PLH Amplifier By Nelson Pass
Introduction: The JLH Amplifier
In 1969 John Linsley쵩ood wrote in Wireless World:
During the past few years a number of excellent designs have been published for
domestic audio amplifiers. 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. Also, most designs have tended to be rather complex.
In the circumstances it seemed worth while to consider just how simple a design could be
made which would give adequate output power together with a standard of performance
which was beyond reproach, and this study has resulted in the present design.
He then described a Class A power amplifier using three gain stages of Bipolar transistors in a
topology which continues to be admired for its elegant simplicity and sound quality.
The centerpiece of this design is the middle stage, an NPN transistor used as a phase splitter,
simultaneously driving the positive half of the output stage and the negative half with symmetric
signals of opposite phase.


Figure 1 shows a simplified version of the JLH topology. Signal input appears at the Base of
Q1, and is amplified and inverted to drive the Base of Q2. Q2 acts as a gain device and also a
signal splitter, driving both Q3 and Q4 simultaneously, but out of phase with each other. Q3 and
Q4 form the output transistors, Q3 operating as a Common Emitter gain device, contributing
current and voltage gain, and Q4 operating as a Common Collector device contributing only
current gain. The resistors provide bias for the system, and R1 and R2 feed the output of the
amplifier in a loop back to the emitter of Q1.
Q2 is the heart of the design, and in my opinion, it is the elegant economy with which it performs
the complementary gain to drive the output devices that gives the circuit its classic beauty.

The JLH was designed at a time when ``the tube era was in decline'' and the new generation of
designers were pulling out all the stops to create big science amplifiers ?pure voltage sources
with high power and infinitesimal distortion -- complex circuits with lots of feedback.
36 years and a little progress later, we can perhaps appreciate the simple charm of the JLH
topology as an exercise in minimalism, but if you haven't listened to one, you might be very
surprised by the quality of sound, which is extraordinarily good within it's power limitations. If
you have efficient speakers and you like to listen to two춃hannel sound at reasonable levels, the
JLH is still in the top rank.
The amplifier has reasonable specifications; nothing special that isn't wildly exceeded by a $3
chip, but it produces real music. Its flaws are not irritating and it does a wonderful job wringing
more music out of modern recordings and even MP3's. I can't think of another transistor design
from that era that works as well.
Figure 2 shows the circuit rendered more completely, but for more extensive documentation on
the versions of the JLH amplifier, I recommend The Class A Amplifier Site:
www.tcaas.btinternet.co.uk
In Figure 2 additional details of setting up the DC bias for each device are shown, where
capacitors are used to separate DC values from AC values. C1 separates feedback from bias
current. C2 separates input signal from input DC bias voltage and C3 blocks the output DC of
the amplifier from the load. C4 removes supply noise from the voltage powering the front end of
the amplifier, and C5 forms a ``bootstrap'' circuit, making resistors R5 and R6 behave more like a
constant current source at audio frequencies.
The original JLH amplifier has approximately 55 dB of open loop gain divided into 22 dB of
amplifier gain and about 33 dB of feedback. As detailed in the original article, it delivered 10
watts at approximately .1% harmonic distortion or less.

The amplifier's popular longevity speaks volumes about the quality of its sound, and this is
understandable given its simplicity coupled with excellent measured performance. It has a
particularly tube춍ike quality compared to the more complex solid춖tate designs of the era and
since.
The distortion is largely 2 nd harmonic, and is closely proportional to the output voltage. This
means that .01% distortion at .1 watts becomes 1% at 10 watts, and you can draw a pretty
straight line between the two points on a logarithmic graph. Such a curve is characteristic of a
single춅nded output topology, and there have been arguments regarding whether or not the
output stage is single춅nded Class A, push춑ull Class A or a mixture of both. We will be having
some fun with that later.
One flaw in the original JLH design was that its bias current, that idling current which flows
through the parts of the circuit, had some dependency on the power supply voltage, resulting in
altered performance for different AC line voltages. Power supply regulation solves this problem
neatly, but there were other ways this was addressed in later versions of the circuit.
Newer JLH Circuits
John Linsley쵩ood published an update to the amplifier in 1996 that addressed bias stability
issues, parts substitutions, and provided a version that had a direct춃oupled output, eliminating
the output capacitor. At the same time, it was in many ways the same amplifier, the measured
performance being very similar.
The JLH circuit continues to be interesting to the audiophile community and has been the
subject of several updates. Figures 3 and 4 show simplified schematics of later generations of
JLH amplifiers.

