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Old 17th April 2001, 10:40 AM   #11
Geoff is offline Geoff  United Kingdom
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Argo

I'll email you the URLs and transistor substitutions.

Geoff
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Old 17th April 2001, 10:47 AM   #12
argo is offline argo  Estonia
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Thank's
Finding a MJE371 was starting to develop me some gray hairs.

Argo
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Old 17th April 2001, 09:46 PM   #13
Asen is offline Asen  Bulgaria
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Default Transistors

Geoff,
Why don't you put the transistor substitutions here?
JLH says the devices are not critical for this amp. The output devices should be 4 MHz or better. The standart 2N3055 version is 0.8 MHz though (as I recall). I personaly have around Toshiba devices and will use them but it's interesting what other transistors will do the job. Substitutions for the BC and the 2N1711 is also interesting.
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Old 17th April 2001, 10:58 PM   #14
Geoff is offline Geoff  United Kingdom
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Asen

Will do - post transistor substitutes for the JLH amp that is.

A lot of 2N3055s are spec'ed higher these days, eg the fT for ON-Semi (Motorola) devices is 2.5MHz and for ST devices 3MHz according to the latest data sheets.

Geoff
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Old 18th April 2001, 03:59 PM   #15
Geoff is offline Geoff  United Kingdom
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Default Transistor Substitutions

There are a great many alternative transistors that could be used in this design (I have never understood why there are so many diffent transistors produced that perform the same or a similar function). The ones listed below are just a very small sample and are those that I know have worked well in this and similar amps and that should also be readily available. The case styles and pinouts are not necessarily the same as the original device.

BC212 - BC212L, BC556, BC560, 2SA872
2N1711 - BD139 (preferably selected for high hFE)
MJE371 - BD140
2N3055 - 2SC5200, 2SC3281, MJL3281A, TIP3055 (parallel pair)

Another suitable output device would be the MJL21194 or, if you prefer the TO-3 style case, the MJ21194.

Because to the high dissipation in the output devices (about 45W each), I suggest that any proposed output transistor should have a thermal resistance (junction to case) of less than 1 degC/W, or alternatively a parallel pair should be used (with 0R1 emitter resistors).

The BD140 will need a larger heatsink than the MJE371 since its thermal resistance (j-c) is much higher than the MJE371 and variations in the temperature of this device will cause the quiescent current to drift.

For a similar reason, R10 should be three 1ohm 3W resistors in parallel (or a single 0R33 7W or 10W) which should be stood-off from the pcb for good ventilation since temperature induced changes in the resistance value will also affect the quiescent current stability.

If alternative transistors are used, it may be necessary to alter the value of R1 (22k) to enable the output dc offset to be set to zero. Similarly, you may need to change D1 (4V7) or RV2 (4k7) to achieve the desired quiescent current. Any changes in required component value should be small. If you need a large change then it is likely that something is wrong elsewhere.

The component identification above refers to the circuit diagram (Fig 3) in the 1996 Electronics World article. Please note that there is an error in this diagram. The negative end of C4 should go to 0V (earth) not the -ve supply rail, otherwise supply rail ripple will be injected into the feedback path (TR4 emitter) causing excess hum. Also, there is an updated, but unpublished, circuit for the power supply using 5A ic voltage regulators. If anyone would like a copy then send me a note.

If anyone wishes to query alternative transistor substitutions either post a message or email me (the same goes for any other questions on this amp).

Geoff

[Edited by Geoff on 04-19-2001 at 06:16 AM]
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Old 19th April 2001, 12:57 PM   #16
rmgvs is offline rmgvs  Netherlands
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Listen:

Thanks to Geoff my adapted JLH amp works beautifully. Geoff suggested some minor changes. So now I have a working JLH old style but without the capacitor at the output. And without all the extra circuitry of the 1996-ciruit (which did not sound as good to my ears).

I honestly think this is the best sounding JLH-design around. I must listen more carefully, but I suspect this amp is even better than the Hiraga 20 Watt (which is a symmetrical design from the outset). I have the official factory Hiraga here in my house, so comparison should be easy.

Some more details:

I've build double mono, so in effect 2 amplifiers. Per amplifier I use a 2 x 16 Volt/6A toroidal transformer of English make. Then there are 4 capacitors of 6800 mF/25V per channel. There is no hum whatever. Just like Hiraga did I still use a 0,47 ohm/5 Watt resistor in the power rails. Now it is more easy to measure the current and even less hum is there. I use rugged Motorola 2N3055's because these sound very good (also in Hiraga designs), no need for improvements here. All other transistors are Motorala too. For the moment I set the amplifier on a relative small current of 1,25 Amperes (runnig at 21 Volts).

Yes, there still is some initial offset. The amplifier starts at sround 1 Volt and slowly goes to zero offset. Thereafter the offset is very stable. The initial offset is no problem for the speaker (okay, it is not a designer's wonder).

I suggest we put the working design on the net. For that I need the help of Geoff (who made this possible) and Matthijs (who started this project with me 2 years ago).

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Old 19th April 2001, 07:11 PM   #17
Asen is offline Asen  Bulgaria
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Geoff,
Thanks for the info.

RMGVS,
Updated old version JLH souns interesting. If the circuit's not a secret, you can publish it here or at least send it by e-mail to those who are interested. I'm deffinitely interested in it.

tutekov@hotmail.com

BTW - The 1 volt DC at the output bothers me. I know what hapens to my drivers when I conect a small 1.5V battery to the terminals to make a phase check.

[Edited by Asen on 04-19-2001 at 03:55 PM]
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Old 19th April 2001, 11:11 PM   #18
Geoff is offline Geoff  United Kingdom
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I have some very interesting (well they are to me :-)simulation figures comparing the %THD for the original 1969 design and the later 1996 update. I have also compared various output devices, input transistors and driver transistors.

There is too much data to post it here, but if you would like a copy then send me your email address.

Just to whet your appetite, the original design appears to offer better performance than the updated circuit and more expensive output transistors are not necessarily better.

Of course, simulations are not always accurate, but I think they are fair for comparisons. So far I have only simulated into an 8ohm load. When time permits I will repeat the exercise for 4ohm and probably a simulated speaker load.

Geoff
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Old 21st April 2001, 11:58 AM   #19
rmgvs is offline rmgvs  Netherlands
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A short impression of my listening experiences, the JLH 1969 plus symmetrical (as described above) versus the Hiraga 20 Watt factory-model.

Well, the Hiraga is the better one of these two. Both are very good for tranistor-standards and I guess the comparison as I have made it sofar is not fair. The Hiraga has a very big (several 100.000 mF's) power supply and carefully selected components. The 1969 JLH as I built it (same sort of big power supply as the Hiraga) sounds more like the Hiraga (and betters it at several points, though not over-all) than the newer symmetrical one. The new one is more transparent and 'quicker' than the old one though.

The schematics and some foto's are to be shown on the site of Matthijs Tinholt (near future). More details are to follow.
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Old 22nd April 2001, 12:06 PM   #20
Asen is offline Asen  Bulgaria
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Geoff,

The simulation results are very interesting. Thank you for sending them to me.

About the output cap of the 10W version.
Another way to avoid the use of output cap is to use two amps in parallel. This will require balanced signal source. This solution was mentioned in one of the old articles for the amp. This means all to be done X2. I can't even think about it.

BTW - I have Eagle files for the PSB of the 10 watter, made by me. I've taken measures for possible star-ground connecting. If s.o. is interested - let me know.


[Edited by Asen on 04-22-2001 at 06:23 AM]
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