Old JVC pre-amp/casette desk with no Ground

[ElectroNewby]

Hello folks !

I just got and old 1978 JVC KD-25. This has 2 inputs for microphones, VU meters and stuff... A cool vintage piece. I also got the amplifier (another module) and those don't have a ground pong.

It's just a simple cable with no ground. I do not want to risk myself and get a shock while touching those two separately at the same time. So I'd like to have them secure in case of a bad unit.

Can I simply change the cord and attach the ground wire to the metal chassis of the KD-25 and the same for the amplifier ??

Thanks for the infos. Btw, if you wanna check it out, here's a picture that I've found on the net..
**broken link removed**

 

[KeepItSimpleStupid]

It's probably best to leave the ground out. The problem is trying to have a single ground point. Each phono plug also adds a ground UNLESS there happens o be some resistance by design. Home audio doesn't have balanced inputs.

If you have at least one component, say amplifer, with a ground prong, the system generally will be grounded. It has a much better chance to be grounded at one point too.

 

[ElectroNewby]

If you have at least one component, say amplifer, with a ground prong, the system generally will be grounded. It has a much better chance to be grounded at one point too.

That's it, the amplifier does'nT have a ground pong either.
The whole system is not ground.

I think my brother used to get some little shock on them, be he doesn't remember for sure. And I think it's all about the ground ;P

 

[KeepItSimpleStupid]

Does it have a plastic or metal case?

Is one of the line prongs larger? i.e. you can insert the plug only one way?

I remember one amp that I serviced which had a bad transformer and it was only enough to cause a leakage current. Enough current to shock, bit not enough to trip a breaker.
A GFCI outlet/breaker would be a better choice if your really that worried. Basically a ground prong won't really do you any good.

 

[Nigel Goodwin]

It was designed NOT to have a ground, it's a class-II appliance (double-insulated).

 

[ElectroNewby]

It is a metal case. How can something be better off without grounding ?

 

[ElectroNewby]

is I get some shock, is there a solution ?
Can I just trouble shoot the case and jack inputs, etc, and assume it's same ?
can I connect it with balanced studio all grounded ?

I dunno if I'll add that to my studio since it's all analogue, I might just make a listening spot, with a turntable if I find another vintage piece

 

[Nigel Goodwin]

It is a metal case. How can something be better off without grounding ?

You need to understand what grounding is, and why it 'can' be helpful (under certain conditions), uniformingly grounding things can be more dangerous.

It's designed NOT to be grounded - it's double-insulated.

 

[carbonzit]

Believe me--unless there's something really, really wrong with your receiver, you won't get shocked. I actually have some similar equipment of the same vintage which I use every day, connected to other equipment, and have never gotten a shock. As Nigel points out, it's double-insulated and designed to be ungrounded.

Perhaps you're thinking of the Bad Old Days when we had such abominations as line-operated 5-tube radio receivers where one side of the chassis was connected directly to one side of the power line (ouch!). It is possible for you to get a shock, but the chances are slim to none, and Slim just left town.

If you're really concerned about getting zapped by this unit, set it up with another piece of equipment, plug both in, take your multimeter and measure between the two chassis (bare metal on back) of the units, using a sensitive AC volts range. My guess is you're going to see pretty close to zero. (Just to be sure, reverse one of the power plugs and repeat the test.)

 

[KeepItSimpleStupid]

As I said earlier, if your having shock issues, then there is something wrong. The likely place for things to go wrong is breakdown in the power transformer and anything elese directly connected to the AC line. The power transformer has the best chance of causing problems.

 

[Nigel Goodwin]

As I said earlier, if your having shock issues, then there is something wrong. The likely place for things to go wrong is breakdown in the power transformer and anything elese directly connected to the AC line. The power transformer has the best chance of causing problems.

Mains transformers in such equipment are specifically designed for double-insulated use, and shouldn't ever break down across the windings - a massive lightning stike 'might' do it, but the clue will be in the fact that it's now a molten blob splattered all over the room

 

[carbonzit]

As Nigel (and others) point out, the only component that could possibly lead to a condition where one side of the power line or the other is connected to any part of the cassette deck chassis is the power transformer.

To put your mind at ease, look at this picture of a typical power transformer. The one in your deck is very similar to this. Notice how the coils are wound on plastic bobbins, not directly on the iron core laminations. In order for part of the primary to make contact with the core, it would have to almost completely melt the bobbin, and by that time, as Nigel described, you'd probably have flaming goop inside the cassette deck, not to mention clouds of smoke.

 

[KeepItSimpleStupid]

These https://images.google.com/imgres?im...ndsp=25&ved=1t:429,r:2,s:121&biw=1366&bih=563 are common and they short.

Agreed, In the 10 years of doing part-time audio repair, I only saw one bad transformer.

 

[carbonzit]

You seem to be contradicting yourself, KISS. First you say that those transformers are common (but what type are they?) and that they short. Then you say it's not likely. Which is it?

My contention is that a shorted power transformer is an extremely rare occurrence.

 

[Nigel Goodwin]

You seem to be contradicting yourself, KISS. First you say that those transformers are common (but what type are they?) and that they short. Then you say it's not likely. Which is it?

My contention is that a shorted power transformer is an extremely rare occurrence.

I've been repairing such equipment professionally for 40 years, I've NEVER seen (or ever heard of) such a transformer breaking down primary to secondary - the transformer (as with the complete design) is double insulated.

 

[KeepItSimpleStupid]

Agreed a shorted xfomer is rare, but probable in this case. I have seen more metal encased ones than plastic insulated windings in vintage equipment. Metal encased are more likely to fail than the xformer style posted by carbonzit. I hope I cleared that up.

 

[carbonzit]

But the metal-cased ones are just like the one I posted a picture of, except with a metal case around them.

If you don't believe me, open one up sometime.

 

[ericgibbs]

I've been repairing such equipment professionally for 40 years, I've NEVER seen (or ever heard of) such a transformer breaking down primary to secondary - the transformer (as with the complete design) is double insulated.

I did service consumer domestic audio equipment for many years and I also have NEVER seen a double wound transformer failure.

 

[ericgibbs]

But the metal-cased ones are just like the one I posted a picture of, except with a metal case around them.

If you don't believe me, open one up sometime.

hi cz,
Its one of those 'terminology' definitions again.
If a transformer develops 'shorted' turns it will most likely 'fry' and have goo every where, but at some point the supply fuse should blow.

If the double wound transformer primary 'shorted' to the transformer frame/chassis then the chassis could be at the mains potential.
The transformer would most likely continue to work OK.

 

[Nigel Goodwin]

But the metal-cased ones are just like the one I posted a picture of, except with a metal case around them.

If you don't believe me, open one up sometime.

It doesn't matter if it has a metal case around it, if it's designed for class-II use then it's a double insulated transformer - the outer appearence is only cosmetic.