Stray Voltage Problem

[[email protected]]

I have a Master Room XL-121 Spring Reverb which I bought used
years ago and haven't powered it on in several years. When I recently
powered it up I received a shock from the case. It has a 2 prong
AC receptacle so it is not a grounded device. I measured about 40
volts AC from the case to ground.

So my question is what might be the cause? This unit is probably
over 30 years old so I might expect the filter capacitors to be
going bad, but I also suspect the power transformer.

Gary V

[John Williamson]

On 25/10/2015 16:37, wrote:
> I have a Master Room XL-121 Spring Reverb which I bought used
> years ago and haven't powered it on in several years. When I recently
> powered it up I received a shock from the case. It has a 2 prong
> AC receptacle so it is not a grounded device. I measured about 40
> volts AC from the case to ground.
>
> So my question is what might be the cause? This unit is probably
> over 30 years old so I might expect the filter capacitors to be
> going bad, but I also suspect the power transformer.
>
If it's been in a storeroom or cupboard, turn it on in a warm dry place
for a while, as there may be dampness inside.

Also, try measuring the voltage or leakage current to earth with a low
impedance meter. I've had minor shocks and tingles from less than a
milliamp of leakage, and can feel a few dozen microamps through my
fingertips.

--
Tciao for Now!

John.

[Mike Rivers[_2_]]

On 10/25/2015 12:37 PM, wrote:
> I have a Master Room XL-121 Spring Reverb which I bought used
> years ago and haven't powered it on in several years. When I recently
> powered it up I received a shock from the case. It has a 2 prong
> AC receptacle so it is not a grounded device. I measured about 40
> volts AC from the case to ground.
>
> So my question is what might be the cause?

An AC line bypass capacitor that's become too much like a resistor. Open
it up and look for a capacitor somewhere between 0.01 and 0.1 uF going
between the AC power leads and the chassis. There will probably be one
for each lead. Replace both of them.



--
For a good time, visit http://mikeriversaudio.wordpress.com

[Scott Dorsey]

In article >,
> wrote:
>I have a Master Room XL-121 Spring Reverb which I bought used
>years ago and haven't powered it on in several years. When I recently
>powered it up I received a shock from the case. It has a 2 prong
>AC receptacle so it is not a grounded device. I measured about 40
>volts AC from the case to ground.
>
>So my question is what might be the cause? This unit is probably
>over 30 years old so I might expect the filter capacitors to be
>going bad, but I also suspect the power transformer.

Likely it's the line filter caps. Dyke them out. Do you still measure
ground fault current with a meter? If so, put them back and look at the
switch and transformer. If not, replace them with modern X1 and Y grade
capacitors from digikey.

These capacitors are specifically rated for line filtering service and
are specifically designed not to go leaky, like the originals likely did.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On Sunday, October 25, 2015 at 1:20:34 PM UTC-7, Mike Rivers wrote:
> On 10/25/2015 12:37 PM, wrote:
> > I have a Master Room XL-121 Spring Reverb which I bought used
> > years ago and haven't powered it on in several years. When I recently
> > powered it up I received a shock from the case. It has a 2 prong
> > AC receptacle so it is not a grounded device. I measured about 40
> > volts AC from the case to ground.
> >
> > So my question is what might be the cause?
>
> An AC line bypass capacitor that's become too much like a resistor. Open
> it up and look for a capacitor somewhere between 0.01 and 0.1 uF going
> between the AC power leads and the chassis. There will probably be one
> for each lead. Replace both of them.
>

Mike, I don't see the capacitors you describe. It has 2 1000uF and a bit
further away I see a couple of 22uF. I don't know if you can see these
photos but if you can, it might be helpful to look at the circuit topology.
Thanks for the help.

https://www.flickr.com/photos/135531103@N04/shares/Bf3R91

Gary V

[[email protected]]

On Sunday, October 25, 2015 at 1:44:22 PM UTC-7, Scott Dorsey wrote:
> In article >,
> > wrote:
> >I have a Master Room XL-121 Spring Reverb which I bought used
> >years ago and haven't powered it on in several years. When I recently
> >powered it up I received a shock from the case. It has a 2 prong
> >AC receptacle so it is not a grounded device. I measured about 40
> >volts AC from the case to ground.
> >
> >So my question is what might be the cause? This unit is probably
> >over 30 years old so I might expect the filter capacitors to be
> >going bad, but I also suspect the power transformer.
>
> Likely it's the line filter caps. Dyke them out. Do you still measure
> ground fault current with a meter? If so, put them back and look at the
> switch and transformer. If not, replace them with modern X1 and Y grade
> capacitors from digikey.
>
> These capacitors are specifically rated for line filtering service and
> are specifically designed not to go leaky, like the originals likely did.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

I think IF I go to the trouble of removing them, I will just go ahead
and replace them. I might be interested in replacing the transformer
too because they used some foam on top of the reverb tank and the
transformer which had dissolved and was quite nasty particularly
where it was heated by the transformer. Is there a particular online
resource for transformers or should I just go to DigiKey or Mouser?

Gary V

[Scott Dorsey]

> wrote:
>
>I think IF I go to the trouble of removing them, I will just go ahead
>and replace them.

Just make one cut for diagnostic purposes, it will take thirty seconds.
Don't remove the whole thing. If it is good, just put a bead of solder
on and put it back in another thirty seconds. It's not worth replacing
them if they are good. Almost certainly they are bad, though.

>I might be interested in replacing the transformer
>too because they used some foam on top of the reverb tank and the
>transformer which had dissolved and was quite nasty particularly
>where it was heated by the transformer. Is there a particular online
>resource for transformers or should I just go to DigiKey or Mouser?

I like the Amveco/Talema transformers from Digikey personally, but
really I doubt there is anything wrong with the transformer. Lighter
fluid should take that foam residue off. If it's not broke, don't replace it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[JackA]

On Sunday, October 25, 2015 at 12:37:22 PM UTC-4, wrote:
> I have a Master Room XL-121 Spring Reverb which I bought used
> years ago and haven't powered it on in several years. When I recently
> powered it up I received a shock from the case. It has a 2 prong
> AC receptacle so it is not a grounded device. I measured about 40
> volts AC from the case to ground.
>
> So my question is what might be the cause? This unit is probably
> over 30 years old so I might expect the filter capacitors to be
> going bad, but I also suspect the power transformer.
>
> Gary V

Probably normal, using [assumed] a digital, high impedance voltmeter. 40 volts won't shock you.

Jack

[JackA]

On Sunday, October 25, 2015 at 12:37:22 PM UTC-4, wrote:
> I have a Master Room XL-121 Spring Reverb which I bought used
> years ago and haven't powered it on in several years. When I recently
> powered it up I received a shock from the case. It has a 2 prong
> AC receptacle so it is not a grounded device. I measured about 40
> volts AC from the case to ground.
>
> So my question is what might be the cause? This unit is probably
> over 30 years old so I might expect the filter capacitors to be
> going bad, but I also suspect the power transformer.

Most (replies) are talking DC side, you measure AC line to ground. If you don't have a megohmeter, might be tough determining transformer health. Seems costly to replace it, but you're probably correct with your assumption.

Jack
>
> Gary V

[Mike Rivers[_2_]]

On 10/25/2015 6:42 PM, wrote:

> Mike, I don't see the capacitors you describe. It has 2 1000uF and a bit
> further away I see a couple of 22uF. I don't know if you can see these
> photos but if you can, it might be helpful to look at the circuit topology.

Without a schematic, we can only guess. It's hard to tell from your
photo just where the AC line cord goes. I can see what are probably the
wires from the secondary of the transformer, the two red and one yellow
twisted wires, but it looks like the line cord might be connected
directly to the transformer primary without going through a filter or
bypass capacitors, or a power switch.

