Loud hum from technics 1500c = broken unit?

[GearNostalgia]

Hello.

I have been using my Technics 1500c with the build in preamp and into one of the AUX ports of a home cinema amp for over a years. Last week there was a loud hum when I started the amp with no other equipment turned on. I instantly assumed the old amp had died, but after investigations I have discovered that if the 1500c is connected to the amp and the power cord in in the Record player the hum starts. I don't need to turn on the recordplayer, just have the power cord attached. The store wanted me to jump through the usual hoops and test other cartrigdes, cables etc... I don't have extras cables to test with, but if I remove the cartridge it is the same. is it likely at all the cable should have broken down to cause this in a rack with no cahnges? Is this a common fault? I assume it is just a plain case of returning the 1500c to the store for repair?

 

[MaxwellsEq]

Hello.

I have been using my Technics 1500c with the build in preamp and into one of the AUX ports of a home cinema amp for over a years. Last week there was a loud hum when I started the amp with no other equipment turned on. I instantly assumed the old amp had died, but after investigations I have discovered that if the 1500c is connected to the amp and the power cord in in the Record player the hum starts. I don't need to turn on the recordplayer, just have the power cord attached. The store wanted me to jump through the usual hoops and test other cartrigdes, cables etc... I don't have extras cables to test with, but if I remove the cartridge it is the same. is it likely at all the cable should have broken down to cause this in a rack with no cahnges? Is this a common fault? I assume it is just a plain case of returning the 1500c to the store for repair?

It's tricky to diagnose if you can't swap things.

Is the hum mechanical (coming from the TT) or from the speakers? Do you have anything else you can plug the turntable into with a line-level port? Do other sources into the AVR work normally?

 

[GearNostalgia]

The hum comes from the speakers when the 1500c has a powercable connected. There is no hum playing audio from CD, TV or tapedeck. Hum dies when the powercord is disconnected.

 

[MaxwellsEq]

The hum comes from the speakers when the 1500c has a powercable connected. There is no hum playing audio from CD, TV or tapedeck. Hum dies when the powercord is disconnected.

And it just suddenly happened?

It's unlikely that an RCA to RCA cable would fail, but perhaps it has. Have you tried only one channel plugged in at a time? Can you use an RCA cable from another source temporarily? You could also order a cheap one from AMZN

The most fragile part electrically, are the cartridge pin connectors. Ensure everything is turned off before injecting these! Do they look OK?

Does the turntable have an earth flying lead and is it properly connected?

The internal phono preamplifier may have failed, but it's worth eliminating connectors and earth loops first, otherwise your replacement turntable may arrive and you still have a hum problem.

 

[GearNostalgia]

Hi. yes, it just happened out of nowhere. One day was looking at TV normal. Next day turned on the amp and there was a hum with nothing on except TV.

Yes, the hum comes with only left or right output connected if the powercable to the 1500c is connected. It is a nightmare to dig swap the cable in the map cause it sits super tight to the back wall and cable to another device just leaves 1 inch clearance.

No there is no ground (earth flying lead) cable and never has been since I have been using the internal phono stage in the 1500c with line out. And it has worked really well for over a year this was. I had a separate riaa before with ground cables from both the riaa and the turntable and that was not fully reliable.

As for the cartridge pins. I had not changed anything i that setup for many month and I use the fast heads that screws in and out. Hum is still there with any of ny cartridges or without any attached.

 

[GearNostalgia]

@MaxwellsEq I have made a lot of tests now. I have added a ground cable. It reduced the hum by half. Weird cause two weeks ago without a cable it was dead silent. After that I found a pair of very thin cheap old rca cables and made another test. No difference from the previous more premium pair. Then I discovered that the amp in my sons game room a Yamaha RX-A1030 actually had a phone stage build in. So I carried the turntable in there and hooked it up. No hum. But on the other hand I could hear some whirring motor sound when I turned on the turntable. Also tried the build in phono in the turntable and then there was no noise. No I am so confused. Could it be something introducing hum in just that pair of Aux on my main receiver since there is no hum from the CD or tape? Maybe I should try and swap some input? But it is hell of inconvenient...

 

[IPunchCholla]

Have you unplugged and restarted the cinema amp? Just yesterday I was getting buzz in my speakers that I thought was the turntable. Adjusting the flying lead would reduce the sound noticeable, but not make it go away. My turntable feeds to first a phono pre and then a computer interface before being processed on the computer and the back to the interface and out to the amp/speakers. I tried all sorts of things, but what fixed it was unplugging the interface and plugging it back in.

 

[GearNostalgia]

Have you unplugged and restarted the cinema amp? Just yesterday I was getting buzz in my speakers that I thought was the turntable. Adjusting the flying lead would reduce the sound noticeable, but not make it go away. My turntable feeds to first a phono pre and then a computer interface before being processed on the computer and the back to the interface and out to the amp/speakers. I tried all sorts of things, but what fixed it was unplugging the interface and plugging it back in.

Hi thank you for the tip, but yes I have tried that. Considering that it worked different on another amp in another room I am curious about moving the amp and trying it in another room. Could the wall socket get weird?

 

[IPunchCholla]

Hi thank you for the tip, but yes I have tried that. Considering that it worked different on another amp in another room I am curious about moving the amp and trying it in another room. Could the wall socket get weird?

It really sounds like a ground loop that has suddenly appeared in connection to the system the TT was in. I doubt it is the house electricity. If you haven’t added or removed anything connected to the same system, then it sounds like one of those weird, stray events like mine. The only way to diagnose it is to put the TT back and start unplugging (turning off is not enough as most modern appliances are on even when they are “off” to a certain extent) one component at a time. If that doesn’t solve it, you would have to move on to unplugging anything else that is on the same circuit.

 

[GearNostalgia]

It really sounds like a ground loop that has suddenly appeared in connection to the system the TT was in. I doubt it is the house electricity. If you haven’t added or removed anything connected to the same system, then it sounds like one of those weird, stray events like mine. The only way to diagnose it is to put the TT back and start unplugging (turning off is not enough as most modern appliances are on even when they are “off” to a certain extent) one component at a time. If that doesn’t solve it, you would have to move on to unplugging anything else that is on the same circuit.

I guess so. I moved the turntable to another amplifier in another room and there is no hum there, but there is a whirring sound coming through instead when I turn it on and the motor rotate the disc platter. Is that a normal thing to hear on really cheap amplifiers?

 

[boxerfan88]

If you’ve a antenna cable connected to the system (TV or AVR or set top box), disconnect them and see if the hum goes away.

If u don’t have antenna cable, pls ignore this post.

 

[GearNostalgia]

If you’ve a antenna cable connected to the system (TV or AVR or set top box), disconnect them and see if the hum goes away.

If u don’t have antenna cable, pls ignore this post.

There is a cable for the radio tuner. Will jerk that out.

 

[GearNostalgia]

Problem solved. Thank for all suggestions. @boxerfan88 led me on the right path. I jerked out the radio antenna. No change. Then I discovered a the cable to a composite video jack when my old receiver feeds video to the TV to show the on screen menus (some setup need this). I jerked that out and the hum was gone. Did I add this last week? No, I did not, but LG rolled out and update on the TV, guess that they made some changes to the video there that affected grounding in the video signals. Cable is out. hum is gone!