weird amp issues

xHymnal

bear with me! 

So i just plugged in and heard a slight crackle from my amp (Rivera R30) and so i thought i'd give the tubes a tap to see if one had gone microphonic, they all sounded normal. I sat back down to play and as soon as I engaged the looper on my timeline the volume dropped massively and I got an electric shock. This is super weird as the tubes sound fine and I've never had anything like this before. The only thing i can think is that i've since incorporated a pedal which has a ground lift, though I don't have the lift engaged. 

Anyone got any thoughts? 

ICBM

If you're actually getting a full-on electric shock and not just a little static discharge which goes away immediately, there's something seriously wrong with the earthing, either of your amp or the effect unit if it's mains powered, or of the wall supply you're plugging into.

Are you in North America? Just wondering because you said 'tubes' not 'valves'.

xHymnal

Now no sound whatsoever. I think a component has gone, though nothing went bang

ICBM

Is the power light on the amp on? Do the valves appear to light up?

Any hiss or other background noise from the speaker if you put your ear right up to it?

xHymnal

No, I'm in the UK, I just call them tubes . I didn't stick about long enough to see if it was a full on shock but i doubt it would be one of the effects as the amp now is putting out no output, though it does switch on. I've had it for years and it's been nothing but reliable 

xHymnal

valves light up yes. a slight amount of hiss now 

ICBM

Sounds like a preamp valve might have gone if you get no signal but there is hiss from the power amp. It would be rare for that to send any voltage to ground (and hence to you via the guitar) but not impossible - although for it to happen, the amp can't be properly earthed which would concern me... a lot.

Is the amp plugged directly into the wall, or via an extension cable/4-gang? Is it still giving you a shock? You'd know when you turn it on, if it has metal switches.

xHymnal

Right, bit of an update. It is plugged straight into the wall and but has a plastic switch. I put the jack lead in and touched the end with no shock, which is good. I took the head out of the chassis and it doesn't SEEM like anything has blown up. 

The most alarming part is that though the power indicator lights up the lights for the two channels don't, so i can only assume something has happened between the pre and power amp stages

ICBM

Hymnal said:

Right, bit of an update. It is plugged straight into the wall and but has a plastic switch. I put the jack lead in and touched the end with no shock, which is good. I took the head out of the chassis and it doesn't SEEM like anything has blown up. 

The most alarming part is that though the power indicator lights up the lights for the two channels don't, so i can only assume something has happened between the pre and power amp stages

That sounds like a LT circuit ('low tension', supplies power to the channel switching, and FX loop driver and reverb in some amps) failure, in which case it's a job for a tech - it will need a component or two changing on the PCB... not something you can do yourself unless you're experienced working on this sort of thing.

I'm still concerned about the electric shock - this shouldn't be possible with properly-earthed equipment. It's possible it was some sort of static discharge - and that could itself have fried the LT circuit - but it still should have gone to earth if the amp and the wall supply are earthed.

xHymnal

As i said, one of my pedals has a ground lift, which might have caused static? Thanks very much for your help though, I'll look into some local techs. Any idea what the ballpark price i should pay for that would be?  

ICBM

Hymnal said:

As i said, one of my pedals has a ground lift, which might have caused static?

No. Even with the ground lifted (which you said it wasn't) the signal path will be earthed via the amp and the signal cables. The purpose of the ground lift is to stop it being earthed in two places at once, which causes a loop that can pick up hum.

Hymnal said:

As i said, one of my pedals has a ground lift, which might have caused static? Thanks very much for your help though, I'll look into some local techs. Any idea what the ballpark price i should pay for that would be?  

Hard to say since I don't know what your local techs charge, but if it was me I would say unlikely to be much under £50 if there's any major dismantling involved to get to the parts, and probably not over £100 unless some multiple failure has happened.

The worry about your wall supply wiring is that if you didn't have the ground lifted on the pedal, the signal path would still be earthed even if there was a broken connection at the amp… so your whole supply may not be earthed properly. Was the pedal plugged into the same wall socket as the amp, or a different one?

xHymnal

I just don't see what have caused it. The amp was plugged into a separate wall socket, all the pedals had isolated power and there wouldn't have been an issue with the guitar. I'm completely stumped. The channel indicators don't light up at all and theres not even a buzz when i touch the tip of a jack plugged in. Argh

ICBM

Sometimes things just die for no obvious reason, even in such a well-made amp as a Rivera.

Definitely a LT circuit failure of some sort if the channel indicators don't light. That will stop it working completely if the switching isn't done with relays. I'm pretty sure Riveras are either opto-switched or IC-switched, both of which require continuous power.

Tech time unfortunately.

I would still be inclined to have someone who knows what they're doing check your wall sockets as well.

xHymnal

Our house was rewired in the last 5 years by a proper electrician, though I'll make sure it's plugged into a surge protected plug next time. Off to the tech I go (read; off to shell out more cash i go). Thanks so much for your help though ICBM. 

Do you think taking a copy of the schematic will help?

ICBM

Yes, if you have it. Riveras are so reliable normally that it will probably be a while since he's been inside one.

An RCD plug won't help if it's an earthing problem unfortunately - and if you aren't getting shocks now it can't be an actual supply fault. Are you in a house or a flat? A lot of older flats can have problems with earthing because they commonly use the water main, and if the water company replaces the street main with plastic, you then have no earth!

No prob about the help, don't want to leave you at risk of a shock.

xHymnal

Ah, we live in a very old house and I think we come in on Lead still and then to plastic pretty much on our threshold, so it could be that. 

Is that not a problem with loads of people though because surely now loads of houses are on plastic?! Though i guess the mains ring is earthed to something different. I don't know much about construction despite it being our family business :S