A company in CA is blowing out 12V DC 2A wall-wort type power supplies on eBay for a buck apiece with free shipping. Perhaps because they have a nonstandard output connector? Regardless, it's a handy-enough value to keep some around. I initially ordered a couple to check out. They came Priority Mail and they're good-enough little switchers, with about 1mV of noise over 100kHz BW while delivering 1/2 amp of output. There's no doubt the merchant is losing money on this, but hey...
AC Adapter 12V | eBay
AC Adapter 12V | eBay
As written, it is not only the money (you definitely need to buy a few as these likely won't live too long).
Tell me what the fun of popping caps and 1000 µV of noise in audio is 🙂 I use to replace these for good PSU's. BTW isn't it "wall wart" in your language?
Tell me what the fun of popping caps and 1000 µV of noise in audio is 🙂 I use to replace these for good PSU's. BTW isn't it "wall wart" in your language?
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I think I framed the context of their value and usefulness correctly; I'm not recommending these as high-end devices. But at 1mV of noise they beat the cr@p out of a conventional wallwort. I have several devices (not just audio) that came with those.
Could be. Forgive any imperfections. Aren't you being a bit p!ssy about all of this? You have no idea how long they will last. And there's more to life than just audio. The tracking mounts for two of my telescopes use 12V xfmr-type wall warts. These will be more efficient. And I'll have spares on hand at almost no cost.
No not pissy at all?! I thought I was at an audio site where most want good stuff. Anyway the idea that they won't live long is a little amplified by the price. Whatever. I would not expect too much. Any regulated linear PSU will perform better, in audio at least.
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Again, you'll have to forgive me for posting something that just might possibly have some relevance outside of the audio world.
IOW, lighten up, my friend...
IOW, lighten up, my friend...
In the interest of calming your moderator sensitivities, here's an example of an audio application. My Stax SRM-3100 headphone system came with a POS xfmr-type 12VDC wallwart. It has 35mV of noise (mostly mains-related) at operating load. There are no regulators in the amplifier, so that noise gets amplified by the stepup devices in it. Replacing it with a Boschert switcher made a huge improvement. One of these will be much more convenient, and the noise is higher-freq and much easier to filter.
I am not a moderator where does that come from? Anyway, what about adding linear LDO regulators of low noise fame in the Stax (if the transformer does not hum) ?
BTW beware of the tone of your posts. It is unpleasant.
BTW beware of the tone of your posts. It is unpleasant.
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Not really. That noise is attenuated by the circuit's PSRR (Power Supply Rejection Ratio).
Jan
Under your handle it says "diyAudio Moderator Emeritus"... perhaps I misunderstood what that means.
It's teenie, and there's no room inside to add anything. The 12VDC is stepped up to +-225V to drive the 'stats.
??? I thought I was just addressing your objections. ??? Maybe it's language/cultural difference. Around here, among friends, "lighten up" means "hey, no big deal, let it go."
It is like the difference between "your wife" and "your ex-wife" 😀
All good. It is a pity there is not more space to built a decent regulator in that Stax. Not even a TO220/TO247 can be fitted against the casing?
All good. It is a pity there is not more space to built a decent regulator in that Stax. Not even a TO220/TO247 can be fitted against the casing?
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True, but it's far from perfect... Class A is very temperature sensitive and the balance drifts with use... the audible difference of replacing the xfmr supply is not at all subtle.
With the ripple voltage you mentioned that is not strange. Then most switchers perform better. Unregulated DC does not make devices better in general.
Do you have a picture of the inside of the Stax? I am not at all familiar with Stax but I was thinking of LT1083/1084/1085 depending on how much power is needed. With 1.3V dropout voltage these can be used. There are better ones but in the wrong package.
Do you have a picture of the inside of the Stax? I am not at all familiar with Stax but I was thinking of LT1083/1084/1085 depending on how much power is needed. With 1.3V dropout voltage these can be used. There are better ones but in the wrong package.
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Understood now... 🙂
In theory, it's a reasonable idea. The entire power supply chain is the main weakness of this little amp, it really is "built to a size and price." If, as you suggest, we supply 15V and regulate to 12 inside, at ~400mA output, a TO220 reg would generate appreciable more heat in the unit, which would then require venting. And, the noise problem is not the main issue with this design.
The real issue with the supply comes post-PWM stepup. Limited current, and awful output impedance profile. A mosty-accurate schematic is attached. I will be doing an article soon-ish on optimizing it.
Attachments
With only 400 mA I would choose TPS7A4700 or LT1764 as that one has a metal tab. With a 12V transformer selected on the lowish side of 12V and large filter cap and Schottky diodes. Is CLC at the high(er) voltage side for the 470 Ohm resistors already been tried out!?
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As I said, the noise is not the big issue. With just a decent 12V switcher, replacing C31 with a 1000-2200uF 16V 'lytic (there's just barely room to fit it!) results in a plenty good-enough noise profile.