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Are all 7 speakers blown or is it my receiver?

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frend2001

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Is the receiver rated at 220/240v or it's some other voltage ? It is being run thru some step down or stabilizer ?
 
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jls001

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7 speakers can't misbehave at the same time. The problem has to be something common to them all like a bad contact in the analog interconnects or digital cables from your sources. It could also be the volume pot as that usually comes before preamp stage.

Did you try playing from different sources and do they all misbehave?

Your scope plot shows a clear case of distortion which is likely because your AVR is being over driven. What was the source of that input and what was the level? Is your vertical scale properly set to display the expected level of the AVR output?
 

superczar

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Here is an image of the oscilloscope reading of the amplifier connected to an 8 ohm resistor:
View attachment 37569



In this picture the blue graph is the pre-out output (which seems to be fine) and the yellow is the speaker output (severe clipping) with an 8 ohm resistor load

View attachment 37570

So, it is the amplifier in my receiver that has malfunctioned. Any solutions? This clipping happens with all inputs and even with no inputs connected and just FM radio running.
It's an unusual reading in that only the lower part of the waveform is clipping -
Can you check if this pattern repeats on other channels also?
frend2001 may be onto something here , is it possible to use another step-down to test?
 

codwapeace

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7 speakers can't misbehave at the same time. The problem has to be something common to them all like a bad contact in the analog interconnects or digital cables from your sources. It could also be the volume pot as that usually comes before preamp stage.

Did you try playing from different sources and do they all misbehave?

Your scope plot shows a clear case of distortion which is likely because your AVR is being over driven. What was the source of that input and what was the level? Is your vertical scale properly set to display the expected level of the AVR output?
Different sources: Yes (including FM tuner. All show distortion on the scope)
Source of input in the case of the plot: Youtube app on Firestick with DD+ output (So, there was no level setting)
Vertical scale: What should be the expected level of the AVR output? I don't know. Do you? But, I changed the scale so that complete output was captured.
 

codwapeace

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It's an unusual reading in that only the lower part of the waveform is clipping -
Can you check if this pattern repeats on other channels also?
frend2001 may be onto something here , is it possible to use another step-down to test?
Yes, it repeats on other channels also. I tested the front 3 channels and all show clipping in the lower region.
I tested with a different step down and the result is the same. That was my first thought as well.
 

jls001

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Different sources: Yes (including FM tuner. All show distortion on the scope)
Source of input in the case of the plot: Youtube app on Firestick with DD+ output (So, there was no level setting)
Vertical scale: What should be the expected level of the AVR output? I don't know. Do you? But, I changed the scale so that complete output was captured.
A distant possibility is that since the positive and negative cycles of the audio waveform are amplified by two different sections on both the preamplifier and power amplifier, the section for the negative waveform on either may be having issues.
 

codwapeace

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A distant possibility is that since the positive and negative cycles of the audio waveform are amplified by two different sections on both the preamplifier and power amplifier, the section for the negative waveform on either may be having issues.
Yes. And most likely it is the power amplifier because the preamp output is fine and shown by the oscilloscope (My receiver has a preamp output).
 

superczar

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A distant possibility is that since the positive and negative cycles of the audio waveform are amplified by two different sections on both the preamplifier and power amplifier, the section for the negative waveform on either may be having issues.
Since all 7 channels are affected , it is also possible that the negative rail of the symmetrical supply (+V / 0 / -V) is messed up
If you can open up the Amp and check the voltages on the three rails going to the amp section, you may be able to check for this possibility
 

frend2001

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What is the AVRs power rating n what's the step down trans rating ?
 
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frend2001

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Are you referring to step down as isolation also or you have 2 different transformer in power line. May sound stupid to ask but wanted to rule down things.

Can you describe the total chain from power plug to receiver ?
 

codwapeace

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Are you referring to step down as isolation also or you have 2 different transformer in power line. May sound stupid to ask but wanted to rule down things.

Can you describe the total chain from power plug to receiver ?
Power plug -> Single step down transformer (which is isolation type, i.e., it has different primary and secondary coils)-> AVR.
Is there a problem in this setup which could cause the AVR to malfunction. I have been running this for 1.5 years.
 

codwapeace

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Hmmm.... I thought transformers always have them separate.
Thats what I thought too. Most transformers on Amazon are autotransformers, i.e., there is a center tap to get the right voltage (not two different coils). So, there is a high chance of supplying 230 V if there is a malfunction.
 

frend2001

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well if possible you may want to change that step down and see if it's ok.

Prima facie it seems like some current related issue. An amplifiers may start distorting due to low voltage.

Can you measure the voltage output from your transformer ?

Please BE VERY CAREFUL and if you don't know how to do it better don't attempt it at all and refer to some electrician.
 

codwapeace

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well if possible you may want to change that step down and see if it's ok.

Prima facie it seems like some current related issue. An amplifiers may start distorting due to low voltage.

Can you measure the voltage output from your transformer ?

Please BE VERY CAREFUL and if you don't know how to do it better don't attempt it at all and refer to some electrician.
I looked at the insides using scope and multimeter. The + and - DC high voltage rails are fine, the input to the final amplifier transistors (The biggest transistors with heatsink) itself is distorted. The preamp output is fine. So, there is some distortion happening between the preamp output and the input to the final amplifying stage. To do anymore digging, I need to remove the video boards and all which I don't want to do. I will see if the service center can repair it.
 

abeyaby

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I have a yamaha receiver (RX-V781) which is connected to 7 speakers. Suddenly speakers started sounding "hoarse" at higher volumes. I think the problem has become worse in a couple of days. I thought may be my front speakers have gone bad. So, I tried running the center channel alone. That also sounds bad. Every speaker sounds bad in every channel combination at high volumes. Do you think all my speakers have gone bad? Or, is it my receiver that has gone bad?
I have access to an oscilloscope, but I don't have another amplifier (or receiver) or another speaker (other than the 7), to test whether the speakers are bad or the receiver.
What could cause either of the two problems?
Thanks.
Sad to hear
 
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