Son of Dork: Power Supply - diyAudio
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Old 17th May 2002, 09:44 PM   #1
dorkus is offline dorkus  United States
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Default Son of Dork: Power Supply

The Son of Dork (SOD) project is the result of the diyAudio.com multi-channel preamp initiative (The diyAudio.com preamp project!). The project has been split into threads dedicated to discussion of the preamp's different functional units:

- General Discussion (project status, functional requirements)
- Active Circuitry
- Attenuator
- Power Supply
- Connections and Layout (including input switching)
- Chassis and Construction
- Hardware Logic, Controls, Display
- Microprocessor (programming, implementation)

I will be managing the project as a whole, as well as initially overseeing individual threads. For a background on the project, please see the original thread referenced above. A website dedicated to the project will be located at http://dorkus.org/diy/sod.

Let the fun begin!
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Old 17th May 2002, 10:12 PM   #2
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Default power supply?

so, each preamp module (which includes input switching, attenuation, and gain stages) will have local regulation on-board near the signal circuitry. the type of regulation is up for debate, but i sense a general distaste for active regulators, so probably some sort of passive/shunt regulation will be used.

as for the main DC supply, i think a single very large supply feeding all preamp modules (up to 6) would work fine. some people may object and want separate transformers, rectifiers, etc. for each channel, but that would be a huge pain with 6 channels. besides, i think a single supply with 6x the VA transformer and 6x the supply capacitance with 6x the load has some advantages over 6 individual, proportionately smaller supplies (we can lower output impedance and less ripple for one).

i would like the main supply to be choke-regulated, probably in a traditional choke-input filter config. it has some desirable characteristics (reduced turn-on surge, reduced transient currents on transformer, longer capacitor life), and as long as we can ensure min. current draw for the given inductance and a low-enough resonant frequency i think it should work ok. the superior regulation over a regular capacitor-input filter also will allow for much more efficient operation of the down-stream shunt regulators. thoughts?
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Old 18th May 2002, 12:12 AM   #3
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Default Power supply considerations

Shunt regulators are inherently inefficient as are heavily biased Mosfet stages. Efficiency of the unreglated power supply seems like a moot point in consideration that most of power dissapation will be in the gain modules and local supply regulation when using series or shunt regulators. Your desire to drive 600 ohm loads will call be some fairly highly baised mosfet drivers in the gain modules. I would plan on some very good heatsinking and ventilation.

H.H.
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Old 18th May 2002, 04:18 AM   #4
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i would like the circuit to be capable of driving 600 ohm loads, but in practice it will not be driving anything near that low a load (at least in my system). my front amp has 100k input impedance, my rear amp 10k, and i doubt i will be hooking up anything lower than that. i just feel that low impedance drive capability translates to better dynamic performance into normal impedances. let's assume the final target load is 10k however.
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Old 19th May 2002, 10:03 PM   #5
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Given that this is a preamp design, my feeling is that a watt or two here and there aren't going to be a problem.
By all means, burn an extra watt if it makes it sound better.
For a power amp...that's another question entirely. Yes, I'm willing to go the extra bit to do class A with all the inherent waste heat, but it may not be to everyone's liking.
I know Jam is hot (pun intended) on the shunt regulator idea, but I have no opinion, myself, not having tried one against a series regulator. If the active circuitry ends up being discriminating enough, it might provide an interesting test bed for shunt vs. series regulation, but that would imply a separate regulator (not necessarily at great distance; surely within the same chassis) that could be swapped in and out.
That goes back to how modular you want this thing to be.

Grey
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Old 20th May 2002, 12:54 PM   #6
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To obtain a truely modular system, the power supply could be variable to allow for those who wish to (say) try out op-amp circuits as well as higher voltage discrete circuits (wouldn't be me, but there are obviously those who might).

Perhaps a variac in there? Wouldn't have to be too expensive, as small surplus variacs are widely available very cheaply. How that would fit with a regulated supply is moot, though (but presumably would just require some tweaking of component values).

It would have the benefit (if it is possible to still achieve the desired other characteristics) of giving an adaptive platform for future "plug and play" experimentation with gain stages.

Just a suggestion. Seems like if the rest of the pre-amp is going to be as ambitious as it seems, it would be a waste not to ensure that the all the peripheral (control, etc) design and build effort could still be used if the "newest and bestest" gain stage uses a different supply voltage (within reason, of course).

Jake
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Old 20th May 2002, 02:37 PM   #7
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Default Shunt Regs!

Like all regulators shunt regulators work best when placed close to the gain stage. If we keep the voltages and current draw reasonable we should be able to place the regulator on the same PCB.

Jam
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Old 20th May 2002, 03:42 PM   #8
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Smile voltages and current draw reasonable

You mean 50 volt rails and the ability to drive 600 loads?
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Old 20th May 2002, 04:09 PM   #9
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Default He's Back!

No! 25v rails . If 600ohm loads are required the buffers could configored as a comp. pairs.

Jam
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Old 20th May 2002, 04:14 PM   #10
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As I recall the last target was 10k, not 600ohm.
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