Linear Power Supply DIY Weekend Project

[ezkcdude]

Crooner, what about the barrel plug? I assume you did some soldering for that. Could you show us a pic? I'm thinking about doing a power supply for my NOS DAC, so I'd like to have a reference for how that should look, assuming you've got everything working properly.

[crooner]

I only soldered the binding posts. The rest is all solderless "lug" connections.

I plan to "burn-in" the supply for 24 hours before using it regularly. I'll attach the Fluke meter and monitor the voltage.

I should point out that this supply also generates other voltages (-5V, 12V and -12V). I wonder if disabling these extra voltages would make it run cooler...

As for the "buzz", I added some blue-tack to the chassis near the transformer. Hopefully, this should take care of it.

[crooner]

Here are some conclusions I have drawn from this project:

5 volts at 2 amps is a hefty figure for a regular wallwart power supply, specially if good regulation is desired. It's no wonder Slim Devices chose a switcher for this application. A comparable linear supply would have been larger than the Squeezebox itself and very expensive!

If you are using a linear wallwart and it runs cool to the touch, then you have less than ideal regulation. My DIY power supply puts out 5.02 volts loaded, which is pretty good regulation. It does run quite warm despite the large transformer, regulator heatsinks and metal enclosure.

If absolutely cool operation is desired the dimensions of the transformer would be cost prohibitive in my opinion.

5 volts at 2 amps (of the original switcher) are specified mainly because of the Vacuum Flourescent Display (VFD). The power requirements are very similar to standard tube filaments. Tube equipment trannies also run quite warm in operation since most of the current drain comes from the filament windings.

[ezkcdude]

5 volts at 2 amps are needed mainly because of the Vacuum Flourescent Display (VFD). The power requirements are very similar to standard tube filaments. Tube equipment trannies also run quite warm in operation since most of the current drain comes from the filament windings.

The SB3 doesn't require 2 amps. It requires 1 amp. Anything more than that is extra capacity. Of course, it's probably a good thing to overspec the PSU, rather than run the supply at full load.

[crooner]

Exactly, the 2 amp rating is a loose figure, since you want some extra capacity in the power supply. Running a SB3 on a 1 amp supply is pretty much at the limits....

As for my DIY supply, it runs quite warm. Sometimes I wonder if there's a tube rectifier in there :-)
I am still not 100% comfortable with this, specially when I am not home using the device. Perhaps I should unplug it when not in use. In doing this, however, I lose the weather plug-in feature on the SB3....

[richidoo]

Nice project, crooner. I have a linear frame PS too, one given to me by a friend years ago. The biggest difference in sound that I noticed was in the bass, that it was more powerful, more dynamic, not as compressed as the stock wart.

I can imagine a couple scenarios of how it could affect bass, but I am just guessing. Could the stock switching PS have trouble delivering current fast enough to accurately amplify large cycles which demand longer sustained current than higher freqs? It has very low power reserves and no magnetics to draw on through transients. I don't think the switching noise, if any, would have much effect on dynamics, maybe just on tone smoothness.

I also noticed better dynamics and smoother tone in mids, and just smoother and clearer highs. To me the differnce was night and day. Switching the PS in and out was a definite improvement with the linear.

Like you I need a box. I have mine sitting on a piece of cardboard on the threaded studs of the PS. You did a nice job on the assembly. Metal working is not as easy as it seems! I have read that wood boxes are suitable for audio projects, I may try that, with plenty of ventilation, and leaving the three aluminum sides of the frame exposed to air.
Rich

[crooner]

Thanks for your comments richidoo. After some burn-in, the sound has improved considerably. Bass performance in my system is already quite good so it was hard to detect a difference in this area. The mids, however, are another story. Much smoother, with less grit. A definite improvement, IMHO.

There's no going back to the stock switcher. I butchered it for the cable and connector. Couldn't find a suitable one locally. Besides, I was lazy to go to RadioShack after a long day of work ;-)

I have a question: do you leave your supply constantly on?

