Got a new (to me) older audio stack. Not used to some of the earlier electronics conventions.
The system has two pronged cords, and has external grounding. How much danger am I looking at here? I’m not 100% certain how to use it properly.
The ground lugs are for a turntable, not a power ground. The audio signal from a record player is incredibly tiny, which means it needs more amplification stages (usually if you have a phono input, it has another pre amp stage). Because of this it is important that the turntable and pre-amp have a common ground reference to eliminate things like a DC offset or ground loop which would otherwise be amplified more than other audio artifacts from other sources.
The strap looks like an antenna ground for an AM input
Sounds like you’re confirming what I’ve been hearing from other people, that neither of these grounds contains any real danger?
And as for grounding the turntable, that makes a bit of sense, however I have a fairly modern one and I’ll have to check it. I don’t know that it actually has an external ground beyond the three prong plug.
Is grounding of the turntable still relevant in that case?
I think most modern turntables have a built in pre-amp so it’s less of an issue. If it doesn’t have a ground lug itself then it’s probably not an issue.
Yes, I believe I have a selector switch that allows me to select either the internal pre and for an external. I was thinking of going with the old external for a bit of additional configurability.
Zero danger as long as you don’t connect something other than a ground or shield to these.
Nice, thanks!
I’d see if you can find a circuit diagram for the equipment, then compare it against what you actually have.
It might be that there was a genuine issue with the equipment that was fixed, or it might be that the fix was actually something else entirely.
There’s no way for us to know what you’re dealing with.
I have the manuals and I can check those. I can also easily get the model numbers off the units. Are diagrams something that you can find for old hardware online?
And I appreciate the assistance. My background is in computer science, so my electrical engineering abilities are slim.
Fellow computer geek here … also a radio amateur.
No idea what the availability of circuit diagrams is for your gear. In amateur radio equipment the user manual regularly has them, sometimes as big foldout sheets. I’d be surprised if they didn’t exist.
Thanks for the information. The two units are by Fisher an FM-2421 and CC-3000.
I’m not seeing full circuit diagrams, but they do have some information on what to wire up.
Antenna ground needs to be used for signal to be read properly.
Turntable audio grounding (different from electrical power grounding) may help prevent hums when the common 0V grounding passes by the power ground.
That is what it looked like, but that surprised me. My turntable is more modern and doesn’t require a ground. As for the antenna, yes, that makes sense!
But am I misreading something… neither of those seems like an actual dangerous situation? Oddly enough the components that I would normally guess were more dangerous (specifically the pre-amp and amp) don’t seem to have a ground circuit exposed despite the two-prong set-up.
They don’t have a power ground to prevent hums. There might be a marginal risk if something comes loose in the amp, but your modern electrical cabinet would have a differential switch to save you in that case. I remember my audio engineer degrounding one of my audio components when in had the issue.
My guess for the audio ground is that older turntables had poorer electrical isolation and power lines were more noisy. For more technical explanations we need an old school audio engineer.
I’m hoping this means that the system is probably safe to use? XD
I’m not really finding grounding needs on any of the other equipment. Even though the power amp, for instance, is something that I would associate with more danger and it only has two prongs, there doesn’t seem to be exposed ground circuitry.
The dangers are limited unless you hit an edge case which you’ll want to avoid. In other words, you’d have to be really unlucky. Surges can happen with audio equipment easily though.
The principle of grounding is actually simple enough: when something goes wrong with the current, for instance if it can’t move through the wires it should move through, it’ll try to escape. Grounding makes sure that it moves through a dedicated wire to somewhere it can no longer do harm. Cars, for instance, use their frame as a ground, which will conduct the current into the tires and into the ground (ie Earth) if necessary.
This is probably 25% accurate so I’ll invite any electrician to correct me but I am fairly confident this will do as a basic answer.
You hook up the GND contacts to anything that is not connected to anything electrical, preferably something non-conductive at the end of it, you’ll be fine.
Thank you for the first response. I look forward to possible second opinions as you suggest.
And this makes a bit of sense to me. If the medium doesn’t matter I could probably just stick a bolt in the wood next to the units. That’ll keep any wires fairly short.
Basically I was showing the system on the audio forum and asking some questions regarding the unusual number of AC plugs. One of them asked about the age and grounding, and suggested there might be a serious danger.
I have only a very basic knowledge of electricity and an even smaller knowledge of amps but I have heard about certain amps that would be susceptible to immense power surges which would short out some circuits and that power needs to go somewhere. If it’s not grounded properly it might release its current into the air where it’ll find you, or maybe catch fire.
The specifics of this and why or how this happens should be findable online.
Most likely it’ll also have something to do with the higher voltage direct current being transformed into a lower voltage alternating current. But why and how you’d need to be properly grounded for that is beyond me.
Is an external surge protector sufficient for such a case? You may not know the answer either.
I certainly don’t plan to plug them right into the wall.
It’s not. If you mean an extension cord with built-in ground and surge protection, that is.
If your amp had a ground in its power plug, we wouldn’t be having this conversation. If there is a surge in the actual power to the outlet, the surge protector might catch it. But since this is about surges inside the device itself, it means you should no longer actually touch the amp because you might get a shock. You can imagine that the higher the amperage flowing through the amplifier, the more dangerous this is.
That is sort of what I figured, but asking obvious questions still helps me learn.
I appreciate the feedback.
If you are worried about grounding the system, and don’t mind cutting the cord/ crimping stuff, you could get a 3 prong cord from the hardware store and screw the ground into the box via a case screw on the back.
That’s not exactly the worst surgery I’ve done on electronic device before. Interesting idea.
