rb2013
Author of The 6922 Tube Review
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Ok now to part 2 - in the next section I will cover existing lower cost power supplies available. But first a description of the different linear power supply regulators - or LDO's (low drop out) regulators as they are sometimes referred to. Also some alternatives to a IC based LDO regulator.
Just a note on linear power supplies - they do come in both regulated and unregulated versions. Typically the unregulated ones will be cheaper wall wart looking devices. Due to the lack of regulation they are not recommended, their voltages can swing by wide amounts and even damage some equipment. The following is a discussion of methods of regulation. Here is a great primer on the history of linear power regulation from simple discrete, and discrete/opamp circuits to the more advanced circuit designs: Sulzer, Sulzer-Borbly, Jung Super Reg, Jung 2000, etc:
https://tangentsoft.net/elec/opamp-linreg.html
Later came IC (Intregrated Circuit) designs with a 'low dropout' efficiency (low loss from the feed voltage to the ouptut voltage). At the bottom of the thread is a list of many popular IC LDO regulators.
https://en.wikipedia.org/wiki/Low-dropout_regulator
From what can tell from previous threads there are a few important characteristics about DC linear regulation schemes - the biggest from an audio perspective is the level of noise these circuits output to the respective audio components like XMOS processors, DAC chips, audio clock oscillators, etc... In fact the latest generation of digital audio devices have very sensitive femto clocks that need the cleanest possible power source for best quality sound. This noise output of the LDO or other regulation scheme is measured and quoted in µV RMS (microvolt or 1/millionth of a volt) but typed as just uV (as most keyboards do not have greek letters). Another way that LDO noise is quoted is % of Vout.
http://hifiduino.blogspot.com/2010/03/comparing-noise-figures-in-linear.html
https://en.wikipedia.org/wiki/Low-dropout_regulator
Quote:
And the other noise characteristic is the above mentioned ability of the regulator to reject ripple (noise) on the AC power input - when it converts this AC to a DC output:
Ok so we have two measures of a LDO or really any power regulation scheme in a linear regulator - internal noise quoted as µV and PSRR quoted in dB's. When you read a datasheet for a LDO commonly you will see a chart of the PSRR at various frequencies. Many LDO's are good at low frequency but have a much reduced capability at higher frequencies - including far above human hearing. Are these important - you bet! As this high freq noise can still modulate with the sensitive audio clocks operating at high freq.
Lower is better - that is the greater the -dB the greater the noise rejection.
The last factor to consider is the heat generated by the LDO and it's ability to handle current. For very low current drawing devices like a USB DDC chip (500mA or a TXCO clock (150mA) there are a wide choice of excellent LDO's available. But for high current needs (like a PC for example 3A to 10A)) many IC based LDO's can not handle the heat generated.
Final comment - so as a package both the type and quality of the transformer (see PART 1) and the regulation scheme will work together to filter AC line noise out and produce a clean DC power source to the rest of the audio circuit. I will discuss the commonly available LPS and DIY boards available and they're possible use as say USB power supplies.
Further info:
http://www.ti.com/lit/an/slyt202/slyt202.pdf
http://www.richtek.com/selection-guide/en/selection-ldo-criteria.html
Now for some of the common and better LDO's available:
A great comparison of the noise on various common LDO's:
Ok how about some of the newer generation of LDO's? Claiming sub 4uV RMS noise- even sub 1uV!
LM723: http://www.ti.com/lit/ds/symlink/lm723.pdf
2.5uV (100-10K) 5.9uV (10-100K), PSRR -74dB
Looks like a good solution for low current digital uses - Schitt uses in the Wyrd USB 'cleaner' - more on that in PART 3.
LT3042: http://www.linear.com/product/LT3042
0.8uV (10-100K)!, PSRR -79dB @ 1Mhz
This is about as low as it gets!
