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Accessories for DIY audio projects

Low Voltage Power Supply

power supply kitAfter cobbling together untold numbers of small power supplies for "auxiliary" functions in tube preamps and power amps, I decided to design something with a regulator that is better than the ubiquitous 7800 series three terminal regulator and try it in places where it powers something more than relay coils. In locations like low voltage negative supplies and as power for a USB to SPDIF digital audio converter I found this supply sonically superior to my previous slapdash efforts. This power supply uses the LT3080 regulator, which is adjustable by changing one resistor for output voltages between 1 and 24 volts DC in this implementation. A charging slope lowering resistor and Schottky rectifier diodes are provided to be kind to the power transformer and reduce both supply noise and radiated magnetic field noise. Along with plenty of output bypass capacitance, this compact package does a thorough job of supplying up to 4 watts of power at low voltages. Resistors are provided for 5, 6.3, 8, and 12VDC. You can obtain other 0.25w resistors for other voltages. The supply can accommodate both 115V and 230V mains voltage and has an on-board fuse holder for safety. With the standard supplied 8+8 volt secondary power transformer, the maximum possible DC current draws are approximately:

  • 5VDC 870mA
  • 6.3VDC 700mA
  • 8VDC 550mA
  • 12VDC 470mA

The PC board is 2.75" (7cm) x 3.3" (8.4cm) and the height is 1.6" (4cm).

Low Voltage Power Supply Kit: $36

Two Terminal Constant Current Source

These products are based on the sonically transparent IXYS IXTP01N100D and IXTP08N100D2 depletion mode MOSFETs to enable constant current operation of tube circuits without having to worry about a source of bias. They are very simple and easy to integrate into existing designs. Use current sources 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. Several versions are offered: an economical basic current source with very good performance, a cascode current source for improved measured performance and a slight sonic improvement, a large cascade current source that accommodates an even larger heat sink, a cascode current source that is configured so the MOSFET can be attached to the chassis or a very large heat sink for high current/voltage operation, and a compact cascode current source that can be used to replace resistors for easy upgrading to constant current operation. These 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 10VDC + 1/2 peak-to-peak AC signal amplitude and the voltage rating maximum is 1000VDC.

PC board sizes:

  • Basic CCS 1.55" (4cm) x 1.2" (3.1cm)
  • Cascode CCS 1.55" (4cm) x 1.3" (3.3cm)
  • Large Cascode CCS 1.75" (4.5cm) x 1.7" (4.3cm)
  • Attachable Cascode CCS 1.3 (3.3cm)" x 1.2" (3.1cm)
  • Compact Cascode CCS 1.7" (4.3cm) x 0.7" (1.8cm)

Current source kit
Current source kit
Cascode current source kit
Cascode current source kit
Compact Cascode current source kit
Compact Cascode current source kit
Large Cascode current source kit
Large Cascode current source kit
 Cascode Heatsink mountale current source kit
Cascode Heatsink mountable current source kit

Basic Current Source Kit (up to 1 watt without a heat sink) $8
Cascode Current Source Kit (up to 1 watt without a heat sink) $12
Small Heat Sink Kit (up to 3 watts) $3
Large Heat Sink Kit (up to 5 watts) $3.50
Cascode Current Source Kit attachable to an external heat sink (up to 20 watts with adequate heat sink) $13
Compact Current Source Kit (up to 2 watts w/included heat sink) $14
Large Cascode Current Source Kit (up to 7 watts w/included heat sink) $18

High Voltage Shunt Regulator Kits

This combined current source / shunt regulator kit has been designed to provide a high quality, simple-to-implement regulator to isolate amplifier input stages from the output stage and raw power supply or to provide high quality power supply isolation for line stages or phono stages.

shunt regulator kit

The current source part of the circuit is identical to that used in the Cascode Current Source Kit. The shunt regulator circuit is similar to that originally developed by Salas ( It's a simple circuit that performs very well, like the cascode CCS, and is stable under a variety of operating conditions. The shunt regulated voltage is set by a simple JFET current source, which controls the shunt transistor by means of a driver transistor. An RC network across the output manages the transient response to provide quick recovery from transient demands without significant overshoot. The regulated voltage is adjusted using a trimpot that sets the current through the reference current source.

