Help: Noise from one channel even without source
My vintage integrated amplifier just started to have noise on one channel. The noise is quite loud during cold startup and the noise is still present (much softer) thereafter even there is no signal with the volume control at zero. The affected channel still reproduces the signal normally except that the noise is always present.
It does appear that some "leakage current" manage to flow through the preamp and perhaps even the power amp section to the speaker output. When I reverse the speaker's connection, the other channel has the noise.
I have no plan to recap the amplifier and hope to be able to nail down to the problem and replace.
Appreciate very much for your sharing.
My vintage integrated amplifier just started to have noise on one channel. The noise is quite loud during cold startup and the noise is still present (much softer) thereafter even there is no signal with the volume control at zero. The affected channel still reproduces the signal normally except that the noise is always present.
It does appear that some "leakage current" manage to flow through the preamp and perhaps even the power amp section to the speaker output. When I reverse the speaker's connection, the other channel has the noise.
I have no plan to recap the amplifier and hope to be able to nail down to the problem and replace.
Appreciate very much for your sharing.
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You have to find out the faulty stage. Can you locate the input of the power amp stage...
If you can then find out which stage is having problem by cross coupling the signal by opening the coupling capacitor.
I hope the power amp is conventional.
Gajanan Phadte
Edit: Alternatively, you can use a crystal earphone to listen to the audio signal
If you can then find out which stage is having problem by cross coupling the signal by opening the coupling capacitor.
I hope the power amp is conventional.
Gajanan Phadte
Edit: Alternatively, you can use a crystal earphone to listen to the audio signal
Make and model ? 
Favourite problems (generally) would be dry joints on driver and VAS transistors (anything that runs hot) and beyond that a fair chance that it is a failing transistor, typically a driver.
If the amp is DC coupled you risk a catastropheic failure where DC could appear on the output and blow both amp and speaker. You need to fix it immediately.
Favourite problems (generally) would be dry joints on driver and VAS transistors (anything that runs hot) and beyond that a fair chance that it is a failing transistor, typically a driver.
If the amp is DC coupled you risk a catastropheic failure where DC could appear on the output and blow both amp and speaker. You need to fix it immediately.
I have tried the following to nail down the source of the problem.
1. I connect the preout of the said amp to an Aux input of another amp and the noise stops.
2. I connect the preout of the said amp to the power input of another amp and the noise persist.
3. I connect the preout of another amp to the power in of the said amp and the noise persist.
I could not figure out where is the problem. Hopefully someone with a good understanding of electronics could nail it down.
1. I connect the preout of the said amp to an Aux input of another amp and the noise stops.
2. I connect the preout of the said amp to the power input of another amp and the noise persist.
3. I connect the preout of another amp to the power in of the said amp and the noise persist.
I could not figure out where is the problem. Hopefully someone with a good understanding of electronics could nail it down.
Hello Mooly,
I can confirm that when I connect the preout of the said amp to the AUX of another amp, the noise stop.
However, when I connect the preout to the power in of another amp, the noise from one of the channel persist.
I did not try to connect the preout of the other amp to the power in of the said amp this time.
Still confusing
That points to the noise being generated by a faulty power amp in your "vintage amp" which you still haven't named Your preamp is silent when fed to another amps aux input.
That reads... the preamp output is noisy when connected to another power amp. So the preamp now is not silent when connected to a power.
An aux input and power amp inout are essentially the same loading wise but with the aux input probably having higher sensitivity any noise should be apparent there... and its not.
So
Lets start at the beginning. To be able to help you we need to know...
1) Make and model of the amp so that we can hopefully find circuit information and diagrams. Without that we can't really advise much beyond general info.
With the faulty amp coupled to speakers (and it all configured normally with preamp outputs connected to power amp inputs) and with NO input leads or anything else connected to the amp...
2) Is the noise affected by the volume setting ?
3) Is the noise affected by choice of input ?
4) Is the noise affected by any physical movement of the amp ?
That points to the noise being generated by a faulty power amp in your "vintage amp" which you still haven't named
Your preamp is silent when fed to another amps aux input.That reads... the preamp output is noisy when connected to another power amp. So the preamp now is not silent when connected to a power.
An aux input and power amp inout are essentially the same loading wise but with the aux input probably having higher sensitivity any noise should be apparent there... and its not.
So
Lets start at the beginning. To be able to help you we need to know...
1) Make and model of the amp so that we can hopefully find circuit information and diagrams. Without that we can't really advise much beyond general info.
With the faulty amp coupled to speakers (and it all configured normally with preamp outputs connected to power amp inputs) and with NO input leads or anything else connected to the amp...
2) Is the noise affected by the volume setting ?
3) Is the noise affected by choice of input ?
4) Is the noise affected by any physical movement of the amp ?
Still confusing
That points to the noise being generated by a faulty power amp in your "vintage amp" which you still haven't named
That reads... the preamp output is noisy when connected to another power amp. So the preamp now is not silent when connected to a power.
An aux input and power amp inout are essentially the same loading wise but with the aux input probably having higher sensitivity any noise should be apparent there... and its not.
So
Lets start at the beginning. To be able to help you we need to know...
1) Make and model of the amp so that we can hopefully find circuit information and diagrams. Without that we can't really advise much beyond general info.
With the faulty amp coupled to speakers (and it all configured normally with preamp outputs connected to power amp inputs) and with NO input leads or anything else connected to the amp...
2) Is the noise affected by the volume setting ?
3) Is the noise affected by choice of input ?
4) Is the noise affected by any physical movement of the amp ?
1. The amp in question is Toshiba SB-420
2. Noise not affected by volume setting
3. Noise not affected by choice of input
4. Noise not affected by physical movement of amp
Appreciate very much for your help.