If the plug isn't polarized (one blade wider than the other), try
flipping it over in the socket and see if the chassis is still hot. If
it isn't, reversing the plug isn't the cure, but it's a clue.


--
For a good time, visit http://mikeriversaudio.wordpress.com

[JackA]

On Sunday, October 25, 2015 at 9:37:39 PM UTC-4, Mike Rivers wrote:
> On 10/25/2015 6:42 PM, wrote:
>
> > Mike, I don't see the capacitors you describe. It has 2 1000uF and a bit
> > further away I see a couple of 22uF. I don't know if you can see these
> > photos but if you can, it might be helpful to look at the circuit topology.
>
> Without a schematic, we can only guess. It's hard to tell from your
> photo just where the AC line cord goes. I can see what are probably the
> wires from the secondary of the transformer, the two red and one yellow
> twisted wires, but it looks like the line cord might be connected
> directly to the transformer primary without going through a filter or
> bypass capacitors, or a power switch.
>
> If the plug isn't polarized (one blade wider than the other), try
> flipping it over in the socket and see if the chassis is still hot. If
> it isn't, reversing the plug isn't the cure, but it's a clue.

Looks like it has a shield on the outside, though I'd guess the secondary is wound over the primary, if so, not a/the problem.

Guess that pad, or whatever, under the transformer, is to dampen vibration. Looks dangerous to me!

Jack
>
>
> --
> For a good time, visit http://mikeriversaudio.wordpress.com

[[email protected]]

Measure the resistance from the ac line prongs to the chassis with the plug out of the wall of course.
If it is 100,000 ohms or more, don't worry about it. But I would replace the cord with a proper 3 wire grounded cord. If the resistance is under 100,000 Ohms or so, something has got excessive leakage, from what I could see in the photo, the only suspect would be the power xformer.
Mark

[JackA]

On Sunday, October 25, 2015 at 7:09:20 PM UTC-4, wrote:
> On Sunday, October 25, 2015 at 1:44:22 PM UTC-7, Scott Dorsey wrote:
> > In article >,
> > > wrote:
> > >I have a Master Room XL-121 Spring Reverb which I bought used
> > >years ago and haven't powered it on in several years. When I recently
> > >powered it up I received a shock from the case. It has a 2 prong
> > >AC receptacle so it is not a grounded device. I measured about 40
> > >volts AC from the case to ground.
> > >
> > >So my question is what might be the cause? This unit is probably
> > >over 30 years old so I might expect the filter capacitors to be
> > >going bad, but I also suspect the power transformer.
> >
> > Likely it's the line filter caps. Dyke them out. Do you still measure
> > ground fault current with a meter? If so, put them back and look at the
> > switch and transformer. If not, replace them with modern X1 and Y grade
> > capacitors from digikey.
> >
> > These capacitors are specifically rated for line filtering service and
> > are specifically designed not to go leaky, like the originals likely did.
> > --scott
> >
> > --
> > "C'est un Nagra. C'est suisse, et tres, tres precis."
>
> I think IF I go to the trouble of removing them, I will just go ahead
> and replace them. I might be interested in replacing the transformer
> too because they used some foam on top of the reverb tank and the
> transformer which had dissolved and was quite nasty particularly
> where it was heated by the transformer. Is there a particular online
> resource for transformers or should I just go to DigiKey or Mouser?

Looks to me, maybe, a 30VA Transformer. You should measure secondary voltage, red-red lead, to determine what you have. I do not see it being filter capacitor problem, but if you're curious, just disconnect the secondary leads and fire it up and re-measure AC voltage to ground. Looks like DC side might be tied to ground/chassis via Center Tap lead.

Unlike Mark, I'd want to see at least 20 Megohms resistance :)

Jack

>
> Gary V

[Phil Allison[_4_]]

JackA wrote:

>
>
> Looks like it has a shield on the outside,


** For magnetic field suppression - it is right next to a spring unit with a sensitive pickup coil.


> Guess that pad, or whatever, under the transformer,
> is to dampen vibration. Looks dangerous to me!

** Might be just insulation where the mains voltage connects to some solder tabs on the underside of the tranny.

Whatever the case, the OP is probably worrying about nothing.

40VAC, measured by a DMM, is normal for that type of appliance.

A leakage test requires connecting a 1000 ohm resistor from case to ground and measuring the voltage across it.

Should be under 0.1V in a case like this.


.... Phil

[JackA]

On Sunday, October 25, 2015 at 10:43:53 PM UTC-4, Phil Allison wrote:
> JackA wrote:
>
> >
> >
> > Looks like it has a shield on the outside,
>
>
> ** For magnetic field suppression - it is right next to a spring unit with a sensitive pickup coil.

Agreed, but is it or isn't it at ground potential?

>
>
> > Guess that pad, or whatever, under the transformer,
> > is to dampen vibration. Looks dangerous to me!
>
> ** Might be just insulation where the mains voltage connects to some solder tabs on the underside of the tranny.

I see to AC lines spliced to Primary lines of xfmr (transformer). See three secondary leads. Nothing else around xfmr. Not sure how it's secured, pop rivets, screws, etc..

>
> Whatever the case, the OP is probably worrying about nothing.

- But he did "feel" the problem.

>
> 40VAC, measured by a DMM, is normal for that type of appliance.
>
> A leakage test requires connecting a 1000 ohm resistor from case to ground and measuring the voltage across it.
>
> Should be under 0.1V in a case like this.

If it from deterioration of insulating, an Applied Voltage (HiPot - High Potential) test is what you need. 1kV AC, primary leads to core and secondary. But getting too complex. Wiki' states 1 Megohm (DC resistance), but that's so vague.

Jack

>
>
> ... Phil

[JackA]

On Sunday, October 25, 2015 at 10:16:49 PM UTC-4, wrote:
> Measure the resistance from the ac line prongs to the chassis with the plug out of the wall of course.
> If it is 100,000 ohms or more, don't worry about it. But I would replace the cord with a proper 3 wire grounded cord. If the resistance is under 100,000 Ohms or so, something has got excessive leakage, from what I could see in the photo, the only suspect would be the power xformer.


Generally, an output voltage, 500-1000VDC (or more), is needed to verify insulation integrity (ohmmeter). A simple 9 VDC battery (digital voltmeter) won't tell you much.

Jack

Jack


> Mark

[JackA]

On Sunday, October 25, 2015 at 7:09:20 PM UTC-4, wrote:
> On Sunday, October 25, 2015 at 1:44:22 PM UTC-7, Scott Dorsey wrote:
> > In article >,
> > > wrote:
> > >I have a Master Room XL-121 Spring Reverb which I bought used
> > >years ago and haven't powered it on in several years. When I recently
> > >powered it up I received a shock from the case. It has a 2 prong
> > >AC receptacle so it is not a grounded device. I measured about 40
> > >volts AC from the case to ground.
> > >
> > >So my question is what might be the cause? This unit is probably
> > >over 30 years old so I might expect the filter capacitors to be
> > >going bad, but I also suspect the power transformer.
> >
> > Likely it's the line filter caps. Dyke them out. Do you still measure
> > ground fault current with a meter? If so, put them back and look at the
> > switch and transformer. If not, replace them with modern X1 and Y grade
> > capacitors from digikey.
> >
> > These capacitors are specifically rated for line filtering service and
> > are specifically designed not to go leaky, like the originals likely did.
> > --scott
> >
> > --
> > "C'est un Nagra. C'est suisse, et tres, tres precis."
>
> I think IF I go to the trouble of removing them, I will just go ahead
> and replace them. I might be interested in replacing the transformer
> too because they used some foam on top of the reverb tank and the
> transformer which had dissolved and was quite nasty particularly
> where it was heated by the transformer. Is there a particular online
> resource for transformers or should I just go to DigiKey or Mouser?

