Marantz SR7015 Radio Interference from Radio Station

jwlawler

Active Member
I guess your choices are keep trying different filtering techniques, a different AVR - or maybe just move house!!
Which is cheaper: a new AVR or a new house? I would not be surprised if some members have A/V systems whose value rivals their house.
 

jwlawler

Active Member
I'd still suggest my capacitor idea. Expert advice would be good but I'll try to calculate a value for you.
 

CaptainJames

Well-known Member

CaptainJames

Well-known Member
Didn't prices fall when the transmitter was built?
Well, they may have temporarily dipped below an average of £1 Million, but probably not for long!
 

CaptainJames

Well-known Member

JDGL

Standard Member
I may have missed something from earlier, but was the effect of mains power input earthing discounted - as stated it appears to be linked to appliance's behaviour? A filtered power cable might help (as above, often considered unnecessary but occasionally useful).

I've been involved in CE EMC/EMI testing in the past, it's very easy for a circuit board mounted component, PCB track design or any other aspect of the electronics to pickup interference in unexpected ways. Not always due to bad design, but these things can be modelled with reasonable accuracy before production if warranted.
This is normally picked up through RF testing done in specialist test chambers.
However, CE marking can be done as self-certification, a less-good performance for a particular RF sweep might/could be argued away prior to sign-off...

It'd be interesting to see if the next model down/up in the range behaves the same. They will share some components & internal design but not everything.
 

jwlawler

Active Member
I'd still suggest my capacitor idea. Expert advice would be good but I'll try to calculate a value for you.

A 10 nF (nano-farad) capacitor will have an impedance of 800 Ohms at 20 kHz but only 11 Ohms at 1458 kHz. So, it should have a negligible effect on audio frequencies but it should damp the radio frequency well.

Ideally, you would get expert advice but it is hard to see any risk from such a tiny capacitance. I'll stop short of guaranteeing that.

There's nothing very special about 800 Ohms, I picked it as being very unlikely to have any noticeable audible impact. A larger value would probably also have no noticeable effect and greater radio frequency damping.

You can play with this site: Capacitor Impedance Calculator
 

noiseboy72

Distinguished Member
I may have missed something from earlier, but was the effect of mains power input earthing discounted - as stated it appears to be linked to appliance's behaviour? A filtered power cable might help (as above, often considered unnecessary but occasionally useful).

I've been involved in CE EMC/EMI testing in the past, it's very easy for a circuit board mounted component, PCB track design or any other aspect of the electronics to pickup interference in unexpected ways. Not always due to bad design, but these things can be modelled with reasonable accuracy before production if warranted.
This is normally picked up through RF testing done in specialist test chambers.
However, CE marking can be done as self-certification, a less-good performance for a particular RF sweep might/could be argued away prior to sign-off...

It'd be interesting to see if the next model down/up in the range behaves the same. They will share some components & internal design but not everything.
The device doesn't have a mains earth and it seems that the speaker leads are acting as the antennae. They are probably dumping the RF into the final stage of the amplifier, where the signal is being partially demodulated and reamplified. With RF this strong, any length of wire is going to pick up quite a strong signal! It's one reason why large AM transmitters are generally not located near housing.

A 10 nF (nano-farad) capacitor will have an impedance of 800 Ohms at 20 kHz but only 11 Ohms at 1458 kHz. So, it should have a negligible effect on audio frequencies but it should damp the radio frequency well.

Ideally, you would get expert advice but it is hard to see any risk from such a tiny capacitance. I'll stop short of guaranteeing that.

There's nothing very special about 800 Ohms, I picked it as being very unlikely to have any noticeable audible impact. A larger value would probably also have no noticeable effect and greater radio frequency damping.

You can play with this site: Capacitor Impedance Calculator
This is a good call and putting the capacitor across the amplifier terminals might well reduce the level enough to prevent the audio being re-broadcast. The filters I recommended should do the same thing, but not present any change in load to the amplifier.
 

jwlawler

Active Member
The device doesn't have a mains earth and it seems that the speaker leads are acting as the antennae. They are probably dumping the RF into the final stage of the amplifier, where the signal is being partially demodulated and reamplified. With RF this strong, any length of wire is going to pick up quite a strong signal! It's one reason why large AM transmitters are generally not located near housing.


This is a good call and putting the capacitor across the amplifier terminals might well reduce the level enough to prevent the audio being re-broadcast. The filters I recommended should do the same thing, but not present any change in load to the amplifier.

Didn't the OP try that or was he using a different filter?
 

Dem

Active Member
I admire your persistence, but I would give up and try a different AVR! There's obviously something inherent with the Marantz, and the speaker cables are probably just aggravating it.
I just can't believe that there is a component in a 2020 launched AVR that is that susceptible to AM band RFI. And I like the blue circle of light on the front of this amp, which is the only reason I bought it! No others I've seen that have a more interesting looking fascia unfortunately. Well, at least none with 8K capability and within a budget.
 

Dem

Active Member
So if you just have this 1 speaker and filter connected, do you get interference? If not, does it come back if you remove the filter?

