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Old 4th December 2011, 05:40 PM   #1
frasco is offline frasco  Finland
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Join Date: Nov 2011
Location: Finland
Default One PSU to rule them all!

As I've just started on the path of building amplifiers - the first one is (hopefully) soon finished and the second is at the planning stage - I realized that as all of them need a power supply - which can easily be the most expensive part of the amp - and I obviously only use one amp at a time, it would be very convenient to have just one power supply which would work with most of the projects.

So the question is, if you had to live with just one power supply, what type would you build and why? Type, volts/power etc.. I'm mainly focused on chip amps at the moment but I'm also interested in building tube amps in the future, are there any specific differences between those respective PSU's?
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Old 4th December 2011, 05:52 PM   #2
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Yes, there's a difference between supplying several hundred volts at a few milliamps and few tens of volts at a few amps. Easier to have multiple specific supplies than one configurable one.
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Old 5th December 2011, 08:35 PM   #3
tvrgeek is offline tvrgeek  United States
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Location: Md
The power supply is actually a critical part of the audio circuit. It by definition is in series with your outputs. Detail design, and I mean both physical and electrical, can make or break an amp be it solid state or tube. Why do you think Bryston's sound so good ( or basically, have no sound of their own). Physical design attention to detail! Yea the supply is expensive, but it is half the amp. As tw said, a 6v filament supply and 380V B+ sure is not the same as a 40V chipamp supply. Best do a bit of reading on the subject. ( Actually a tube amp, the supply can be more complex and expensive than the amp by a lot. ) Believe me? My headphone amp is one chip and about a dozen resistors for a cost of maybe 12 bucks. The power supply is is a remote box with the electronics on a 8 x 6 inch board and the parts cost well over 100. Yes, it sounds cleaner and more detailed than a pair of 9V batteries.
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Old 6th December 2011, 11:46 AM   #4
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
For experimental work and testing of a part built project, a universal supply is very useful.

Most chipamps will take +-20Vdc and will switch on and operate properly at this low supply voltage.

You could use a 100VA, 15+15Vac transformer feeding a bridge rectifier and a small bank of smoothing capacitors. This will need a mains fuse and secondary fuses to help prevent damage when inevitably you connect something wrongly.
I would also suggest you have it permanently fed via a Bulb Tester to detect and save mis-wirings.

If you want/need lower DC voltages then either extra transformer windings or chip regulators could give an unlimited range of fixed DC outputs. 4mm output sockets on the front panel to feed projects. Light bulb and ON/OFF switch on the top.

The final integrated PSU must be designed as part of the project. It must not be considered as an "add-on".
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 6th December 2011 at 11:49 AM.
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Old 12th December 2011, 01:03 PM   #5
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what about a simple +-35 volt supply from a bridge and some caps . whit fuses mounted on the front . or overcurrent protection and a

variable part where you take the 5 amp LM338 and the negative counterpart and use that to supply a regulated output . and some pass transistor as a current limiter

then + and - 15 volt rails might come handy 7815 7915
12v 9v 5v

for tube audio look at some sweep tube regulated supplies
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Old 12th December 2011, 03:06 PM   #6
Join Date: Jun 2011
One audio power supply to rule all.....just use a this 500W flyback example which is 91% efficienct.........

500W SMPS for audio

Flyback gives you..........

- great transient response
-coupled inductors for the split rails are in the topology so no external inductors
-No high side drive
-no current sense transformer
-no problems with staircase saturation as in bridge

So your answer is flyback for all audio supplies, regardless of power level......unless you have very tight size constraints, then youll need something else.
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Old 25th January 2013, 11:28 AM   #7
slungu is offline slungu  Germany
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Location: Germany
I plan to do something like this also, since I hope to get one LM3886 based stereo amplifier soon, but would like to use the power supply maybe for other amps too. I am eying a 2x24V 300VA transformer but was wondering how much of the supply should go into the "universal" power supply and how much is left to go into the "variable" amplifier part. If I compare the power supply for a gainclone that has one half-big cap on the PS and then one near the chip for both V+ and V- or the one for the F5 that has a complete CRC I was wondering if my "PSU-box" should only have the transformer, rectifier and then leave the smoothing caps out or build directly the "big" variant, that would be overkill for a chipamp. What is the general opinion on this, or do you guys never build the power supply externally ?

Regards, Stefan
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Old 26th January 2013, 01:41 AM   #8
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You'll get the most useful design answers from simulating the configurations of interest in Spice with an appropriate set of parasitics and working through the amplifier's PSRR to determine what's required to hit your desired SnR/DnR. You'll likely quickly find 1) RC or LC filters need to corner at or above the maximum frequency drawn by a class B load (or the class B portion of a class AB), 2) it's very expensive to build a passive supply where the output stays clean at typical uW or mW home audio power levels, 3) a regulated control loop is more cost effective than throwing bulk capacitance at the problem, 4) class AB chipamps lend themselves to composite amplifiers (often referred to as nested feedback amplifiers here on DIYA; composite is the formal name), 5) point of load regulation is rather useful at audio frequencies, 6) a composite class AB amplifier with a point of load regulated control loop is relatively insensitive to remote supply topology, and 7) ripple is a fairly weak function of typical impedances between the diodes and reservoir caps.

In other words, the 3886 by itself probably isn't going to be all that great and a decent amount of cap close to the bridge doesn't hurt.

Last edited by twest820; 26th January 2013 at 01:49 AM.
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