General life expectancy of a transformer = 25 years. If yours ran hot (outside copper shield looks discolored), then life expectancy drops appreciably. Yours is probably Class A (low temperature materials).

Jack

>
> Gary V

[Phil Allison[_4_]]

JackA wrote:


> > > Looks like it has a shield on the outside,
> >
> >
> > ** For magnetic field suppression -
>
> Agreed, but is it or isn't it at ground potential?

** Could be, when the case is grounded but irrelevant in any case.


> >
> > Whatever the case, the OP is probably worrying about nothing.
>
> - But he did "feel" the problem.


** Then he took a voltage measurement that was completely normal.



> > A leakage test requires connecting a 1000 ohm resistor from case
> > to ground and measuring the voltage across it.
> >
> > Should be under 0.1V in a case like this.
>
>
> If it from deterioration of insulating, an Applied Voltage
> (HiPot - High Potential) test is what you need. 1kV AC,
> primary leads to core and secondary. But getting too complex.


** For 120/240VAC appliances, leakage current measured at rated supply voltage is the usual way.

It's what PAT testers do and simple enough for anyone to copy.


..... Phil

[geoff]

On 26/10/2015 4:18 p.m., JackA wrote:

>
> General life expectancy of a transformer = 25 years.

Then you must have crappy transformers where you are.

In my experience transformers made of modern materials (ie not waxed
paper or cotton) when used normally and not subject to external
corrosion, last to all intents and purposes, forever.

geoff

[JackA]

On Sunday, October 25, 2015 at 11:44:39 PM UTC-4, Phil Allison wrote:
> JackA wrote:
>
>
> > > > Looks like it has a shield on the outside,
> > >
> > >
> > > ** For magnetic field suppression -
> >
> > Agreed, but is it or isn't it at ground potential?
>
> ** Could be, when the case is grounded but irrelevant in any case.
>
>
> > >
> > > Whatever the case, the OP is probably worrying about nothing.
> >
> > - But he did "feel" the problem.
>
>
> ** Then he took a voltage measurement that was completely normal.

Completely normal? Not sure how you came to that conclusion.

>
>
>
> > > A leakage test requires connecting a 1000 ohm resistor from case
> > > to ground and measuring the voltage across it.
> > >
> > > Should be under 0.1V in a case like this.
> >
> >
> > If it from deterioration of insulating, an Applied Voltage
> > (HiPot - High Potential) test is what you need. 1kV AC,
> > primary leads to core and secondary. But getting too complex.
>
>
> ** For 120/240VAC appliances, leakage current measured at rated supply voltage is the usual way.
>
> It's what PAT testers do and simple enough for anyone to copy.

Oh, okay.

Jack

>
>
> .... Phil

[JackA]

On Monday, October 26, 2015 at 2:00:49 AM UTC-4, geoff wrote:
> On 26/10/2015 4:18 p.m., JackA wrote:
>
> >
> > General life expectancy of a transformer = 25 years.
>
> Then you must have crappy transformers where you are.
>
> In my experience transformers made of modern materials (ie not waxed
> paper or cotton) when used normally and not subject to external
> corrosion, last to all intents and purposes, forever.

I see....

http://www.electricaltechnology.org/2013/01/what-is-normal-or-average-life.html

Thanks.

Jack
>
> geoff

[[email protected]]

On Sunday, October 25, 2015 at 4:35:09 PM UTC-7, Scott Dorsey wrote:
> > wrote:
> >
> >I think IF I go to the trouble of removing them, I will just go ahead
> >and replace them.
>
> Just make one cut for diagnostic purposes, it will take thirty seconds.
> Don't remove the whole thing. If it is good, just put a bead of solder
> on and put it back in another thirty seconds. It's not worth replacing
> them if they are good. Almost certainly they are bad, though.
>
> >I might be interested in replacing the transformer
> >too because they used some foam on top of the reverb tank and the
> >transformer which had dissolved and was quite nasty particularly
> >where it was heated by the transformer. Is there a particular online
> >resource for transformers or should I just go to DigiKey or Mouser?
>
> I like the Amveco/Talema transformers from Digikey personally, but
> really I doubt there is anything wrong with the transformer. Lighter
> fluid should take that foam residue off. If it's not broke, don't replace it.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

I'm not sure exactly what you mean. Are you suggesting I cut the copper
trace or traces to the filter caps so they are out of the circuit?

Gary V

[[email protected]]

On Sunday, October 25, 2015 at 6:37:39 PM UTC-7, Mike Rivers wrote:
> On 10/25/2015 6:42 PM, wrote:
>
> > Mike, I don't see the capacitors you describe. It has 2 1000uF and a bit
> > further away I see a couple of 22uF. I don't know if you can see these
> > photos but if you can, it might be helpful to look at the circuit topology.
>
> Without a schematic, we can only guess. It's hard to tell from your
> photo just where the AC line cord goes. I can see what are probably the
> wires from the secondary of the transformer, the two red and one yellow
> twisted wires, but it looks like the line cord might be connected
> directly to the transformer primary without going through a filter or
> bypass capacitors, or a power switch.
>
> If the plug isn't polarized (one blade wider than the other), try
> flipping it over in the socket and see if the chassis is still hot. If
> it isn't, reversing the plug isn't the cure, but it's a clue.
>
>
> --
> For a good time, visit http://mikeriversaudio.wordpress.com

You're right Mike, the ac is connected directly to the transformer.
Kind of surprised me when I saw this. I did flip the plug which is
not polarized which didn't make any difference.

Gary V

[[email protected]]

On Sunday, October 25, 2015 at 10:41:04 AM UTC-7, John Williamson wrote:
> On 25/10/2015 16:37, wrote:
> > I have a Master Room XL-121 Spring Reverb which I bought used
> > years ago and haven't powered it on in several years. When I recently
> > powered it up I received a shock from the case. It has a 2 prong
> > AC receptacle so it is not a grounded device. I measured about 40
> > volts AC from the case to ground.
> >
> > So my question is what might be the cause? This unit is probably
> > over 30 years old so I might expect the filter capacitors to be
> > going bad, but I also suspect the power transformer.
> >
> If it's been in a storeroom or cupboard, turn it on in a warm dry place
> for a while, as there may be dampness inside.
>
> Also, try measuring the voltage or leakage current to earth with a low
> impedance meter. I've had minor shocks and tingles from less than a
> milliamp of leakage, and can feel a few dozen microamps through my
> fingertips.
>
> --
> Tciao for Now!
>
> John.

As you suggested, I turned it on and left it over night. I'm not measuring
any AC voltage from the chassis to ground now. Also for JackA, I did feel
a shock when I attempted to plug the reverb output into a properly
grounded guitar amplifier. My paranoid meter went up.

Gary V

Gary V

[Mike Rivers[_2_]]

On 10/26/2015 11:04 AM, wrote:
> I did feel
> a shock when I attempted to plug the reverb output into a properly
> grounded guitar amplifier. My paranoid meter went up.

Don't use that test too often. ;) "Properly grounded" is relative,
particularly with instrument amplifiers. Even if they were plugged into
the same circuit or outlet strip, there could be a potential difference
between the chassis of the two units.

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Mike Rivers[_2_]]

On 10/26/2015 10:51 AM, wrote:
> You're right Mike, the ac is connected directly to the transformer.
> Kind of surprised me when I saw this. I did flip the plug which is
> not polarized which didn't make any difference.

