Channels Fading Out While Playing

[drumace]

Hello,
I have an Anthem multichannel power amp connected to a Marantz Pre-Pro.
After I turn my system on and play something through the Marantz, one of the channels fades out after about half a minute.
I sent the amp for a check and no problem was found. I also switched cables and still couldn't find the root cause.
Please advice what could be the reason for this misbehavior.

Thanks.

 

[3db]

We need more information. What are your source inputs? Is it always with the same input device or does this problem show up across all of the inputs? Is always the same channel? Which channel is fading out?

 

[drumace]

We need more information. What are your source inputs? Is it always with the same input device or does this problem show up across all of the inputs? Is always the same channel? Which channel is fading out?

I I tried all sort of sources and inputs and the results are the same.
It is usually on the right side of the system (fronts and backs).
I'm usually using the system for 2 channel stereo and the right front speaker is the one that fades out. If I switch between the R/L interconnects between the pre-pro and the amp, the problem switches to the left front speaker.

 

[3db]

If it happens with any source input and if you have switched the l/r channels on the preamp side and now the left channel is affected, I'm certain that the Marantz pre-pro is at fault.

 

[TLS Guy]

If it happens with any source input and if you have switched the l/r channels on the preamp side and now the left channel is affected, I'm certain that the Marantz pre-pro is at fault.

I agree the Marantz pre/pro is defective. The problem is that the fault is intermittent. Unless it misbehaves on the test bench right while it is wired up in front of the technician you won't find the problem. In addition the fault has to persist long enough to be able to trace it.

This is just the sort of fault that in modern equipment is impossible to find.

If this unit is still under warranty, I would demand a new replacement unit. If the unit is not replaced I highly doubt you will solve this problem, unless you are very lucky. If the unit is out of warranty, you will end up sending it to the recycling center most likely, unless you are very lucky.

 

[drumace]

If it happens with any source input and if you have switched the l/r channels on the preamp side and now the left channel is affected, I'm certain that the Marantz pre-pro is at fault.

I see.
The strange thing is that I fully tested this pre-pro at the original owner's house and it appeared to be working properly. I also have no problems when I listen to music through headphones connected to the pre-pro.
There are few differences between my setup and the original system owner's setup:
1. I'm using surge protector for the whole system and I'm starting to wonder if it can cause such issues.
2. The pre-pro is used with a step down transformer (toroidal 100VA). The original owner had a different and bigger one but he also needed such a big transformer because his amp (different amp than I have) was hooked to it too.

Do you think any of these differences can be the reason for the issues I'm experiencing in my system

I agree the Marantz pre/pro is defective. The problem is that the fault is intermittent. Unless it misbehaves on the test bench right while it is wired up in front of the technician you won't find the problem. In addition the fault has to persist long enough to be able to trace it.

This is just the sort of fault that in modern equipment is impossible to find.

If this unit is still under warranty, I would demand a new replacement unit. If the unit is not replaced I highly doubt you will solve this problem, unless you are very lucky. If the unit is out of warranty, you will end up sending it to the recycling center most likely, unless you are very lucky.

I see. The unit is not under warranty.
The strange thing is that I fully tested this pre-pro at the original owner's house and it appeared to be working properly. I also have no problems when I listen to music through headphones connected to the pre-pro.
There are few differences between my setup and the original system owner's setup:
1. I'm using surge protector for the whole system and I'm starting to wonder if it can cause such issues.
2. The pre-pro is used with a step down transformer (toroidal 100VA). The original owner had a different and bigger one but he also needed such a big transformer because his amp (different amp than I have) was hooked to it too.

Do you think any of these differences can be the reason for the issues I'm experiencing in my system?

 

[TLS Guy]

I see.
The strange thing is that I fully tested this pre-pro at the original owner's house and it appeared to be working properly. I also have no problems when I listen to music through headphones connected to the pre-pro.
There are few differences between my setup and the original system owner's setup:
1. I'm using surge protector for the whole system and I'm starting to wonder if it can cause such issues.
2. The pre-pro is used with a step down transformer (toroidal 100VA). The original owner had a different and bigger one but he also needed such a big transformer because his amp (different amp than I have) was hooked to it too.

