UPDATE: Problem Solved
Swapped V101 12AU7 Tube from the other identical Amplifier and behavior normalized.
Culprit was the The 12AU7 Tube.
Swapped the tube to the other amplifier to cross check other parts.
The behavior shifted.
Case Closed!
Hi Everyone!
It all Started when i noticed my Left Speaker Woofer drivers moving in & out Slowly, flexing too much,even when there was no input signal from my pre-amplifier.
After some troubleshooting & exploring internet and measured dc voltage on output terminals of my speakers and measured abnormal readings from one of my amplifier.
Amplifier in question is Vincent SP-T800 Power Amplifier Monoblocks with Tube Input Stage.
Cross checked with the other amplifier and noticed my left monoblock is measuring dc volts from 2.0mv to 1.0v and fluctuating back and forth on both speaker A & Speaker B.
I am sharing some videos for reference.
Unfortunately there is no service from Vincent in my country and also these amplifiers are over the warranty period anyway.
I can import small replaceable parts like Resistors or Capacitors or Tubes if Required.
https://www.connect.de/testbericht/endverstaerker-vincent-sp-t-800-329060.html
https://www.hifi-regler.de/p/vincent-sp-t800.html
Swapped V101 12AU7 Tube from the other identical Amplifier and behavior normalized.
Culprit was the The 12AU7 Tube.
Swapped the tube to the other amplifier to cross check other parts.
The behavior shifted.
Case Closed!
Hi Everyone!
It all Started when i noticed my Left Speaker Woofer drivers moving in & out Slowly, flexing too much,even when there was no input signal from my pre-amplifier.
After some troubleshooting & exploring internet and measured dc voltage on output terminals of my speakers and measured abnormal readings from one of my amplifier.
Amplifier in question is Vincent SP-T800 Power Amplifier Monoblocks with Tube Input Stage.
Cross checked with the other amplifier and noticed my left monoblock is measuring dc volts from 2.0mv to 1.0v and fluctuating back and forth on both speaker A & Speaker B.
I am sharing some videos for reference.
Unfortunately there is no service from Vincent in my country and also these amplifiers are over the warranty period anyway.
I can import small replaceable parts like Resistors or Capacitors or Tubes if Required.
https://www.connect.de/testbericht/endverstaerker-vincent-sp-t-800-329060.html
https://www.hifi-regler.de/p/vincent-sp-t800.html
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Could be defective power supply capacitors. Look for leakage or bulging tops.
Any schematics?
If the power supply capacitors become much too small in value due to degradation,
their low frequency poles move higher in frequency and interact with other LF poles
already present in the circuit, causing instability.
Any schematics?
If the power supply capacitors become much too small in value due to degradation,
their low frequency poles move higher in frequency and interact with other LF poles
already present in the circuit, causing instability.
No Schemetics,i have uploaded two short videos on YouTube and shared links in first post.
Please take a look i believe i suspect few capacitors bulging on main board
1. If you measure your power mains, and you read DC Volts on a DC Voltmeter (DMM), it might be that the average voltage of the positive alternation and the average voltage of the negative alternation are not equal. A RC low pass filter (which is what the DC meter effectively has) will show a DC voltage when the average voltage of the alternations are un-equal.
You have a very dirty power mains, or a very non symmetrical load, or both.
If there really is DC in series with the AC mains, you have a Very Serious Problem!
Troubleshoot:
220V mains
Get a two channel oscilloscope and a pair of 10X probes.
Measure from one Hot to Ground
Measure from the other Hot to Ground
Do Not connect the scope probe ground clip to Neutral, if there is a Neutral!
Then use the scope invert on one channel, and use the subtract ch 1 from ch 2. Does that look like a sine wave, or nearly so?
2. For US:
Measure from Hot to Ground
Measure from Neutral to Ground
Do not connect the scope probe ground clips to Neutral!
3. DC on the primary of the amplifiers power transformer, does not cause DC on the secondary.
There is no transmission of DC from primary to secondary, transformers are High Pass Filters.
DC never passes through a High Pass Filter.
4. Now, return to troubleshooting your power amplifiers.
You have a very dirty power mains, or a very non symmetrical load, or both.
If there really is DC in series with the AC mains, you have a Very Serious Problem!
Troubleshoot:
220V mains
Get a two channel oscilloscope and a pair of 10X probes.
Measure from one Hot to Ground
Measure from the other Hot to Ground
Do Not connect the scope probe ground clip to Neutral, if there is a Neutral!
Then use the scope invert on one channel, and use the subtract ch 1 from ch 2. Does that look like a sine wave, or nearly so?
2. For US:
Measure from Hot to Ground
Measure from Neutral to Ground
Do not connect the scope probe ground clips to Neutral!
3. DC on the primary of the amplifiers power transformer, does not cause DC on the secondary.
There is no transmission of DC from primary to secondary, transformers are High Pass Filters.
DC never passes through a High Pass Filter.
4. Now, return to troubleshooting your power amplifiers.
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Great Advice!
But...
Ground connection is not active right now.
As you described,i believe and suspect,there was DC on my AC Line for some time and it might have malfunctioned one of my amplifier.
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Under the hood.
Its very tricky to access the main board.
The power transformer hangs on top with connections soldered down to main board.
Looks like to access the main board it must me dissembled completely.
I have added a link of review in my first post.
It may add some information in the layout of this amplifier.
