Mains Balancer + Adapter from 230-240-250 to 230V.
From this schematic, we only offer the transformer at the regular price. Mains plugs, the relay etc, you need to buy yourself. This is a very good working item, build by quite a few people already, including myself. I needed it for my 1954 Hammond B3 organ, which own since 1990, but it was suffering from some very low hum ever since.
As it appeared later, the problem was the electric field, and not the magnetic field. The B3 is build entirely with tubes, and has a mechanical tone wheel generator, which supplies in parallel all frequencies needed. By pressing a single key, you connect this key to the appropriate tones. Up to 6 harmonics and 2 sub harmonics are mixed in an adjustable way, and the result is a tone which is remarkably programmable in sound. The difficulty with this method lies in the very low signal coming from the tone wheel generators, in the range of 15 millivolt. The generator works completely passive. It uses rotating wheels of iron, with a wave pattern on the edge. A magnetic needle is positioned near to the edge of the tone wheel, and the result is a changing magnetic flux inside the needle. All we need to do now, is pick up this field with a coil, and we have a sound signal. It works the same as an electric guitar pick up. So far so good. However, this method is suffering very much from external field radiation, simply because the signal is so low. When playing with 10 fingers, you pick up hum from perhaps 50 single tones, so from 50 of those coils all together. This adds up to an audible hum signal. I can tell you, my search for a good solution was fruitless ever since, and also discussions with members of the German Hammond club didn't get me the tiniest bit further. Then I wondered why the mains transformer is arranged at an angle of 45 degrees to the chassis. That looks so odd. At it's outside has a fat, copper layer around it. This layer acts a a short circuit winding to radiated fields. So this transformer obviously was intended to radiate as little as possible. However, some residue bypassed the steel of the whole amplifier chassis, and also the steel of the tone wheel chassis which is positioned underneath the amplifier chassis. I removed the transformer from the chassis, and connected it with longer wires, so I could lift it out a little bit, and rotate it too. What I found out, didn't come as a real surprise. The Hammond engineers obviously have chosen the best position already, up to the centimeter, and also the best angle to mount it. But I did find out, the radiation field of this transformer was the trouble cause. Now you need to know, the B3 was designed in the USA, and the mains was only 110V there at the time. (So not even 115V). However, in Germany, we connect the whole organ with an auto transformer, and we have this unbalanced power line of 230V entering the machine, instead of 110V as intended.
So what can I improve? Coming back to the original problem, the mains outlets as a matter of principle are always unbalanced. So one wire of the mains cable has 230V AC on it, and the other wire has zero volt. My solution is shown in the schematic on the left. I discovered this way to use an isolation transformer, after searching for 20 years, what caused the hum in my Hammond B3. And I can say: This solution works! I think I got rid of 2/3 of the hum signal. There is now an LL1662 in my B3, and it will stay in there. The B3 is large size, and inside is enough space. For HiFi purposes, you need to build an external box, and connect all equipment to this box. The box can even be build from wood, because the Lundahl LL1662 is a very low radiation isolation transformer for HiFi purposes.
The solution:
The explanation is valid for any equipment, not just a Hammond B3. I suppose at some moment, we all have experienced how mains cables can be a nasty source of hum, due to field radiation. At some point, a residue remains, no matter what you try. In such a case, I recommend to BALANCE the mains voltage directly after the mains outlet. In all cable theory, and practice too of course, we learn that balanced circuits are s not susceptive to hum, and also not radiating any signal, because sending or receiving of hum works by the same mechanism. Well, the mains outlet must itself is the unbalanced item you have in your house, There is 230Volts signal on one wire, and zero Volts on the other. As unbalanced as can be. There are many cases, where an unbalanced audio input can pick up hum, but we talk about an audio signal of maximum 1Volt. With a mains cable, we have not 1Volt, but 230V unbalanced. That is really very much! Unbalanced and unshielded, and just like that, we lay those cables behind the equipment where passes the record player, CD player, signal inputs, etc. Before you pay a fortune for a 'black mamba' or 'anaconda' mains cable, with gold plated mains connectors, consider pay just a fraction of it, and build this nice box, and I am sure it will help you more than voodoo cable.
So if we say there is '230V' on the mains, there is actually that voltage only on one of the two wires. We call it this line 'hot' or 'live'. The other one is the neutral, and it has zero volts on it, or a few single volts only. Using an isolation transformer with a secondary center tap, we can connect the center tap to the primary 'neutral'. (Not meaning the electrical ground). So we loose the isolation transformer property, but we get back something else: We get a balanced mains voltage! So no more 230V, but 2x 115V, which are in series, and in anti phase. For the equipment it looks like 230V, but in fact one line is at 115Volt, and the other at 115V with 180° phase shift. Of course, the balancing point must be connected to the 'Neutral' and not to the 'live' . For this you just need to plug in the primary the right way. As we do not know what is the right way, there is a relay used in such that is becomes active, when you connect the mains wrong. In that case, the relay comes up, and switches off the primary. It gives a 'clack' and a red lamp burns. So you can't go wrong. When you connect the mains plug the right way, the relay will be off, the green lamp will burn, and the voltmeter indicates the voltage to your equipment.
This AC volt meter I saw new made on Ebay, for only 10 Euro.
A problem today, is variations on the primary voltage. The transformer used, gives us elegantly the option to adapt the voltage is steps of 10V. Moreover, the transformer is still giving the filtering it is intended for, as well as it removes the (small) DC components from the mains, the output is floating, given by the way it is connected. All in all, this is a very useful box, to connect your equipment, offering many advantages, by just using the Lundahl LL1662 at the best of it's possibilities. LL1662 is an AIR GAPPED transformer, making this possible.
Please read the text on the schematic as well, for more explanation.