Lots of gear doesn't have a power switch, though from the circuit board,
it looks like the secondary of the power transformer might be switched,
but not the primary. I guess it's no worse than a wall wart transformer
supply that's plugged in all the time.

Unless there are capacitors going from the line cord to the chassis, or
the transformer has a winding shorted to the mounting bracket, the
chassis of the reverb unit should be well isolated from the AC ground .
.. . until you connect something else to it (like your guitar amplifier)
that might have some leakage to ground. A 3-wire power cable with a wire
between the chassis and the safety ground pin would take care of that.

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Mike Rivers[_2_]]

On 10/26/2015 10:48 AM, wrote:
> I'm not sure exactly what you mean. Are you suggesting I cut the copper
> trace or traces to the filter caps so they are out of the circuit?

I believe Scott was thinking that there was a power line filter on the
circuit board, but apparently there isn't. You don't want to cut the
traces from the DC filter capacitors!

--
For a good time, visit http://mikeriversaudio.wordpress.com

[John Williamson]

On 26/10/2015 14:48, wrote:

> I'm not sure exactly what you mean. Are you suggesting I cut the copper
> trace or traces to the filter caps so they are out of the circuit?
>
The two capacitors visible on your pictures are the smoothing
(reservoir) capacitors for the low voltage DC supply. The AC comes on to
the board from the transformer, through the power switch, then is
rectified by the four diodes (Guessing 1N4002 type or equivalent), then
the DC is smoothed by the reservoir caps near the top right corner of
the board. There might be a voltage regulator further along the line,
but there probably isn't.

The filter caps Mike is talking about, if they exist, will be on the HT
(input) side of the transformer, which in this case is *not* on the PCB
so cutting PCB traces or removing capacitors from the PCB in this
instance would not be a good idea.

However, if leaving it running overnight in a warm place has solved the
problem, then you're good to go as is. It seems there may have been some
moisture in the mains transformer area which has been driven off by the
heat.

And as has been suggested, your "properly grounded" guitar amp may not
be, and there have been cases of spectacular sparks between touching
guitars connected to different amps due to their grounding schemes being
different. When I'm recording I *never* connect directly to any guitar
or amp for this reason, I always use a ground lifter.
--
Tciao for Now!

John.

[Scott Dorsey]

> wrote:
>
>I'm not sure exactly what you mean. Are you suggesting I cut the copper
>trace or traces to the filter caps so they are out of the circuit?

The line filter caps will probably not be on the board. If they are, you
can desolder one lead and let it float up in the air, or you can just dike
off one of the leads above the board if you're going to replace it anyway.

They are likely to be on the power connector or as close to the power
connector as possible. The idea is that they form a filter as close as
possible to the case, where the case is acting as a demarcation point
between the noisy outside world and the quiet inside world. The farther
from the power connector they are, the more noisy wiring is radiating junk
inside the case.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

> wrote:
>
>You're right Mike, the ac is connected directly to the transformer.
>Kind of surprised me when I saw this. I did flip the plug which is
>not polarized which didn't make any difference.

No switch? No line filter caps or corcom module?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[John Williamson]

On 26/10/2015 15:50, Scott Dorsey wrote:
> > wrote:
>>
>> You're right Mike, the ac is connected directly to the transformer.
>> Kind of surprised me when I saw this. I did flip the plug which is
>> not polarized which didn't make any difference.
>
> No switch? No line filter caps or corcom module?
>
And what looks to be an unregulated DC supply to the board. The power
switch is on the LT side of the transformer.

--
Tciao for Now!

John.

[JackA]

On Monday, October 26, 2015 at 11:04:54 AM UTC-4, wrote:
> On Sunday, October 25, 2015 at 10:41:04 AM UTC-7, John Williamson wrote:
> > On 25/10/2015 16:37, wrote:
> > > I have a Master Room XL-121 Spring Reverb which I bought used
> > > years ago and haven't powered it on in several years. When I recently
> > > powered it up I received a shock from the case. It has a 2 prong
> > > AC receptacle so it is not a grounded device. I measured about 40
> > > volts AC from the case to ground.
> > >
> > > So my question is what might be the cause? This unit is probably
> > > over 30 years old so I might expect the filter capacitors to be
> > > going bad, but I also suspect the power transformer.
> > >
> > If it's been in a storeroom or cupboard, turn it on in a warm dry place
> > for a while, as there may be dampness inside.
> >
> > Also, try measuring the voltage or leakage current to earth with a low
> > impedance meter. I've had minor shocks and tingles from less than a
> > milliamp of leakage, and can feel a few dozen microamps through my
> > fingertips.
> >
> > --
> > Tciao for Now!
> >
> > John.
>
> As you suggested, I turned it on and left it over night. I'm not measuring
> any AC voltage from the chassis to ground now. Also for JackA, I did feel
> a shock when I attempted to plug the reverb output into a properly
> grounded guitar amplifier. My paranoid meter went up.

Can'y blame you! Gar', it HAS to be the transformer. Just measure secondary voltage at PC board, red-red, to find replacement. I doubt you'll get a direct replacement (one with outer shield), but a 30VA size transformer would be a decent guess, probably a little big, but bigger the better.

Good luck and stay safe :)

Jack


>
> Gary V
>
> Gary V

[John Williamson]

On 26/10/2015 15:48, Scott Dorsey wrote:
> > wrote:
>>
>> I'm not sure exactly what you mean. Are you suggesting I cut the copper
>> trace or traces to the filter caps so they are out of the circuit?
>
> The line filter caps will probably not be on the board. If they are, you
> can desolder one lead and let it float up in the air, or you can just dike
> off one of the leads above the board if you're going to replace it anyway.
>
> They are likely to be on the power connector or as close to the power
> connector as possible. The idea is that they form a filter as close as
> possible to the case, where the case is acting as a demarcation point
> between the noisy outside world and the quiet inside world. The farther
> from the power connector they are, the more noisy wiring is radiating junk
> inside the case.
> --scott
>
Scott, have you looked at the pictures of the PCB and transformer that
the OP put on line? There is no visible filtering on the mains
transformer apart from a screen to stop the stray fields affecting the
spring coils.

--
Tciao for Now!

John.

[[email protected]]

On Sunday, October 25, 2015 at 7:16:49 PM UTC-7, wrote:
> Measure the resistance from the ac line prongs to the chassis with the plug out of the wall of course.
> If it is 100,000 ohms or more, don't worry about it. But I would replace the cord with a proper 3 wire grounded cord. If the resistance is under 100,000 Ohms or so, something has got excessive leakage, from what I could see in the photo, the only suspect would be the power xformer.
> Mark

Mark, I tried this test and I didn't measure any resistance. But I will
certainly replace the the ac connection with a 3 wire ground plug.

Gary V

[[email protected]]

On Sunday, October 25, 2015 at 9:37:22 AM UTC-7, wrote:
> I have a Master Room XL-121 Spring Reverb which I bought used
> years ago and haven't powered it on in several years. When I recently
> powered it up I received a shock from the case. It has a 2 prong
> AC receptacle so it is not a grounded device. I measured about 40
> volts AC from the case to ground.
>
> So my question is what might be the cause? This unit is probably
> over 30 years old so I might expect the filter capacitors to be
> going bad, but I also suspect the power transformer.
>
> Gary V

As a follow up, I followed John Williamson's advice and left it on
overnight which alleviated the problem. For now I will not do any
invasive surgery because when I put it to use, it sounded pretty
darn nice. This reverb unit has enough gain so you can directly insert
a guitar and use the output into a guitar amplifier - in this case
a 1970's Fender Champ. In spite of the transformer's close
proximity to the reverb tank (as Phil Allison pointed out), it
is remarkably quiet and lacking any noticeable hum.

