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Old 27th April 2012, 10:36 PM   #1
vyju is offline vyju  India
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Default Luxman m4000 transistors

Hi,

My Luxman M4000 power amp suddenly started acting up last week.

It was working fine but suddenly the left channel cutoff. On switching off and
powering it on again both channels worked but the left channel cut off after a
few seconds.

I took the amp to a service tech. who traced the fault to the front end
transistors.(first differential amplifiers)

The transistors are 2SA810. Part number Q301 and Q302 as per the M4000
service manual.

I require four of these transistors.(I will change the ones in the right channel
also.)

Please tell me a source for these transistors.

Regards
Rajiv
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Old 28th April 2012, 05:45 AM   #2
vyju is offline vyju  India
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Hi,


What are the equivalent transistors for the 2SA810 that can be used ?

Regards
Rajiv
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Old 28th April 2012, 07:24 AM   #3
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Hi,

2SA970 should work. Very similar specs. I've always used these when replacing differential pairs in vintage gear.

They are rated at 120V vs 150 of the originals, though.
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Old 29th April 2012, 04:37 AM   #4
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The M4000 differential input runs at +/-68V, the 2SA970 will be running above its rated voltage. Try a 2N5401 instead.
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Old 29th April 2012, 07:08 AM   #5
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I suspected something such.

Also remember to get a handful of them, not just the bare minimum. Get at least 10, preferably more. You need to match them closely (use a multimeter with hFE testing capability), for the best possible performance.
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Old 29th April 2012, 12:17 PM   #6
djk is offline djk
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The diff pair only need withstand the one rail voltage, not the P-P.

The Vas must withstand the P-P.

The Luxman M4000 suffers from poor solder joints and speaker relay issues as well. I would check for these issues before replacing the diff pairs (unless they actually measure defective).
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Old 29th April 2012, 12:24 PM   #7
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Replacing the differential pair is always a good idea in vintage equipment. Regardless if they work or not. They are rarely well matched, and having the lowest possible dc offset is, at least to me, an important thing.
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Old 29th April 2012, 10:40 PM   #8
djk is offline djk
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That is probably not the problem in this amplifier, unless one of them has actually failed.

Cross-coupled full-complementary diff inputs are subject to temperature drift, no matter how well they are matched.
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Old 30th April 2012, 06:41 AM   #9
vyju is offline vyju  India
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Hi,

Thanks for all the inputs.

Quote:
That is probably not the problem in this amplifier, unless one of them has actually failed.
The transistors from the working channel were swaped into the defective channel and the channel started working.

When the transistors from the defective channel were put into the working channel it stopped working.

Regards
Rajiv
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Old 30th April 2012, 06:58 AM   #10
djk is offline djk
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In this case it sounds like one was bad.

HiFi Engine has the M-2000 schematics, basically the same. Also download the M-4000 manual for the parts list.
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Last edited by djk; 30th April 2012 at 07:19 AM.
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