Engl Invader making LOUD buzzing and giving me electric shocks...

[MDV]

Not mine thankfully, a mate brought his round for a tryout, and this happened.

Any explanation amp dudes?

And when I say buzzing, I mean buzzing, not hiss or hum, but a BZZZZZZZZZZZZZZZZZ, like a giant bee.

And electric shocks off the guitar strings. Yes the guitar is spec, properly grounded and shielded, and has never done anything like this with any of my other 7 amps.

With everything else the same (same signal path through my radial J48 and decimator into the amp then into my cab) all my heads are behaving normally with the same input route, cab and guitar

Just trying to give the chap a headstart on the diagnostics for taking it back to the dealer.

[Dmoney]

ive had loud buzz in amps before
50hz I put down to heater noise sometimes, bad grounding, bad wiring...
100hz hum can be a filtering problem. bad filter caps etc.
that was true in my case anyway. I had both the above and it sounded pretty naff. didn't shock me though.

The guitar isn't grounded as such.
It's ground is through the jack to the ground connection inside the amp, which may or may not be where the ground references for the high voltage bits live. Even so, it's all eventually connected to the chassis, but you should have an Earth connection from the IEC on a separate lug with nothing connected to it. If that comes loose then you might have a problem. So if you get 'ground' referenced to a voltage inside the amp, your body can become the path the least resistance to earth via connection from amp, cable 'ring', guitar ground, strings/bridge.

Probably why people should use RCD's and such. relying on fuses is a waste of time. though I'm not sure an RCD would help you out in this situation... id like to think it would.

I reckon he should take it back and ask for a totally new one if possible. id be blowing my mind if that happened to me. It can make you dead.


EDIT: just wanted to add you should probably take what i wrote with a pinch of salt as I may not be that accurate, and with this subject, i guess you need to be. I'm sure there can't be too many causes for this.

[hunter]

With those symptoms I would immediately stop using it, you might get some serious injury from electric hazard if you have a short inside the amp. Bring it to a qualified tech is what I'd advise.

[shobet]

If it's shocking you stop playing it! As hunter says take it to someone qualified and get them to have a look at it.

[dave_mc]

yeah, i'm uber-cautious, if it's shocking you, stop immediately.

Speaking of RCDs, do they do anything or not? I got one on the basis that if I did get electrocuted I'd feel like a right prat for skimping out of a tenner, but will it actually prevent you from being electrocuted? :lol: I'm guessing it will (hopefully) on the basis that if any current is seeping out (i.e. through me) the circuit should shut off, but I could be wrong...

[Dmoney]

yeah, i'm uber-cautious, if it's shocking you, stop immediately.

Speaking of RCDs, do they do anything or not? I got one on the basis that if I did get electrocuted I'd feel like a right prat for skimping out of a tenner, but will it actually prevent you from being electrocuted? :lol: I'm guessing it will (hopefully) on the basis that if any current is seeping out (i.e. through me) the circuit should shut off, but I could be wrong...

yeah thats right. it should work. it should detect current loss and switch off. it switches off VERY quick, maybe not SUPER VERY quick, but there is a max length of time for the switch to physically happen once it detects a fault.

A fuse will just stop your equipment from catching fire. It won't save your life.

[Oli]

You should have RCDs on the ring that all your outlets are connected to, and they're designed to save lives-- it might be worth checking the rating of the RCD on your mains-- it can vary, as there will be a threshold at which current leakage (between live and neutral) will trip the RCD; if you haven't got many appliances on that ring, there's a chance that you might trip before the RCD does!

[MDV]

Well, I thought it would be implicit that if the amp is giving shocks then dont play it, but I'll make sure the fella knows that.

Again, its not my amp and I only played through it for about 10 minutes. Theres no similar problem with any of my gear.

A thought crossed my mind; the amp has a ground lift, and I believe it was lifted at the time. I think nothing of lifting the ground on a splitter or DI or whatever, but with the current and voltages of an amp, could this have been the problem?