Figure 3 shows a simplified schematic of the 1996 version published by John Linsley쵩ood that
fixes the bias stability issue with the addition of Z1 and the Q5 portion of the circuit. This version
also direct coupled the output of the amplifier, using dual supply rails.
In 2000 someone else produced the circuit seen in Figure 4, where constant current sources are
used to bias the first two gain stages, giving good power supply rejection to the circuit. This
version also doubled up on the number of output devices. You will notice that Fig 1 -- 4 have
their feedback loop addressing the Emitter of the feedback transistor. Nowadays they have
gotten fancy and call it ``current feedback''.
Just for your entertainment, I cobbled together the circuit of Figure 5 shows an example with a
differential input. An obvious variation, but I haven't seen it used. You can drive this input stage
with a balanced signal by lifting C1 from ground and driving it as a negative input. At 100 ohms
each, R6 and R7 will give this input about the same open loop gain as the original input
transistor with the 220 ohms degeneration of the original feedback impedance.

I recently measured the performance of a working copy of the circuit of Figure 4. It had 17.5 volt
supply rails and was biased at about 2 amps per channel. The open loop gain is also about 55
dB into 8 ohms, and its measured performance is comparable to the original circuit.
Figure 6 shows the distortion versus output power. The bandwidth of the amplifier is --3 dB at
100 KHz, the damping factor is about 35, and the distortion versus frequency is fairly flat, rising
slightly at 20 KHz.
The PLH Amplifier
One of the issues that arise from adding gain stages to amplifiers is that while they increase the
open loop gain and allow more feedback correction, they themselves are the source of
additional distortion. While the extra feedback can lower the distortion numbers, usually the
additional circuitry is reflected in a more complex distortion character having higher order
harmonics and inter춎odulation components. These are generally agreed to be less musical
sounding.
Michael Cunningham wrote, ``Novelists must usually decide what degree of slavish accuracy
would make their stories more alive, and what degree would make them less.'' The amplifier
designer has a similar problem to solve. It's not hard to make an amplifier that measures well --
it's comparatively hard to please audiophiles.
My own approach is to make the signal path as simple as possible, work to lower the distortion
of that basic circuit before feedback is applied, and then apply minimal (or no) feedback, largely
in agreement with the comments in Linsley쵩ood's original article. The result is not always the
best objective measurements, but the sound is often interesting.
The 3춖tage topology of the JLH amplifier routinely uses simple Class A operation and about 33
DB negative feedback to achieve this performance, and this lured me to consider what kind of
amplifier I could achieve with an even simpler circuit and less feedback. The output stage and
the intermediate phase splitter cannot be dispensed with and still resemble a JLH, but you can
certainly remove the input transistor.

4.  diyaudio 에 나오는 쓰레드 2003년의 글에는 여러가지 대화가 나오고 170여 페이지 뷰를 넘어간다.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3075&perpage=10&pagenumber=36


http://www.diyaudio.com/forums/showthread/t-40355.html



그중의 하나는 없어진 웹사이트에 있던 내용이다.
Graham Maynard presented a jlh output class A amp in the september Electronics World

I뭭e abstracted the input as an ideal gm vccs and used ideal current sources to look at the output stage operation ?

http://www.zero-distortion.com/test...wertrans_05.htm

suggests 2sc3281 is similar to Graham뭩 2sc5200 output devices, I was able to find onsemi spice model for mj3281 and already had fairchild bd139 model for a driver



(despite the LTSwCad file header names this is the mj3281 sim)

my question/issue is the poor current division as Vce gets within 5 V of the rail with the 200 V device, the ancient 2n3055 actually looks much better in this regard (i1 has to go up to ~150mA due to the low hfe of the 3055 model in LtSwCad) ?so is this real or modeling error?

Given that spice transistors are perfectly matched and only deviate due to differential biasing this is probably optimistically good current division so another question is how can the jlh deserve its reputation when built by diyers lacking power curve tracers to match the output devices?

And finally the sim offers an example of how to step a parameter in LtSwCad Spice for mikes

Added spice directive:

.step param A LIST .17 .35 .7 1.4

V5 input voltage source amplitude defined with {A} as parameter which is stepped from LIST in .step directive

SINE(0 {A} 2K)

see LTSpice asc file:

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2010.02.08 22:39

오디오 ) 에르노보벨리

2010.8 .15 추가:
 보벨리의 사이트는 곧 폐쇄될 것 같다. 
더글라스 셀프의 사이트가 폐쇄된 것도 오디오 자작파들의 큰 손실인데 다시 보벨리의 사이트마저 문을 닫는다. 
좋은 소리의 중요성은 줄어들지 않을 것 같은데 뛰어난 디자이너들이 점차 손을 놓고 있다. 
아마 사업성이 감소하고 관심도 줄어든 탓으로 보인다. 
사실 우리나라도 마찬가지다. 