You need to treat each channel individually. 1 filter will not fix interference on other channels. Perhaps try with 2 speakers both connected through the filtering and the normal length of speaker cabling. See what effect this has.

I guess your choices are keep trying different filtering techniques, a different AVR - or maybe just move house!!
I will try wiring in both the TDK filters that I was able to buy to the existing speaker wiring for the Left Rear and Right Rear speakers (the Right Rear at least has the longest run of wire buried in the wall). I just expected that even the speaker with one filter added would not reproduce the interference, but I get what you're saying that any of the attached speaker wires could be setting off the weak component in the amp.....
 

Dem

Active Member
Just as a brief update.....

I chased up ARQIVA who advised that they've passed the info onto their engineers for feedback.....

I sent a bit of a complaint into Marantz, with my views on their initial response that the unit "meets CE specification". I was then called by one of their Senior Engineers based in Germany who was quite sympathetic about the situation. The plan is for me to prep as much of the problem information as possible and he will forward that to Marantz engineering in Japan (as I have worked for a major Japanese automotive OEM supplier for 25 years now, I know the level of detail and diagrams that they would need to give it their best shot, so that'll take a bit of time....).

Yesterday afternoon, for a few hours, the interference could not be heard at all (without any TDK filters attached, but there were still quite a few ferrite beads left on the speaker wires). However, later in the evening it was noticeable again and today I'd say it was slightly louder again...

I've just wired in the 2 TDK RF filters to the Left Rear and Right Rear speakers (each also with a single ferrite bead around the brown wire and one around the blue wire). I would say that I have to put my ear right up against the centre speaker to hear our friends at Lyca Radio. Frankly, if this is the level it stays at, I would say this is a good result. However, I'm hoping it's not just coincidence given that yesterday there was no noise at all.

The additional 3 TDK RF filters I have on order are delayed, but hopefully they will arrive next week.
 

noiseboy72

Distinguished Member
I'm glad the filters seem to be helping. Hopefully you will resolve this.

I'm assuming the filters haven't affected the sound at all?
 

Dem

Active Member
I'm glad the filters seem to be helping. Hopefully you will resolve this.

I'm assuming the filters haven't affected the sound at all?
Thanks, and be great if they do work, so really appreciate your suggestion on this originally. I'm not sure if I've wired them the right way round or if it matters?!?! (from an RFI prevention and / or sound quality point of view). There isn't a clear 'input' / 'output' designation.

I'm no audiophile, but it all still sounds good to me. Maybe an expert would think it sounds crap, but it sounds fine to me! Be interesting if the additional filters help when I add them to the remaing 3 speakers. Will update when I receive and install them.

I'm also still hopeful that ARQIVA can take their foot off the transmitter gas a bit and maybe Marantz will also consider the robustness against EMC of their new line up!
 

Dem

Active Member
Thanks, and be great if they do work, so really appreciate your suggestion on this originally. I'm not sure if I've wired them the right way round or if it matters?!?! (from an RFI prevention and / or sound quality point of view). There isn't a clear 'input' / 'output' designation.

I'm no audiophile, but it all still sounds good to me. Maybe an expert would think it sounds crap, but it sounds fine to me! Be interesting if the additional filters help when I add them to the remaing 3 speakers. Will update when I receive and install them.

I'm also still hopeful that ARQIVA can take their foot off the transmitter gas a bit and maybe Marantz will also consider the robustness against EMC of their new line up!
So, success!!!

The additional TDK RFI filters arrived to day and I wired them into the existing speaker wires. I decided to keep the Ferrite beads on as well as assume they can't hurt. With the four main speaker cables modified to have the filters in series, the broadcast from Radio Lyca 1458 AM is no longer audible, even with my ear against a speaker. I didn't bother with one for the centre speaker or sub as seemingly no need.

Thanks so much for everybody's input, especially @noiseboy72 for suggesting the TDK devices.

At least hope that this thread helps any others with similar issues in future.

For the record, I never heard back from Radio Lyca and still awaiting a response from ARQIVA.... Sound United Europe have sent my summary report to Marantz Japan for their feedback as I still think its important they know that this AVR model does seem weak AGAINST certain RFI versus, for example, the Onkyo units in my house.
P_20210304_171208.jpg
 

noiseboy72

Distinguished Member
I'm really glad this worked for you!
RF interference is a black art and being able to use off the shelf components to cure the problem is a major win. Probably worth pointing out to Marantz what your fix was and share a link to the components, as it will give them a head start with developing a better output stage that doesn't suffer in the same way.
 

Dem

Active Member
I'm really glad this worked for you!
RF interference is a black art and being able to use off the shelf components to cure the problem is a major win. Probably worth pointing out to Marantz what your fix was and share a link to the components, as it will give them a head start with developing a better output stage that doesn't suffer in the same way.
Totally, I've worked on a few EMC engineering problems over the years with prototype cars before mass production and it's always a lot of 'fun'..................... lol

I've sent a few pages of a summary report to Marantz, along with the TDK RFI filter information, so be interesting what they're reaction is. Of course, I'm not expecting that they'll come up with a product change now, but maybe in the future, it's something they'll consider for upgrades / other models.

Thanks again!
 

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