Best regards,
crooner

[crooner]

There's a track that's a revelation on my setup, specially since I added the SB3, DAC and power supply. It's Peggy Lee's Big Spender. It came on a Kohls department store compilation and man it's dynamite!
It has everything: dynamics, deep bass, powerful horns, delicate percussion and lush, sultry vocals from Ms Lee. Way recommended!

[Skunk]

The mids, however, are another story. Much smoother, with less grit. A definite improvement, IMHO.

There's no going back to the stock switcher. I butchered it for the cable and connector. Couldn't find a suitable one locally. Besides, I was lazy to go to RadioShack after a long day of work ;-)

I have a question: do you leave your supply constantly on?

The radioshack N connectors are crap. I bought a pack of two and one of the solder tabs broke off before I had it put together. The other one's just sitting here, because I found a hub's power supply lying around with a heavier guage wire than SB's, and a heavier duty 'N' connector. Snip. I plan to custom make a cord when I can get the switchcraft connector, and also a power cord when I can afford the hospital grade plugs. My IEC inlet (and case) came from a PC's switching supply, and needs to be upgraded to 15 amp. The IEC makes noise through the speakers when I wiggle the male connector, and that can't be good.

I turn mine off at the surge protector it's connected to if I'm not going to listen that day, just for peace of mind. I'm sure I'll get over that, because it doesn't even get warm when the SB is off. I have a tube amp, so leaving my stereo on for 72 hours straight is not unusual. Even during those stretches it's never gotten what could be considered warm, especially compared to the amp or even most wall warts.

My Power One is surplus, and came with a varistor attached to the AC input. Since I plug it into a protector, i just removed it for now. My next step is to make a power conditioner because the house I'm in has antiquated electrical. I read a DIY article on how to make a Shunyata power strip, with a varistor and some x-caps for around $50 I'm thinking I might be able to wire it directly to the AC input of my PS, where the varistor was.

Clean AC can't be underestimated. The linear supply keeps me smiling because of the increased focus in the microdynamics. It's almost as if a spotlight were shone on the strange little noises my favorite artists love including in albums. A lot of the noises now go up and away from the listener, rather than sounding like they're simply background noises that fade in/out. I never heard height or depth from my soundstage like I do now. Eg, on My Life In The Bush Of Ghosts by David Byrne and Brian Eno, in the first song there is a real push-pull dynamic going on between the rear and front of the soundstage. I had listened to the cd repeatedly before, and had heard all the same noises, but they never grabbed my head and took control, like they do now. With a switching supply, the effects fade in/out without much ado, and I end up focusing on the left to right qualities of the soundstage. It's not that I'm hearing things I never heard in my albums, but rather, hearing things presented in a more interesting way. Don't get me started on how good Nine Inch Nails the Fragile sounds..

[tyler_durden]

Do you know why the output transistors are bolted to that big piece of aluminum that makes up the chassis of the power supply? That is done to cool the output devices. Do you know how it cools them? It cools them by transfering the heat to the surrounding air. Do you know what happens if you put the supply inside a box? You will heat the air inside the box. Do you know what will happen if the air gets too warm? Your power supply will die.

Those supplies are usually installed in equipment that has some air space and fans to move cool air through the cabinet. Unless your installation is that type, you should bolt the smooth side of the supply chassis to your aluminum box (without standoffs!) to transfer the heat out of the supply to your room air.

If you must use a power supply that requires fan cooling, try using a 220VAC fan running on 117VAC (or a 12VDC fan running at 6-8VDC). It will turn slowly and quietly and should provide sufficent air motion to keep a small power supply cool.

On yes, just as your box needs to allow the heat to escape to the outside world, the fan needs to blow air THROUGH the box. That means you must provide holes to allow air flow.

Once you install a fan you will have all the audio maniac questions about vibration, power line noise, and varying magnetic fields from the fan motor and how they will all affect your sound.

You see, you can't win no matter what you do.

TD