safety ground

[Colette]

My only (limited) experience with electronics is tube guitar amps.
One of the first things anybody will suggest is to make sure (on an "old" amp) the amp has a 3 wire power cord.
I recently bought a Kenwood Integrated Amp and am getting ready to Pull it apart and recap/check/clean it.......so i joined here to get some Knowledge/Help.
From what little i have read, it does not seem like a 3 wire power cord is a concern with SS Audio Amps. Is it a bad idea for some reason.?
Thank You

 

[Alan0354]

It's not a bad idea, more like people are cheap to put 3 prong plug. All the high quality ( say expensive) ones have 3 prong with the ground connecting to the chassis.
That said, I am not suggesting you must add the 3 prong. There's something to if it's not broken, don't fix it.

 

[Oldsansui441]

Is it a bad idea for some reason

Welcome to AK, l haven't experienced this myself because l haven't converted any but l know it can lead to a hum in the unit.

 

[Eastham]

Like Oldsansui said It could lead to ground loops if one of your components isn't grounded properly. I was going to add a earthed cord to my Yamaha but in the end couldn't bring myself to replace the original which was in amazing condition, I wouldn't worry about it to much.

 

[woodj]

It is a bad idea. Those units were engineered to use 2 wire.

 

[c.coyle]

From an electrical and safety standpoint, there is nothing wrong with doing this. But, It can supposedly introduce ground loops (hum, see below), and it may affect resale value. A good middle ground is to replace the original 2 prong, non-polarized plug with a 2 prong, polarized plug. You need to understand hot and neutral, but that's not hard.

I personally have added three prong plugs to a number of old amps and receivers, and never had a problem with hum. But that's a small sample, and maybe I'm just lucky.

 

[Colette]

Yeah.....OK. There is not the inherent danger with a stereo amp that there is with a Guitar/Instrument amp, but it never hurts to err on the side of.......
There is no collector value to a Kenwood 7100, so i am not worried about that. Getting a 3 wire through a 2 wire strain relief is often difficult. I like your idea about switching to a polarized, 2 wire plug. I will probably do that instead. Good Idea.
Thank You

 

[c.coyle]

Yeah.....OK. There is not the inherent danger with a stereo amp that there is with a Guitar/Instrument amp, but it never hurts to err on the side of.......
There is no collector value to a Kenwood 7100, so i am not worried about that. Getting a 3 wire through a 2 wire strain relief is often difficult. I like your idea about switching to a polarized, 2 wire plug. I will probably do that instead. Good Idea.
Thank You

There you go. My everyday beater amp at my bench is an old KA-3500 and it's got a 3 prong plug. I have never had a problem. Since it's not a show-off amp, I just took out the original strain relief, put a rubber grommet in the hole, fed the three conductor cord through it, and tied off a knot inside as a strain relief. I am not a purist.

 

[c.coyle]

I

It is a bad idea. Those units were engineered to use 2 wire.

Isn't that primarily because, unlike modern gear, old units weren't designed with anti-ground loop features, such as star grounding? Any other reason?

 

[Alan0354]

Tube guitar amps has 400V inside, a lot more dangerous. SS amps have lower voltage, a lot safer......for you and me!!!

For sure if you don't have the 3prong, you don't ground the chassis and it's easier to avoid ground loop. I just wonder why all the amps I've seen tie the signal ground to the earth ground at one point on the chassis. They can easily isolate the signal ground from the earth ground by a low value resistor to break the ground loop. The secondary of the power transformer is totally isolated from the primary and earth ground, they don't have to tie directly to the ground, just a big 10ohm resistor will do magic in breaking the ground loop.

 

[whoaru99]

And, FWIW, if your amp (or whatever) was UL certified/approved with a 2-wire cord and you change it to 3-wire/grounding cord, the UL certification is likely void. I suspect not that most will give a shit, but it's still true.

 

[whoaru99]

Yeah.....OK. There is not the inherent danger with a stereo amp that there is with a Guitar/Instrument amp, but it never hurts to err on the side of.......
There is no collector value to a Kenwood 7100, so i am not worried about that. Getting a 3 wire through a 2 wire strain relief is often difficult. I like your idea about switching to a polarized, 2 wire plug. I will probably do that instead. Good Idea.
Thank You

If you are worried about electrocution just use a GFCI. No modification is necessary to the equipment. GFCI does not rely on equipment grounding to function.

It works by sensing the current differential between the hot and "neutral" wire. If there is an excessive difference between the "in" and "out" current it's assumed to be potentially hazarous leakage so the GFCI opens the circuit.

 

[Colette]

The GFI is a good idea, but no.....i am not worried about electrocution, more just curious.
Like i say, the "danger" is probably pretty small with an audio amp that just sits, and is not plugged into an instrument.
Anyway.......Most of you guys have Way More Experience/Knowledge than i do, but i would think ground loop would be a much bigger problem with a guitar amp than an audio amp.
Most ("good") guitar amps are Tube and hand-wired via Turret or Eyelet boards, some are still even Point to Point.
I thought SS Audio Amps are pretty much all chassis isolated PCB. Is there current in the chassis of your typical Pioneer/Kenwood amp from circa 1975.? I have yet to work on one.
Thank You

 

[larryderouin]

Most of these will have a cap between one side or the other (input wires) and the chassis or between the input lines. These are the supposed "DEATH CAPS". These caps are normal caps and when they fail, they fail closed (or shorted). X-Y Safety caps are usually installed in place of these "Death caps" to prevent 120v short and full line voltage on the chassis. When the Safety Caps fail, they fail OPEN. If you feel a tingle when you touch the case, or slide your finger along the case, the cap is failing. Good idea to read up on X-Y rated caps here. http://www.justradios.com/safetytips.html Even tho the title says "FOR TUBE RADIOS" It applies to Solid State Radios/amps/preamp/Tuners.

 

[Alan0354]

The GFI is a good idea, but no.....i am not worried about electrocution, more just curious.
Like i say, the "danger" is probably pretty small with an audio amp that just sits, and is not plugged into an instrument.
Anyway.......Most of you guys have Way More Experience/Knowledge than i do, but i would think ground loop would be a much bigger problem with a guitar amp than an audio amp.
Most ("good") guitar amps are Tube and hand-wired via Turret or Eyelet boards, some are still even Point to Point.
I thought SS Audio Amps are pretty much all chassis isolated PCB. Is there current in the chassis of your typical Pioneer/Kenwood amp from circa 1975.? I have yet to work on one.
Thank You

Guitar is loud, any little hum is not going to be noticeable as easy. Most of the hum is from the guitar pickup....even hum buckers. You listen to stereo in quiet room, any hum will be very noticeable.

I was a guitarist for a long time. One time, I took a cord that was for speaker cabinet ( not shielded) and played the whole performance. Only when we stop, I notice the hum!!!

No, ground loop created when you have different units that plugged into the wall AC along the signal chain. Most guitar plug into effect board and straight to amp. When you have CD player going to preamp, then preamp driving the power amp, you have 3 unit in the signal chain. It's a lot easier to create ground loop like that.