It may add some information in the layout of this amplifier.
Tom Bavis,
Any $25 DMM has a high enough sample rate for 50Hz and 60Hz power mains.
It is much more likely that the power mains load is heavier on one polarity of alternation, and not as heavy a load on the other polarity of alternation.
For example, if one of the loads has a half wave rectifier, it will do that.
Get your scope out, and a scope probe, and Very Carefully measure the + peak voltage, the - peak voltage.
Even the least expensive Tektronix Oscilloscope will read out those values, and also give the True RMS voltage.
For our 3 wire US power, measure Hot to ground, then measure Neutral to ground.
Neutral and ground are only the same voltage at the Power Panel; and are different everywhere else. I once saw an 8V difference.
The ground wire does not carry ground, and current in it is supposed to be non-existent, or extremely small.
The Neutral wire has the same current as the Hot wire; if not there is a major problem.
If you have looked at very many different power mains like I have, you will be surprised by some of the wave shapes and voltage transients on the power mains.
Clipping, Yes.
Distortions, Yes.
Spikes, Yes.
Jumping Voltage values, Yes.
The various power mains around the world are fascinating.
Single phase, 3 phase, and even the Scott-Star 4 phase.
2 Hots and a ground; Hot and Neutral and a ground, etc.
No ground . . . watch yourself, you may become the ground return!
Everyone should know and understand their own power mains well, before treading where sparks, welding, shocks, fire, and death can occur.
Any $25 DMM has a high enough sample rate for 50Hz and 60Hz power mains.
It is much more likely that the power mains load is heavier on one polarity of alternation, and not as heavy a load on the other polarity of alternation.
For example, if one of the loads has a half wave rectifier, it will do that.
Get your scope out, and a scope probe, and Very Carefully measure the + peak voltage, the - peak voltage.
Even the least expensive Tektronix Oscilloscope will read out those values, and also give the True RMS voltage.
For our 3 wire US power, measure Hot to ground, then measure Neutral to ground.
Neutral and ground are only the same voltage at the Power Panel; and are different everywhere else. I once saw an 8V difference.
The ground wire does not carry ground, and current in it is supposed to be non-existent, or extremely small.
The Neutral wire has the same current as the Hot wire; if not there is a major problem.
If you have looked at very many different power mains like I have, you will be surprised by some of the wave shapes and voltage transients on the power mains.
Clipping, Yes.
Distortions, Yes.
Spikes, Yes.
Jumping Voltage values, Yes.
The various power mains around the world are fascinating.
Single phase, 3 phase, and even the Scott-Star 4 phase.
2 Hots and a ground; Hot and Neutral and a ground, etc.
No ground . . . watch yourself, you may become the ground return!
Everyone should know and understand their own power mains well, before treading where sparks, welding, shocks, fire, and death can occur.
It would be very good to advise NOT to use an oscilloscope for measuring mains voltages as the oscilloscopes GND is connected to PE. This can result in spectacular short circuits.
jean-paul,
Yes, power mains measurements are not always safe.
Depends on the particular power mains; and depends on the person doing the measurements.
In most of the US, we have nominal 120VAC, 3 Wire, Hot, Neutral, Ground.
Power is from Hot to Neutral.
You are Correct: The only direct measurement of Hot to Neutral on an oscilloscope requires a floating differential probe.
The probes are not inexpensive.
An alternative measurement scenario:
You can safely measure from Hot to ground with one probe on channel 1; and can safely measure from Neutral to ground on channel 2.
10X or higher probes only, a 1X probe will take out the scopes front end.
The probe tips Always connect to Hot, or to Neutral.
The scope ground clips Never connect to Hot, and never connect to Neutral; they connect to ground (at the same point as the ground for the scope).
The key is to know that the power mains outlets are just as I stated above; then knowing which wire is Hot, Neutral, and ground.
There are inexpensive devices that plug into the 3 wire wall outlet, that verify the correct (or bad) wiring of the outlet.
Always use a 3 Wire grounded oscilloscope.
Safety First!
Prevent the "Surviving Spouse Syndrome".
Yes, power mains measurements are not always safe.
Depends on the particular power mains; and depends on the person doing the measurements.
In most of the US, we have nominal 120VAC, 3 Wire, Hot, Neutral, Ground.
Power is from Hot to Neutral.
You are Correct: The only direct measurement of Hot to Neutral on an oscilloscope requires a floating differential probe.
The probes are not inexpensive.
An alternative measurement scenario:
You can safely measure from Hot to ground with one probe on channel 1; and can safely measure from Neutral to ground on channel 2.
10X or higher probes only, a 1X probe will take out the scopes front end.
The probe tips Always connect to Hot, or to Neutral.
The scope ground clips Never connect to Hot, and never connect to Neutral; they connect to ground (at the same point as the ground for the scope).
The key is to know that the power mains outlets are just as I stated above; then knowing which wire is Hot, Neutral, and ground.
There are inexpensive devices that plug into the 3 wire wall outlet, that verify the correct (or bad) wiring of the outlet.
Always use a 3 Wire grounded oscilloscope.
Safety First!
Prevent the "Surviving Spouse Syndrome".
The 3 wire connected (so with L, N and PE as we call it) oscilloscope often is more a curse than a blessing in such measurements. In times long gone that was as today everything is exaggerated big time. Many have learned in the past to use isolation transformers and a tiny amount of brain capacity for the purpose.