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When a Luxman clone is not a clone
When a Luxman clone is not a clone
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Old 16th February 2018, 03:10 PM   #1
carlmart is offline carlmart  Brazil
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Default When a Luxman clone is not a clone

For a long time I have been listening to a friend of mine's Luxman 5M20 power amp. A fantastic amplifier designed in the late '70s and still considered one of the best Luxman made. It can easily stand its own on any comparison with a more modern amp in audio quality and else.

Some months ago I decided to start my research to see if it was possible to clone it, but all the active parts are extinct now. So the question was: is it possible to use the Luxman as an inspiration, using modern active transistors?

It's mi belief that you can call something a clone when it's exactly alike, which in this case was not possible. So I decided to call this enterprise "The Shadow". And the first design was to be the Shadow 5M20.

As a start what I wanted to do was to simulate the Shadow 5M20 in Ltspice.

The first thing to do was to find capable replacements for each transistor. So I asked Keantoken to help me navigate this sea and see where we could get to.

The input dual fet was a very delicate point, and looking around on what was available I found the 2N5566 to be a suitable choice. I bought a pair. An LSK389 would certainly work too, but at the time it was hard to find. I didn't want to start this project until I got the dual fet.

So my modeling is all based on the 2N5566 at the input. Of course I tried other duals and even singles to see if they made any difference. But the simulation result changes were minimal.

You are free to look for the original Luxman 5M20 schematics. I will only put here the Shadow's.

Let's put the final version I got to, and then explain where it departs from the original design, first to model the electrical characteristics of the original drivers, and second to tame a glitch on the LTP stage.

So now let's see what are the first comments I get

Carlos
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File Type: jpg Shadow 5M20 schematic.jpg (116.7 KB, 1083 views)

Last edited by carlmart; 16th February 2018 at 03:14 PM.
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Old 16th February 2018, 03:44 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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"When a Luxman clone is not a clone"
A Clone is a close copy of the original and sometimes conflicts with copyright laws.
Be careful!
A Clone is not a Clone when it is original and made by the manufacturer.
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Old 16th February 2018, 04:46 PM   #3
PB2 is offline PB2  United States
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I find the placement of Q201,202 to be a bit odd since they are just EF's - not a big deal. Also 10 ohm off of one and 680 on the other, is that deliberate?

Last edited by PB2; 16th February 2018 at 05:15 PM.
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Old 16th February 2018, 04:58 PM   #4
llwhtt is offline llwhtt  United States
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The B12 is similar but with 10 Ohms and 220 Ohms.

Craig
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Old 16th February 2018, 05:14 PM   #5
carlmart is offline carlmart  Brazil
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This is strictly a personal project I'm sharing with you. I don't think Luxman might care for it. Goldmund clones are more popular here and nobody seems to care. With exactly the same parts types. I don't see why I should be careful.

In any case this is an investigative quest, to see what makes thinks tick.

Q202/202 placement and the different resistors values are exactly right.

Do you want to see the asc files?
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Old 16th February 2018, 05:16 PM   #6
PB2 is offline PB2  United States
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You have nothing to worry about as far as copyright or patents go for self use and learning.

Sure .asc's

Are you going to tell us why 10 ohm vs. 680?
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Old 16th February 2018, 06:01 PM   #7
carlmart is offline carlmart  Brazil
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Quote:
Originally Posted by PB2 View Post
Are you going to tell us why 10 ohm vs. 680?
Well, that's on the original circuit.
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Old 16th February 2018, 06:12 PM   #8
carlmart is offline carlmart  Brazil
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Here's the asc for this version.

Tell me if you need any models you may not have.
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File Type: asc Shadow.5M21.main.x32.asc (17.9 KB, 64 views)
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Old 16th February 2018, 06:14 PM   #9
forr is offline forr  France
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Quote:
Originally Posted by PB2 View Post
I find the placement of Q201,202 to be a bit odd since they are just EF's - not a big deal.
They buffer the inputs of the VAS transistors. Known as doing a lot of good. Such buffers are found in Self's single ended VAS, and in Cordell and Groner's differential VAS.
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Old 16th February 2018, 06:24 PM   #10
r_merola is offline r_merola  Brazil
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Default Your Clone is almost a perfect clone

Carlos,

I and Pete would like to see your asc file. Please send also models files applied in your project.

Remember I introduced you simulation files sending you a working template and some devices models file.

In your simulation files there are some differences from original Luxman circuit in output stage. Some changes you did improve amplifier distortions like the connection of output transistors emitter resistor to junction of 470R driver transistors. Why you add there 270pF in the first darlington transistor? Is it your idea or somebody suggested it to you?

There are other improvements that makes lots of results in this old circuit. To get results more near to real amplifier you must also add the signal stage voltage regulator. Luxman makes a little different voltage regulator for signal circuit.

What you did with the Chinese board you order to adapt this circuit?

What are your project objectives?
Regards from SP - Brazil
Ronaldo

Last edited by r_merola; 16th February 2018 at 06:30 PM.
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