Mains interference on power amp

[Gareth Magennis]

Hi,

this really is driving me nuts now.

I have a EV P3000 that is intermittently going into protect. I think I have
established why.

Mains spikes are getting into the amp. A lot of them. I can make the amp
trip every time by switching off my soldering station slowly and making its
mains switch arc. This is putting over 10 volts of HF hash onto the amp
chassis, PCB earth traces and power supplies.

The trip circuit runs on the unregulated -26 volt supply that feeds the -15
volt audio circuit, the +26 volt supplies the +15 audio. When I do the
soldering iron switch arc thing, the up to 10 volts of hash appears on both
the ground and the -26 volt supply, and even the amp chassis. This
immediately trips the circuit, muting the amp for 2 seconds before resetting
and carrying on fine. Note this 26v supply isn't very clean, it has around
2 volts of ripple to start with. (I have compared this to another amp which
has the same ripple).

I have tried 0.1uF caps on the -26v rail on the protect switching
transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help.
I have also tried a 0.1 uF X cap accross the mains live and neutral, still
getting 10 volts of hash. All these are stilll in place, except the one on
the switching transistor.

The mains plug earth to chassis reads good. Switching ground lift on and
off has no effect. (just disconects signal input ground I guess). Both
existing X caps on the mains input read OK.




Not sure where to go from here.


Any ideas? Am I barking up the wrong tree thinking this is the problem?


Cheers,


Gareth.

[Earl Kiosterud]

"Gareth Magennis" > wrote in message
...
> Hi,
>
> this really is driving me nuts now.
>
> I have a EV P3000 that is intermittently going into protect. I think I have established
> why.
>
> Mains spikes are getting into the amp. A lot of them. I can make the amp trip every time
> by switching off my soldering station slowly and making its mains switch arc. This is
> putting over 10 volts of HF hash onto the amp chassis, PCB earth traces and power
> supplies.
>
> The trip circuit runs on the unregulated -26 volt supply that feeds the -15 volt audio
> circuit, the +26 volt supplies the +15 audio. When I do the soldering iron switch arc
> thing, the up to 10 volts of hash appears on both the ground and the -26 volt supply, and
> even the amp chassis. This immediately trips the circuit, muting the amp for 2 seconds
> before resetting and carrying on fine. Note this 26v supply isn't very clean, it has
> around 2 volts of ripple to start with. (I have compared this to another amp which has
> the same ripple).
>
> I have tried 0.1uF caps on the -26v rail on the protect switching transistor, and a pair
> of 0.1uF caps on the +and - 26 volt rails, no help. I have also tried a 0.1 uF X cap
> accross the mains live and neutral, still getting 10 volts of hash. All these are stilll
> in place, except the one on the switching transistor.
>
> The mains plug earth to chassis reads good. Switching ground lift on and off has no
> effect. (just disconects signal input ground I guess). Both existing X caps on the mains
> input read OK.
>
>
>
>
> Not sure where to go from here.
>
>
> Any ideas? Am I barking up the wrong tree thinking this is the problem?
>
>
> Cheers,
>
>
> Gareth.
>

If you're seeing a spike on the 26 Volt line AND on the ground of the amp, then your scope
is not seeing what the amp sees. You might need to float the scope ground, grounding it
only to the amp, or use it in differential mode, putting one probe on the chassis. But...

It doesn't seem likely that a spike could get across the power supply -- not if it's a very
short one. You should probably start at the protection circuit, and try to see what it
sees. Or...

Try disconnecting all cables, speaker, audio, antenna, ground wires -- absolutely everything
except the power cord (no scope leads either - nothing), then do your soldering switch thing
and see if it still trips. It may not, indicating that it's not sneaking into the power
supply. Keep everything else the same; don't even move any cables. Ground-induced
high-frequency noise can be the culprit, but rarely gets looked at.
--
Earl

[Kevin McMurtrie]

In article >,
"Gareth Magennis" > wrote:

> Hi,
>
> this really is driving me nuts now.
>
> I have a EV P3000 that is intermittently going into protect. I think I have
> established why.
>
> Mains spikes are getting into the amp. A lot of them. I can make the amp
> trip every time by switching off my soldering station slowly and making its
> mains switch arc. This is putting over 10 volts of HF hash onto the amp
> chassis, PCB earth traces and power supplies.
>
> The trip circuit runs on the unregulated -26 volt supply that feeds the -15
> volt audio circuit, the +26 volt supplies the +15 audio. When I do the
> soldering iron switch arc thing, the up to 10 volts of hash appears on both
> the ground and the -26 volt supply, and even the amp chassis. This
> immediately trips the circuit, muting the amp for 2 seconds before resetting
> and carrying on fine. Note this 26v supply isn't very clean, it has around
> 2 volts of ripple to start with. (I have compared this to another amp which
> has the same ripple).
>
> I have tried 0.1uF caps on the -26v rail on the protect switching
> transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help.
> I have also tried a 0.1 uF X cap accross the mains live and neutral, still
> getting 10 volts of hash. All these are stilll in place, except the one on
> the switching transistor.
>
> The mains plug earth to chassis reads good. Switching ground lift on and
> off has no effect. (just disconects signal input ground I guess). Both
> existing X caps on the mains input read OK.
>
>
>
>
> Not sure where to go from here.
>
>
> Any ideas? Am I barking up the wrong tree thinking this is the problem?
>
>
> Cheers,
>
>
> Gareth.

It doesn't make much sense that a little soldering station would produce
so much electromagnetic noise. I suspect that your amp prone to
oscillating and that's what's showing up everywhere on your scope. Is
the HF hash still strong if the amp is off while you arc the contacts on
your soldering station?

--
I will not see your reply if you use Google.

[Eeyore]

Gareth Magennis wrote:

> Hi,
>
> this really is driving me nuts now.
>
> I have a EV P3000 that is intermittently going into protect. I think I have
> established why.
>
> Mains spikes are getting into the amp. A lot of them. I can make the amp
> trip every time by switching off my soldering station slowly and making its
> mains switch arc. This is putting over 10 volts of HF hash onto the amp
> chassis, PCB earth traces and power supplies.
>
> The trip circuit runs on the unregulated -26 volt supply that feeds the -15
> volt audio circuit, the +26 volt supplies the +15 audio. When I do the
> soldering iron switch arc thing, the up to 10 volts of hash appears on both
> the ground and the -26 volt supply, and even the amp chassis. This
> immediately trips the circuit, muting the amp for 2 seconds before resetting
> and carrying on fine. Note this 26v supply isn't very clean, it has around
> 2 volts of ripple to start with. (I have compared this to another amp which
> has the same ripple).
>
> I have tried 0.1uF caps on the -26v rail on the protect switching
> transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no help.
> I have also tried a 0.1 uF X cap accross the mains live and neutral, still
> getting 10 volts of hash. All these are stilll in place, except the one on
> the switching transistor.
>
> The mains plug earth to chassis reads good. Switching ground lift on and
> off has no effect. (just disconects signal input ground I guess). Both
> existing X caps on the mains input read OK.
>
> Not sure where to go from here.
>
> Any ideas? Am I barking up the wrong tree thinking this is the problem?

How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw ?

Graham

[Gareth Magennis]

"Earl Kiosterud" > wrote in message
news:B6sak.197$713.167@trnddc03...
>
> "Gareth Magennis" > wrote in message
> ...
>> Hi,
>>
>> this really is driving me nuts now.
>>
>> I have a EV P3000 that is intermittently going into protect. I think I
>> have established why.
>>
>> Mains spikes are getting into the amp. A lot of them. I can make the
>> amp trip every time by switching off my soldering station slowly and
>> making its mains switch arc. This is putting over 10 volts of HF hash
>> onto the amp chassis, PCB earth traces and power supplies.
>>
>> The trip circuit runs on the unregulated -26 volt supply that feeds
>> the -15 volt audio circuit, the +26 volt supplies the +15 audio. When I
>> do the soldering iron switch arc thing, the up to 10 volts of hash
>> appears on both the ground and the -26 volt supply, and even the amp
>> chassis. This immediately trips the circuit, muting the amp for 2
>> seconds before resetting and carrying on fine. Note this 26v supply
>> isn't very clean, it has around 2 volts of ripple to start with. (I have
>> compared this to another amp which has the same ripple).
>>
>> I have tried 0.1uF caps on the -26v rail on the protect switching
>> transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no
>> help. I have also tried a 0.1 uF X cap accross the mains live and
>> neutral, still getting 10 volts of hash. All these are stilll in place,
>> except the one on the switching transistor.
>>
>> The mains plug earth to chassis reads good. Switching ground lift on and
>> off has no effect. (just disconects signal input ground I guess). Both
>> existing X caps on the mains input read OK.
>>
>>
>>
>>
>> Not sure where to go from here.
>>
>>
>> Any ideas? Am I barking up the wrong tree thinking this is the problem?
>>
>>
>> Cheers,
>>
>>
>> Gareth.
>>
>
> If you're seeing a spike on the 26 Volt line AND on the ground of the amp,
> then your scope is not seeing what the amp sees. You might need to float
> the scope ground, grounding it only to the amp, or use it in differential
> mode, putting one probe on the chassis. But...
>
> It doesn't seem likely that a spike could get across the power supply --
> not if it's a very short one. You should probably start at the protection
> circuit, and try to see what it sees. Or...
>
> Try disconnecting all cables, speaker, audio, antenna, ground wires --
> absolutely everything except the power cord (no scope leads either -
> nothing), then do your soldering switch thing and see if it still trips.
> It may not, indicating that it's not sneaking into the power supply. Keep
> everything else the same; don't even move any cables. Ground-induced
> high-frequency noise can be the culprit, but rarely gets looked at.
> --
> Earl
>