Different circuit but should give you an idea of whats involved.
http://www.diyaudio.com/forums/soli...ba-330-power-amp-problem-possible-repair.html
This picture shows your amp. Check the transistors marked for poor soldering and possible intermitent failure.
http://www.diyaudio.com/forums/soli...ba-330-power-amp-problem-possible-repair.html
This picture shows your amp. Check the transistors marked for poor soldering and possible intermitent failure.
Attachments
Hi Mooly,
Thank you for all your efforts to help.
I have checked and resoldered any possible loose or dry joints including replacing most of the capacitors at the output stage as in the circuit you attached. The right channel cracking noise still persists.
I am prepared to replace the transistors if necessary. Which are the transistors do you think need replacement? I am not familiar with transistor and not sure the equivalent type since most of the existing transistor you indicated in red already obsolete.
Appreciate very much if you could help me to narrow down the parts that need replacement.
Those transistors can be replaced by general purpose generic types.
The 2SC170's can e replaced by 2N5551 or BC546
The 2SA818 can be replaced by an MJE350 or BD140
The 2SC1382 can be replaced with an MJE340 or BD139
The 2SA682 can be replaced with an MJE350 or BD140
There are many suitable devices. The above are common and generally easily available parts.
The pinouts of the 2N5551 and BC546 are different from each other and different from the originals. You can get all the pinouts etc here,
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
Just type the device number in the blank box. Any manufacturer of the offered data sheets is fine.
If you replace any I would advise powering the amp up with a bulb tester first (and no speakers). The bulb tester will save any expensive mistakes. Its just a 100watt mains filament bulb in series with the mains. Any drastic fault drawing a lot of current and the bulb lights.
After replacing parts always check that the DC offset is zero. Thats the voltage measured on the fuse F002 (of the appropriate channel) and when the amp is OK VR006 is adjusted to reset the bias correctly. Thats easy.
The 2SC170's can e replaced by 2N5551 or BC546
The 2SA818 can be replaced by an MJE350 or BD140
The 2SC1382 can be replaced with an MJE340 or BD139
The 2SA682 can be replaced with an MJE350 or BD140
There are many suitable devices. The above are common and generally easily available parts.
The pinouts of the 2N5551 and BC546 are different from each other and different from the originals. You can get all the pinouts etc here,
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
Just type the device number in the blank box. Any manufacturer of the offered data sheets is fine.
If you replace any I would advise powering the amp up with a bulb tester first (and no speakers). The bulb tester will save any expensive mistakes. Its just a 100watt mains filament bulb in series with the mains. Any drastic fault drawing a lot of current and the bulb lights.
After replacing parts always check that the DC offset is zero. Thats the voltage measured on the fuse F002 (of the appropriate channel) and when the amp is OK VR006 is adjusted to reset the bias correctly. Thats easy.
It can indeed. The secret is to drip tiny blobs of the stuff onto devices rather than blast a whole area. But yes... good suggestion and its extremely useful.
(Mind you, the price of it here in the UK is extortionate with it being a greenhouse gas and all)
Hi Mooly,
I managed to purchase the following transistor:
1. 2N5551
2. BD140
3. BD 137 instead of BD 139 that you suggested.
I am not train in electronic so could not quite understand how to check the DC offset. Are you able to guide me through step by step after replacing the above transistors.
If I have to replace the speakers with electric bulbs for testing, what is the voltage and wattage of the bulbs? Should I connect the bulbs similar to the way the speakers are connected?
I had bad experience replacing transistors for another amplifier which caused the amplifier to "burnt out".
Your advice is greatly appreciated.
First thing to do is to familiarise yourself with the pinouts. Get the data sheets for each device from the link I posted.
The BD137 is only a 60 volt device... its not enough because the amp runs on around 73 volts total and although under quiescent conditions the devices only see half that, under drive they see more, approacing full supply. You can still replace the others and lets where that gets it all
On diagrams the emitter is always the one with the arrow, the collector is the one above or below it and the base always the one in the middle.
The light bulb (ordinary 100 (or 60) watt mains filament bulb goes in series with the mains supply to the amp. Bearing in mind safety... you can solder two wires to a bulb and solder these across the main fuse holder in the amp having first removed the fuse. You haveno speakers connected for all the testing and work done on the amp.
DC offset is the DC voltage that is present at the speaker output and it should be near zero.
If you are unsure with anything then ask
Most important is to get the pin outs correct on all the transistors.
The BD137 is only a 60 volt device... its not enough because the amp runs on around 73 volts total and although under quiescent conditions the devices only see half that, under drive they see more, approacing full supply. You can still replace the others and lets where that gets it all
On diagrams the emitter is always the one with the arrow, the collector is the one above or below it and the base always the one in the middle.
The light bulb (ordinary 100 (or 60) watt mains filament bulb goes in series with the mains supply to the amp. Bearing in mind safety... you can solder two wires to a bulb and solder these across the main fuse holder in the amp having first removed the fuse. You haveno speakers connected for all the testing and work done on the amp.
DC offset is the DC voltage that is present at the speaker output and it should be near zero.
If you are unsure with anything then ask
Most important is to get the pin outs correct on all the transistors.
I noted from our local supplier the following:
1. MJE350 - 0.5A, 300V, HFE 30V; while BD140 - 3A, 80V, HFE25V
2. MJE340 - 0.5A, 300V, HFE 30V; while BD139 - 3A, 80V, HFE25V
3. 2N5551G instead of 2N5551; there is no BC456 at all (is there a typo error)
Since the spec are quite different between MJE and BD, should I go for BD instead?
Is there any equivalent for 2N5551? BC456 does not exist.
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