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Simple High Performance DC Coupled Class A HPA with sub PPM THD

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vvs07

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xrk971

xrk971

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stellarelephant said:
Cool PSU... Out of curiosity, does it sound any different to you compared with the torroid?
Click to expand...

I could hear a tiny bit of 60Hz hum when using linear supply on more sensitive headphones. There is no audible hum with the new DC-DC PSU. Also, turn-on transient thumps are completely eliminated with the new PSU as cap multipliers have about 20 second long time period to get up to full voltage. With music playing there is no discernable difference with dynamics as that is all based on bias current in SE Class A design.
 
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Morde

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s610adam

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xrk971

xrk971

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silasmellor said:
What are you planning with the psu? Can that be fed off a trafo/diode bridge instead of an alps?
Click to expand...

The input for the on-board PSU is 8v to 18v, so a
Ideally a 12vdc Class 2 wall transformer (like those for old routers), or a 12v smps work fine. If you want to use a trafo and diode bridge and a few caps to generate your 12v that’s fine. One of the main goals was to get away from mains AC levels for safety.
 
stellarelephant

stellarelephant

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xrk971 said:
The input for the on-board PSU is 8v to 18v, so a
Ideally a 12vdc Class 2 wall transformer (like those for old routers), or a 12v smps work fine. If you want to use a trafo and diode bridge and a few caps to generate your 12v that’s fine. One of the main goals was to get away from mains AC levels for safety.
Click to expand...

One option: DDU120100H4480: Jameco Reliapro : AC to DC Power Supply Wall Adapter Transformer Single Output 12 Volt 1 Amp 12 Watt : Power Supplies & Wall Adapters

I'm using this 12V 1A Jameco Reliapro linear wall wart, along with three(!) of the 5V version, to separately power each board in my RPi DAC setup. Mine were modified by member Greg Stewart, so I haven't heard them stock, but at least in modified form, they absolutely walk all over the much pricier iFi iPower for noise performance and natural sound. I'm sold on Class 2 vs. SMPS now.

From what I understand, Greg's mods include an AC filter cap (that works as the final C in a CLC filter that has a CL between the wall and the power strip), as well as upgraded diodes and some DC caps. I know he is working on providing a mod tutorial but not sure when that'll be posted.

Anyway, for $15, I reckon its a good candidate, even in stock form.
 
xrk971

xrk971

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Some Measurements with DC-DC PSU

I think we can see that the new DC-DC PSU is working very well with the data here. It is almost like a battery in terms of a flat noise floor. A DC-coupled amp has a slight rise as frequency goes down to sub-audio (rumble range). But clearly, there is no 60Hz mains or any of its harmonics present.

This is my usual standard of 1Vpp into 47ohms FFT for intercomparison with my other amps. The level of third harmonic distortion is 10x less than second harmonic, which is very nice. This amp will have a clean and engaging natural sound to it. Data below is for 142mA bias made possible using 2.2R source resistors.

1.02Vpp into 47ohms:
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4.0Vpp into 47ohms:
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I think the higher distortions I am seeing may be result of thick film SMT resistors being used. I will need to order metal thin film equivalents.
 

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  • TimS-HPS-DC-DC-PSU-142mA-1.02Vpp-47R-FFT-2.png
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  • TimS-HPS-DC-DC-PSU-142mA-4.11Vpp-47R-FFT.png
    TimS-HPS-DC-DC-PSU-142mA-4.11Vpp-47R-FFT.png
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pstech

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xrk971

xrk971

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stellarelephant said:
Wow, X, looks like you nailed it!
Click to expand...

Thanks. To get this performance requires use of the TP7A4xxx LDO regulaors which are only available in quad flat pack with no leads and underside power pad for heatsink. They are rather tricky to solder (must be done with reflow) as needs a hot air gun from above and a hot plate from below, plus the pin pitch is 0.5mm. They don't make them in a larger package like SOTxxx or even SOIC where legs are visible. JPS64 is looking into getting some made to conform to a standard larger trough hole adapter board to resemble an LM3x7 TO220. One could use an LM317N or LM337N in SOT223, but the noise is about 10x higher at 38uV rms vs 4uV rms.
 
xrk971

xrk971

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badboygolf16v said:
Could they be ordered from someone like say www.ldovr.com? Maybe we could do a GB for them?
Click to expand...

I have bought one from there before - they are kind of pricey at $23 ea. Some Chinese ones are now in the circa $8 range (but not TO-220 pin compatible -but that's ok).

TPS7A3301 -5V -9 -12 -15V -18V 1A Ultra Low Noise LDO Negative Voltage Regulator 699924389058 | eBay

TPS7A4700 Low Noise Power Module DC-DC 3-36V to 3V 3.3V 5V 12V 15V 1A Adjustable 699901905578 | eBay

So these are also an option.
 
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