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Muffsy Hifi Dual Power Supply

...without handling mains power

skrodahlskrodahl
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Many people refrain from building cool projects because of the need to handle mains power. I'm eliminating that risk with this high quality regulated dual power supply.

The detailed step-by-step instructions makes this project suitable for everyone.

The second version of my power supply features an additional unregulated AUX power supply. It's got a standard 84mm width and a nice deep blue color.

This is a +-/- 15 volts DC, regulated dual power supply that has been designed for hifi purposes. It is powered by a single 15-18VAC wallwart supply, and has a very low 0.1 mV (RMS) ripple.

The wall adapter can of course be substituted with a single AC transformer, 15-18VAC.

The PSU was originally built for the Muffsy Phono Preamp and is equally useful for any other hifi equipment, be it discrete or opamp based.

The PCB for this power supply is available on Tindie and Muffsy.com:

Hackaday Weekly Prize Winner, Stickvise

The Muffsy Hifi Dual Power Supply is one of the winners of a Stickvise!

What is it for?

This regulated power supply is intended for audio applications that don't require a lot of power. Typically pre-amplifiers , fully discrete or based on operational amplifiers.

Features

This PSU takes a single 15-18VAC input and gives dual 15VDC output.

It is dead simple, has fantastic performance, and consists of the following stages:

  • Single 15-18VAC input
  • Two half-wave rectifiers
  • Voltage doublers
  • LM317/337 voltage regulators
  • Filter capacitors
  • Regulated +/- 15VDC output and ground.

And, as regulated power is limited:

  • Unregulated AUX power ~20-23V
  • Extra power output with resistor for LED

By using a wallwart, there is no risk of electrocution or fires.

Performance

The PSU performs superbly. Used together with the Muffsy Phono Preamp PP-2 or the new PP-3, it has only 0.1 mV noise on the DC output. Well below the Power Supply Rejection Rate (PSRR) of any operational amplifier, and very suitable for discrete circuits.

The PSU gives up to 100 mA of current when used without heatsinks. That's enough to power four phono stages. Mounting heat sinks on the LM317/337 will give you up to 200 mA.

The AUX power gives an additional (unregulated) 500 mA of current, or more, depending on your transformer.

Additional Information

  • 7 × 1N4004 Discrete Semiconductors / Diodes and Rectifiers
  • 2 × 300 ohm 0.25W metal film resistors, 1% tolerance
  • 3 × 3300 ohm 0.25W metal film resistors, 1% tolerance
  • 2 × 4.7 ohm 1W resistor
  • 5 × 0.1 uF (100 nF) Ceramic disc capacitor

View all 14 components

  • Make Your Own Muffsy Power Supply

    skrodahl • 07/15/2016 at 07:29 • 0 comments

    A few things have happened to this project since I last updated it, but they've never really made it to hackaday.io. Jump over to http://muffsy.com for the latest info.

    I'm writing this project log because I have a treat for you. Gerbers (for ordering PCBs) and PDFs (for etching your own) are now available: http://www.muffsy.com/blogs/post/Make-Your-Own-Muffsy-Power-Supply/

    Granted, it's lacking the AUX power. You'll want to get the kit for that. The board is also single layer so that it will be easier to etch. And it really is easy to etch, as only the tiny black areas (see below picture) need to be etched away.

    Please note that the gerbers and PDFs are released for personal, non-profit use only.

  • Muffsy has a New Home (page)

    skrodahl • 07/14/2015 at 14:40 • 1 comment

    After a long time, spreading the efforts between Hackaday.io, Instructables and Tindie, Muffsy now has a home. There's still some way to go, but all the information that was spread around will become available at this new home page.

    Here it is: http://muffsy.com

  • Schematic

    skrodahl • 05/27/2015 at 12:36 • 0 comments

    Here's the schematic for the power supply, should you want to build it on breadboard:

    Click on the picture to view the high resolution version.

    Note: The AUX power is not shown on this schematic.

  • Change the Output Voltage

    skrodahl • 05/22/2015 at 13:37 • 0 comments

    The output voltage of this power supply can be changed to suit your needs. Let's have a look at how this can be done, and how to make sure that your transformer is able to deliver sufficient voltage.

    Here's the layout of the printed circuit board. There are only two resistors that need to be replaced to change the output voltage, and they are shown here in orange:

    With the resistors at 3300 ohms, the power supply will deliver +/-15 volts.

    Resistor Values

    You might want less than this. Let's say +/-12.5 volts. Or more, for instance +/-17.5 volts. These output values are well within reach using the recommended 15-18VAC wall adapter.

    This table will give you the resistor values for 12.5, 15 and 17.5 volts dual output:

    Resistor, ohmsOutput voltage, +/- volts
    2.700 (2k7)12.5
    3.300 (3k3)15.0
    3.900 (3k9)17.5

    Other output voltages are easily obtainable, just use a calculator such as this one. The R1 value to provide in the calculator is 300 ohm.