That said, that was how it wa set when it arrived at my house, and apparently it never did anything like that (either the noise or the shocking) and theres nothing to indicicate that it was flipped in the 10 minute journey on the back seat of a car.

[Dmoney]

Well, I thought it would be implicit that if the amp is giving shocks then dont play it, but I'll make sure the fella knows that.

Again, its not my amp and I only played through it for about 10 minutes. Theres no similar problem with any of my gear.

A thought crossed my mind; the amp has a ground lift, and I believe it was lifted at the time. I think nothing of lifting the ground on a splitter or DI or whatever, but with the current and voltages of an amp, could this have been the problem?

That said, that was how it wa set when it arrived at my house, and apparently it never did anything like that (either the noise or the shocking) and theres nothing to indicicate that it was flipped in the 10 minute journey on the back seat of a car.

I'm going to say yes that could be the problem.
ground lifts in gear are to stop Hum right? even in a US amp with polarity reversal and ground lift, i think a 3 pin with a solid ground is the way to go.
I guess if you have other gear attached to the input, or loop, its possible the ground lift would cancel hum but the amp would still be earthed through some other gear's earth... probably not ideal.
If you have the ground lifted at the IEC, then I guess all the other grounds just float on an isolated chassis. Until you touch it while not insulated.

thats what common sense would tell me.
when I did broadcast installations, building earth and technical earth had to be separate for that reason. A problem with the building earth used as a tech earth means the technical earth points (ground connections a 40U rack unit) can get voltage coming back up them. Then if you touch the equipment rack you can get zapped. When I worked in New Delhia this was the case, and wiring personal were getting constantly shocked by metal racking.

[Frank]

I guess if you have other gear attached to the input, or loop, its possible the ground lift would cancel hum but the amp would still be earthed through some other gear's earth... probably not ideal.
If you have the ground lifted at the IEC, then I guess all the other grounds just float on an isolated chassis. Until you touch it while not insulated.

ok ... this discussion is getting a bit scary to me and there's a lot of half-tuths and misconceptions flying around about grounding and safety

first off - and I can't stress this enough - NEVER DISCONNECT THE CHASSIS EARTH FROM THE IEC INLET

if you don't know why that's important then you shouldn't be allowed near an amp!

the only ground connections that you can safely disconnect to trace earth loop hum problems are SIGNAL GROUNDS, NOT POWER SUPPLY GROUNDS

lifting all an amp's grounds and leaving the chassis floating, relying on grounds in other gear - this frightens the hell out of me! you'd be relying on signal cables to provide the earth connection, there's absolutely no guarantee they're up to the job and what if you then operate the amp with no other gear attached? it would be entirely ungrounded, potentially live chassis and the only route to earth would we down the guitar cable, onto the guitar strings and THROUGH YOU

TL:DR - switch the amp off, leave it off and take it to a qualified tech before your friend fries himself

[Dmoney]

lifting all an amp's grounds and leaving the chassis floating, relying on grounds in other gear - this frightens the hell out of me! you'd be relying on signal cables to provide the earth connection, there's absolutely no guarantee they're up to the job and what if you then operate the amp with no other gear attached? it would be entirely ungrounded, potentially live chassis and the only route to earth would we down the guitar cable, onto the guitar strings and THROUGH YOU

TL:DR - switch the amp off, leave it off and take it to a qualified tech before your friend fries himself

Just like to say... I don't have any misconceptions. i didn't suggest that relying on earth connections in other equipment was a good idea at all!

A mains IEC ground lift is a terrible idea and probably doesn't meet basic electrical safety standards for equipment that can be sold here. IEC grounds on sockets should be fixed to their OWN lug with nothing else. not the bolt holding a transformer in your amp, and not the main star ground etc. one hole, one bolt, one ground for the IEC.

If you have no IEC socket and the 3 core mains flex comes into your amp, then the same applies, only the ground wire from the flex wiredinside the amp must be longer than both the live and neutral wires, this means if the flex gets ripped out, the LAST connection to break will be the mains ground.