Thanks, I have just gone back and noted that if I probe the ground of the
scope some hash is there, so this is indeed a misleading reading, the probe
must be an aeriel. With the probe removed from the scope there is still a
small amount of hash. Maybe this explains why putting caps on the power
supplies has no effect - there may not be any hash on the power supplies at
all.

I now have a second P3000 from the same guy with exactly the same symptoms.
It is here on my bench unopened. It has nothing connected to it, and when I
arc my soldering station this too goes into protect. He has brought me
these amps because they trip randomly at different venues, and I am assuming
now it is spikes on the mains that are the trigger. I am also assuming that
the amps should be able to tolerate an arcing mains switch without jumping
into protect.



Ah, while writing this I have just realised that it may not be going into
protect at all - it may be going into its power up cycle, which behaves
exactly the same as a momentary protect/reset. (The 2 protect LEDs light,
and the fans go full speed). There are 3 relays on the power supply input
side, 2 for soft start, a third for protect. These are situated within the
mains input/fusing part of the PCB. It could be that these mains spikes are
triggering a tired relay somehow and starting the power on cycle? I've been
looking at hash on the power supplies that probably isn't there, this is
starting to make a little more sense.



Cheers,


Gareth.

[Gareth Magennis]

"Eeyore" > wrote in message
...
>
>
> Gareth Magennis wrote:
>
>> Hi,
>>
>> this really is driving me nuts now.
>>
>> I have a EV P3000 that is intermittently going into protect. I think I
>> have
>> established why.
>>
>> Mains spikes are getting into the amp. A lot of them. I can make the
>> amp
>> trip every time by switching off my soldering station slowly and making
>> its
>> mains switch arc. This is putting over 10 volts of HF hash onto the amp
>> chassis, PCB earth traces and power supplies.
>>
>> The trip circuit runs on the unregulated -26 volt supply that feeds
>> the -15
>> volt audio circuit, the +26 volt supplies the +15 audio. When I do the
>> soldering iron switch arc thing, the up to 10 volts of hash appears on
>> both
>> the ground and the -26 volt supply, and even the amp chassis. This
>> immediately trips the circuit, muting the amp for 2 seconds before
>> resetting
>> and carrying on fine. Note this 26v supply isn't very clean, it has
>> around
>> 2 volts of ripple to start with. (I have compared this to another amp
>> which
>> has the same ripple).
>>
>> I have tried 0.1uF caps on the -26v rail on the protect switching
>> transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no
>> help.
>> I have also tried a 0.1 uF X cap accross the mains live and neutral,
>> still
>> getting 10 volts of hash. All these are stilll in place, except the one
>> on
>> the switching transistor.
>>
>> The mains plug earth to chassis reads good. Switching ground lift on and
>> off has no effect. (just disconects signal input ground I guess). Both
>> existing X caps on the mains input read OK.
>>
>> Not sure where to go from here.
>>
>> Any ideas? Am I barking up the wrong tree thinking this is the problem?
>
> How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw
> ?
>
> Graham
>


See my reply to Earl - the hash is being picked up by the probe acting as an
aeriel. Doh!



