Linsley Hood SE 10W amp

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power supply

Hi Asen,
i built JLH's 1968 design about a year ago. It worked very well with my speakers, at that time 99dB/W direct radiators.
i used a 460VA toroid as the power supply with ordinary bridge rectification and about 100000uF (0.1F).
There are some photos etc on my website.

These days the chassis houses an Aleph 3 variant.

BTW, shouldn't this thread be in the SolidState forum?
I've run some simulations of it trying to decide if I want to build it or not. Instead of the original, I would get a copy of the update he did to it in 1996, it has more power (15W), better current control, and uses parts that are available today.

I've run some sims with much better, modern parts (MJL1302 outpus, BC559 inputs, etc) and it definitely benefits from the upgrade. It also does 25W before clipping with these parts.

Mind you, this is all simulated, so YMMV...

Hi Asen

I've looked at the JLH 15w myself, but I have to many projects going on right now, so i'm not reallly getting any further. If you like, you can get more info about the updated version by following this link:

BTW, I think Jon is right, getting audio-grade parts for the design is worth the extra cost - it is a very promising design with lots of potential.

The URL in the last posting is out of date. The correct one is:

There are several other sites on the Web with write-ups on this amp. If anyone wants the URLs, let me know.

To the previous correspondents, stop simulating and get building (preferably the 1996 version), you won't be disappointed!

If anyone wants advice about this amp then contact me. It is my pet project so I know it well.
I've build the 10 Watter a few years ago and find that this amplifier still is among the best (despite the capacitor at the output).

Then I heard the Hart-kit from a friend of mine. This kit takes the later symmetrical Linsley-Hood amplifier as a basis. I found the results inferior on all counts via-a-vis my old amplifier. Okay, I used a really big power supply and first class components..

Still I wondered how to get rid of the capacitor. I then used the original 1969 circuit and modified it for a symmetrical power supply. Only a few changes have to be made (I have the schematics in gif format but don't know how to display that on this page).

Now some strange things happened. Firstly: when the amplifier is turned on, there is a large temporary DC-offset voltage at the output (10-15 Volts). After 10 seconds it fades away to zero Volts. Secondly: there is a big very big hum (while the original schematics with the same components is dead quite). I can only get rid of the ripple by using a big power resistor (3-4 ohms, 15 Watts) in the power rails (plus and minus rails). I want to avoid regulated supplies because I think the less electronic stuff the better. But okay, it works.

Some friends of mine have had the same experience and not solved the problem till this day. Anybody suggestions?

By the way: the sound of the 'old-plus' version is great!


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.
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).


[Edited by Geoff on 04-19-2001 at 06:16 AM]

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).
Thanks for the info.

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.

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]
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.

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.

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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