You can also run into trouble if you have multiple sockets in one room with reverse polarity wiring and your using gear plugged into them all at the same time.

I think a lot of old amps built in the US have this ground lift feature. along with the mains polarity switch... which can also help to make you dead.

There are massively dangerous wiring conventions in even the newest amplifiers.

[Dmoney]

oh

also

The ground lift in an amp is not necessarily the IEC ground.
The IEC can have its own ground, but the Live and Neutral can also be switched to ground via a cap, or you can have neither to ground.

USA made 5150's have this.
a bunch of Fenders have this.

That is probably what we are talking about. not switching the IEC ground.
http://www.schematicheaven.com/fenderamps/cbs_70w_mstrvol_pullsw_super-pro-bmstr_rev.pdf

you can see it there above where it says "caution".

[dave_mc]

yeah thats right. it should work. it should detect current loss and switch off. it switches off VERY quick, maybe not SUPER VERY quick, but there is a max length of time for the switch to physically happen once it detects a fault.

A fuse will just stop your equipment from catching fire. It won't save your life.

yeah, it's like 30 ms or something, i think, which (supposedly) is fast enough for it not to do you any harm.

You should have RCDs on the ring that all your outlets are connected to, and they're designed to save lives-- it might be worth checking the rating of the RCD on your mains-- it can vary, as there will be a threshold at which current leakage (between live and neutral) will trip the RCD; if you haven't got many appliances on that ring, there's a chance that you might trip before the RCD does!

Er... could you explain that in a bit simpler language, please? :lol: My RCD is a multi-plug extension with 4 plugs (with RCD built into it), so I can plug everything I need into that. That's ok, right?

[Dmoney]

you mains 'fuse' box in your house should contain breakers which are RCD's.
you normally have a bunch. upstairs outlets, upstairs lights, downstair outlets, downstairs lights. then other things like boilers and ovens and electric showers might have their own.
Each of those is probably fed from a bigger one. I can't quite remember so don't take my word for it.

its also worth checking your kettle leads for the correct size fuse. most come with 13Amp fuses which isn't protecting your amp very well! It's probably worth lowering these down to more appropriate value relating to what you use the cable with. Doing this have saved me a repair job once in the past.

RCD's monitor the current on the live and neutral connections and they should be equal. In a fault condition you get a lack of balance between live and neutral currents and RCD's detect current leaking to earth. the RCD detects this and makes a switch-off of the live and neutral.

your 4 way plug will probably have all its outputs monitor by the RCD. the sockets will be wired in parallel to the power coming in (input to the RCD). each bit of kit you plug in should have the same current on its individual L and N. if you have 4 things plugged in, and one develops a fault, you will get an error that should cause the RCD to break the circuit.

If it was fused... you have to have 1 fuse big enough for the total current draw of everything plugged in. so say it had 1x13amp fuse, and you only had an 1 amp plugged in drawing 3Amps. If for some reason that amp got messed up (and say for example you were an idiot and replaced the 3amp fuse with a nail) it would have to draw 13amps before the fuse in the extension blew. If there was no RCD and your body was the path to ground for 240v 50hz 13amps.... well, lets just say you'd have limited job prospects after that (you'd be dead) and your amp would probably be on fire.

[dave_mc]

thanks for the detailed explanation. I know about the trip switches on our mains, they blow fairly often when we turn on the living room lights :lol: I just didn't realise that that's what he was talking about, thanks.

I think I checked the fuses before in the kettle leads, but i should probably check them again at some point.

I think I understand (in basic terms) how the RCD works, as you say, it monitors the incoming and outgoing current, and if there's a discrepancy, shuts off the circuit.

Regarding the last bit- I haven't replaced any fuses with nails, lol, don't worry. I guess what you're saying is that as long as it's plugged into RCD it should be ok? Though it's probably not just as good as a single plug, because it has to have a higher fuse rating... :)