Nasty mains sparks. What to do?

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#1
What to do and where to search when an amp is very sensitive for mains sparks?
Even when powered from a variac, the slightest spark from let’s say a (neon) light turned on in the other room sometimes gives sharp ticks in the speakers.
I assume I should start looking at the power supply .
It’s a Phase Linear700 with a very simple supply. Not much to look for at first glance. Should I try some small caps over the bridge?
Any ideas?

Thanks

/Hugo
 
#5
Are you testing this with just the amplifier connected to the speakers, and with the input shorted (i.e. not connected to anything else). Mains ground loops are very good for coupling noise into the signal path, so I would make sure this isn't the problem first.

Chances are the noise isn't being coupled in the obvious way through the mains transformer into the power supply - there will be lots of PSU capacitors in the way.

The other problems might be (i) mains input wiring is routed too close to the signal path, and is capacitively or inductively coupling in, or (ii) poor grounding / screening means that noise coming in through the mains earth (relative to signal ground) is being coupled into the signal path.

The rules on safety forbid me saying "disconnect the mains earth from the amp and see what happens", but if you can (safely!) perform some equivalent test it might be useful in narrowing it down.

Cheers
IH
 
#6
Jojo
Other people can give you a better explanation but have a look at this meanwhile: http://www.beyschlag.de/Uploads/Datasheets/var584.pdf

Ian:
The amp is an old Phase Linear 700, Schematic here: http://hometown.aol.com/phasetek2/pl20.jpg
I happen to live in a house with no ground at all. :bigeyes:
The electricity has been renewed about 20 years ago in a very professional way, except the guys forgot the earth. 😉
(Don't sinbin me guys, not my fault :clown: )
I'm still alive and in the workplace all equipment to be repaired is powered up through a variac.
Back to the amp: Inputs are shorted. Capacity is two X 10.000µF, replaced about 10 years ago and still in perfect shape. Ever since I had the amp the problem was there. I had a few 700's before this one (Been stolen long ago :cannotbe: ) but they didn't have that 'spike' problem.

Per
I've been looking at Farnell to order a couple of decent VDR's.
Now, looking at about 200 different pieces isn’t easy to choose.
Could you point me to a correct device? K14 or K20? Never heard of those numbers.

/Hugo
 
#7
Sounds like you are sharing your audio mains line with other appliances. Short of "snubing" every sparking offender, you can try isolating the line first by transferring all appliances to other lines. Better still, get an electrician to run a new power line from your switchboard only for audio.

Cheers
 
#8
Every mains spark produces a very high dV/dt and this means RF pulses are radiated into the air and also conducted throug mains wiring

Is the case of the amplifier made from metal and connected to the star ground or speaker ground? This should produce enough screening for RF pulses

For conducted pulses you may try some common mode and differential mode filtering applied to mains as it enters the amplifier [to start with, you may try a simple 100-470nF capacitor of appropiate voltage rating between phase and neutral as it enters the case of the amplifier]
 
#11
Netlist said:

I happen to live in a house with no ground at all. :bigeyes:
Click to expand...

So - let me get this straight, the metal cases of all your mains-powered equipment are connected to nothing at all ?

:boggled: ! Do you like wearing rubber?

I suspect this has a lot to do with your problem. The mains earth on the amplifier is going to act like an aerial - picking up any stray noise and coupling it right into the circuitry. I would seriously consider installing an earth rod in your back yard, and connecting at least your amplifier's mains earth to it. This will improve your life expectancy and probably your sound quality as well...

Cheers
IH
 
#13
IanHarvey said:

I suspect this has a lot to do with your problem. The mains earth on the amplifier is going to act like an aerial - picking up any stray noise and coupling it right into the circuitry.
Click to expand...

I agree that the house should be grounded. No doubt about that.
This however wouldn't help the Phase Linear because there is no mains earth on these amps. Look at the posted schematic.
As far as I remember, none of the old Phase Linear amps had a mains earth. This is not the amp I use every day, I'm happy with the AlephX, but it's just sitting there on a shelf and every now and then I listen to it. Sometimes I use it to test some big PA-speakers.
Years ago the amp was living in another house; (Me too 😉 ) and the problem was the same.
I happen to use it for parties in the past so it has been hooked up on all sorts of mains systems.
Clearly the problem is the amp. Now if someone can point me to a correct type of VDR I'll be happy to try that proposed solution.
Thanks for the good advice!

/Hugo
 
#15
I happen to live in a house with no ground at all
Click to expand...

ya me too, no ground wires at all, im in spain for the time being, have been for the last 2 years, one day i decided to put a few new power sockets in, and low and behold no earth! none anywhere in the house not just on mine either, others too in different houses.

Trev
 
#16
Netlist said:


I agree that the house should be grounded. No doubt about that.
This however wouldn't help the Phase Linear because there is no mains earth on these amps. Look at the posted schematic.
Click to expand...

Weird. So signal earth is just floating. Is it connected to the metal case? This amp does have a metal case, doesn't it?

A VDR will help if the problem is voltage spikes on the live relative to the neutral leads. If the noise is 'common-mode' (i.e. both live and neutral have a spike relative to earth) it won't, though. A remedy against common-mode noise is a ferrite choke (as on computer monitor leads) clamped around the mains cable.

Let us know how you get on...

Cheers
IH
 
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