Again, thanks to the group for the excellent advice. My order
list for DigiKey is growing...

Also, glad you could see the photo's; I'm not much into social
media web sites so I stumbled a bit figuring out how to
make it work.

Gary V

[Scott Dorsey]

John Williamson > wrote:
>On 26/10/2015 15:50, Scott Dorsey wrote:
>> > wrote:
>>>
>>> You're right Mike, the ac is connected directly to the transformer.
>>> Kind of surprised me when I saw this. I did flip the plug which is
>>> not polarized which didn't make any difference.
>>
>> No switch? No line filter caps or corcom module?
>>
>And what looks to be an unregulated DC supply to the board. The power
>switch is on the LT side of the transformer.

That's no reason not to have a line filter!

But if there's no line filter and no switch, all there is left is the
transformer. So put a three prong plug on it and wait.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

John Williamson > wrote:
>On 26/10/2015 15:48, Scott Dorsey wrote:
>> > wrote:
>>>
>>> I'm not sure exactly what you mean. Are you suggesting I cut the copper
>>> trace or traces to the filter caps so they are out of the circuit?
>>
>> The line filter caps will probably not be on the board. If they are, you
>> can desolder one lead and let it float up in the air, or you can just dike
>> off one of the leads above the board if you're going to replace it anyway.
>>
>> They are likely to be on the power connector or as close to the power
>> connector as possible. The idea is that they form a filter as close as
>> possible to the case, where the case is acting as a demarcation point
>> between the noisy outside world and the quiet inside world. The farther
>> from the power connector they are, the more noisy wiring is radiating junk
>> inside the case.
>>
>Scott, have you looked at the pictures of the PCB and transformer that
>the OP put on line? There is no visible filtering on the mains
>transformer apart from a screen to stop the stray fields affecting the
>spring coils.

No, I am on the road with no graphics. But what I'd want to see is the
point where the line comes into the box, not necessarily the board with
the transformer.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[John Williamson]

On 26/10/2015 18:40, Scott Dorsey wrote:
> John Williamson > wrote:

>> Scott, have you looked at the pictures of the PCB and transformer that
>> the OP put on line? There is no visible filtering on the mains
>> transformer apart from a screen to stop the stray fields affecting the
>> spring coils.
>
> No, I am on the road with no graphics. But what I'd want to see is the
> point where the line comes into the box, not necessarily the board with
> the transformer.
> --scott
>
One of the pictures shows that. The power line comes in through a strain
relief grommet and is then apparently soldered or welded directly to the
transformer primary without even an internal fuse. The transformer is
mounted on a pad directly to the case. It's a really 'orribly cheap
looking design. If it were being sold here, I'd expect to see an added
internal fuse to comply with the laws on electrical safety.

--
Tciao for Now!

John.

[Scott Dorsey]

John Williamson > wrote:
>On 26/10/2015 18:40, Scott Dorsey wrote:
>> John Williamson > wrote:
>
>>> Scott, have you looked at the pictures of the PCB and transformer that
>>> the OP put on line? There is no visible filtering on the mains
>>> transformer apart from a screen to stop the stray fields affecting the
>>> spring coils.
>>
>> No, I am on the road with no graphics. But what I'd want to see is the
>> point where the line comes into the box, not necessarily the board with
>> the transformer.
>>
>One of the pictures shows that. The power line comes in through a strain
>relief grommet and is then apparently soldered or welded directly to the
>transformer primary without even an internal fuse. The transformer is
>mounted on a pad directly to the case. It's a really 'orribly cheap
>looking design. If it were being sold here, I'd expect to see an added
>internal fuse to comply with the laws on electrical safety.

Maybe adding a corcom filter on the input might not be a bad plan. They
are cheap, and give you a three-prong input with a real chassis ground
and some nice filtering. If you pick the right one, you can get a fuse too.

I'd definitely put a three-prong cord on that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Angus Kerr]

On Monday, October 26, 2015 at 8:55:44 PM UTC+2, John Williamson wrote:
> On 26/10/2015 18:40, Scott Dorsey wrote:
> > John Williamson wrote:
>
> >> Scott, have you looked at the pictures of the PCB and transformer that
> >> the OP put on line? There is no visible filtering on the mains
> >> transformer apart from a screen to stop the stray fields affecting the
> >> spring coils.
> >
> > No, I am on the road with no graphics. But what I'd want to see is the
> > point where the line comes into the box, not necessarily the board with
> > the transformer.
> > --scott
> >
> One of the pictures shows that. The power line comes in through a strain
> relief grommet and is then apparently soldered or welded directly to the
> transformer primary without even an internal fuse. The transformer is
> mounted on a pad directly to the case. It's a really 'orribly cheap
> looking design. If it were being sold here, I'd expect to see an added
> internal fuse to comply with the laws on electrical safety.
>
> --
> Tciao for Now!
>
> John.

One of the smoothing capacitors on the pcb looks like it's bulging a bit.....

I can't believe that a product like that could be sold where there is no protection for the transformer which is never switched off! Just humming away until..... The incoming AC line looks like it's insulated with electrical tape and is soldered to the transformer wires. I don't know if there is an earth connection from the transformer core to the case.

To my mind, depending on the secondary voltage, this thing shouldn't even tickle you at all. There must be something wrong with the transformer: it's the only part that could interacts with the mains supply at all. I would either replace the transformer pronto. The secondary part should float and take the potential of whatever you connect it to.

Like Jack says, it will probably fail an insulation test. Find a 500V or 100V insulation tester, disconnect the secondary windings from the pc board, and then test between the primary and secondary windings, the primary to the case, and the secondary to the case. You should get readings in the tens of megaohms at least, preferably in the 100's Even 110V AC can kill, and you don't want 110 V coming into your other gear, killing those also.

Be Safe.
-Angus.

[Mike Rivers[_2_]]

On 10/26/2015 3:38 PM, Angus Kerr wrote:
> I can't believe that a product like that could be sold where there is
> no protection for the transformer which is never switched off! Just
> humming away until..... The incoming AC line looks like it's
> insulated with electrical tape and is soldered to the transformer
> wires. I don't know if there is an earth connection from the
> transformer core to the case.

Well, remember, this was an inexpensive reverb from the days when a
studio reverb was an EMT plate for about $5,000. MicMix didn't stay in
the reverb business for very long once affordable digital reverbs came
along.



--
For a good time, visit http://mikeriversaudio.wordpress.com

[david gourley[_2_]]

said...news:1be5c756-5ea8-417b-a293-1864ec141c28
@googlegroups.com:

> On Sunday, October 25, 2015 at 9:37:22 AM UTC-7, wrote:
>> I have a Master Room XL-121 Spring Reverb which I bought used
>> years ago and haven't powered it on in several years. When I recently
>> powered it up I received a shock from the case. It has a 2 prong
>> AC receptacle so it is not a grounded device. I measured about 40
>> volts AC from the case to ground.
>>
>> So my question is what might be the cause? This unit is probably
>> over 30 years old so I might expect the filter capacitors to be
>> going bad, but I also suspect the power transformer.
>>
>> Gary V
>
> As a follow up, I followed John Williamson's advice and left it on
> overnight which alleviated the problem. For now I will not do any
> invasive surgery because when I put it to use, it sounded pretty
> darn nice. This reverb unit has enough gain so you can directly insert
> a guitar and use the output into a guitar amplifier - in this case
> a 1970's Fender Champ. In spite of the transformer's close
> proximity to the reverb tank (as Phil Allison pointed out), it
> is remarkably quiet and lacking any noticeable hum.
>
> Again, thanks to the group for the excellent advice. My order
> list for DigiKey is growing...
>
> Also, glad you could see the photo's; I'm not much into social
> media web sites so I stumbled a bit figuring out how to
> make it work.
>
> Gary V

Does that Fender Champ have a 2-conductor plug? Were you using that when
you got that shock?