Cheers,


Gareth.

[Gareth Magennis]

"Kevin McMurtrie" > wrote in message
et...
> In article >,
> "Gareth Magennis" > wrote:
>
>> Hi,
>>
>> this really is driving me nuts now.
>>
>> I have a EV P3000 that is intermittently going into protect. I think I
>> have
>> established why.
>>
>> Mains spikes are getting into the amp. A lot of them. I can make the
>> amp
>> trip every time by switching off my soldering station slowly and making
>> its
>> mains switch arc. This is putting over 10 volts of HF hash onto the amp
>> chassis, PCB earth traces and power supplies.
>>
>> The trip circuit runs on the unregulated -26 volt supply that feeds
>> the -15
>> volt audio circuit, the +26 volt supplies the +15 audio. When I do the
>> soldering iron switch arc thing, the up to 10 volts of hash appears on
>> both
>> the ground and the -26 volt supply, and even the amp chassis. This
>> immediately trips the circuit, muting the amp for 2 seconds before
>> resetting
>> and carrying on fine. Note this 26v supply isn't very clean, it has
>> around
>> 2 volts of ripple to start with. (I have compared this to another amp
>> which
>> has the same ripple).
>>
>> I have tried 0.1uF caps on the -26v rail on the protect switching
>> transistor, and a pair of 0.1uF caps on the +and - 26 volt rails, no
>> help.
>> I have also tried a 0.1 uF X cap accross the mains live and neutral,
>> still
>> getting 10 volts of hash. All these are stilll in place, except the one
>> on
>> the switching transistor.
>>
>> The mains plug earth to chassis reads good. Switching ground lift on and
>> off has no effect. (just disconects signal input ground I guess). Both
>> existing X caps on the mains input read OK.
>>
>>
>>
>>
>> Not sure where to go from here.
>>
>>
>> Any ideas? Am I barking up the wrong tree thinking this is the problem?
>>
>>
>> Cheers,
>>
>>
>> Gareth.
>
> It doesn't make much sense that a little soldering station would produce
> so much electromagnetic noise. I suspect that your amp prone to
> oscillating and that's what's showing up everywhere on your scope. Is
> the HF hash still strong if the amp is off while you arc the contacts on
> your soldering station?
>



No, the amp is not oscillating.

I think I know what the problem is now. The 3 relays that do the soft start
and the protect switching are on the same PCB as the protection circuitry.
I removed all 3 and the PCB underneath was not too clean. Since the relays
switch mains voltages, it is not beyond the realms of possibility that mains
voltage and any hash will make its way over to the circuitry via the dirty
PCB. The main protect line runs along all 3 relays, only 5mm from the relay
coils. I have also established beyond doubt that the protect circuitry is
actually being pulsed on briefly via this protect line.

I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully
the nightmare will be over. I might even re-route that protect line.



Cheers,


Gareth.

[Earl Kiosterud]

"Gareth Magennis" > wrote in message
...
>
> "Earl Kiosterud" > wrote in message news:B6sak.197$713.167@trnddc03...
>>
>> "Gareth Magennis" > wrote in message
>> ...
>>> Hi,
snip
>>> Gareth.
>>>
>>
>> If you're seeing a spike on the 26 Volt line AND on the ground of the amp, then your
>> scope is not seeing what the amp sees. You might need to float the scope ground,
>> grounding it only to the amp, or use it in differential mode, putting one probe on the
>> chassis. But...
>>
>> It doesn't seem likely that a spike could get across the power supply -- not if it's a
>> very short one. You should probably start at the protection circuit, and try to see what
>> it sees. Or...
>>
>> Try disconnecting all cables, speaker, audio, antenna, ground wires -- absolutely
>> everything except the power cord (no scope leads either - nothing), then do your
>> soldering switch thing and see if it still trips. It may not, indicating that it's not
>> sneaking into the power supply. Keep everything else the same; don't even move any
>> cables. Ground-induced high-frequency noise can be the culprit, but rarely gets looked
>> at.
>> --
>> Earl
>>
>
>
> Thanks, I have just gone back and noted that if I probe the ground of the scope some hash
> is there, so this is indeed a misleading reading, the probe must be an aeriel. With the
> probe removed from the scope there is still a small amount of hash. Maybe this explains
> why putting caps on the power supplies has no effect - there may not be any hash on the
> power supplies at all.
>
> I now have a second P3000 from the same guy with exactly the same symptoms. It is here on
> my bench unopened. It has nothing connected to it, and when I arc my soldering station
> this too goes into protect. He has brought me these amps because they trip randomly at
> different venues, and I am assuming now it is spikes on the mains that are the trigger. I
> am also assuming that the amps should be able to tolerate an arcing mains switch without
> jumping into protect.
>
>
>
> Ah, while writing this I have just realised that it may not be going into protect at all -
> it may be going into its power up cycle, which behaves exactly the same as a momentary
> protect/reset. (The 2 protect LEDs light, and the fans go full speed). There are 3
> relays on the power supply input side, 2 for soft start, a third for protect. These are
> situated within the mains input/fusing part of the PCB. It could be that these mains
> spikes are triggering a tired relay somehow and starting the power on cycle? I've been
> looking at hash on the power supplies that probably isn't there, this is starting to make
> a little more sense.
>
>
>
> Cheers,
>
>
> Gareth.

