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Old 15th October 2004, 07:00 AM   #1001
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serosmaness. NO. I think it is 0.1 ohm or to put ot another way one tenth of an ohm. The m is for milli not meg, okay? Check to be sure but I think you'll find it's a low value.
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Old 15th October 2004, 10:28 AM   #1002
ralf is offline ralf  Germany
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Default Emiter resistor

..as i know emiter resistors are regular low values, mostly under 1 Ohm.

Since i have build few of the JLH`s i can tell you that the resistors are 0,1 = 0R1 Ohm for the JLH for ESL and 0,33 = 0R33 Ohms for the JLH Update version

Ralf
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Old 15th October 2004, 02:02 PM   #1003
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Thanks. I went to bed last night and realized how much of a moron I was.
Thanks. Steve
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Old 17th October 2004, 05:14 PM   #1004
SunRa is offline SunRa  Romania
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Hi, well I guess I'll start one too. In facti allready started..i will use KD503 as finals. The rest are those in the schematic (2SA970, 2SA1358 etc.) but i'd like to use somting like SC3281..as tymo said..are there any stability problems?
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Old 17th October 2004, 09:57 PM   #1005
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Default 2N3055 again, the last return hihi

Hi people. I donīt wish opine about the polemic discussion about 2N3055, not that I donīt have one, but I (my dad, better saying) have a lot of 2N3055 transistor, so I have a easy option. Iīm looking for projects of power amplifier with then. I would like with single power supply and simetrical power supply too.
I thank for sugestions and schematics.
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Old 18th October 2004, 03:23 PM   #1006
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Use this ones rather like hobnails in your belt .
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Old 23rd October 2004, 07:05 PM   #1007
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Default newbie question on jlh

I compilated this JLH 1969-1997 design. I plan to mount the PCB on the heatsink on the opposite side than the MJ15003. I have two 1.05C°/W heatsinks "H" shaped with 35 x 150mm two faces between the vertical "wings". I must eliminate the 1996s Tr5 and specially its heatsink and revert to the 1969 arrangement R2-R1. (R8-R5 in my design). I plan to use only +- 12 to 15V / 1A in order to have a small amount of dissipated heat.
So, please can anybody help me with some questions (I mean answers):

1. Is this the right physical position for C2-C1 ? In the Tim Andrew version they are mounted close to the output stage.

2. Do I really need the 0.33 resistors? (in blue on my diagram). They will be hot too I suppose.

3. The drawing is intended to de derivated directly into the PCB. Does it has the wright configuration?

4. Geoff says somewhere that one of Q5 or Q6 can be replaced with a green LED. Which of them and how ?

Could anybody help me ?. (I’m a newbee as you can see). Many thanks


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Old 24th October 2004, 11:01 AM   #1008
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Default Re: newbie question on jlh

[QUOTE]Originally posted by numbernine

1. Is this the right physical position for C2-C1 ? In the Tim Andrew version they are mounted close to the output stage.
In my opinion they should be mounted near to the point where the rail voltage enters your pcb. Do not forget to use a 0.1uF mkp in parallel.


2. Do I really need the 0.33 resistors? (in blue on my diagram). They will be hot too I suppose.

At the given bias they will dissipate 0.33W and thus not get quit hot.

I think you can do without the resistors.

Success.
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Old 24th October 2004, 11:40 AM   #1009
mikelm is offline mikelm  England
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it's worth trying these resistors before you dismiss them completely.

I tried an emmiter resistor in just the lower transistor and I liked the result.

perhaps try it with

none

one

both

I would be interested to hear what conclusions you come to

good luck

mike
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Old 24th October 2004, 08:05 PM   #1010
Geoff is offline Geoff  United Kingdom
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Default Re: newbie question on jlh

Quote:
Originally posted by numbernine

1. Is this the right physical position for C2-C1 ? In the Tim Andrew version they are mounted close to the output stage.
As Dutch DIY has already stated, the rail decoupling capacitors should be connected close to the point where the supply lines are connected to the pcb. They should also be close to the points where the output transistors are connected to the rails. This therefore determines the optimum layout for the output transistor and supply rail wiring.

Quote:
2. Do I really need the 0.33 resistors? (in blue on my diagram). They will be hot too I suppose.
0R33 resistors are a little larger than necessary for emitter degeneration. Normally, 0R1 or 0R22 would be used. In theory, and in simulation, emitter degeneration gives an improvement in distortion levels, but when Rod Elliott measured his DoZ (a similar output stage to the JLH) he found no difference in distortion with or without emitter degeneration. However, as Mike has said, it can be worth trying both to see if you can hear a difference and, if so, which you consider to be more enjoyable.

Quote:
4. Geoff says somewhere that one of Q5 or Q6 can be replaced with a green LED. Which of them and how ?
I don't remember saying this but, if I did, it would have been for the dc offset ccs (ie the one connected to the input transistor feedback node). This can be either a two-transistor ccs or an LED/transistor ccs (or even an FET connected as an adjustable ccs) but I favour the two-transistor ccs because the tempco of the ccs control transistor offsets that of the input transistor thus reducing output dc offset variations with changes in ambient temperature.

Edit:

Your C3 is not connected properly. If you intend it to improve the PSRR of the ccs, you need to split your R3 into two 4k7 resistors and connect the negative end of C3 to the mid-point of these two resistors. However, as you have included the dc blocking feedback capacitor (C4), C3 should be unnecessary unless you are using very efficient speakers. Fitting C3 (albeit with C4 removed) has caused some instability in this ccs in a couple of cases when using 2SA970 transistors. If you really want to improve the PSRR of this ccs then I would suggest using an FET, connected as a ccs, in place of R3.

Also, I would suggest making your R8 a preset so that you can adjust the output stage quiescent current to the required value (the necessary resistance for R8 will depend on the gain of your output transistors and this can vary quite widely)

Geoff
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