The described Vintage Voltage Device has an issue you should know about:
Plugged into a wall socket, it will work exactly as expected, but it can get confused about a missing ground. It will still alarm, but the alarm will be “reversed polarity”. If the ground is present, but the outlet has reversed polarity, the correct reversed polarity alarm will sound.
Long story short, with many wall outlets, in the absence of a ground, there can be enough neutral voltage and current to trick the device into thinking there is reversed polarity.
If an isolation transformer is used between the Device and the wall, both alarms should work as expected.
So… The device does deliver the desired selected voltage, but there is only one alarm, which tells you there is either reversed polarity or missing ground. Either way, you will know something is wrong and can work to correct it, or find another outlet or extension cord.
The fix is to either 1) use it as is, and realize that the alarm could mean either no ground or reversed polarity, or 2) incorporate an isolation transformer into the build. This would require a transformer rated at about 500 VA.
Best Regards,
Don
The Vintage Voltage Device allows the user to select the voltage for a vintage amplifier. Settings are:
- 0 Volts (off)
- -12 Volts (about 110 VAC)
- -6 Volts (about 117 VAC)
- Line Voltage ( 120 – 125 VAC )
The unit provides EMI filtering, spike protection, and fused input and output.
In addition, the Device will set an alarm if the ground is absent or if the polarity is reversed. The latter condition is exceedingly dangerous and all too common. Reversed polarity can cause electrical shock and in some cases has resulted in death.
I have built one unit and it works very well.
Missing Ground Connection Event
In this case, when a ground connection is missing from the wall, the voltage from the Device neutral wire to the chassis ground of the device can be 90 V or more (higher than the Line side of the device to the chassis ground, which is about 30 V). This is because the neutral is current-carrying for all the branch circuits downstream, all the way to the service entrance, where the neutral is connected to earth ground. The potential shows up in reference to the chassis ground, which in essence is floating with no reference to earth ground. Of course, the voltage between Line and Neutral measures as 125 VAC, or thereabouts.
In the fault condition of missing ground, the absence of a true earth ground, the relay in the device will energize when connected to neutral and ground (90V), as in the case of relay #2b – this causes the Reversed Polarity alarm.
An isolation transformer will have a continuous ground connection from input to output unless it is an Isolated Ground transformer, which requires a separate earth ground local to the transformer. These are often used for medical equipment that is very sensitive to ground faults. An isolated ground transformer will not work for what we are trying to do. We want an isolation transformer with a continuous ground. There are also isolation transformers out there which are advertised as “isolated ground”, where they just tie the transformer secondary neutral to ground; we don’t want that one, either.
Due to the ferric isolation of the circuit, the neutral and line voltages will be essentially equal with respect to the device chassis ground. (you no longer “see” the effect of current-carrying neutral branch circuits on the neutral wire).
With an isolation transformer between the wall and the device, a missing ground will be detected and alarmed by the device. A reversed polarity condition will also be separately alarmed when it exists. When and if both conditions exist, both alarms will go off.
Bootleg grounds are a problem in older houses and venues before the Electrical Code required a separate ground wire in all branch circuits. House flippers are notorious for wiring older homes with bootleg grounds to provide modern receptacles with grounds. The Device will not detect bootleg grounds, nor will most receptacle testers. There are testers that will detect bootleg grounds, but they are very expensive.
The Vintage Voltage Device was designed primarily as a means to reduce the modern wall voltage to be more appropriate for vintage amps, through the use of a CT bucking transformer. The technology has been around for many years. The added value of this device is to alert the user in the event of a miswired power outlet, either the absence of ground or reversed polarity. Both of these conditions are very dangerous and life-threatening. The good news is that the device will alarm if either of those conditions exist – but if you want to separate the missing ground fault from the reversed polarity fault, you will need to add an isolation transformer with a continuous ground. You can buy an appropriately sized isolation transformer with continuous ground for about $75 if you look long enough.
I’m sorry for the confusion, but this is an experimental device, and as such, I only recently uncovered this unexpected behavior, and immediately let people know so they could adjust their build accordingly.
The build is not inexpensive because it is built to code and with safety of paramount importance. It is possible to buy the 4-position switch for maybe $20 from China, for instance, but it is not trustworthy. It is not UL listed, and I’m not even sure of its current ratings.
If all you want is a voltage-reducing device, then by all means just get a 6 or 12VAC transformer and build it into a box with an outlet. My idea was to help protect musicians from being exposed to potentially lethal electrical shock.
Of course, you could (and should) carry a good quality outlet tester around with you and use it every time; this is a much less expensive alternative – but sometimes people forget to check an outlet, or forget the tester. If the tester is combined with a device you are going to always use with your amp, then you don’t have that problem. Also, a tester used on a wall outlet won’t find an extension cord with a cut-off ground pin unless you separately test the extension cord. The Vintage Voltage device will check every extension cord plugged into the power inlet.
I think the best solution is for manufacturers to build fault detectors into their amps. This would not be expensive to incorporate into the power section of an amp, particularly with the advantages of mass production and computerization.
I grew up when amps were designed with “2-prong” plugs and turning the plug around 180 degrees in the socket was the best way to reduce hum. You just inserted the plug into the wall in the way that gave the least hum. You were essentially reversing the polarity of the circuit deliberately. Getting shocked was an almost daily occurrence with equipment (like the PA and the guitar amp) that was plugged into two different outlets. As you may know, musicians have died from being shocked by this condition.
