Rockola 426 GP II turntable cartridge Ground hum question

[bob63]

Hi Everyone , I am Bob, in Ontario Canada , I just found the forum and joined . I have a few questions regarding my Rock Ola 426 GP II only had this for a few weeks , mechanically its fine , sound wise it has a hum , you dont really hear it when the record is playing but you sure do when the needle is up . it has a magnetic cartridge on it , soldering is mediocre at best , if i move the wires from the cartridge to the amp I can change the tone of the hum.

questions are , is the magnetic cartridge supposed to be grounded to a common ground ? the amp is a 40218-A  there is a magnetic preamp 40201-A the plug in from the cartridge is only 2 pins . Since i can move the wires for various "hums" what to you guys think I should do to go at this problem ? rewire and solder and change the magnetic cartridge out ?

Has any one gone back to ceramic cartridge ? If you unplugged the preamp would the ceramic work ? I dont see this 426 model as high fidelity at any rate and wondered if going back to a ceramic cartridge would make any sense at all. I am sure by now you have guessed, I know nothing about these things. Thanks in Advance , Bob   

[Ron Rich]

Hi Bob,
Got the "book" ? It will answer most of your questions-- if you don't know where to find a good copy, see our FAQ's section--"books---" post. I would stick with a mag cart.--but you need to find out what happened to the other two wires ? Do NOT, NEVER, EVER, solder to a cartridge-- use slid-on connectors- they just do not like heat !! Ron Rich

[bob63]

Thank you Ron, I will go to the FAQ and find the book, thank you again sir, Bob

[bob63]

Ron, I guess I should have said m there are 4 wires coming off that mag cartridge, I have to look tomorrow in better light to see how they are on there, but the plug it goes into to plug into the 40218-A amp only has 2 large pins and the amp itself only accepts 2 large pins, there are not 4 holes to plug into on the amp, only 2

[jukenorman]

Hi Bob,
You do really need to get a copy of the manual! There are four wires coming from the magnetic cartridge but the two cartridge grounds are commoned at the cartridge end of the cable. The two large pins at the amplifier end carry the two positives from the cartridge. The overall shield at the amp. plug carries the ground. The cable from the cartridge to the amp. also has an overall screen which must only be connected to ground at the amplifier end. And I agree with Ron, you should stick with the magnetic cartridge!

Norman

[Ron Rich]

Hi Norman,
I don't know what it's called in Merry old England, but a "shield wire" (stranded wire, wrapped around other wires) but only connected on the powered end (amp), is called a "drain", here-- The idea is to "drain off" un-wanted radio frequencies-- Ron Rich

[bob63]

Thank you Norman, Thank you Rich , just bought a service manual download PDF , going to download it now and have a look , and I will keep you posted, thank you , Bob

[Ron Rich]

Hi Bob,
Well, what can I say-- Obviously, you did not read the "Hi Newbies" post, as you were asked to do, in a PM. I hope you have not wasted your money on that PDF version, of the manual-- but I sure would not bet against it ! Ron Rich

[jukenorman]

Hi Ron,
To go back to cabling, we in the UK call the shield wiring the screen. In industrial applications like the oil and gas industry, a multi pair control cable for example - typically each pair would be individually screened and there would also be an overall screen. The wire which connects the screen to earth (or ground) is called the drain wire.

Norman.

[bob63]

Hi Ron, no, I didnt even see the PM , I will check it out now, the PDF manual is over 80 pages , lots of schematics and pics and fixes to all parts of the unit , I will go read what I was supposed to before

[bob63]

I grounded the 2 ground wires off the cartridge to the black that is in the cable that holds the left and right wires , Hum is gone , plays fine altho, a few records seem to fade in and out a bit on the left or right side, I could chalk those up to poor 45s I suppose . Most are playing very nicely now