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Looking for help with Luxman L-80V

you're probably good with that setting, but since you have it apart, resistor time I'm thinking.
 
dr*audio said:
Is the bias now ok on both channels, and if so, how did you fix it?
Do you see the spikes if there is no input signal?
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I see an hear the noise with no input signal. I got the bias to be OK by turning the pot a lot more in this channel, its practically turned the whole way clockwise.
 
I had a few minutes before leaving for work this morning so I replaced Q107, the Fairchild KSA940, with the original 2SB536 and turned it back on - I no longer see most of the noise in the scope!

I do still see that the right channel is a little bit noisier than the left but that might be my 1980's scope (which you are familiar with Dr Audio).

One other scope related question. At zero input signal, both channels hooked to the scope, if I turn the timing the whole way down to .2uSec and look at the 'straight' lines, the left channel is rock solid straight, and the right channel is straight but bounces up and down slowly as if the DC was modulating. The word that popped in to my mind was 'oscillation' but I do not know if that is indeed what I am witnessing or if its just my scope.
 
ecluser said:
The KSA940/KSC2073 are slow (Ft: ~4MHz) by comparison to the 2SB536/2SD381 (Ft: 40~45MHz).
Click to expand...

I see that now, thank you for your input. I have another KSA940 that I will replace when I get home from work.

I learned a lot this time around thanks to AK again!
 
I came home from work today and finished putting the old transistors back in. I now see that same noise in the right channel.

I thought it might be something environmental so I tried switching the polarity of the power cord, turning off all the lights in the house, changing the amplitude of the input signal, etc.

The noise is still there. I swear it wasn't when I tested this morning but I didn't even change my testing situation when I came home.

Is there good way to debug this? If I left the leads on the temporary 33k ohm resistor too long could that introduce noise? I ask this because I have real 33k ohm resistors on the way here so in order to reuse the 30k and the 3.3k in the future I left their legs real long and just soldered the ends together. So there is a good 4 inches of extra wire sticking out for this temporary resistor.

When I restored a Pioneer SA-9100 once I had some noise in a channel while it was on the bench but after buttoning it up and adding the shielding it went away. I am going to see if that is the same case here and try putting her back together perhaps. It may just be a red herring.
 
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Well I decided to give the scope probing a break and actually listen to the thing. I put it back together and put on some headphones. With no input signal the buzzing is barely audible in the right channel. The moment the source starts playing you can no longer hear the buzz. The music sounds wonderful - I mean really good! I listened to 'The Divided Sky' by Phish and it gave me chills.

This is a little gem of amplifier in my opinion.

If I could get rid of this buzz in the right channel it would be perfect.

ps the buzz stays in the right channel when I use the 'reverse' mode switch, also when I reverse the inputs themselves, so I am thinking the issue is still somewhere in the right channel circuitry.
 
I tested resistors right vs left and couldn't find anything that was a red flag. I actually have the left and right channels mirrored parts-replacement-wise now with the exception of that DIY 33k ohm resistor (which I have since shortened the leads on to make sure it wasn't acting as an antenna).

The only thing I can think of is to look at the schematic and determine what collateral damage would happen if R117 (the 33k ohm) opened up, since that's what happened. D101 is new, R115 and R116 seem fine ohms-wise, as do all the transistors in the channel.

I've spent a few more hours on this tonight. Time to go to bed.
 
xoaphexox said:
ps the buzz stays in the right channel when I use the 'reverse' mode switch, also when I reverse the inputs themselves, so I am thinking the issue is still somewhere in the right channel circuitry.
Click to expand...

This reverse switch is well ahead in the circuit, just after the input selector switch. Your right channel problem may be in the boards preceding the power amplifier board.

Switch the output from pin 2 of the PB-893 board (for the right channel) to the left channel pin 1 on the power amplifier board, and vice-versa. If the problem switches to the left speaker output, then the problem is in the right channel pre-amp section.

If so, switch the signal at the pin 1 on board PB-893, to see if the problem comes from board PB-892.
 
I checked the input to the right channel power amp board (pin 1) and I see no noise at all, I think that clears the buffer and tone control boards as suspects? Also, trying to follow the signal path, I see no noise at the base of Q101, Q102.

I do, however, see the noise at the base of Q107 and Q108, as well as pins 3,4,5 and 6.

So the noise is being introduced somewhere after the differential pair and before the pre drivers it seems.

In this area I have replaced the zener diode D101, both multijunction diodes D102,D103 as well as all electrolytic and mylar capacitors. I did not replace any ceramics.

I do see the noise on one side of R113 but not on the other side (the side connected to the base of Q102).
 
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I am wondering if this noise might be generated somewhere else in the circuit and it's being picked up by this channel due to layout or wire routing. Check the grounds, especially the screws that connect the boards to ground. Also try shorting out the power switch (with the power cord unplugged) with a clip lead, it could be arcing internally.
 
xoaphexox said:
I do see the noise on one side of R113 but not on the other side (the side connected to the base of Q102).
Click to expand...

But the signal at the base of Q102 is reduced by a large factor. It is only (R114 / (R113 + R114)) of the output signal. If you change the sensitivity of the scope by a factor ~50, you don't see this noise at the base of Q102 and Q101?
 
For crying out loud, I moved the unit off my bench and took it upstairs. The freaking thing is dead silent now! I apologize for not trying this earlier - the outlets in my basement must all be on the same circuit.

Time to button this one up and enjoy it!

Thanks Dr*Audio and Ecluser (and ryuuoh), you guys are first class in patience and knowledge!
 
You won't believe it but I've got a L-85V in an exchange last month and I didn't cleaned the controls yet. He is sitting in a corner waiting for me... I know they are fantastic amps. I love the Luxman look! Enjoy yours for me too! I think it's about time to open mine...
 
ecluser said:
You won't believe it but I've got a L-85V in an exchange last month and I didn't cleaned the controls yet. He is sitting in a corner waiting for me... I know they are fantastic amps. I love the Luxman look! Enjoy yours for me too! I think it's about time to open mine...
Click to expand...

You will love the sound even more. Time to get busy!
 
:thmbsp:
I'm finally going to button up my L-80V, and insert it into the main system. Mine just had blown out puts in one channel, and open emitter resistors. Got it off Ebay for $75, excellent cosmetics. I'm going to finish recapping the main board, and then I'm done. It does sound pretty good with my test speakers, and the offset and bias is stable so far (2 weeks of on/off use). I like this amp~ great tone controls.
 
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xoaphexox said:
For crying out loud, I moved the unit off my bench and took it upstairs. The freaking thing is dead silent now! I apologize for not trying this earlier - the outlets in my basement must all be on the same circuit.

Time to button this one up and enjoy it!

Thanks Dr*Audio and Ecluser (and ryuuoh), you guys are first class in patience and knowledge!
Click to expand...

I know this was almost ten years ago, but man, what an odyssey! And it was the danged outlet in your basement? You did some amazing troubleshooting (switching power cord polarity, turning house lights off...). You're making me think having a separate, dedicated line (plenty of room in the electrical panel) for bench testing would be a good idea. Wow, what a story.
 
ecluser said:
"I will be damned! R117 is wide open!" ... No damnation... I've been there before...

Bias? 23mV between point 4 and point 3

35mA X (0.33 Ohm + 0.33 Ohm) = 23mV
Click to expand...

Would you mind helping me out by giving me a bit more detail on this one?

What do you mean by point 4 and 3?
 
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