15V to 12V adaptor

15V to 12V adaptor populated PCB
15V to 12V adaptor populated PCB

From time to time I want to integrate a 12V Eurorack module in my 15V banana setup. So I needed a 15V to 12V adaptor. Nothing spectacular. Just from the datasheet. This is the bigger brother for up to five modules from the single one.

Specs and features

  • Input +/-15V DC (or higher)
  • Output +/-12V DC

The documentation and the Gerber files for download can be found in my website.

15V to 12V adaptor schematic
15V to 12V adaptor schematic

Just the standard configuration from the datasheets.

15V to 12V adaptor front view
15V to 12V adaptor front view
15V to 12V adaptor side view
15V to 12V adaptor side view

15V to 12V Adaptor

15V to 12V Adaptor: Schematic
15V to 12V Adaptor:populated PCB

From time to time I want to integrate a 12V Eurorack module in my 15V banana setup. So I needed a 15V to 12V adaptor. Nothing spectacular. Just from the datasheet.

Specs and features

  • Input +/-15V DC (or higher)
  • Output +/-12V DC

The documentation and the Gerber files for download can be found in my website.

15V to 12V Adaptor: Schematic

Just the standard configuration from the datasheets.

15V to 12V Adaptor: Side view
15V to 12V Adaptor: Side view
15V to 12V Adaptor: Front view
15V to 12V Adaptor: Front view

Dual PSU with 3 pole external AC input

Dual voltage PSU with 3 pole external AC input
Dual voltage PSU with 3 pole external AC input populated PCB side view

For a standalone project with a small case I was in need of an small dual voltage PSU. I can’t find a dual voltage wall wart, but I had an external AC Power Adapter from Yamaha the PA-30. The PA-30 has a 2x18V AC output with a three pole connector. So I decided to build a small PSU with the LM317L and LM337L. The design is straight forward. It is easy to expand for more current and other voltages if you need to. If you don’t want to use a external AC Power Adapter you can use a center tapped transformer.

Specs and features

  • Input: Select 3 pole AC power adapter like Yamaha PA-30 or center tapped transformer according to your needs
  • Output: +/-xV; Voltage depends on the voltage divider around LM317 and LM337. Values given here are for +/-15V.

The documentation and the Gerber files for download can be found in my website.

Dual voltage PSU with 3 pole external AC input schematic
Dual voltage PSU with 3 pole external AC input schematic

Nothing special here. Just refer to the data sheet of the LM317L/LM337L. Calculate R1/R2 and R3/R4 to your needs. The given values here are for +/-15V. Input is from a center tapped transformer or external AC Power Adapter like the Yamaha PA-30. For more current replace the LM317L/LM337L Version with the TO220 version. You’ll need to redesign the PCB then

Dual voltage PSU with 3 pole external AC input populated PCB top view
Dual voltage PSU with 3 pole external AC input populated PCB top view

Basic PSU with 78xx voltage regulator

Basic PSU with 78xx voltage regulator

Basic PSU with 78xx voltage regulator

In many cases it is useful to have a easy to build fixed voltage PSU at hand. For this case I have made a PCB which works with the 78xx series voltage regulators in TO220 housing. The implementation follows closely a straight forward design as in the data sheet. I have tested this design with a current load of 1A for some hours. No problems whatsoever.

Specs and features
• Input: Select transformer according to your needs
• Output: Voltage depends on the regulator used / 1A DC

The documentation for download can be found in my website.

Basic PSU with 78xx voltage regulator schematic

Basic PSU with 78xx voltage regulator schematic

Nothing special here. Just refer to the data sheet of the 78xx. Calculate R1 to keep the current through the LED within the specs.

Basic PSU with 78xx voltage regulator

Basic PSU with 78xx voltage regulator

Next Generation Formant Project: Housing and PSU

First step of the Next Generation Formant Project is the housing and the PSU. I want my Elektor Formant based clone to be portable. Therefore I ordered a custom made 19’’ flightcase, build to my specifications. The enclosure holds four rows of modules in Eurorack format. As PSU two of my basic PSU with LM350 are used.

