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"ghost" frequency coming over vintage Hitachi receiver?

174.21.217.192
Posted on October 31, 2015 at 20:09:56
waltjohns
Audiophile

Posts: 102
Joined: November 15, 2009
 Hi, I'm writing for a friend. They have a 70's Hitachi receiver that sounds fine except for one glaring issue: At all times, the receiver is playing a relatively quiet FM frequency. It has nothing to do with where the dial is and keeps up in the background whether you change the frequency on AM or FM. It plays when the Phono is on. I think it disappears when you turn on the Tape Monitor.

I have no idea what to do about this. I tried using the "B" speaker inputs on a whim but obviously that did nothing. Any advice?

Thanks,

WJ

 

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RE: "ghost" frequency coming over vintage Hitachi receiver?, posted on November 1, 2015 at 21:04:25
dxho
Audiophile

Posts: 86
Location: Virginia, the colonies
Joined: September 24, 2006
 Try changing the connecting RCA cables.

 

RE: "ghost" frequency coming over vintage Hitachi receiver?, posted on November 1, 2015 at 22:28:49
waltjohns
Audiophile

Posts: 102
Joined: November 15, 2009
 Hmmm ... the record player has a cable that comes out of the back, so I can't change that. I tried unplugging the tape player from the receiver and turning it on and off and there was no change.

 

RE: "putting my hands on the top of the receiver made the noise greatly decrease", posted on November 2, 2015 at 08:57:03
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 Since the laying on of hands works, have you tried grounding the chassis to see if it helps?

Run a wire from under a chassis screw, or the phono grounding screw, since it's a receiver, to the ground of the nearest electrical outlet.



 

RE: "putting my hands on the top of the receiver made the noise greatly decrease", posted on November 2, 2015 at 09:00:24
waltjohns
Audiophile

Posts: 102
Joined: November 15, 2009
 Dumb question but where't the ground on an outlet?

 

Depending on how the house is wired, posted on November 2, 2015 at 09:40:17
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007



The ground will be the third (upside down U shaped) prong, if the outlet is grounded, or the screw that holds the wall plate cover on.

 

It will have a mains AC power cable wich plugs into an, posted on November 3, 2015 at 01:23:59
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 AC socket on the wall or one on the back of the receiver, to power the turntable. That is, in addition to the twin RCA lead for the phono audio signal out and into the rcvr, to amplify it.

It might also have a ground wire coming out of it. Many if not most turntables do.

So it is most unlikely that the turntable has only one lead coming out of the back.

Inspect the signal leads right back into the turntable and look for a thin third one that has been cut off or left inside the turntable.

It's a rcvr - so it just WILL have antenna terminals. So, there will be a ground terminal for both AM and for FM, and it might be just a single shared Gd terminal for all radio and phono. Try it with the ground wire from the turntable.

Also put an actual FM antenna on to those terminals and a single length of wire on the AM antenna post. That can't hurt.

I have to ask. Why did they buy an FM receiver if they weren't going to attach an antenna - to receive FM - to it? Most of them come with a basic T antenna in the box for this purpose. Connecting it is a vital step if you want to receive FM signals at all well.

LBNL the rcvr just might need repair.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: "ghost" frequency coming over vintage Hitachi receiver?, posted on November 3, 2015 at 01:39:01
waltjohns
Audiophile

Posts: 102
Joined: November 15, 2009
 Thanks all. The turntable is grounded and doing just fine and these problems started pre-turntable replacement.

If I ran a wire from the receiver into the outlet (which is two-pronged), I couldn't run if off the phono ground, right? What should I attach it to?

Thanks!

 

RE: "ghost" frequency coming over vintage Hitachi receiver?, posted on November 3, 2015 at 03:17:30
stellavox
Audiophile

Posts: 413
Joined: June 23, 2004
 Can you determine the "ghost" station call letters? Since it's coming in on Phono (high gain stage), if the station is nearby the problem could be "electromagnetic interference" - ie an RF signal is getting into the receiver thru the phono input. Try putting "shorting plug" RCA's on the phono inputs and see what happens.

Charles

 

RE: "I couldn't run if [sic] off the phono ground, right?" , posted on November 3, 2015 at 17:03:16
1973shovel
Audiophile

Posts: 10117
Location: Greenville SC
Joined: February 25, 2007
 Why couldn't you? In fact, with the outlet only being hot and neutral (no ground), it may actually benefit the table to take a ground wire from the receiver to the wall outlet screw. Hopefully the outlet's earthed. Make sure there's no paint on the back and threads of the screw holding the ground plate on.

Keep in mind that the radio frequency interference you're hearing may not be cured by this grounding. But it's an easy fix to try.

 

RE: "ghost" frequency coming over vintage Hitachi receiver?, posted on November 6, 2015 at 06:45:21
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 What an interesting problem. I have heard similar with AM not FM. I would have suggested an AC filter but you said it changes when you put your hands on the receiver. Does the receiver not have a metal cover? If it doesn't, maybe shielding the receiver will help. Maybe some kind of metal foil, just as a test.

 

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