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Small dual voltage regulation help
Small dual voltage regulation help
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Old 20th January 2021, 09:24 PM   #1
bloozestringer is offline bloozestringer  United States
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Default Small dual voltage regulation help

I have an old Millett Hybrid headphone amp pcb I am wanting to put into a small case with a Raspberry Pi3+ (with HAT dac) and a 2.5" HDD. I've been trying to determine what would be the best way to power all of this off of one power supply as I want it to be a self contained unit for my office.

The amp requires 24V/0.75A and I currently am using the Pi/HAT/HDD with a 5V/2A wall wart.

I've used a Tangentsoft TREAD back in the day to regulate the voltage to a Millett with good success and I'm looking for something that is similar in size as I would like this to be as small a footprint as possible. So the HDD will go under the amp pcb and the Pi/DAC will be vertical along one of the chassis sides. leaving one end of the 6" x 9" box open (amp pcb is 4" x 6").

I was thinking a dc/dc wall wart 24V/3-5A into a small linear regulator to get the 24V to the amp and to a buck converter to the 5V to the Pi/HAT/HDD. I'm not much on power supplies that have two completely different voltages so I'm kinda lost here.
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Old 21st January 2021, 05:52 PM   #2
indianajo is offline indianajo  United States
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If you don't mind filtering output of a switcher supply to remove the howl, the obvious solution is a PCAT switcher supply. +5 @ 5-10 A, +-12 @ half an amp. I doubt if you are ever going to listen to the headphones at 18 W or even 9 W.
If there is a problem with the 24 not having same return as 5 v, put a capacitor between the output of one & the input of the other. 2.2 uf, up to 10 uf? film caps don't care about the polarity and are not that big these days in the 25 v rating.
PCAT supplies also known as ATX supplies, are sold in 1 year variety at computer repair shops, and 5 year variety at farnell. At least I've never blown the farnell one up. Typically $29 to $49. I have a stack of dead ones from the computer shop I pull parts out of. Diodes, rectifiers, nfets, NTCresistors, heat sink, IEC entry, anti surge inductors, MOS voltage supressor, never the e-caps.
Other obvious solution, wall transformers from abandoned products resold at the charity resale shop. Salvation Army near me gets $1-2 for these. The mating connectors can be bought at Parts-express or the old connector can be cut off. Making a 3.0 v supply out of a 3.8 vac wall transformer today, for a CD player. To replace one that was stolen, but not the CD player. Putting the rectifier+capacitor+voltage dropper in a margerine container.
Never see portable CD player chargers in stores, & farnell/parts-express only sell the 8 connector 10 voltage version, which might short out against some metal object. AC plug CD players all have gotten rubber control problems in 3-5 years. Or they have a remote that the buttons quit working on. This 1988 RCA player with hard contact buttons may live longer than me.
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Last edited by indianajo; 21st January 2021 at 06:15 PM.
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Old 22nd January 2021, 03:44 AM   #3
bloozestringer is offline bloozestringer  United States
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Quote:
Originally Posted by indianajo View Post
If you don't mind filtering output of a switcher supply to remove the howl, the obvious solution is a PCAT switcher supply. +5 @ 5-10 A, +-12 @ half an amp. I doubt if you are ever going to listen to the headphones at 18 W or even 9 W.
The amp is a tube amp. It needs a minimum of 500mA but works better at 750mA. It only outputs a fraction of a watt. Each tube needs at least 10V but Iíve found it sounded better at 11-12V.

Hereís the amp pcb in the enclosure for size reference.

Hereís the amp I built back in 2006 or so with the LM317 TREAD regulator and a overall shot with it on top of a DIY Meier Crossfeed.
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Last edited by bloozestringer; 22nd January 2021 at 03:57 AM.
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Old 25th January 2021, 12:19 AM   #4
bloozestringer is offline bloozestringer  United States
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Could I use a 24V/4A supply (eg meanwell) into a 317 regulator for the amp and into this :
To drop the voltage to 5V for the pi+hat+dac? I won’t be playing anything beyond FLAC so the 180kHz frequency of the XL4015 shouldn’t be an issue.

https://www.amazon.com/dp/B07J9RQ8B6..._laidGbPBGFX16
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