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Ultra low noise regulators


NickK
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So I've been exploring the world of DIY audio.. specially making a headphone "DAC" with an R2R ladder style DAC. So effectively the headphones are connected to the power supply - thus ultra low noise stable DC power regulation is needed.

Now my current power system is a supply (normally battery) that is then fed through a RC style regulator to give the required voltages and current.

However the LT3045 regulator is something worth noting .. 

Quote

Ultralow RMS Noise: 0.8μVRMS (10Hz to 100kHz) Ultralow Spot Noise: 2nV/√Hz at 10kHz
Ultrahigh PSRR: 76dB at 1MHz
Output Current: 500mA

Wide Input Voltage Range: 1.8V to 20V
Single Capacitor Improves Noise and PSRR
100μA SET Pin Current: ±1% Initial Accuracy
Single Resistor Programs Output Voltage
High Bandwidth: 1MHz
Programmable Current Limit
Low Dropout Voltage: 260mV
Output Voltage Range: 0V to 15V
Programmable Power Good
Fast Start-Up Capability
Precision Enable/UVLO
Parallelable for Lower Noise and Higher Current
Internal Current Limit with Foldback
Minimum Output Capacitor: 10μF Ceramic
Reverse-Battery and Reverse-Current Protection

Only 500mA I hear.. well actually you can connect these in parallel and the reference design has a 4-device 2A design that pushes the heat and noise levels down further! So this would be able to run a camera at 12V but another option is to "upgrade" the internal camera power.

The down side.. in singles the regulator chip itself (surface mount) is about $/£/€5 each.

Just wondered if anyone had explored creating an astro "ultra quiet" power regulator that could be plugged inline for example.

 

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Any noise on the power rails can be greatly reduced by a 2 stage LC filter. I run my astro setup from a single SMPSU with a 2 stage LC filter in each distribution output, values tailored to what that output is supplying. This also isolates noise created by the device the output is connected to from affecting the other outlets. Probably overkill but it doesn't cost much extra and gave me an excuse to make a PCB. :smile:

As many cameras are now powered from USB, which will be very noisy anyway, and they don't seem to be affected by it, they have their own on board filtering methods. As regulated power supply noise is all high frequency then only small values of L and C are needed so take up little space.

Probably cheaper than a bank of ultra low noise regulators. :smile:

Alan

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1 hour ago, symmetal said:

Any noise on the power rails can be greatly reduced by a 2 stage LC filter. I run my astro setup from a single SMPSU with a 2 stage LC filter in each distribution output, values tailored to what that output is supplying. This also isolates noise created by the device the output is connected to from affecting the other outlets. Probably overkill but it doesn't cost much extra and gave me an excuse to make a PCB. :smile:

As many cameras are now powered from USB, which will be very noisy anyway, and they don't seem to be affected by it, they have their own on board filtering methods. As regulated power supply noise is all high frequency then only small values of L and C are needed so take up little space.

Probably cheaper than a bank of ultra low noise regulators. :smile:

Alan

 

Lol yes - it's easy to make a filter to kill off anything outside of 50Hz from the mains, then regulate to a voltage. Most cameras I have are 12V with the fans (shock horror) also running from the same power.

Just seemed like an option to provide 12V heavily filtered :) It's possible to run an isolated USB with the regulator providing quiet USB too.

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Audio design is difficult at the best of times and totally different to any other form of electronics because of the minute signals in use, filters are very hard to get right and over zealous use of them can kill the sound completely.

I have used specially selected versions of chips like the LM317 in the past with very good results even in Moving Coil phono stages although still preferred ECC81 valves  even for that application.

Alan

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15 hours ago, Alien 13 said:

Audio design is difficult at the best of times and totally different to any other form of electronics because of the minute signals in use, filters are very hard to get right and over zealous use of them can kill the sound completely.

I have used specially selected versions of chips like the LM317 in the past with very good results even in Moving Coil phono stages although still preferred ECC81 valves  even for that application.

Alan

My initial idea was to get pure digital from PSU to headphones with possibly a passive RC filter at the end.

Going through all the research it became apparent for R2R vs singlebit sigma delta, that the noise from square waves needs careful control (far beyond an active Sallon-Key Butterworth filter. Also the ladder resistances for higher bits requires higher tolerances (0.01%). Then by the time the switching on the ladder is operating at ~3MHz you're starting to get into higher frequency curcuit design.. bypass caps, track layouts etc all become too costly to simply DIY.  I find the software and building digital filters relatively easy (including the fpga) but low volume cost of high precision resistors and large number of mistakes in hardware.. it would be easier selecting an OEM board. 

In the end I will go with a Soekris R2R OEM board (this has usb, fgpa, ultra stable clock, switches and resistors at 0.01%). The board then requires line buffer or headphone amp, power supplies and control boards. Those are easier to build or source. 

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Remember that there is a great deal of potential for RF noise pickup from sources other than the power supply. So careful decoupling, shielding and screening will be necessary whatever else you do.
As an example, for an entirely different application, I an running an RFM96 433MHz as a receiver for some remote control signals. The received noise level is increased massively whenever I have the receiver near my computer monitor or phone.

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