UPDATE: Solid state amp 2-prong to 3-prong conversion

[Mrd34d]

I have an old Japanese made bass head that has a 2 prong plug. I was looking at converting it to a 3 prong for grounding.

It's a fairly simple amp with treble, bass, gain (volume), 3 inputs (low/high/bright), power switch and light.

I've been reading around the last couple of hours, and starting reading about a "Death cap"?

If I were to go ahead and swap the plug on my own (after doing more research), would I have to worry about something like this?

Or would it be as simple as replacing the two existing wires with the ones from the new cord, and attaching the ground to the chassis?

Would it just be to the chassis, or would it be to the chassis where it meets the transformer?

 

[throbbinnut]

Replace the cord with a 3-wire one, wire black and white to where the old cord wires went, connect green to chassis. Good to go.

 

[Mrd34d]

Awesome. Thank you good sir

 

[Jazz Ad]

The earth prong is here to protect you and the amp. The idea is simple, any accessible metal part is to be grounded.
So yeah connecting to the chassis is the right thing to do but there may be more to it. Often on old designs there are separate grounds for each circuit. You want to bring these to earth too, which can sometimes prevent the amp from working properly. Do it step by step it's not hard.

 

[Mrd34d]

The earth prong is here to protect you and the amp. The idea is simple, any accessible metal part is to be grounded.
So yeah connecting to the chassis is the right thing to do but there may be more to it. Often on old designs there are separate grounds for each circuit. You want to bring these to earth too, which can sometimes prevent the amp from working properly. Do it step by step it's not hard.

That makes sense. Thanks for the heads up

 

[cheechi]

I've been reading around the last couple of hours, and starting reading about a "Death cap"?

The things that look like big D batteries are capacitors. They are essentially batteries. They can kill you if you discharge them, generally the bigger the badder.

Be careful at very least. For what you are doing there isn't a need to touch them or anything but be careful not to short them with anything you're holding.

 

[Mrd34d]

The things that look like big D batteries are capacitors. They are essentially batteries. They can kill you if you discharge them, generally the bigger the badder.

Be careful at very least. For what you are doing there isn't a need to touch them or anything but be careful not to short them with anything you're holding.

Ya I know what caps in general are. But a lot of places were seemingly talking about one in particular with a specific value. It seemed to focus more on old fender tube amps.

 

[cheechi]

well yeah.

Generally the big ones in older stuff are the most deadly. All are at least unpleasant. But that's all it was.

 

[Mrd34d]

well yeah.

Generally the big ones in older stuff are the most deadly. All are at least unpleasant. But that's all it was.

This...

 

[cheechi]

yeah that's not a good thing. and that's a pretty small cap also.

If you were worried about that failing though, replace it while you're in there.

 

[B-string]

You can't just use any cap of the correct value. An XY safety cap is needed.

 

[waltdogg]

yeah that's not a good thing. and that's a pretty small cap also.

If you were worried about that failing though, replace it while you're in there.

^ wrong

These are giant 500V+ caps and are dangerous it was just the only way to filter out line noise before the ground prong came about.

 

[B-string]

You need to be more specific, which part of this do you consider wrong? Even without a polarity switch the chassis is never free floating to act as an antenna.

 

[waltdogg]

 

[cheechi]

sorry it didn't come through I was obviously being a smartass suggesting a filter cap is small.

I don't claim to be an electronics guru but I was talking about big bad old caps just a moment before that comment. sooo....

 

[B-string]

Oh the edit after thing . They are still not a giant cap and line noise filtering was not their only function.
They are still a small value (mfd) cap and a safety cap must be used if you don't just eliminate it after installing a 3 wire cord.

 

[moody]

yeah that's not a good thing. and that's a pretty small cap also.

If you were worried about that failing though, replace it while you're in there.

These caps aren't to be replaced. A grounded power lead needs to be added and the death cap removed.

They are a dangerous time bomb waiting to happen. You don't want to leave the amp in your will to your kids, or sell it to somebody and have it fail 20 years down the track and kill somebody.'

Also look out for 3 prong leads with the ground prong removed.

 

[nashvillebill]

There is an awful lot of faulty information here in this thread.

The so-called "death cap" actually is still in wide use, and preferred for low-noise applications. However, this cap MUST be a Class XY cap (as B-string wrote). IEC connectors actually can come pre-wired with them installed, perfectly safe, as intended for critical applications.

Also, do NOT arbitrarily try to tie grounds together inside the amp. Amps may have many grounds, sitting at a particular potential as designed by the amp's designer. Chassis ground is one thing, but these virtual grounds are totally different, and not to be connected--you may introduce hum (at best) and at worst, damage the amp (by inducing HF oscillation, for one example). Don't randomly try to re-engineer the amp.

 

[Slevage]

The earth prong is here to protect you and the amp. The idea is simple, any accessible metal part is to be grounded.
So yeah connecting to the chassis is the right thing to do but there may be more to it. Often on old designs there are separate grounds for each circuit. You want to bring these to earth too, which can sometimes prevent the amp from working properly. Do it step by step it's not hard.

Not all circuit grounds are meant to be earth ( chais) grounds.

 

[Slevage]

That makes sense. Thanks for the heads up

Don't ground the circuits unless you can read and understand the schematic.

Grounding the chassis will give you more protection than you have now.