The first picture shows the enclosure, the rails and the PSU used. The lid is not shown.

Next Generation Formant Housing

Next Generation Formant Housing

The first step was mounting the stand offs for the PSU and power distribution. The hole for the mains connecter and switch was cut out and the mains connector mounted.

Next Generation Formant Housing: Enclosure

Next Generation Formant Housing: Enclosure

Next was to install the power supply unit, the power distribution and the mains transformer. The wiring was done and tested.

Next Generation Formant Housing: PSU mounted

Next Generation Formant Housing: PSU mounted

The frame to hold the modules is build from 19’’ rails. The sides are plain aluminum stripes.

Next Generation Formant Housing: Frame

Next Generation Formant Housing: Frame

The frame is mounted in the enclosure, the first module attached. The enclosure is ready for more.

Next Generation Formant Housing: Ready for modules

Next Generation Formant Housing: Ready for modules

Basic PSU with LM350

Basic PSU with LM350

Basic PSU with LM350

In most cases it is not necessary to use an ultra low ripple PSU for driving a synthesizer. A normal basic PSU with low ripple is sufficient in most cases. Those basic PSU has the advantage off better thermal and power efficiency. My implementation here is the same as my ultra low ripple PSU without the input low pass filter. Leaving this filter out lowers the power consumption at about 50%. And avoids the additional internal heating of the housing. It is possible to use a lower rated transformer with 15V/50VA (75VA for two PSU). The output current is increased. Those changes lowers the overall parts count and cuts the cost down as well. The PSU is build around the well known LM350 and follows mostly a straight forward design as in the data sheet. I have tested this design with a current load of 2.5A for some hours. No problems whatsoever. For a +/- 15V PSU you need two of those. You have to daisy chain them and use the connection as ground

Basic PSU with LM350 - schematic

Basic PSU with LM350 – schematic

 

This design is straight forward like in the data sheet of the LM350. After the rectifier diodes C6 and C7 are the reservoir capacitors. LED1 indicates the presence of the unregulated voltage before the LM350. R1 limits the current for the LED. The LED is a low current 2mA type D5 serves as protection diode against reverse biasing the voltage regulator. R6, R7 and TR1 serves as voltage divider to adjust the output voltage to 15V. The 1.2V reference voltage between ADJ and out is amplified about 12-times to make a 15V output. So is the noise and ripple. C11 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D6 is needed to safely discharge C11 if the output is short-circuited. D8 protects against short-circuited when you daisy chain two PSU for a +/- PSU if the other output is short circuited. With the above measures the ripple is quite low. With a 15V/75VA transformer (for two PSU) this PSU is good for output current of about 2.5A (both). Above this value the voltage drop over the regulator drops under the necessary 3V. To stay on the save side the recommended fuse is rated for 2.5A/slow-blow.

Basic PSU with LM350 front left view

Basic PSU with LM350 – front left view

Basic PSU with LM350 - front view

Basic PSU with LM350 – front view

Basic PSU with LM350 - left view

Basic PSU with LM350 – left view

Basic PSU with LM350 - right view

Basic PSU with LM350 – right view

 

Basic PSU with LM317

Basic PSU with LM317

Basic PSU with LM317

In most cases it is not necessary to use an ultra low ripple PSU for driving a synthesizer. A normal basic PSU with low ripple is sufficient in most cases. Those basic PSU has the advantage off better thermal and power efficiency. My implementation here is the same as my ultra low ripple PSU without the input low pass filter. Leaving this filter out lowers the power consumption at about 50%. And avoids the additional internal heating of the housing. It is possible to use a lower rated transformer with 15V/50VA. The output current is increased. One more benefit is more room on the PCB which is used to integrate a fuse on the PCB. Those changes lowers the overall parts count and cuts the cost down as well.