ADM7150ARDZ: http://www.analog.com/media/en/technical-documentation/data-sheets/ADM7150.pdf
1uV(100-100K)! 1.6uV (10-100K), PSRR -90dB (1-100kHz), -60dB 1Mhz
LT3032: http://cds.linear.com/docs/en/datasheet/3032fe.pdf
20uV, PSRR -64dB 1K, -38dB 1Mhz
LM2941: http://www.ti.com/lit/ds/symlink/lm2941.pdf
180uV, PSRR -65dB (10-100K), -68dB 1Mhz
Used in the Breeze Audio DU-U8 as a dual stage PS filtering circuit
LT1963: http://cds.linear.com/docs/en/datasheet/1963fc.pdf
40uV, PSRR -63dB
Used in the Melodious MX-U8
ADP150: http://www.analog.com/media/en/technical-documentation/data-sheets/ADP150.pdf
9.5uV, PSRR -50dB (10-100K), -38dB 1Mhz
Used in the Singxer F-1
LT1764: http://cds.linear.com/docs/en/datasheet/1764fb.pdf
40uV (10-100K), PSRR -20dB (10-100K), -20dB 1Mhz
LM2940: http://www.ti.com/lit/ds/symlink/lm2940c.pdf
150uV, PSRR -58dB (10-100K), -70 1Mhz
Used in the Singxer SU-1
LT1083: http://cds.linear.com/docs/en/datasheet/108345fh.pdf
180uV, PSRR -30dB (10-100K)
TPS7A47: http://www.ti.com/product/TPS7A47
4.6uV, PSRR -60dB (100K)
Just a note on linear power supplies - they do come in both regulated and unregulated versions. Typically the unregulated ones will be cheaper wall wart looking devices. Due to the lack of regulation they are not recommended, their voltages can swing by wide amounts and even damage some equipment. The following is a discussion of methods of regulation. Here is a great primer on the history of linear power regulation from simple discrete, and discrete/opamp circuits to the more advanced circuit designs: Sulzer, Sulzer-Borbly, Jung Super Reg, Jung 2000, etc:
https://tangentsoft.net/elec/opamp-linreg.html
Later came IC (Intregrated Circuit) designs with a 'low dropout' efficiency (low loss from the feed voltage to the ouptut voltage). At the bottom of the thread is a list of many popular IC LDO regulators.
https://en.wikipedia.org/wiki/Low-dropout_regulator
From what can tell from previous threads there are a few important characteristics about DC linear regulation schemes - the biggest from an audio perspective is the level of noise these circuits output to the respective audio components like XMOS processors, DAC chips, audio clock oscillators, etc... In fact the latest generation of digital audio devices have very sensitive femto clocks that need the cleanest possible power source for best quality sound. This noise output of the LDO or other regulation scheme is measured and quoted in µV RMS (microvolt or 1/millionth of a volt) but typed as just uV (as most keyboards do not have greek letters). Another way that LDO noise is quoted is % of Vout.
http://hifiduino.blogspot.com/2010/03/comparing-noise-figures-in-linear.html
https://en.wikipedia.org/wiki/Low-dropout_regulator
Quote:
And the other noise characteristic is the above mentioned ability of the regulator to reject ripple (noise) on the AC power input - when it converts this AC to a DC output:
Power supply rejection ratio: PSRR refers to the LDO's ability to reject ripple it sees at its input.[11] As part of its regulation, the error amplifier and bandgap attenuate any spikes in the input voltage that deviate from the internal reference to which it is compared.[12] In an ideal LDO, the output voltage would be solely composed of the DC frequency. However, the error amplifier is limited in its ability to gain small spikes at high frequencies. PSRR is expressed as follows:[11]
{\displaystyle PSRR=20\times log{\frac {Ripple_{IN}}{Ripple_{OUT}}}}
As an example, an LDO that has a PSRR of 55 dB at 1 MHz attenuates a 1 mV input ripple at this frequency to just 17.78 µV at the output. A 6 dB increase in PSRR roughly equates to an increase in attenuation by a factor of 2.
Most LDOs have relatively high PSRR at lower frequencies (10 Hz - 1 kHz). However, a Performance LDO is distinguished in having high PSRR over a broad frequency spectrum (10 Hz - 5 MHz). Having high PSRR over a wide band allows the LDO to reject high-frequency noise like that arising from a switcher. Similar to other specifications, PSRR fluctuates over frequency, temperature, current, output voltage, and the voltage differential.
Ok so we have two measures of a LDO or really any power regulation scheme in a linear regulator - internal noise quoted as µV and PSRR quoted in dB's. When you read a datasheet for a LDO commonly you will see a chart of the PSRR at various frequencies. Many LDO's are good at low frequency but have a much reduced capability at higher frequencies - including far above human hearing. Are these important - you bet! As this high freq noise can still modulate with the sensitive audio clocks operating at high freq.