I don't remember when they changed those to a grounded plug, but they
eventually did. My '68 Champ has a 2-conductor, which I'm changing over to
a grounded one just for that reason. As is, it hums more if the plug is in
one position as opposed to the other position. I've been 'bit' by it
before.

david

[mcp6453[_2_]]

On 10/26/2015 4:58 PM, david gourley wrote:
> said...news:1be5c756-5ea8-417b-a293-1864ec141c28
> @googlegroups.com:
>
>> On Sunday, October 25, 2015 at 9:37:22 AM UTC-7, wrote:
>>> I have a Master Room XL-121 Spring Reverb which I bought used
>>> years ago and haven't powered it on in several years. When I recently
>>> powered it up I received a shock from the case. It has a 2 prong
>>> AC receptacle so it is not a grounded device. I measured about 40
>>> volts AC from the case to ground.
>>>
>>> So my question is what might be the cause? This unit is probably
>>> over 30 years old so I might expect the filter capacitors to be
>>> going bad, but I also suspect the power transformer.
>>>
>>> Gary V
>>
>> As a follow up, I followed John Williamson's advice and left it on
>> overnight which alleviated the problem. For now I will not do any
>> invasive surgery because when I put it to use, it sounded pretty
>> darn nice. This reverb unit has enough gain so you can directly insert
>> a guitar and use the output into a guitar amplifier - in this case
>> a 1970's Fender Champ. In spite of the transformer's close
>> proximity to the reverb tank (as Phil Allison pointed out), it
>> is remarkably quiet and lacking any noticeable hum.
>>
>> Again, thanks to the group for the excellent advice. My order
>> list for DigiKey is growing...
>>
>> Also, glad you could see the photo's; I'm not much into social
>> media web sites so I stumbled a bit figuring out how to
>> make it work.
>>
>> Gary V
>
> Does that Fender Champ have a 2-conductor plug? Were you using that when
> you got that shock?
>
> I don't remember when they changed those to a grounded plug, but they
> eventually did. My '68 Champ has a 2-conductor, which I'm changing over to
> a grounded one just for that reason. As is, it hums more if the plug is in
> one position as opposed to the other position. I've been 'bit' by it
> before.
>
> david
>

If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
get 120 volts on the chassis.

[John Williamson]

On 26/10/2015 21:12, mcp6453 wrote:
> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
> get 120 volts on the chassis.
>
Just to confirm. The unit in question has a total of zero, none, zip
capacitors connected between the power line and the rest of the circuit,
so a failing capacitor cannot give the user a shock. I would estimate
the internal DC supply voltage does not exceed about 24 volts. The worst
that any of the visible capacitors failing can do is to give an
incredible amount of hum on the output and possible chemical damage to
the PCB.

However, as one of them does seem to be bulging somewhat, it might be a
good idea to replace all the electrolytics as a matter of course, but
not as a safety concern.

--
Tciao for Now!

John.

[david gourley[_2_]]

mcp6453 > said...news:gYudnYnrg-GnCrPLnZ2dnUU7-
:

> On 10/26/2015 4:58 PM, david gourley wrote:
>> said...news:1be5c756-5ea8-417b-a293-1864ec141c28
>> @googlegroups.com:
>>
>>> On Sunday, October 25, 2015 at 9:37:22 AM UTC-7,
wrote:
>>>> I have a Master Room XL-121 Spring Reverb which I bought used
>>>> years ago and haven't powered it on in several years. When I recently
>>>> powered it up I received a shock from the case. It has a 2 prong
>>>> AC receptacle so it is not a grounded device. I measured about 40
>>>> volts AC from the case to ground.
>>>>
>>>> So my question is what might be the cause? This unit is probably
>>>> over 30 years old so I might expect the filter capacitors to be
>>>> going bad, but I also suspect the power transformer.
>>>>
>>>> Gary V
>>>
>>> As a follow up, I followed John Williamson's advice and left it on
>>> overnight which alleviated the problem. For now I will not do any
>>> invasive surgery because when I put it to use, it sounded pretty
>>> darn nice. This reverb unit has enough gain so you can directly insert
>>> a guitar and use the output into a guitar amplifier - in this case
>>> a 1970's Fender Champ. In spite of the transformer's close
>>> proximity to the reverb tank (as Phil Allison pointed out), it
>>> is remarkably quiet and lacking any noticeable hum.
>>>
>>> Again, thanks to the group for the excellent advice. My order
>>> list for DigiKey is growing...
>>>
>>> Also, glad you could see the photo's; I'm not much into social
>>> media web sites so I stumbled a bit figuring out how to
>>> make it work.
>>>
>>> Gary V
>>
>> Does that Fender Champ have a 2-conductor plug? Were you using that
when
>> you got that shock?
>>
>> I don't remember when they changed those to a grounded plug, but they
>> eventually did. My '68 Champ has a 2-conductor, which I'm changing over
to
>> a grounded one just for that reason. As is, it hums more if the plug is
in
>> one position as opposed to the other position. I've been 'bit' by it
>> before.
>>
>> david
>>
>
> If your equipment has a "death cap" you want to get rid of it. The shock
could be a leaking death cap. If it shorts, you
> get 120 volts on the chassis.

I will as I install the grounded power cable on the amp. It hasn't changed
though, as it's been like that since I got the amp in '68.

david

[[email protected]]

On Monday, October 26, 2015 at 2:01:10 PM UTC-7, david gourley wrote:
> said...news:1be5c756-5ea8-417b-a293-1864ec141c28
> @googlegroups.com:
>
> > On Sunday, October 25, 2015 at 9:37:22 AM UTC-7, wrote:
> >> I have a Master Room XL-121 Spring Reverb which I bought used
> >> years ago and haven't powered it on in several years. When I recently
> >> powered it up I received a shock from the case. It has a 2 prong
> >> AC receptacle so it is not a grounded device. I measured about 40
> >> volts AC from the case to ground.
> >>
> >> So my question is what might be the cause? This unit is probably
> >> over 30 years old so I might expect the filter capacitors to be
> >> going bad, but I also suspect the power transformer.
> >>
> >> Gary V
> >
> > As a follow up, I followed John Williamson's advice and left it on
> > overnight which alleviated the problem. For now I will not do any
> > invasive surgery because when I put it to use, it sounded pretty
> > darn nice. This reverb unit has enough gain so you can directly insert
> > a guitar and use the output into a guitar amplifier - in this case
> > a 1970's Fender Champ. In spite of the transformer's close
> > proximity to the reverb tank (as Phil Allison pointed out), it
> > is remarkably quiet and lacking any noticeable hum.
> >
> > Again, thanks to the group for the excellent advice. My order
> > list for DigiKey is growing...
> >
> > Also, glad you could see the photo's; I'm not much into social
> > media web sites so I stumbled a bit figuring out how to
> > make it work.
> >
> > Gary V
>
> Does that Fender Champ have a 2-conductor plug? Were you using that when
> you got that shock?
>
> I don't remember when they changed those to a grounded plug, but they
> eventually did. My '68 Champ has a 2-conductor, which I'm changing over to
> a grounded one just for that reason. As is, it hums more if the plug is in
> one position as opposed to the other position. I've been 'bit' by it
> before.
>
> david

Yes, it's a 2 prong ac plug. Some years ago I put a little piece of tape
on one side for the reason you mentioned. Seems at the time I may
have had a similar problem getting shocked. I know I should upgrade
it to a grounded plug but it's served me well for years and I must say,
it sounds really good as is, particularly with single coil pickups. My
favorite is a Fender Mustang - and with a spring reverb in front of it,
simply amazing.