-----------------------
상당히 오랜기간 존경을 받아온 회로 디자이너다. 특별히 욕심을 부린 적도 없고 오랜 동안 오픈소스에 가깝게 활동한 분이다. 
만약  오디오 특히 fet 회로에 대해 배우고 싶다면 이  사이트의 글글을 읽어 보면 아마 많은 것을 배우게 될 것으로 안다. 
사진은 전형적인 오디오 작업 세팅이다. 공간만 더 있다면 이렇게 했으면 좋겠다고 항상 부러워하고 있다. 
그보다는 시간이 더 절박하지만 ... 아무튼 사진이 분위기는 정말 멋지지 않은가?



Who is BORBELY AUDIO?

BORBELY AUDIO�s primary objective is to develop and sell high quality kits for DIY audio amateurs. We started 25 years ago by offering hard-to-find components to Mr. Borbely�s amplifier designs, which were published in the AUDIO AMATEUR in the USA and the HIGH FIDELITY in Denmark. Today we are offering high quality kits and audiophile components to the audio amateur community and to OEM customers.



Mr. Borbely at his workbench, testing a custom-made ALL-FET lineamp.
About Mr. Borbely...
Mr. Borbely received an MSc Degree in Electronic Engineering from the Norwegian Institute of Technology, University of Trondheim. He worked seven years as a design engineer at the Norwegian Broadcasting Corp., developing studio equipment, both in tube and in semiconductor technology. In 1969 he moved to the US and worked for David Hafler at DYNACO. Mr. Borbely was named Director of Engineering for DYNACO in 1972. He developed the Cascode output stage for the Stereo 400 power amplifier, and the DYNATUNE circuit for the FM5 FM tuner, for which he received a US patent. In the 70s he worked at Motorola Semiconductor, developing power amplifiers, low-noise preamplifiers and FM-tuners. Some of this work was put to good use, when he joined The David Hafler Company as Director of Engineering. Mr. Borbely developed the DH101 preamplifier and the DH200 power amplifier, which was the first one to use MOSFETs in the US. From 1980 until 1997 he worked for National Semiconductor in Germany as its Technical Training Manager. In 1984 Mr. Borbely and his wife Irene started BORBELY AUDIO, which is selling high quality Kits to end-users. Since 1982 he has been publishing his designs in the Audio Amateur Publications (Audio Amateur/Audio Electronics, Speaker Builder, Glass Audio and now in AudioXpress). In the last several years Mr. Borbely has developed a line of ALL-FET audio amplifiers. Besides the kit business, Mr. Borbely is designing audio products for OEM customers. 

A selection of Erno Borbely�s articles from the Audio Amateur Publications:
  • 60W MOSFET Power Amplifier, Audio Amateur, 2/82
  • Third Generation MOSFETs: The Servo 100 (Part I), Audio Amateur, 1/84
  • Third Generation MOSFETs: The DC 100 (Part II), Audio Amateur, 2/84
  • The Borbely Preamp, Part I, Audio Amateur, 4/85
  • The Borbely Preamp, Part II, Audio Amateur, 1/86
  • A Moving Coil Preamp, Part I, Audio Amateur, 4/86
  • A Moving Coil Preamp, Part II, Audio Amateur, 1/87
  • A Simple Curve Tracer, Part I, Audio Amateur, 4/90
  • A Simple Curve Tracer, Part II, Audio Amateur, 1/91
  • Balanced Audio Amplifiers, Audio Amateur, 1/91
  • The New Borbely Preamp: The Modules, Audio Amateur, 2/91
  • The Gaertner-Borbely Line-Level Preamp, Part I, Audio Amateur, 1/93
  • The Gaertner-Borbely Line-Level Preamp, Part II, Audio Amateur, 2/93
  • New Power Amp Modules, Part I, Audio Amateur, 3/93
  • New Power Amp Modules, Part II, Audio Amateur, 4/93
  • Modular Active Crossovers, Speaker Builder, 1/94
  • A 15W SE Power Amp With 6C33C-B, Glass Audio, 5/96
  • A Differential Line Amp with Tubes, Glass Audio, 1/97
  • An MC/MM Preamplifier with Tubes, Glass Audio, 2/97
  • Class-A Power Modules, Audio Electronics, 4/97
  • Low-Voltage Tube/MOSFET Line Amplifier, Glass Audio, 1/98
  • JFETS: The New Frontier, Part 1, Audio Electronics, 5/99
  • JFETS: The New Frontier, Part 2, Audio Electronics, 6/99
  • The ALL-FET Line Amp, AudioXpress, 5/02
  • Starter Kits Part 1: EB-604/410 All-JFET Line Amp, AudioXpress, 3/05
  • A Hybrid TUBE/MOSFET Headphone Amplifier, AudioXpress, 4/05 


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