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Originally Posted by brucegseidner /img/forum/go_quote.gif
It has been a very long time since I have fired up my soldering iron and made anything. If memory serves it was an early 80's Hafler. My knowlege of power supplies is therefore dated. I remember raiding surplus shops and Ham Fests for very large iron - transformers/chokes and enormous blue caps that could power the oven for a half hour after being unplugged.
Long story short, I think I have goofed up by purchasing a switching power supply in anticipation of building my SSMH. I bought first and am asking questions later. I am learning that these are very sophisticated little buggers and appear not to take kindly to output "filtering" or further regulation. I got a new MEANWELL SR-25-48 48VDC trolling on Ebay and while it is impressively stable in terms of voltage, the max ripple is 200mVp-p.
I am new to these forums and my searches have been like going down rabbit holes. I have been looking for filtering strategies and loading strategies that would optimize a SMPS for this SSMH amp. I think I have painted myself in a corner having only 48VDC coming out of this power supply.
It may end up a cute paperweight but if someone could direct me to information or strategies to clean this DC up I would be much obliged.
Bruce
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Pete Millett strayed from conventional DIY-headphone-amplifier wisdom with his use of a switching power supply for the Starving Student. It's worked quite well, but there is little data of successful use of switching power supplies for headphone amps beyond that (AFAIK).
The Cisco PSA18U is the specified power supply for the Starving Student. It's spec'd for 48VDC at 0.38A and performs quite well in the Starving Student. As a VoIP telephone power supply, it's also ubiquitous on ebay and other places, and very inexpensive - sometimes even turning up in surplus and used sales at some outlets.
Short of that recommendation, you are probably best to pursue a linear-regulated power supply for headphone amps. The simplest of these start with an LM317 (TO-220 style) voltage regulator with a bank of electrolytics for filtering and the parts recommendation as provided in National Semi's datasheet for the LM317. Tangent's TREAD (
Tangentsoft) is probably the simplest PCB version of such a circuit and can be powered with a simple AC walwart. You can easily achieve ripple values of less than 1mV with this (~55uV?). Other more sophisticated designs include Tangent's new Young-Jung Power Supply and AMB's Sigma 11 and Sigma 22 and the ripple is in single-digit microvolts with those. Cetoole and I achieved 45uV in the Millett MiniMAX's onboard power supply as well - using the LM317 circuit as a basis.
However, we often caution everyone in this thread to think twice before expanding on the Starving Student's design. After all, the low cost is a primary design feature. The PCB version increased costs with the addition of the PCB and the custom case from Hammond, but those are mostly structural changes for convenience in building. Dsavitsk applied a couple of new additions to the actual circuit on the SSMH PCB, but these amounted to a couple of pennies's worth of resistors and a couple of dollars for a couple of cathode bypass caps and output bypass film caps. The changes are well worth incorporating and definitely make the amp sound better, but are trivial in cost and added building effort.
Note that we still recommend the same power supply for the PCB version, however - the Cisco PSA18U.