Gary V

[Scott Dorsey]

John Williamson > wrote:
>On 26/10/2015 21:12, mcp6453 wrote:
>> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
>> get 120 volts on the chassis.
>>
>Just to confirm. The unit in question has a total of zero, none, zip
>capacitors connected between the power line and the rest of the circuit,
>so a failing capacitor cannot give the user a shock. I would estimate
>the internal DC supply voltage does not exceed about 24 volts. The worst
>that any of the visible capacitors failing can do is to give an
>incredible amount of hum on the output and possible chemical damage to
>the PCB.

No, no, he is referring to a line filter cap on the Fender Champ, which
is in fact likely to be the original poster's actual problem.
Adding cords with safety grounds to both devices is probably a good plan
although it may be nontrivial with the Champ.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[John Williamson]

On 26/10/2015 22:05, Scott Dorsey wrote:
> John Williamson > wrote:
>> On 26/10/2015 21:12, mcp6453 wrote:
>>> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
>>> get 120 volts on the chassis.
>>>
>> Just to confirm. The unit in question has a total of zero, none, zip
>> capacitors connected between the power line and the rest of the circuit,
>> so a failing capacitor cannot give the user a shock. I would estimate
>> the internal DC supply voltage does not exceed about 24 volts. The worst
>> that any of the visible capacitors failing can do is to give an
>> incredible amount of hum on the output and possible chemical damage to
>> the PCB.
>
> No, no, he is referring to a line filter cap on the Fender Champ, which
> is in fact likely to be the original poster's actual problem.
> Adding cords with safety grounds to both devices is probably a good plan
> although it may be nontrivial with the Champ.
>
In that case, I slouch corrected. I thought we were still talking about
the OP's problem.


--
Tciao for Now!

John.

[Scott Dorsey]

John Williamson > wrote:
>On 26/10/2015 22:05, Scott Dorsey wrote:
>> John Williamson > wrote:
>>> On 26/10/2015 21:12, mcp6453 wrote:
>>>> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
>>>> get 120 volts on the chassis.
>>>>
>>> Just to confirm. The unit in question has a total of zero, none, zip
>>> capacitors connected between the power line and the rest of the circuit,
>>> so a failing capacitor cannot give the user a shock. I would estimate
>>> the internal DC supply voltage does not exceed about 24 volts. The worst
>>> that any of the visible capacitors failing can do is to give an
>>> incredible amount of hum on the output and possible chemical damage to
>>> the PCB.
>>
>> No, no, he is referring to a line filter cap on the Fender Champ, which
>> is in fact likely to be the original poster's actual problem.
>> Adding cords with safety grounds to both devices is probably a good plan
>> although it may be nontrivial with the Champ.
>>
>In that case, I slouch corrected. I thought we were still talking about
>the OP's problem.

The OP had the reverb unit plugged into a Champ, it seems. And something
was leaking. Given that the Champ is famous for that, I suspect it was
not the reverb unit leaking at all.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On Monday, October 26, 2015 at 3:31:21 PM UTC-7, Scott Dorsey wrote:
> John Williamson > wrote:
> >On 26/10/2015 22:05, Scott Dorsey wrote:
> >> John Williamson > wrote:
> >>> On 26/10/2015 21:12, mcp6453 wrote:
> >>>> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
> >>>> get 120 volts on the chassis.
> >>>>
> >>> Just to confirm. The unit in question has a total of zero, none, zip
> >>> capacitors connected between the power line and the rest of the circuit,
> >>> so a failing capacitor cannot give the user a shock. I would estimate
> >>> the internal DC supply voltage does not exceed about 24 volts. The worst
> >>> that any of the visible capacitors failing can do is to give an
> >>> incredible amount of hum on the output and possible chemical damage to
> >>> the PCB.
> >>
> >> No, no, he is referring to a line filter cap on the Fender Champ, which
> >> is in fact likely to be the original poster's actual problem.
> >> Adding cords with safety grounds to both devices is probably a good plan
> >> although it may be nontrivial with the Champ.
> >>
> >In that case, I slouch corrected. I thought we were still talking about
> >the OP's problem.
>
> The OP had the reverb unit plugged into a Champ, it seems. And something
> was leaking. Given that the Champ is famous for that, I suspect it was
> not the reverb unit leaking at all.
> --scott
>
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

Sorry for the confusion. The original amp where I was shocked was a
modern amp with a 3 prong ground plug. I was only using the Champ
to make point about the combined Champ/Spring Reverb sound I appreciate.

Gary V

[Phil Allison[_4_]]

JackA wrote:
>
>
> > ** Then he took a voltage measurement that was completely normal.
>
> Completely normal? Not sure how you came to that conclusion.
>
>

** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.

At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.

A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.

So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.

The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.

With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.



..... Phil

[John Williamson]

On 27/10/2015 03:57, Phil Allison wrote:
> JackA wrote:
>>
>>
>>> ** Then he took a voltage measurement that was completely normal.
>>
>> Completely normal? Not sure how you came to that conclusion.
>>
>>
>
> ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.
>
> At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
>
> A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
>
> So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
>
> The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
>
> With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
>
Quite. I frequently feel a "sticky" feeling when I lightly brush my
fingers along the exposed metalwork of any portable device that's on
charge. Repeated checks of the wall wart power supplies show no defects
in the insulation. I even feel it when I'm wearing rubber soled shoes
standing on a dry wooden floor, so am insulated from the ground myself.
My capacitance and the frequency of the charge current ripple lets a
small but feelable current flow between me and the device in question.


--
Tciao for Now!

John.

[Phil Allison[_4_]]

John Williamson wrote:
>
> >
> >
> > ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.
> >
> > At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
> >
> > A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
> >
> > So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
> >
> > The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
> >
> > With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
>
>
> >
> Quite. I frequently feel a "sticky" feeling when I lightly brush my
> fingers along the exposed metalwork of any portable device that's on
> charge. Repeated checks of the wall wart power supplies show no defects
> in the insulation. I even feel it when I'm wearing rubber soled shoes
> standing on a dry wooden floor, so am insulated from the ground myself.
> My capacitance and the frequency of the charge current ripple lets a
> small but feelable current flow between me and the device in question.
>
>

** Switch mode PSUs and chargers normally have EMI suppression caps wired from the "hot" side to the load side that makes the problem much worse than with transformers.

The caps used are typically 1000 to 2200pF, class Y types.

The possible peak surge currents have enough energy to damage semiconductors at the inputs and outputs of many audio/video devices.


