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Old 8th August 2006, 09:04 PM   #1
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Default JLH with modern output transistors

I want to build the 1969 version of the JLH amplifier. As I have a couple of MJL4281A, I would like to use then as output devices, but I'm very afraid about oscilations.

How I can avoid this?
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Old 8th August 2006, 10:03 PM   #2
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Default Re: JLH with modern output transistors

Quote:
Originally posted by diegot
I want to build the 1969 version of the JLH amplifier. As I have a couple of MJL4281A, I would like to use then as output devices, but I'm very afraid about oscilations.

How I can avoid this?
I'm not certain if this is completely up to date or if you have had a look at it yet?

Shawn.
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Old 8th August 2006, 11:24 PM   #3
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Yes Shawn.

In my simulations the oscilation occours, but i'm not a very experienced with this programs.
So, I'm not the right person to help myself with the modifications.
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Old 9th August 2006, 03:29 AM   #4
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Quote:
Originally posted by diegot
Yes Shawn.

In my simulations the oscilation occours, but i'm not a very experienced with this programs.
So, I'm not the right person to help myself with the modifications.
I was just wondering if you could follow the suggested substitutes on the above link as the author seems to have much already figured out. You could also suggest your own substitutions to the author of "that site" and you may get some additional input.

There seems to be much information on the net by using "JHL amplifier" as a search in Google.

Also there is this and that

Cheers,

Shawn.
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Old 9th August 2006, 03:36 AM   #5
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It never ends...

These too!

I guess the info is plenty if you are willing to do a few searches and sort through a bunch of text.

Shawn.
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Old 9th August 2006, 11:23 PM   #6
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Default High BW Transistors may be trouble

I looked up the spec sheet on your transistors and see they have a BW of up to 34MHz. These are pretty fast and could certainly be trouble in the JLH69. From my understanding the design is fairly forgiving on slower transistors, but stability problems may result like you mention.

I just completed my JLH69 amp using MJL21193/4 parts. They have similar voltage/current ratings from your parts, but only have a 4MHz BW which is why I went with them.

For what it's worth, the amp sounds very nice....but very hot. I've got it running at 24V biased at 1.5amps.

Do you have PCBs or are you doing PTP wiring?
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Old 10th August 2006, 02:13 PM   #7
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I would like to do a PTP wiring, but this is another problem when using these devices.
I don't want to buy another devices because good transistors are hard to find and expensive, because most are fake in Brazil. A good source for me it is Farnell's local distribuitor, but as I sad before, it turns de project very expensive.

I have found a lot of information about JLH, but I don't have much time to look at all, today I will start to read the thread about the JLH/Graham output stage.
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Old 13th August 2006, 08:53 PM   #8
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have you read the very long "JLH 10 watt class A thread"? Its up around 1500 posts by now but might be more useful for you to start there.
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Old 13th August 2006, 09:05 PM   #9
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I'm reading it, may be in a week I will read all the posts.
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