Hello,
I have fixed a Luxman L31 amplifier and recapped all the power supply and power amp stage and also the preamp. The 3300uF power supply capacitors have been upgraded to 6800uF
I works great, but produces an annoying noise when it’s powered on. The amp doesn’t have any soft start circuit.
The only solution I have found is to mute the speakers switching it to off and wait until the start process ends. It last almost 20 seconds.
Does anyone have experienced this? Any advice in order to reduce this noise or its duration?
Thanks,
Contax
I have fixed a Luxman L31 amplifier and recapped all the power supply and power amp stage and also the preamp. The 3300uF power supply capacitors have been upgraded to 6800uF
I works great, but produces an annoying noise when it’s powered on. The amp doesn’t have any soft start circuit.
The only solution I have found is to mute the speakers switching it to off and wait until the start process ends. It last almost 20 seconds.
Does anyone have experienced this? Any advice in order to reduce this noise or its duration?
Thanks,
Contax
Many causes for the power ON "dc thump" however 20 seconds indicates an abnormality.
Where fitted mute periods are typically 4-10 seconds.
Suggest you check all replaced caps in the power amp, orientation and value.
Do you have the same noise at power off?
Is the noise on both channels?
A very long shot however try removing and cleaning the fuses and holders on the
power amp supply rails F201,2,3,4
If you are comfortable with live measurements you could monitor the rail voltages
at power ON, need 2 multimeters, monitor at F201 and F203. The should settle within
1-2 seconds, can't explain the 20 seconds. You can also monitor at power off, identify
which rail collapses quicker, this will depend on load etc...
Where fitted mute periods are typically 4-10 seconds.
Suggest you check all replaced caps in the power amp, orientation and value.
Do you have the same noise at power off?
Is the noise on both channels?
A very long shot however try removing and cleaning the fuses and holders on the
power amp supply rails F201,2,3,4
If you are comfortable with live measurements you could monitor the rail voltages
at power ON, need 2 multimeters, monitor at F201 and F203. The should settle within
1-2 seconds, can't explain the 20 seconds. You can also monitor at power off, identify
which rail collapses quicker, this will depend on load etc...
Hello mbz,
Thanks for your help. The noise is in both channels.
I think the source is the preamp section, because the noise is lower reducing the gain with the volume pot. Or maybe the preamp and the power amp.
I'll check the rail power supply voltages at power ON and I'll check the capacitors in the preamp section.
In this page Luxman audio products, the authot recommends to by pass some capacitors. I do not know the purpose of this and I do not if this would reduce the problem I have.
"Add to C203 and 207 a capacitor of approx 0.047 uF 100V, (parallel to these electrolytic caps)"
"Add to these C219 and C220 caps parallel a capacitor of approx 0.047 uF 100V, same procedure as above."
Best regards,
Mario
Thanks for your help. The noise is in both channels.
I think the source is the preamp section, because the noise is lower reducing the gain with the volume pot. Or maybe the preamp and the power amp.
I'll check the rail power supply voltages at power ON and I'll check the capacitors in the preamp section.
In this page Luxman audio products, the authot recommends to by pass some capacitors. I do not know the purpose of this and I do not if this would reduce the problem I have.
"Add to C203 and 207 a capacitor of approx 0.047 uF 100V, (parallel to these electrolytic caps)"
"Add to these C219 and C220 caps parallel a capacitor of approx 0.047 uF 100V, same procedure as above."
Best regards,
Mario
I'm familiar with the hilberink luxman site, some good information however
bypass capacitors won't help you on this (or any?) occassion.
Since the volume control has effect on the loudness noise/pop then the problem
is likely to be before the volume pot.
Suggest you clean all switches (function, monitor etc...) use a lubricant
rather than a solvent cleaner. Also check switch solder connections.
Please indicate what type of noise it is, a pop or hiss/white noise or...
bypass capacitors won't help you on this (or any?) occassion.
Since the volume control has effect on the loudness noise/pop then the problem
is likely to be before the volume pot.
Suggest you clean all switches (function, monitor etc...) use a lubricant
rather than a solvent cleaner. Also check switch solder connections.
Please indicate what type of noise it is, a pop or hiss/white noise or...
Hello mbz,
Please, find enclosed the link to the audio file
06-11-12.m4a - Google Drive
Best regards,
Contax
Please, find enclosed the link to the audio file
06-11-12.m4a - Google Drive
Best regards,
Contax
AC Capacitors
Hello,
Maybe the problem is caused by the capacitors I selected for the AC section. I replaced this 3 capacitors. I chose 22nF poliester caps 250v AC. Maybe I chose a wrong type for this duty.
Condensadores de Pelicula de Poliester y piezas para Condensadores
Thanks for your help.
Best regards,
Contax
Hello,
Maybe the problem is caused by the capacitors I selected for the AC section. I replaced this 3 capacitors. I chose 22nF poliester caps 250v AC. Maybe I chose a wrong type for this duty.
Condensadores de Pelicula de Poliester y piezas para Condensadores
Thanks for your help.
Best regards,
Contax
Attachments
any body looked at teh schematic before placing an answer ?
1) disconect main amplifier input just the signal lead keep ground as is then power up to notice if you still have the same problem . If not your problem lays elsewhere not in the amplifier.
2) check with the values of capacitors you placed its ok to place in bigger voltage ( up to the next available level , bigger temperature like 105 degrees) but the capacitance there is areas that you can boost them to a higher capacitance and there will be improvement with that.
But there is areas that if you mess up with the capacitance things go wrong .
If your problem doesn't lay in the main amplifier then inspect the area of the secondary PSU of -40 V that feeds the preamp ....you might have some problem there .
Kind regards
Sakis
1) disconect main amplifier input just the signal lead keep ground as is then power up to notice if you still have the same problem . If not your problem lays elsewhere not in the amplifier.
2) check with the values of capacitors you placed its ok to place in bigger voltage ( up to the next available level , bigger temperature like 105 degrees) but the capacitance there is areas that you can boost them to a higher capacitance and there will be improvement with that.
But there is areas that if you mess up with the capacitance things go wrong .
If your problem doesn't lay in the main amplifier then inspect the area of the secondary PSU of -40 V that feeds the preamp ....you might have some problem there .
Kind regards
Sakis
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.