Synthesizer Power Supples ----- Linear Vs Switching

When building a synthesizer power supply, there are two choices:

1. Regulated Linear Power supply
2. Switch Mode Power Supply (SMPS)

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1. Regulated Linear Power supply.

These are quite simple in design.
Low noise ... most supply types produce no high-frequency interference.

But they are inefficient when compared to a SMPS . Output voltage is regulated by dissipating excess power as heat resulting in a typical efficiency of 30–40%.
Often uses heavy line-frequency transformers

It's hard to find AC Linear Wall Warts larger than 2A. This is a problem if you are building a large modular.

 This is a NLC linear power supply. It's very easy to build.

 aND ANOTHER example of a DIY linear PSU. One advantage is their ease to build. The components are cheap.

I use a 2A  AC brick with both of these.
Something like this:

I find that powering 3U to 6U (max) of Eurorack is OK with these ... check your modules power requirements of course.

You could of course use something like this if you needed more juice:

 This is a power one HCC 15-3A
This transformer based design has a center tap to give the centre ground. Both voltage outs are rectified and regulated to create dual voltage rails

Its very very heavy and would be hard to fit into a eurorack case. I used this in a Serge case.

Above is a doepfer A-100PSU2
Its a Linear PSU with ring core transformer
Output voltages/currents: +12V DC/1200mA, -12V DC/1200mA
Input voltage: 230V AC or 115V AC

Below is the L1 linear PSU

 It's a great kit.  1.5A per rail. 5V regulator on busboards.

2. Switch Mode Power Supply (SMPS) 

These first came out in the 1970s They are very efficient and their performance is much higher than linear regulators. SMPSs use PWM (pulse with modulation) to regulate the output voltage.
Their efficiency is very high, but the process is extremely complicated & creates high frequency noise.
They use diodes & capacitors to produce high voltage DC. This high DC voltage is then decreased and converted into a steady DC output using a system of transistors, capacitors, diodes, inductors & ferrite transformers.

The power bricks (wall warts) are a modern example of SMPSs. You will find them powering computer laptops and mobile phones.

This is a ATX SMPS from a desktop computer.


The advantages of this type of regulated PSU are that its smaller. There is very little heat generated.
Noisier due to the switching frequency of the SMPS. An unfiltered output may cause glitches in digital circuits or noise in audio circuits.

Above is the Doepfer A-100SSB. Its a small switcher PSU, suitable for up to 8 modules. (380mA)

Below is the Doepfer A-100PSU3
It's a +/-15V switching supply (wide range input 100...240V for mains voltage) followed by a linear regulation circuit that generates +12V and -12V. The +5V is a pure switching supply without linear regulation.

Really interesting design as it combines both linear & switching supplies. The black boxes are
Meanwell switching supplies. They create +15v, -15v, and +5v. The +/-15V must be passed through linear regulators to get +/-12V. I can't see the regulators in the photo ...maybe they are under the heat sink fins ???

The transformer in a switching power supply is also smaller than a traditional line frequency (50Hz or 60Hz depending on region) transformer,

If you need a high current wall wart a SMPS PSU will be easier to find. I use a 10A brick to power one of my Buchla cases.(though the OEM brick is expensive).

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Meanwell RT65B.
Mouser

A great switching PSU which seems ideal for a small eurorack case (around 200HP)

Output Voltage-Channel 1: 5 VDC(5A)

Output Voltage-Channel 2: 12 VDC (2.8A)

Output Voltage-Channel 3: - 12 VDC  (0.5A)

You can use a Bus board with filtering  to remove the PSU ripple noise.

Use something like a LC filter.

This consists of an inductor ( represented by the letter L) connected in series with the power flow and a capacitor (represented by the letter C) from the filtered voltage to ground.


I guess before you do this you need to ask the questions;

1. Are you better off filtering the noise, or preventing noise in the first place?
2. Is there actually much noise ?
3. Is the LC filter making more noise than it is removing?

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Below is another example of a switching PSU
Its a Meanwell PD2515
Mouser: 709-PD2515

 It supplies : 24W 15V/0.8A -15V/0.8A 

iTS ok FOR a small buchla system

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Finally, this is the PSU for my amalgamod Eurorack system:

Plenty of juice for  this:

Links
+ NLC Build notes - Linear PSU