OK, if nothing (absolutely nothing) is connected to the amp, and it still trips, then it's
almost certainly coming in the mains cord, not from other cables acting as antennas putting
HF currents through the PCB, where they can cause havoc (radio stations get picked up, etc),
a not-too-uncommon problem. And if it's doing a power-up sequence, then perhaps it's
falsely sensing something that triggers that.

You have 2/2 units doing it, so it may be a known problem. Probably the first thing to do
is either a Google search, or contact EV.

Failing that, there are HF filters for mains you can get that might help.
--
Earl

[Eeyore]

Gareth Magennis wrote:

> I think I know what the problem is now. The 3 relays that do the soft start
> and the protect switching are on the same PCB as the protection circuitry.
> I removed all 3 and the PCB underneath was not too clean. Since the relays
> switch mains voltages, it is not beyond the realms of possibility that mains
> voltage and any hash will make its way over to the circuitry via the dirty
> PCB. The main protect line runs along all 3 relays, only 5mm from the relay
> coils. I have also established beyond doubt that the protect circuitry is
> actually being pulsed on briefly via this protect line.
>
> I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully
> the nightmare will be over. I might even re-route that protect line.

Did I ever mention you chat with Bruce at Shuttlesound ? He's very helpful. Nice
bloke.

Graham

[gareth magennis]

"Eeyore" > wrote in message
...
>
>
> Gareth Magennis wrote:
>
>> I think I know what the problem is now. The 3 relays that do the soft
>> start
>> and the protect switching are on the same PCB as the protection
>> circuitry.
>> I removed all 3 and the PCB underneath was not too clean. Since the
>> relays
>> switch mains voltages, it is not beyond the realms of possibility that
>> mains
>> voltage and any hash will make its way over to the circuitry via the
>> dirty
>> PCB. The main protect line runs along all 3 relays, only 5mm from the
>> relay
>> coils. I have also established beyond doubt that the protect circuitry
>> is
>> actually being pulsed on briefly via this protect line.
>>
>> I'm going to fit 3 new relays tomorrow and clean it all up, and hopefully
>> the nightmare will be over. I might even re-route that protect line.
>
> Did I ever mention you chat with Bruce at Shuttlesound ? He's very
> helpful. Nice
> bloke.
>
> Graham


Yes I have spoken to Bruce about this a few times, he did give me some good
tips generally, but didn't seem to have come across this before.


Cheers,


Gareth.

[Eeyore]

Gareth Magennis wrote:

> "Eeyore" wrote
> >
> > How does this hash appear on the GROUND ? Do you mean Chassis or '0V' btw
> > ?
>
> See my reply to Earl - the hash is being picked up by the probe acting as an
> aeriel. Doh!

Worse things have happened at sea ! ;~)

Graham

[Eeyore]

Gareth Magennis wrote:

> "Eeyore" wrote
> >
> > Did I ever mention you chat with Bruce at Shuttlesound ? He's very
> > helpful. Nice bloke.
>
> Yes I have spoken to Bruce about this a few times, he did give me some good
> tips generally, but didn't seem to have come across this before.

OK, well, worth trying anyway.

I've seen 'something' a little like this once before on a Chinese amp but I'm
damded if I can remember what it was now.

Marginal stabilty perhaps, causing 'RF' breakthrough into the protection.
Shouldn't happen on an EV though.

Graham