Tony Gee's Solo-206 Rear-loaded horn loudspeaker
If it happens to have a lot of ground loops with other equipment, adding this line isolator will completely eliminate them and it will allow for new wider headroom by lowering the noise. For me at least, worked well. It is expensive and bulky but it rewards the efforts.
Very high inrush currents flow when a 1500VA toroidal transformer first connects to the mains that cause, among other things, fuse blowing. A soft-start circuit is just a timer of around 0.5-3 sec, energized when the power switch is pressed to the ON position. During this short period, the primary of the transformer is connected to the prime power input with a low-value (22-100 Ohm) power resistor in series and using a relay contact which immediately after the timer's period shorts this resistor out of the circuit. This technique reduces the in-rush current significantly The brass bar shown is for holding all ground wires together on the same point.. The soft-start PCB accommodates 2 more power relays for ON/OFF, so a heavy front panel switch is not required.
Well, this is not a proper setup of audio equipment, I know. Any vibrations of the bottom unit can travel up to the CD player. It was just for a quick wiring to "see" if we can "hear" anything different.
On the top is my heavily modified Philips CD723. The two small ECC83 tubes ends protruding through it's top cover are visible.
The rear panel is equipped with 5 ordinary power sockets of the "schuko" type with dust covers. The transformer secondary winding ends are secured on the top of the giant red insulators with a 7mm screw together with the wires connecting the power sockets. To the right, 2 fuse holders are shown together with a 15-amp RFI filter. For the wiring I used teflon (PTFE) insulated silver plated stranded copper wire.
The BALUN was placed inside a steel cabinet, grounded at the input IEC-320 socket/RFI filter and for ornamental reasons, not wanting to have just an empty panel on a large cabinet, I placed a "quiet" type of panel AC multimeter that measures AC voltage, current, power, frequency and power factor on the front panel. To the right, a current transformer can be seen, needed by the multimeter for measuring the AC current.
That large 1500VA toroidal transformer has a primary winding for the input of mains line voltage of 230VAC, a Faraday-shield winding that is connected to ground and reduces common-mode noise and a secondary winding 2 x 115V connected in series but the connected branch tied to ground (or 230V center tapped). The center tap is connected to ground and by this way, the two winding ends have 230V voltage of balanced power (180 degrees phase difference) that can be delivered to your loads. Using a multimeter, one can measure 115V across the ground and each of the secondary ends, or 230V across them. This is actually a BALanced to UNbalanced transformer (BALUN) and is used to feed with balanced voltage and balanced current any load less than the maximum of 94% of 1500VA (transformer efficiency). If you order such a transformer, ask for a bit higher voltage output, say 250V, so for the loads will bring the voltage down to normal when connected.
When I got hit by the well known "Audiophile" virus I have started building some class-a audio power amplifiers trying transistors, MOSFETs, triode tubes, a couple of loudspeakers with banana-plant paper cone wide-range emitters (FOSTEX), magnesium tweeters, volume control units with matched photo-sensitive resistors, tried piggy-tailed CAT-5 cable for feeding the loudspeakers, replaced the output op-amps of my CD player with tubes, used ultra -low Passive Inter Modulation (PIM) connectors, tried different DACs, made oscillators at a high frequency and then used a high division ratio divider in order to make a very low jitter clock for the DAC. (I remember I bought a second-hand LeCroy Disk Drive Analyzer - 8 GHZ Oscilloscope just to measure jitter) and I have also carried some river sand,not sea sand, with my car from a distant river to fill the bottom of the loudspeakers, after placing the special anti-damping bitumen sheets inside. I remember that pain in my back started the next day. I did some things more but I'm a bit shy to publish them all here...
But there is something that publishing it worth it's space, time and money. Placing a power-line isolator in the system, greatly improves the dynamic range of sensitive amplifiers (audio or RF), by lowering the noise originating at the prime power input (power line noise). It eliminates ground-loops with other equipment and helps reducing in-rush currents. In addition, it isolates DC from coming in, if any.
Copyright © Makis Katsouris, SV1AFN. All Rights Reserved.