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Loud buzz with Marantz receiver preout to amp

Hi Team —

I’m trying to connect an amp to my Marantz 4270 via the preouts so I can control volume with the Marantz (the amp, an Ashly CFT-1800, has no volume controls). I’m getting loud buzz that gets louder with every gain dial increase on the amp, and there’s no music coming through from my phono or aux sources.

I can hear FM radio, but have to really crank the Marantz volume to get the FM loud enough over the buzz. Something’s not right. I don’t think it’s a ground loop issue because of the total lack of any phono or aux source audio. The RCA jacks from the Marantz preouts go to the Ashly’s screw terminal inputs (the RCA cable heads were cut off and the 4 wires run to both sides, channel 1 + and -, and channel 2 + and 1. The Ashly has two more screws between those channel inputs dedicated for additional grounds — input and chassis — both of which are empty in this case.

 

The Marantz uses shared jumpers in its preout and front main in jacks that must be removed to plug in an amp — which means the front main in jacks are then empty. The manual indicates that I should connect the main in jacks to the rear pre outs to get sound from front and rear speakers, but I don’t use rear speakers. I tried it though, to see if that made a needed connection that was missing, but it didn’t help. Same buzz. I should also say, the Marantz just came back from my tech, who specifically gave the preouts a clean bill of health, knowing I wanted to set this up.

Any ideas? Thanks very much!

jlcase
Post removed 
jlcase OP
4 posts
 

Making progress: The amp has a clip that connects its “input” and “chassis” grounds. The manual states that while the clip should remain there in most cases, a ground loop can be helped by removing it. I removed it, and while a loud hum remains, I DO finally get sound from the Marantz’s preamp output — the only change I’ve made that’s done that. The hum seems to be improved slightly by reversing the AC plug into the power strip, as you mentioned, @jea48 — thank you. I removed all the other source inputs — no difference.

The Ashly makes a slight hum while it’s on that’s coming from inside its chassis. This is regardless of speaker output — it remains audible even with the gain turned all the way down, not from the speakers, from the amp itself. The hum sounds like the little version of what comes from the speakers when the gain’s turned up. The Marantz is silent when on — no buzz or hum coming from inside its case.

I wonder if getting an RCA-to-XLR box and the associated cables would improve the situation at all. I’ve been looking around the house for a ground cheater plug. May need to run to the HW store…

toddalin's avatar
toddalin
260 posts
 

OK, it is my recollection that Marantz jumper plugs have an extra long pin to engage the internal connection or such. 

I had actually considered this, but it seems like you would end up with no sound, rather than a loud hum..., but who knows?

This is a Marantz Jumper.  Note how long the positive pins are.  You can readily find examples on ebay.  

jlcase OP
4 posts
 

Thanks, @toddalin — yes, I have four of those: One for each set of Preamp-to-Mains (front and rear). I removed the top two (front) so that I could plug in the preamp output to the amp. The mains are sitting empty — I tried them with an RCA cable between the rear preamp out and the Front mains in (as the manual suggests so that you can have the Marantz running power to the rear speakers). I don’t use rear speakers, but I tried it just in case, and it didn’t make a difference in the hum.

toddalin's avatar
toddalin
260 posts
 

I am suggesting that perhaps your "RCA cable" does not have long enough positive pins to properly engage the signal through the jack.  Are the pins on your cable as long as shown on that jumper?

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