Question Marantz PM KI Ruby amp hiss and hum

mark1811

Novice Member
Mark, I have your same couple, PM-KI Ruby and the SA-KI Ruby.
After your post I have checked and I confirm it is exactly the same by me.
I have the Grado GW 100, wired through a QED precision Jack-to-Jack cable.
I could hear a feeble hiss from the PM-KI headphone output, not dependant on the volume level. No audible hiss when using the headphone output of the SA-KI.
The hum disappeared when I switched off the "video" devices (TV, DVD player, Nintendo switch), unplugging them from the power outlet (I have them on a dedicated power strip with a switch). I have also unplugged the cable TV cable from its socket (even though I have put a high pass filter there, because it was causing hums with the turntable).
So, no hum, just some feeble hiss. And I noted that I like the output of the SA-KI slightly more, at least with my Grado headphones. The SA-KI is connected to the PM-KI though a 60 cm Audioquest Golden Gate, the longer signal path is of course putting the PM-KI at disadvantage, but I am not sure the difference (hiss aside) can be explained only by this fact.
Interesting. I notice if I disconnect the phono cables from the power amp input (I use this as the to power the front channels from my avr) the hum is reduced. TBH, I've stopped worrying about it as it's not noticeable in day to day use. This is my first experience of high end hi fi so I thought issues like this wouldn't occur. Live and learn.
 

Helix Hifi

Well-known Member
Interesting. I notice if I disconnect the phono cables from the power amp input (I use this as the to power the front channels from my avr) the hum is reduced. TBH, I've stopped worrying about it as it's not noticeable in day to day use. This is my first experience of high end hi fi so I thought issues like this wouldn't occur. Live and learn.
You could always try and use another power cable,or new main block strip of some kind. Now I’m not saying it we’ll make the sound better (it could, but doubtful). Still it could help with RF interference from other powered equipment nearby. Or try a new AVR.
 

mudan

Active Member
Well thanks for the tips... Let's see if anyone can improve the situation. It's a very low level hum on mine however and barely noticeable.
 
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MMi

Novice Member
Hi here, I received my silver/gold PM-KI Ruby last week. Lots of fun to say the least. I am absolutely in love with the sound and the build quality is next to nothing. The point of concern is the static hum I am getting in the headphones, exactly as reported in this forum.
The hum goes away when I turn off and disconnect from the power grid my Oppo UHD-203 I use as a DAC. I own 2 other amplifiers, one being Marantz PM8004. I tested them with the same signal and power cables and their headphone output generate sound only if I play music on my Oppo. Otherwise the headphones are dead-silent but not when hooked up to Ruby.

I cannot afford amplifier without the option of headphone listening. Sending it for repair is too much hassle. Besides someone from this forum sent the unit with identical issue and they had not repeaired it. Would you recommend I start my return process or there is a way to tackled this problem?
 
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Helix Hifi

Well-known Member
Hi here, I received my silver/gold PM-KI Ruby last week. Lots of fun to say the least. I am absolutely in love with the sound and the build quality is next to nothing. The point of concern is the static hum I am getting in the headphones, exactly as reported in this forum.
The hum goes away when I turn off and disconnect from the power grid my Oppo UHD-203 I use as a DAC. I own 2 other amplifiers, one being Marantz PM8004. I tested them with the same signal and power cables and their headphone output generate sound only if I play music on my Oppo. Otherwise the headphones are dead-silent but not when hooked up to Ruby.

I cannot afford amplifier without the option of headphone listening. Sending it for repair is too much hassle. Besides someone from this forum sent the unit with identical issue and they had not repeaired it. Would you recommend I start my return process or there is a way to tackled this problem?
Maybe a ground loop...Do you have all of your hifi kit connected directly to the same power strip? And do you experience hiss/hum from your hifi speakers? Or only from headphones? If let’s say you hear hiss from the hifi speakers. Then that to some degree is perfectly normal. It is the amplifier noise floor you hear. But you should not have any hum from the hifi speakers. But If you only hear hiss/hum from the headphones then I don’t think the Ruby is broken, since other people are experiencing the same problem. One option could be to use different headphones, or use other headphone cables. If that is possible.
 

MMi

Novice Member
Much appreciate your hints Helix.

No, nothing comes out of the speakers when no music is played; even on a max volume, while the headphones produce hum under identical circumstances, even with the volume set to min. I have 2 pairs of headphones, Sony MDR-Z7M2 and Sehheiser HD599 and getting the same result with both.
I hooked up my old Marantz NR1403 AVR to the same power outlet and same signal cable as Ruby and use the same headphones and there is no hum.

Since you made a remark about ground-loop, I am thinking this might actually be the reason, even though Ruby and Oppo are connected to the same power outlet. I experimented a bit and found that the level of hum drops if I wire-connect the chassis of my Oppo to Ruby's GND screw, although it does not go away entirely. I am going to look into this more and will post an update.
 

Helix Hifi

Well-known Member
Much appreciate your hints Helix.

No, nothing comes out of the speakers when no music is played; even on a max volume, while the headphones produce hum under identical circumstances, even with the volume set to min. I have 2 pairs of headphones, Sony MDR-Z7M2 and Sehheiser HD599 and getting the same result with both.
I hooked up my old Marantz NR1403 AVR to the same power outlet and same signal cable as Ruby and use the same headphones and there is no hum.

Since you made a remark about ground-loop, I am thinking this might actually be the reason, even though Ruby and Oppo are connected to the same power outlet. I experimented a bit and found that the level of hum drops if I wire-connect the chassis of my Oppo to Ruby's GND screw, although it does not go away entirely. I am going to look into this more and will post an update.
Marantz usually makes very good amplifiers. Still they are not immune to problems regarding their amplifiers. You can’t just live with it? If it is working order elsewhere. Still I know it’s annoying, and to be honest I would exchange to the Model 30. I’ve had many Marantz-amplifiers-no hiss/hum.
 

MMi

Novice Member
Thank you Helix. I am a long-time enthusiast of Marantz. I admire their attention to details and uncompromising pursuit of musical perfection. Ken Ishiwata's and his team managed to build not just amazing audio equipment but also the philosophy around reproduction of musical arts. And Ken's heritage survives in new models like PM-12 and 30 which are outstanding.

I have an update on humming headphones. A close friend was dying to listen to my Ruby. He happened to be an engineer with solid exposure to sound systems. We spent over 2 hours listening to music and another hour poking around the problem. He eliminated ground loops as a cause with high quality isolation transfomer. Eventually we realized a very simple but disturbing truth: the hum actually appears as soon as headphones are connected to the unit. If noting else is connected, the level is very low but it is clearly noticeable.

It looks like Ruby's headphone amplifier generates response to electrical noise coming from headphones cable. Given other people report the same problem, a glitch in headphone channel desing might be the reason. We tried 3 different pairs of headphones and noticed that noise tone and volume changes a bit between them, but never goes away. We could not reproduce this effect with any other equipment that can drive headphones.

Can I live with it ? Probably yes. However, given the reputation of Marantz reference series and the price point, we set the expectations higher and it is harder to accept such a problem. I opened a ticket with Marantz support and hope they will come up with something. We shall see.... I will post an update as soon as I know more.
 
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