Luxman L-111a - Bad sound on left channel

[coojoe_213]

Hi. This is my first Luxman, i buy to use in garden for the summer, but i have problem. Right channel work fine, but left channel have very bad sound.
There is no shcematic for my amp, but service manual for Luxman L-1/A is 100% same.
I check bias adjustment /is 50ma on both channel/
I try every inputs (+monitor 1/2) same situation.
I clean all potentiometers with contact cleaner.
Check all capacitors with esr meter - fine.
Check voltages on both chanells - they are same.
Resolder all pots, check all wires in amp they are good...:/
If i put headphones sound is good.
No short transistors or diodes .Please for some solution.

[budm]

Re: Luxman L-111a - Bad sound on left channel

Does it have distorted sound?
You have switches on the headphone jack that cut out the speaker connection when the headphone is insert into the headphone jack, you also have output switches S001C, S001D did you clean those switches and all other switches as well?
What are the DC offset at the power amplifier outputs?

[dick_barton]

Re: Luxman L-111a - Bad sound on left channel

Swap speakers over (left to right output & right to left output) and check if you still have the problem on the same channel.

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

I upload clip with my problem. Yes, i clean all connection and switches. Yes i swap speakers, but the problem is same. On left channel is 3.5mV, right channel is 1mV.
https://www.youtube.com/watch?v=l9lq...ature=youtu.be

[budm]

Re: Luxman L-111a - Bad sound on left channel

I am not sure what I am listening for in that Video.

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

I am not sure what I am listening for in that Video.

From 6 second of clip you can listen, how sound is bad /especially quality bass/.

[redwire]

Re: Luxman L-111a - Bad sound on left channel

Why are the high cut, low cut, mono switches etc. looking ON?

Can't tell anything in 12 second video

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

Hi. I upload new video. The sound is only from left channel. I hope to hear my problem :/
https://www.youtube.com/watch?v=Rbqq...ature=youtu.be

[redwire]

Re: Luxman L-111a - Bad sound on left channel

I hear lots of intermodulation distortion on the bass on one channel.

This Luxman has no preamp so the tone controls are part of the power amp's feedback network, I think called "Duo Beta".

I would replace the 7 small electrolytics for bypass and decoupling.
C201, C203, C205, C208, C206, C215, C216

Or use a scope and see which cap it is exactly, but this is vintage gear from 1980-1990.

[petehall347]

Re: Luxman L-111a - Bad sound on left channel

just to be sure try swapping inputs .
and trying playing different music .. that sort of music sounds like that all the time to me .

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

I replace all caps, the problem is same. I replace also volume potentiometer, same.

[petehall347]

Re: Luxman L-111a - Bad sound on left channel

does it have a mono switch ? if so try in mono .
if you can find the coupling caps to each channel jumper them together and see if it sounds better or distorts good channel .
you could also try quickly turning up the vol to see if it clears the fault . if so its likely speaker relay

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

does it have a mono switch ? if so try in mono .

Yes, i have mono switch, if i push the button mono/stereo situation is same.

you could also try quickly turning up the vol to see if it clears the fault . if so its likely speaker relay .

I try this one yesterday but no result, same. This amp is without relay.

[petehall347]

Re: Luxman L-111a - Bad sound on left channel

do you have a signal tracer ? dead easy to make with a small capacitor and external amp .

[redwire]

Re: Luxman L-111a - Bad sound on left channel

It's hard to tell microphone/recorder distortion on a video vs the amp.
I thought I heard distorted bass but the mids were ok. No rectified/half-wave distortion like a bad transistor would make.

OP say he has good bias and no offset, that's 6 transistors OK.

All that's left is the speaker output switch contacts, bass/treble potentiometer, +19V rail.

[coojoe_213]

Re: Luxman L-111a - Bad sound on left channel

If i remove fuses from right chanell, left chanell i 90% perfect??? May zener diod make a problem?
http://www.audiokarma.org/forums/ind...13182%2Fpage-2

[redwire]

Re: Luxman L-111a - Bad sound on left channel

coojoe_213, you say you measure the voltages and all are ok.
Check +/-34VDC and +19VDC on each amp.
Removing a fuse and the sound is no longer distorted- does not make sense to me.

[petehall347]

Re: Luxman L-111a - Bad sound on left channel

looking like when right channel fuse is removed its allowing more current to the left channel .. it could be a simple bad connection on the left channel fuse . or the 19v zener might be bad .
or the bias is set rather high on the right channel .