Continental 1 Hum

[gordo]

HI,

I have a Continental 1 (mono amp) that has developed a loud hum.

The hum is hard to hear when a record is playing, however, at the start and finish of a record it is quite loud (before the volume control shuts off).
Also if I lift the arm off the record it is quite loud.


I pulled the amp out and had an audio guy check the tubes and capacitors, he said all is OK.


I am suspecting the volume control may be the problem?

Can this be checked?

Any advice appreciated.


Regards

Gordon.. 

[Ron Rich]

Hi Gordon,
Remove the input plug from the amp, play a record--still have hum ? If so, the problem is inside that amp-- if not, it is usually a poor connection in the pick-up, ground, wiring--(there is no way I know, that a tube tester can detect a tube "hum"--) 99.9999% sure it won't be the volume control-- Ron Rich

[gordo]

Thanks Ron,

I removed the input plug and no hum.
So, it appears to be in the connections/needle/wiring.

This is where it becomes a little odd.
If I lift the arm off the record (while it is playing a record) the hum starts low but increases over about 10 seconds.
If I replace the arm back onto the record and run it for 10 seconds, then lift it again, same occurs.
The hum is bearly audible for a few seconds and then gets louder.

It gets louder with added volume.

I have checked the connections are clean and tight.

Anything else I can try?

Regards

Gordon...

[Ron Rich]

Gordo,
Sounds as if it's "normal" to me--AVC is attempting to even out the no-sound from the pick-up ? Ron Rich

[robnyc]

Mar 11, 2018 2:31:40 GMT gordo said:

Thanks Ron,

I removed the input plug and no hum.
So, it appears to be in the connections/needle/wiring.

This is where it becomes a little odd.
If I lift the arm off the record (while it is playing a record) the hum starts low but increases over about 10 seconds.
If I replace the arm back onto the record and run it for 10 seconds, then lift it again, same occurs.
The hum is bearly audible for a few seconds and then gets louder.

It gets louder with added volume.

I have checked the connections are clean and tight.

Anything else I can try?

Regards

Gordon...

Gordon, this will be 60HZ  (or 50HZ) hum and it is due to either resistance in the shielding ckt,  or a ground loop, or lack of proper grounding of the mech deck.

Typically, the shell of the RCA pickup plug should have no continuity with the mech. It must float electrically till it reaches the amp input. Check that neither pin on the cart is touching the tonearm shell. BTW: Do you have the original G.E. cart?

The AMI mechs of that era had a separate ground wire (black w/spade lug) that tied all components together. Look for it around the edges of the mech base casting. If it comes loose hum and clicks will result.

The rising hum is as Ron suggested, a function of the AGC bringing up the gain with no drive signal.

RobNYC

[gordo]

Thanks for your time Ron and Rob.

Thats why I cannot hear the hum while the record is playing.

I worry too much....

Regards

Gordon...

[gordo]

Hi All,

I have revisited this 'old' post as the hum is becoming annoying.
It is loud enough to hear with the music playing.
What I have done to try to fix this is....

If I remove the input plug, the hum stops.

I have removed the amp and cleaned and checked all the plugs and tubes are conecting correctly.

Nothing appears to be burnt in the amp, however, I am not a technician and unfortuntely none
are available in Australia. The amp was professionally rebuilt a few years ago.

The wires from the cartridge do not have continuity to the tone arm if the input plug is removed from the amp.

The tone arm and the cartridge wires do have continuuity if the input plug is inserted in the amp.

Can anyone offer anything I can check?

Regards

Gordon....

[jukenorman]

Hi Gordon,
If you remove the iput plug and the hum stops, you will likely have a gound loop in the cartridge wiring. Is it still the original cartridge or has it been replaced? Go through the wiring and connections making sure that it is all in order and neat and tidy. Pay particular attention to the negative wiring from the cartridge through the tonearm making sure that it is not touching any bare metal on its route.

Norman.

[gordo]

Hi Norman,

I will have another look at the tone arm. I might be best to remove it.

I have a Stanton 400 V3 cartidge installed.

The jukebox sounds great, just the bloody hum.....

Cheers Gordon...

[gordo]

Hi Norman,

I removed the tone arm and checked the wiring and the plug.

All good.

I also resoldered the wires that connect to the cartridge, all appears okay.

How else can I check the 'ground loop' you suggested above?

There is no conectivity between the tone arm wires and the tone arm (as long as the input cable to the amp is not inserted).

Cheers

Gordon

[jukenorman]

Hi Gordon,
There is one other thing to look at. The Stanton cartridge has a small metal strap going from one of the negative terminals to the case for shielding purposes. Theoretically, the paint on the cartridge body provides insulation but it only requires the merest nick on the paint to destroy that. When I fit that type of cartridge in the likes of a Continental, I put heat shrink sleeving over the fixing lugs for better insulation. Others that I know simply snip off the metal strap.

Norman.

[gordo]

Thanks Norman,

I removed the metal strap years ago.
I think I was advised by either Ron or Rob/NYC to do that.

The hum is now gone!!!

I'm not sure why, it was there one day and gone the next.
I can only assume a loose connection somewhere.

My next problem is to fix those lights in the radar unit, they are so difficultto get to.

Have a great Christmas and New Year.

Thanks for your help throughout the year to everyone.

Cheers Gordon.

[gordo]

Hi All,

Unfortunately the hum has returned (I knew I hadn't done enough to fix it).

Could it be coming from the cartridge?

I think I checked everything else that I can.....

Cheers Gordon,

[jukenorman]

When you have hum, if you disconnect the input phono (RCA) plugs at the amplifier and it disappears, then it's in the cartridge or wiring. What to look for - bad connections, are the connectors at the cartridge nice and tight? If it comes and goes, you might be able to identify the area of problem by jiggling the cables. There is also a plug/socket midway between cartridge and amplifier - are the soldered connectins there sound?

Norman.

[gordo]

Thanks Norman,

The only thing I have not checked is the cartridge.
I think I may still have the old one that I removed years ago.
I'll reinstall it and see if that fixes the problem.

Thanks again
Gordon..