Grounding an Old Amp.

[ChanMin]

Ive just acquired a jc50 ... a 1980s roland jazzchorus amp...

it comes with a 2pin plug and a transformer to convert to our local voltage.

the amp isnt grounded... so i get little "zaps" frm the metal parts of my guitar.
im aware that if i insulate myself from the ground (floor) im ok...
but i cant possibly be playing wearing rubber slippers all the time right~??~


How do i go about grounding the amp?

 

[fibredrive]

hey bro, wouldn't the usual way work? i.e. cut the wire and buy the 3 pin head and fix 'er up...?

 

[ChanMin]

im scared that there isnt 3 wires inside...

cus this amp is from the early 80s... so back then the 3 pin plug might not have been realized yet. i couldt be wrong... so i just wanna check with the amp gurus

 

[KennethC]

the amp isnt grounded... so i get little "zaps" frm the metal parts of my guitar.

Mojo mah bro...I'm sure Hendrix always got zapped..

My gut feeling is it could be the same as the current day wiring..

the best way may just be to cut it and see

 

[fibredrive]

Mojo mah bro...I'm sure Hendrix always got zapped..

ahhhh...explains the hairdo...hmm.

 

[fibredrive]

is the power cable detachable? or fixed? i bought those PC 3 pin cables from sim lim ($5 each) to replace all my power cables at home, mixer, fx rack, amp etc.

 

[widdly]

im scared that there isnt 3 wires inside...

cus this amp is from the early 80s... so back then the 3 pin plug might not have been realized yet.

3 pin grounded mains wiring was invented in 1928 by Philip F. Labre.

I'd check the amp mains but I'd have a good look at the transformer too.

 

[ChanMin]

well ... heres a picture of the back i found online. the plug is the dual blade type.

cable doesnt seem to be detachable. i will probably remove the back panel and take a look to confirm this.

 

[jasonbruce]

I had the exact same problem with an old Sears I brought back from the US.

Old 2-pin setup, fear that there wouldn't be the all-important 3rd earth wire upon cutting, and most importantly, an undetachable cable that's affixed to the transformer. These old transformers are pretty much where all the old juice comes from, so I'm not keen on replacing it even though there are a few niche sellers online for this sorta thing...

Plus, even if you do successfully get the three-pin job done, will it still fit thru the transformer's input end? That is designed to take the old 2-pins right?

For what it's worth, another potential issue is whether or not the step-down transformer is sufficient to handle the voltage of the amp. I was told that while the step-down's listed capacity may be high enough, playing thru the amp for prolonged periods might still be too much to handle.

*Sigh* The perils of amp-gas.

And by the way, those zaps are pretty damn frightening. Brought a whole new meaning to the term "electric guitar", cos I was getting fried each time my fingers touched the "ashtray" of the 52.

 

[ChanMin]

haha hmmm but all the jc120s i see have 3 pin plugs? or perhaps they are the newer ones?

man i would really hope some one has done grounding on a jc50 before... ANYONE???

 

[widdly]

According to these schematics, you should be able to re-wire the amps power transformer to run straight off a 240v supply and get rid of the external step-up transformer.

http://www.blueguitar.org/new/schem/_ss/roland_jazz-chorus1.gif
http://www.blueguitar.org/new/schem/_ss/roland_jazz-chorus2.gif

...in schematic 2 you can see the different wirings for different supply voltages. You can also see that there is only a 2-pin connection to the power if it's running at 100v (~110v) so the cable is probably the original.

If you are not confident with a soldering iron, I'd get some one in the know to check it out. Sounds like there might be some other issue with it.

 

[Cavett]

Bring it to a certified electrician and let him do the redo wiring for you.

 

[ChanMin]

most definitely.

wont wanna die trying to rewire a $400 amp...

 

[Indigo_blues]

hey my Dad's in China at the moment but if you need help just gimme a buzz. cheers