The combination of the current source and the shunt regulator provides all that's necessary for a simple first-class high voltage regulator. There are two versions of this circuit with different voltage ranges. The 100V-350V version uses board mounted heat sinks and is applicable to many phono stage, line stage and amplifier input stage applications. The 300V-600V version is similar in size and appearance to the lower voltage version, but is optimized for a higher voltage range.

To determine if either kit meets the needs of your circuit and to properly specify the heat sink size, you should read the instructions (High voltage regulator manual and Low voltage regulator manual ) and do the simple calculations necessary to determine how tall the board-mounted heat sinks need to be. The PC board dimensions are:

100V-350V version: 3.9" (9.9cm) x 2.3" (5.9cm)
300V-600V version: 4.6" (11.6cm) x 2.3" (5.9cm)

Both kits have the potential to add from 1" (2.5cm) to 2.5" (6.4cm) tall heat sinks. If not specified otherwise, 2.5" (6.4cm) heat sinks will be supplied.

Shunt Regulator Kit, 100V-350VDC $45
Shunt Regulator Kit, 300V-600VDC $55

Time Delay and Soft Start Kits
Time Delay kitSoft Start kit

It is often very useful to delay the application of the high voltage in a tube circuit until the tube filaments have had several seconds to warm up. This prevents the phenomenon known as "cathode stripping," where the presence of full voltage to the tube's electrodes before the cathode is at emitting temperature prematurely depletes the coating on the cathode that is responsible for the electron emission which, in turn, makes the tube work. In a choke loaded power supply design, delaying the application of high voltage until filament warm-up has been achieved also prevents the large over-voltage event that accompanies a sub-critical load for the choke.

In addition, if you find the use of a tube rectifier not to be to your sonic taste, but still desire the "soft start" action implicit in the rectifier filament warm-up, this action can be imitated using a low impedance solid state circuit that is virtually out of the circuit once the voltage has risen to its maximum.

There two kits that address these needs. After a fixed time delay the Time Delay Kit circuit closes a relay that can control the B+ voltage or even the B+ transformer mains voltage, in the case of a separate B+ supply. The time delay is set for 30 seconds by a supplied resistor, but can be changed over a wide range by changing the value of that resistor. The Soft Start Kit incorporates the same time delay circuit to switch the B+ voltage followed by a MOSFET circuit that ramps that voltage up over about 30 seconds, so full B+ is achieved after about a minute.

The Time Delay Kit PC board also accepts a small relay that can be used to add a time delayed mute function to any preamp, so that at power up and for 30 seconds afterward the outputs are shorted by the relay contacts. Once the 30 seconds (or whatever time you want to use) has passed, the relay contacts open and the audio signal is unimpeded. Many tube preamps pass an "ugly noise" onto the amplifier during initial warm-up that this action prevents.

The same PC mount power relay is used in both circuits and is rated for a hefty 8 amps. These relays have been used for years in products switching B+ voltages as high as 550V with no problems. Either circuit can be powered by 6-12VAC or 7-25VDC and draws less than 200mA with the relay actuated.

PC board sizes:

  • Time Delay Kit - 1.9" (4.8cm) x 1.9" (4.8cm)
  • Soft Start Kit 2.4" (6.1cm) x 1.9" (4.8cm)

Time Delay Kit $25
Soft Start Kit $35

Transformer Covers

We have sourced a range of covers for Lundahl transformers in three styles.

Lundahl Covers

coversLundahl commissioned an industrial designer to develop a new transformer cover concept that fit the needs of their particular style of C-core transformer. The designer came up with a very clever, ventilated, space efficient cover that provides some unique functionality. It is a four piece design that uses the transformer itself as a structural member and is configured so the transformer connections are readily accessible without removing the whole assembly from the chassis. The material of construction is very heavy gauge steel, which supplies magnetic shielding allowing close placement of transformers. The finish is a medium charcoal semi-gloss powder coat. The Lundahl name and several lines are silk screen printed in black onto the top surface as a subtle, tasteful accent. Mounting to a chassis surface is accomplished by 4 screws through the bottom and there is a rectangular opening in the bottom through which connecting wires can pass. Because either of the sides facing the connection boards can be removed without disturbing the mounting, rewiring is no big task.