Lower is better - that is the greater the -dB the greater the noise rejection.
The last factor to consider is the heat generated by the LDO and it's ability to handle current. For very low current drawing devices like a USB DDC chip (500mA or a TXCO clock (150mA) there are a wide choice of excellent LDO's available. But for high current needs (like a PC for example 3A to 10A)) many IC based LDO's can not handle the heat generated.
Final comment - so as a package both the type and quality of the transformer (see PART 1) and the regulation scheme will work together to filter AC line noise out and produce a clean DC power source to the rest of the audio circuit. I will discuss the commonly available LPS and DIY boards available and they're possible use as say USB power supplies.
Further info:
http://www.ti.com/lit/an/slyt202/slyt202.pdf
http://www.richtek.com/selection-guide/en/selection-ldo-criteria.html
Now for some of the common and better LDO's available:
A great comparison of the noise on various common LDO's:
Comparing Noise Figures in Linear Regulators
Just like phase noise in clocks, it is difficult to compare noise values among linear regulators because there is no common ground in specifying noise figures. Some companies report noise density, others RMS V noise, and yet others % of Vout. The frequency range for the reported noise figures also varies from company to company.Thefamiliy is a favorite for audio projects because it has low noise figures. Among linear regulators it is probably universally preferred by audio diy aficionados.In order to compare other regulators to this benchmark device, I decided to calculate the Vrms noise in each of the fequency ranges provided by the chart. The Vrms noise is basically the product of the noise density times the frequency delta.The results is shown in the graph below. Total Vrms = 23.2 uVrms for the frequency range 10Hz to 100KHz. This approximation is very close to the specified value of 20 uVrms.I then looked as the specified noise of several common regulators and matched the values to the corresponding value of the LT1763 device.A couple of observations: Theis actually very good, in fact better than the beloved LM317 according to spec. The LM723 seems of lower noise than the LT1763, at least in the reported frequency range.
We can approximate the total noise Vrms for the 10Hz-100KHz interval by noticing that each frequency range contributes a percentage of the total noise. In the case of the LT1763, we notice that the 10Hz-10KHz range contributes about half of the total 10Hz-100KHz noise. The table below compares all the regulators in the 10Hz-100KHz range.
Ok how about some of the newer generation of LDO's? Claiming sub 4uV RMS noise- even sub 1uV!
LM723: http://www.ti.com/lit/ds/symlink/lm723.pdf
2.5uV (100-10K) 5.9uV (10-100K), PSRR -74dB
Looks like a good solution for low current digital uses - Schitt uses in the Wyrd USB 'cleaner' - more on that in PART 3.
LT3042: http://www.linear.com/product/LT3042
0.8uV (10-100K)!, PSRR -79dB @ 1Mhz
This is about as low as it gets!
ADM7150ARDZ: http://www.analog.com/media/en/technical-documentation/data-sheets/ADM7150.pdf
1uV(100-100K)! 1.6uV (10-100K), PSRR -90dB (1-100kHz), -60dB 1Mhz
LT3032: http://cds.linear.com/docs/en/datasheet/3032fe.pdf
20uV, PSRR -64dB 1K, -38dB 1Mhz
LM2941: http://www.ti.com/lit/ds/symlink/lm2941.pdf
180uV, PSRR -65dB (10-100K), -68dB 1Mhz
Used in the Breeze Audio DU-U8 as a dual stage PS filtering circuit
LT1963: http://cds.linear.com/docs/en/datasheet/1963fc.pdf
40uV, PSRR -63dB
Used in the Melodious MX-U8
ADP150: http://www.analog.com/media/en/technical-documentation/data-sheets/ADP150.pdf
9.5uV, PSRR -50dB (10-100K), -38dB 1Mhz
Used in the Singxer F-1
LT1764: http://cds.linear.com/docs/en/datasheet/1764fb.pdf
40uV (10-100K), PSRR -20dB (10-100K), -20dB 1Mhz
LM2940: http://www.ti.com/lit/ds/symlink/lm2940c.pdf
150uV, PSRR -58dB (10-100K), -70 1Mhz
Used in the Singxer SU-1
LT1083: http://cds.linear.com/docs/en/datasheet/108345fh.pdf
180uV, PSRR -30dB (10-100K)
TPS7A47: http://www.ti.com/product/TPS7A47
4.6uV, PSRR -60dB (100K)
