| | |
| | |
|
Accessories for DIY audio projects Universal Power Supply
Applications are too numerous to list here, but include the active output board when used with the Combo Input Stage, either with or without the RAKK dac. In addition, it can be configured to power other tube-based circuitry within its design limits, such as the K&K Audio SE Phono Preamplifier. For other applications, contact us and discuss your specific requirements. High Voltage Section An innovative power supply kit designed using the concept of "Minimal Reactance", draws from the classic tube power supply designs while incorporating modern technology not available to the designers of yesteryear. The result is a marriage of the smoothness of a tube rectifier with the precision of a MOSFET current source that gives an incredibly clean and transparent sonic presentation. Only film capacitors are used in the high-voltage section, eliminating the sonic footprint of electrolytic capacitors. This supply is so clean and transparent that you could hear the grunge contributed by generic resistors if they had been used. Careful listening evaluation resulted in the use of Caddock and Kiwame resistors critically chosen to achieve sonic excellence. Although the basic design is a Minimal Reactance power supply, it may be used a regulated supply following a standard capacitance input or choke input filter. The output voltage of the regulator is adjustable with a range depending on the input AC voltage, the type of input filter (MR, capacitor, choke) and the type of regulator tube used. The current through the constant current source is adjustable and the pass current of the shunt regulator depends upon the type of tube used in the regulator. The board has been laid out to accommodate a much larger heatsink if required. Low Voltage Section The output voltage is adjustable and the board is laid out to accommodate larger diodes and heatsink so the current capability can be extended to 2A. Although the low voltage is usually referenced to the high voltage ground, there is a provision to bias the low voltage above ground. This is useful if the low voltage supply were used as a regulated DC filament supply. Delay featuresThere are two delay circuits in this power supply: a B+ delay and output mute. The use of these delay circuits is optional and the delay times are adjustable. Each delay circuit has a set of relay contact, which may be used to control external functions. Noise Considerations Provisions have been made in the design of this power supply to minimize the effect of external power line noise and internally generated noise. A power line filter is provided for external noise. Several things have been done to minimize internally generated noise. A vacuum tube is used for the high voltage rectifier, and Schottky diodes are used for the low voltage rectifier. An additional filter is placed on the input to the low voltage supply to isolate the two supplies. Both the high voltage and low voltage sections are Minimal Reactance designs, which minimizes ringing in the transformer. For further information on the Minimal Reactance Power Supply concept, see Chapter 5 in the series of line stage articles. To support this power supply, you need to separately provide an input power connector with fuse, a power-on switch, and a power transformer. The transformer should provide two 250VAC windings (500VAC CT) at 70mA, 6.3VAC @ 2.4A and 17VAC at 200mA. The Lundahl LL1683 is recommended. 115VAC or 230VAC mains wiring is accommodated by the LL1683. Here is the schematic of this high voltage power supply. Size 4.5 inches by 6.1 inches. Specifications:
The Universal Power Supply kit is offered in two levels. The levels differ in the amount of parts provided versus the parts that you must procure on your own. The Level 1 kit provides the minimum parts, the Level 2 all of the parts needed. The Level 1 kit also requires that you experimentally determine the value of the current setting resistor. Refer to the Universal Power Supply section of the Digital page for the contents of the Level 1 and Level 2 kits.
Universal Power Supply Kit, Level 1: $159 Two Terminal Constant Current Source This circuit was developed based on the Supertex DN2540N5 depletion mode MOSFET to enable constant current operation of tube circuits without having to worry about a source of bias. It is very simple and easy to integrate in existing designs. Use it to provide excellent balance in "long-tail" pair differential circuits or to obtain highly linear constant current triode operation as a plate load. Add a heat sink kit for operation at higher levels of power dissipation. Two versions are offered: an economical basic current source with very good performance and a cascode current source for improved measured performance and a slight sonic improvement. Both kits feature current adjustability over a wide range (2.5mA to 100mA) and space for a fixed resistor to replace the variable resistor once the “correct” current has been determined. The minimum operating voltage is 4VDC + 1/2 peak-to-peak AC signal amplitude and the voltage rating maximum is 400VDC.
Transformer Covers We have sourced a range of covers for Lundahl transformers in two styles. There are three sizes of these retro looking 3 piece transformer covers. The transformer mounts on the base, then the body/top of the cover screws to flanges on the base. The base and transformer are held to the chassis by the transformer mounting screws. The body and base are steel and are finished with a classic black wrinkle finish, while the top is brushed anodized natural aluminum. The dimensions are given below. Subtract 0.4" from the width, depth, and the height for internal dimensions. Because the body and base are steel, they afford some magnetic field shielding, where necessary, too.
Pictured below is a contemporary-looking cast aluminum cover that fits over the larger (LL1620/1623/1627/1679/9202) and smaller (LL1663/1664/1682/1683) transformers or chokes (LL1638/1673/1685). They are 4.75 x 4.75 inches at the base and taper slightly to 3.56 inches tall. The covers attach to the chassis by 4 x 6-32 threaded holes in the corners. They are stocked finished with matte black powder coat. Unfortunately, they do not fit the somewhat larger power transformers (LL1648/1649/1650/1651/1669A). Transformer cover: $36 each
PC Boards
PC Board #1 - For LL1544A/1550/1635/1678/9206:$6.00
LL1620/1623/1627/9202 PC board, options for secondary connection diagram B or C' :$25 LL1679 PC board, options for secondary connection diagram B or C:$25.00 LL1679 PC board, options for secondary connection diagram C or D:$25.00 PC Board #1 - For LL1544A/1550/1635/1678/9206:$6.00 Inspirations: Music for Solo Flute Catherine LeGrand, Flutist Classical Flute Music composed by C.P.E Bach, Hildegard von Bingen, Astor Piazzolla, Claude Debussy and others This CD was recorded by Kevin Carter using an all-tube analog signal chain direct to a hard drive at 20 bit 88.2kHz resolution. Cad VX-2 vacuum tube microphones were placed in a Blumlein figure 8 crossed pair and amplified by a custom K&K Audio designed and built Lundahl transformer-coupled (using LL1550 and LL1660/PP transformers) microphone preamplifier. To purchase this CD go to www.in1breath.com |
1004 Olive Chapel Rd.
Apex, NC 27502 USA (919) 387-0911 Mon-Fri 8 a.m. - 5 p.m. EST
E-mail
The Raleigh Audio High Voltage Power Supply has been designed with a lot of versatility to accommodate a wide range of requirements for the DIY hobbyist. It features vacuum tube rectification, a vacuum tube shunt regulated B+ supply, AC filament supply, and a regulated 12vDC supply. As frosting on the cake, an input mains power line noise filter is included.
This small PC board (1.2" x 1.7") aids in connecting primaries and
secondaries for several similar Lundahl transformers:
LL1544A/1550/1635/1678/9206.
We have developed PC boards that mount on and solder to the LL1679 and
another for the LL1620/1623/1627/9202. These boards, for the secondary
windings side of the transformers, facilitate simple speaker impedance
matching changes. A picture of one of these is shown below. Either the
terminal/block jumper arrangement shown can be used, or for hair-shirt
purists jumpers can be soldered in place of the terminal strip. Wires
leading to speaker binding posts solder directly to the PC board. See the
individual transformer data sheets for the details of the connections listed
below.