The large version of this cover fits the LL1620/1623/1627/1679/2410/2411/9202 output transformers and the LL1648/1649/1650/1651/1655/1669A power transformers. The overall dimensions are 4.95" (12.6cm) tall and 3.76" (9.6cm) in the other two dimensions and the cover weighs 2.3 pounds (1.05kg). A datasheetwith detailed dimensions is available.

The medium/small cover fits two sizes of transformers, the medium-sized LL1663/1664/1682 output transformers and the LL1638/LL1673 chokes, and the smaller LL1660/LL1671/LL1677/LL1689/LL1692 transformers, as well as the small LL1685 chokes. The overall dimensions are dimensions are 4.33" (11cm) tall with a 3.76" (9.6cm) by 3.15" (8.0cm) footprint and the cover weighs 2 pounds (0.9kg). A datasheet with detailed dimensions is available.

Both sizes are supplied with the assembly hardware. Additional 4mm screw hardware will be needed to attach the cover to the chassis.

Small/Medium Lundahl Transformer cover: $45 each

Large Lundahl Transformer cover: $55 each

Retro Covers

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.

Small retro cover $24 each
External dimensions: 3.4" (w) x 3.0" (d) x 3.85" (h)
Drilled for LL1660 / 1667 / 1668 / 1671 / 1677 / 1685 / 1689 / 1692. Will fit other smaller transformers/chokes, too.
Medium retro cover $36 each
External dimensions: 4.85" (w) x 4.0" (d) x 4.6" (h)
Drilled for LL1620 / 1623 / 1627 / 1638 / 1663 / 1664 / 1673 / 1679 / 1682 / 1683 / LL9202. Will fit other smaller transformers, too.
Large retro cover $42 each
External dimensions: 5.6" (w) x 4.85" (d) x 4.6" (h)
Drilled for LL1620 / 1623 / 1627 / 1648 / 1649 / 1650 / 1651 / 1679 / 9202. Will fit other smaller transformers, too.

Contemporary CoversTransformer cover for Lundahl Transformers and chokes

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).

Contemporary transformer cover: $36 each

PC Boards

We have an array of small PC boards that make application of the smaller low and line level transformers easier. All of these are for the specific transformer types labeled on the PC boards. If you have questions about applicability to specific circuits, contact us at

Single LL1544A/1550/1636/1678/9206/LL9226: $5
Board size: 1.2" (3.1cm) x 1.7" (4.3cm)
pc board
Stereo LL1678/9206/9226 for MC input: $10
Board size: 3.0" (7.6cm) x 1.8" (4.6cm)
pc board
Single LL1931 for MC input (includes gain switching): $10
Board size: 2.1" (5.4cm) x 1.7" (4.3cm)
pc board
Single LL1681/1933 for MC input (includes gain switching): $10
Board size: 2.4" (6.1cm) x 1.7" (4.3cm)
pc board
Stereo LL1931 for MC input (includes gain switching): $20
Board size: 3.2" (8.2cm) x 2.2" (5.3cm)
pc board
Stereo LL1941 for MC input (includes gain switching): $20
Board size: 3.2" (8.2cm) x 2.2" (5.3cm)
pc board
Stereo LL1690 (CT access on secondary): $10
Board size: 2.8" (7.1cm) x 2.4" (6.1cm)
Stereo LL1684/LL1948 (CT access on secondary): $10
Board size: 2.8" (7.1cm) x 2.4" (6.1cm)

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.

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 Inspirations - A CD recorded by Kevin Carter using Lundahl transformers and equipment

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

Printable page


K & K Audio 1004 Olive Chapel Rd. Apex, NC 27502 USA (919) 387-0911 Mon-Fri 8 a.m. - 5 p.m. EST E-mail