The PSU is build around the well known LM317 and follows mostly a straight forward design as in the data sheet. I have tested this design with a current load of 1.25A for some hours. No problems whatsoever. For a +/- 15V PSU you need two of those. You have to daisy chain them and use the connection as ground

Basic PSU with LM317 schematic

Basic PSU with LM317 schematic

 

This design is straight forward like in the data sheet of the LM317. After the rectifier diodes C5 and C6 are the reservoir capacitors. LED1 indicates the presence of the unregulated voltage before the LM317. R1 limits the current for the LED. The LED is a low current 2mA type D1 serves as protection diode against reverse biasing the voltage regulator. R3, R4, TR2 serves as voltage divider to adjust the output voltage to15V. The 1.2V reference voltage between ADJ and out is amplified about 12-times to make a 15V output. So is the noise and ripple. C7 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D5 is needed to safely discharge C7 if the output is short-circuited. D3 protects against short-circuited when you daisy chain two PSU for a +/- PSU if the other output is short circuited. With the above measures the ripple is quite low. With a 15V/50VA transformer (for two PSU) this PSU is good for output current of about 1.3A (both). Above this value the voltage drop over the regulator drops under the necessary 3V. To stay on the save side the recommended fuse is rated for 1.25A/slow-blow.

Basic PSU LM317 top left view

Basic PSU LM317 top left view

Basic PSU LM317 left view

Basic PSU LM317 left view

Basic PSU with LM317 front view

Basic PSU with LM317 front view

 

Vocoder: PSU

Vocoder PSU Front view

Vocoder PSU Front view

For the Vocoder PSU I didn’t make a new PSU. I just took what I have at hand. So this is a very short post. I just took three of my  ultra low ripple PSU with LM350 and put them in a frame. Two are daisy chained for the +/- 15V. The third is for the 6V which is needed for the display unit.

Vocoder PSU rear view

Vocoder PSU rear view

Vocoder PSU close up

Vocoder PSU close up

Ultra low ripple PSU with LM350

Ultra low ripple PSU with LM350 stuffed PCB

Ultra low ripple PSU with LM350 stuffed PCB

Sometimes you need a PSU with very low ripple. With a common voltage regulator this can be achieved by some additional filtering. Here I use a LM350 with an additional RC filter before the smoothing capacitors and a capacitor in the regulation path of the LM350. After the rectifier diodes C6 and C7 are the reservoir capacitors followed by the RC filter build of R2; R3, R4, R8 and C8, C9. D5 serves as protection diode for reverse biasing the voltage regulator. R6, R7, TR1 serves as voltage divider to adjust the output voltage to15V. The 1.2V reference voltage between ADJ and out is amplified about 12times to make a 15V output. So is the noise and ripple. C11 between ADJ pin and GND reduces noise and ripple considerably. Protective diode D6 is needed to safely discharge C11 if the output is short-circuited. D7 protects against short-circuited when you daisy chain two PSU for a +/- PSU if one of the outputs is short circuited. With the above measures the ripple is down in the noise floor. The drawback of this schematic is increased power consumption. The resistors in the RC input filter get rather hot under heavy load Use 2W (minimum) or higher rated resistors and mount them with some distance to the PCB. You should keep the load under 2A. You can drive heavier loads, but watch for the temperature of the resistors. You can find more details in “Small signal audio design” second edition from Douglas Self in chapter 25 p713ff.

Ultra low ripple PSU with LM350 schematic

Ultra low ripple PSU with LM350 schematic

Ultra low ripple PSU with LM350 front view

Ultra low ripple PSU with LM350 front view

Update: Small PSU with LM317 and LM337

Small PSU with LM317 / LM337

Small PSU with LM317 / LM337

Lately I used my small variable PSU with LM317 / LM337 as fixed PSU build in a Module. In an earlier post I wrote: “Because it is small the heatsinks are not that big and close together. Don’t drive it to hard”. This only applies when you want the output to be variable. If used for fixed voltages you can drive it harder when you choose an appropriate AC input voltage. The AC input voltage should match the DC output voltage in this case. This lowers the voltage drop at the voltage regulators LM317 / LM337. It is about 4V then. With 1A load the power dissipation is down to 4W. I have tested the small PSU for several hours loaded with 1A at 15V without any problem getting to hot. The test was done on the bench in free air. If you use an enclosure check for the air flow.

Small PSU with LM317 / LM337 as module

Small PSU with LM317 / LM337 as module