.... Phil

[JackA]

On Monday, October 26, 2015 at 6:48:23 PM UTC-4, wrote:
> On Monday, October 26, 2015 at 3:31:21 PM UTC-7, Scott Dorsey wrote:
> > John Williamson > wrote:
> > >On 26/10/2015 22:05, Scott Dorsey wrote:
> > >> John Williamson > wrote:
> > >>> On 26/10/2015 21:12, mcp6453 wrote:
> > >>>> If your equipment has a "death cap" you want to get rid of it. The shock could be a leaking death cap. If it shorts, you
> > >>>> get 120 volts on the chassis.
> > >>>>
> > >>> Just to confirm. The unit in question has a total of zero, none, zip
> > >>> capacitors connected between the power line and the rest of the circuit,
> > >>> so a failing capacitor cannot give the user a shock. I would estimate
> > >>> the internal DC supply voltage does not exceed about 24 volts. The worst
> > >>> that any of the visible capacitors failing can do is to give an
> > >>> incredible amount of hum on the output and possible chemical damage to
> > >>> the PCB.
> > >>
> > >> No, no, he is referring to a line filter cap on the Fender Champ, which
> > >> is in fact likely to be the original poster's actual problem.
> > >> Adding cords with safety grounds to both devices is probably a good plan
> > >> although it may be nontrivial with the Champ.
> > >>
> > >In that case, I slouch corrected. I thought we were still talking about
> > >the OP's problem.
> >
> > The OP had the reverb unit plugged into a Champ, it seems. And something
> > was leaking. Given that the Champ is famous for that, I suspect it was
> > not the reverb unit leaking at all.
> > --scott
> >
> > --
> > "C'est un Nagra. C'est suisse, et tres, tres precis."
>
> Sorry for the confusion. The original amp where I was shocked was a
> modern amp with a 3 prong ground plug. I was only using the Champ
> to make point about the combined Champ/Spring Reverb sound I appreciate.

I ALL make sense to me!!

Thanks :)

Jack
>
> Gary V

[JackA]

On Monday, October 26, 2015 at 11:57:11 PM UTC-4, Phil Allison wrote:
> JackA wrote:
> >
> >
> > > ** Then he took a voltage measurement that was completely normal.
> >
> > Completely normal? Not sure how you came to that conclusion.
> >
> >
>
> ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF..
>
> At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
>
> A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
>
> So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
>
> The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
>
> With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
>
>
>
> .... Phil

First: OP? Original Poster? Maybe I've been away from usenet too long!

So much for leakage capacitance, inductance and stray magnetic flux heating the ferrous frame, the device (reverb) is faulty. I THINK we agree on that?

Jack

[Scott Dorsey]

> wrote:
>Sorry for the confusion. The original amp where I was shocked was a
>modern amp with a 3 prong ground plug. I was only using the Champ
>to make point about the combined Champ/Spring Reverb sound I appreciate.

Now I am even more confused.

Yes.... it's correct that you can't use a high-Z voltmeter to measure chassis
leakage, so you don't really know how much leakage you have or where it is
coming from.

But you know that if it _is_ coming from the reverb unit, which to be honest
is kind of unlikely, that it's coming from the transformer because there is
nothing else for it to be coming from.

So I would be inclined to put a three-prong cord on the reverb unit and
if the transformer is leaking resistively, it will fail, and if it's just
leaking capacitively, it'll be fine.

But I'd also check that guitar amp and I'd check the outlet with an outlet
tester.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[JackA]

On Tuesday, October 27, 2015 at 4:24:57 AM UTC-4, John Williamson wrote:
> On 27/10/2015 03:57, Phil Allison wrote:
> > JackA wrote:
> >>
> >>
> >>> ** Then he took a voltage measurement that was completely normal.
> >>
> >> Completely normal? Not sure how you came to that conclusion.
> >>
> >>
> >
> > ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.
> >
> > At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
> >
> > A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
> >
> > So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
> >
> > The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
> >
> > With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
> >
> Quite. I frequently feel a "sticky" feeling when I lightly brush my
> fingers along the exposed metalwork of any portable device that's on
> charge. Repeated checks of the wall wart power supplies show no defects
> in the insulation. I even feel it when I'm wearing rubber soled shoes
> standing on a dry wooden floor, so am insulated from the ground myself.
> My capacitance and the frequency of the charge current ripple lets a
> small but feelable current flow between me and the device in question.

Forgive me, but my fist time for, "wall wart"; though you misspelled Wall Mart!!
I see they call AC adapter, Power Bricks, too!!
Go to run, the sun is out and my Cloud is screwed up!! :-)

Jack
>
>
> --
> Tciao for Now!
>
> John.

[JackA]

On Monday, October 26, 2015 at 11:57:11 PM UTC-4, Phil Allison wrote:
> JackA wrote:
> >
> >
> > > ** Then he took a voltage measurement that was completely normal.
> >
> > Completely normal? Not sure how you came to that conclusion.
> >
> >
>
> ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF..
>
> At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
>
> A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
>
> So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
>
> The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
>
> With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
>
>
>
> .... Phil

Phil, if you REALLY want to impress me, you can tell me why transformers are typically designed with insulation NOT EXCEEDING 40 volts/mil, REGARDLESS of the type insulation?

Jack

[Phil Allison[_4_]]

JackA wrote:

>
> >
> > ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.
> >
> > At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
> >
> > A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
> >
> > So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
> >
> > The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
> >
> > With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
> >
>
>
> First: OP? Original Poster?


** Yes, Gary Y.

>
> So much for leakage capacitance, inductance and stray magnetic flux heating the ferrous frame, the device (reverb) is faulty. I THINK we agree on that?
>

** No, IMO the reverb is being falsely accused.



.... Phil

[JackA]

On Wednesday, October 28, 2015 at 2:11:56 AM UTC-4, Phil Allison wrote:
> JackA wrote:
>
> >
> > >
> > > ** Transformers with the secondary wound over the primary have capacitance between the two. Ones similar to the OP's example have about 100 to 150pF.
> > >
> > > At 60Hz, the impedance is about 20Mohms and a standard DMM with 10Mohms input resistance reads about 30% of the AC voltage present on the primary if connected from secondary to ground.
> > >
> > > A similar amount of stray capacitance exists between the primary and the frame of the same transformer, adding to the above when the transformer is bolted to a metal case which itself is electrically connected to the secondary.
> > >
> > > So a reading between 40VAC and 60VAC is to be expected using a DMM connected between the case and supply ground with units like the OP's.
> > >
> > > The steady current available is a only 4 to 6 microamps, however the peak current is much higher under certain conditions.
> > >
> > > With no external connection to the case, it constantly floats at a voltage close to 120VAC. If the OP was holding a grounded jack plug in one hand and touched the case with other, the stray capacitance charges instantly via body resistance with a spike of current of many milliamps. If he brushed his fingertips over the case, the current spikes are rapidly repeated and cause very noticeable tingles.
> > >
> >
> >
> > First: OP? Original Poster?
>
>
> ** Yes, Gary Y.
>
> >
> > So much for leakage capacitance, inductance and stray magnetic flux heating the ferrous frame, the device (reverb) is faulty. I THINK we agree on that?
> >
>
> ** No, IMO the reverb is being falsely accused.

Hopefully, you're not employed by Underwriters Laboratories!! :-)

Jack
>
>
>
> ... Phil

[Phil Allison[_4_]]

JackA wrote:

>
> >
> > ** No, IMO the reverb is being falsely accused.
>
> Hopefully, you're not employed by Underwriters Laboratories!! :-)
>

** You need to get a DMM, switch it to AC volts a test few items that have no supply ground connection.


..... Phil

[JackA]

On Wednesday, October 28, 2015 at 7:47:16 PM UTC-4, Phil Allison wrote:
> JackA wrote:
>
> >
> > >
> > > ** No, IMO the reverb is being falsely accused.
> >
> > Hopefully, you're not employed by Underwriters Laboratories!! :-)
> >
>
> ** You need to get a DMM, switch it to AC volts a test few items that have no supply ground connection.

I'll do that after creating my will!! :-)

Jack
>
>
> .... Phil

[[email protected]]

Maybe not so relevent, but since the era of non-polarized plugs,
I always have handy a simple 10 cent neon lamp.

Holding one wire and touching the other to a chassis shows me
leakage. I use that indication to mark the plug for next time.