    Wall Adapter Voltage

    The PSU needs a higher input value than the desired output value. Then how can a 15 volt AC-adapter be sufficient for 17.5V output? The answer to this is that the rectified DC voltage will be higher than the AC input voltage by a factor of 1.41. Now, there is some loss in the diodes. To be on the safe side, we'll use the factor 1.3 instead:

    • 15V * 1.3 = 19.5V

    This is more than 17.5 volts, and you are in the clear!

    So what is the lowest AC voltage needed for a 15V supply?

    • 15V / 1.3 = 11.54V

    You could actually use a 12V AC-adapter. But, there is the possibility that an adapter rated at 12V will give less than that. Stick with 15V or more, and you will be sure that your PSU works as expected.

  • AUX Power - How and Why

    skrodahl • 05/08/2015 at 07:51 • 0 comments

    This power supply will give you about 100 mA of regulated power, add heat sinks and you will double that.

    Given that the regulated power is a limited resource, wouldn't it be nice to cram some extra juice out of this power supply?

    Notice at the bottom right corner, there are three pads called AUX, GND and LED.

    This is the auxiliary DC power.

    • It is unregulated at about 20-23 volts
    • It will provide about 500 mA, depending on your transformer
    • It is filtered, but not at the same degree as the regulated supply

    You can use this for any additional devices that needs DC power. There is also space for a resistor, called LED.

    AUX Power

    For anything that needs DC power, connect AUX and GND (positive and negative connections).

    Connect an LED

    There is space for an on-board current limiting resistor for LEDs. Add a suitable resistor and connect your LED to the connections LED and GND.

    (It is usually safe to assume that the forward voltage drop of your LED is 2 volts, and that the maximum forward current is 20 mA.)

  • Suitable AC to AC Wall Transformers

    skrodahl • 05/08/2015 at 06:24 • 0 comments

    These AC to AC wall transformer are suitable for use with this PSU:

    120V Input:

    230V Input:

View all 6 project logs

  • 1
    Step 1

    Let's Build a Power Supply

    These instructions will guide you from beginning to end. If anything is unclear, let me know in the comments section.

    You will be able to build this power supply, even if you've never soldered anything before in your life.

    Now let's start with some basics:

    Before You Begin

    • Soldering the power supply should take about an hour or less.
    • Make sure you have enough time, and an environment without distractions. Don't stress, just enjoy building.
    • Take the time to read and understand the instructions.
    • Make sure you understand each step. If not, read again or ask a question in the comments section.
    • Notice that many components must be oriented a certain way.
    • Clicking on a picture will bring up a high resolution version. Use this to make sure your components are placed right.

    How to Solder

    If you're just starting out soldering, or if you need an update on how to solder,SparkFun has a great tutorial for soldering through-hole components.

    If you have never soldered before, I strongly recommend these two videos from EEVBlog:

  • 2
    Step 2

    Required Components

    To build the Muffsy Hifi Dual Power Supply, you need:


  • 3
    Step 3

    Diodes

    Start by soldering the seven diodes:

    Make absolutely sure that they are oriented the right way around. The silver ring on one end of the diode corresponds with the white band of the diode symbol on the PCB.

View all 12 instructions

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Discussions

mikedrz1 wrote 01/22/2017 at 03:33 • point

I just built your PS from the PDF pcb.  Thanks for your contributions, mine has the lower rail with a voltage difference of 101 mV from the top rail, is that okay?  Also I notice the negative rail also shows a higher ripple on my scope.  If I'm measuring ripple correctly I don't know.

  Are you sure? yes | no

Michele wrote 02/01/2016 at 17:14 • point

Hi skrodahl, great project! :-)
May I ask you what are the R1 and R2 resistors for? Why aren't capacitors C1-C3 and C2-C4 just in a simple parallel?

  Are you sure? yes | no

K.C. Lee wrote 02/01/2016 at 20:16 • point

R1, R2 + C3-C6 are part of low pass RC filter.

>Power Supply Rejection Rate (PSRR)

Power Supply Reject Ratio...  Not Rate.  It means the (attenuated usually in dB) amount of power supply noise that is going to be at the output.  Rate is meaningless in the context.

  Are you sure? yes | no

skrodahl wrote 02/03/2016 at 14:24 • point

Thanks K.C. Here's some more info:

http://www.learnabout-electronics.org/PSU/psu12.php

I also found (don't ask :) ) that if I create a short circuit or the circuit draws way too much power, these resistors will be the first to say goodbye. They double as fuses...

  Are you sure? yes | no

skrodahl wrote 10/06/2015 at 10:57 • point

The issue with the power supply was solved. All that was needed was replacing a wrong component.

  Are you sure? yes | no

skrodahl wrote 09/11/2015 at 15:37 • point

You should check the orientation of all the diodes and electrolytic capacitors. Also make sure that you are using LM317 and LM337 and that they are in the right position and orientated correctly. 

Just to make sure, you’re not measuring the AUX power, are you? It's the one close to the LED position/marking.

  Are you sure? yes | no

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