Do you think any of these differences can be the reason for the issues I'm experiencing in my system


I see. The unit is not under warranty.
The strange thing is that I fully tested this pre-pro at the original owner's house and it appeared to be working properly. I also have no problems when I listen to music through headphones connected to the pre-pro.
There are few differences between my setup and the original system owner's setup:
1. I'm using surge protector for the whole system and I'm starting to wonder if it can cause such issues.
2. The pre-pro is used with a step down transformer (toroidal 100VA). The original owner had a different and bigger one but he also needed such a big transformer because his amp (different amp than I have) was hooked to it too.

Do you think any of these differences can be the reason for the issues I'm experiencing in my system?

Strange how we get half the story. Yes, the step down transformer is almost certainly the cause. Why are you using one any way? Have you measured the voltage out of the transformer under load?

The pre/pro will present an inductive load so the power factor will be less than 1. So 100 VA is not the same as watts. The power consumption of a pre/pro is around 65 watts I think. So that transformer may well not provide enough power under all conditions.

I would get a voltage regulated unit of at least 150 VA and preferably 200 VA to have a good reserve.

You should know that low voltage and inadequate power can damage units like pre/pros, so you need good powering.

 

[drumace]

Strange how we get half the story. Yes, the step down transformer is almost certainly the cause. Why are you using one any way? Have you measured the voltage out of the transformer under load?

The pre/pro will present an inductive load so the power factor will be less than 1. So 100 VA is not the same as watts. The power consumption of a pre/pro is around 65 watts I think. So that transformer may well not provide enough power under all conditions.

I would get a voltage regulated unit of at least 150 VA and preferably 200 VA to have a good reserve.

You should know that low voltage and inadequate power can damage units like pre/pros, so you need good powering.

Hi TLS Guy,
My pre-pro (Marantz AV7005) consumes 60W of power.
I bought a Tacoma 100VA step-down transformer for it after I bought the unit when I was told that 90VA and above would suffice.
So, if the step-down is too weak, how do you calculate the required amount of power for the step-down?
Also, I would expect the pre-pro to not even power on if it receives too little power. Am I wrong?

Thanks again.

 

[TLS Guy]

Hi TLS Guy,
My pre-pro (Marantz AV7005) consumes 60W of power.
I bought a Tacoma 100VA step-down transformer for it after I bought the unit when I was told that 90VA and above would suffice.
So, if the step-down is too weak, how do you calculate the required amount of power for the step-down?
Also, I would expect the pre-pro to not even power on if it receives too little power. Am I wrong?

Thanks again.

Unfortunately you are wrong. You are dealing with an inductive load, and what is worse the load will not be constant, depending on the power drawn by the processor.

The VA rating you require is 60 watts divided by the power factor. This will be less than one. I do not know the power factor for that unit, so I can't calculate what you require.

The problem comes with the fact that voltage and current are not in phase with inductive loads. So you have the issue of true and apparent power. Now whist the true power will be 60 watts, the apparent power can be much higher. The supplying device must be able to meet the current demands of the apparent power needs. In practice this means that momentary current draws can be much higher than imagined. So when demands are not met then the AC waveform becomes clipped. This can lead the unit to malfunction and can do permanent damage. It will not stop the unit powering on.

The power divided by voltage to get the current draw only applies to a resistive load in an AC circuit. So we do not know the current draw from your unit even if plugged into an outlet of the correct voltage, but it will be higher than 60/110.

This is how people so often end up on the rocks with step down transformers. You are not the first by a long shot.

From the fact that this unit worked from a 200 VA transformer and not your 100 VA one, leads me to believe that your unit does not meet the current demand required to meet the apparent power requirements of your pre/pro.

So my rule of thumb is to advise a step down transformer have a VA rating in the range of 1.5 to 2 times the rated power in watts of the device.

To be honest I never advise units to be used in jurisdictions they were not designed for. It leads to many issues. I advise selling before leaving the country and replacing it in the destination country.

 

[AcuDefTechGuy]

I I tried all sort of sources and inputs and the results are the same.
It is usually on the right side of the system (fronts and backs).
I'm usually using the system for 2 channel stereo and the right front speaker is the one that fades out. If I switch between the R/L interconnects between the pre-pro and the amp, the problem switches to the left front speaker.

Did you switch speakers, instead of cables?