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-   -   Regulated power supplies (http://www.diyaudio.com/forums/solid-state/569-regulated-power-supplies.html)

Jason Hubbard 14th August 2001 04:54 PM

I'm considering a regulated power supply for whatever my next amplifier ultimately turns out to be. My last amplifier (early JLH 10 watt SE) had a small buzz in the speakers which i reckoned could be removed with a regulated power supply - this became an "accredited" solution to the later revisions to the amplifier.

I have heard that regulated power supplies tend to reduce bass extension and generally strangle the soundstage a bit, but after reading Nelson Pass power supply article i thought about how this might be eradicated with some over-speccing of the supply.

I'm contemplating using multiple LT1084 regulators, each preceded by a 58,000uf capacitor (because i have lots available) and another 58,000uf capacitor connected to the output closeby the output transistor array.

I'm hoping that the capacitors downstream of the regulators will be safely charged via a current limited supply (max 5A) without the regulators shutting down (anyone have any experience of this?), not decided on how to limit the current surge to the pre-regulation capacitors, possibly a relay/timer/surge resistor combo.

Is this worth doing or pointless given that class A SE amplifiers are fed from a CCS anyway?

Yoda 14th August 2001 06:02 PM

Why dont oyu try a capacitance multiplier supply outlined at the ESP site (www.sound.au.com) I have one feeding a small class A, and I have no hum at all, it might also be due to the balanced interconnects that I have... but their is NO hum at all, i even tested it with a very sensitive oscilliscope. Also, do you have a toroidal trans? I hear they have lower noise/hum and stuff. I wouldn't know, i've never used a convemtional in an audio project. One last thing, how many of these 58KuF caps do you have? Have you considered a "battery" PS? I've never used one, but its an option if you have lots of caps... one downside, you have to pause music every 10-15 mins to "recharge" the caps... bummer

HDTVman 14th August 2001 10:17 PM

The cap multplier / zenor refference supply Yoda suggests is a very good idea. The only thing I would add is, design the supply for 50% to 100% more peak current than the amp requires. That way the power supply will always be able to deliver more that enough current to the amp. I would use a small value (220uf to 1000uf )at the power supply connection to the board but not at the output devices, and 4700uf at the output of the supply. Very large caps on the output of any regulator can cause problems for the regulator. Remember to use interconnect wire from P.S. to Amp. outputs that is as good as or better than the speaker cables you use. The signal current delivered to the speakers come from the power supply after all.

Bruce

GRollins 14th August 2001 10:55 PM

I'm in favor of using fairly large amounts of capacitance after the regulator circuit. That way the sound of the caps swamps the sound of the regulator circuit, laying to rest complaints that regulators "don't sound good." It also serves to buffer the current demands of the circuit, allowing more leeway in the design of the regulator.

Grey

ppl 15th August 2001 06:25 AM

I am also a big fan of large capacitors after the regulator stage. I also noticed a trend away from this as it may reduce the Speed of a high performance Wide-bandwidth regulator Circuit.It seems alot of folks are in favor of using just small film type capacitors and High Speed Shunt type regulators.I would be most interested in other Thoughts on this.

Jason Hubbard 15th August 2001 08:04 AM

Prefer real caps to cap multiplier
 
I want to have a bottomless pit of energy available to the output devices - if they each have 58,000uf to draw from then i figure that's about as good as i can make it.

The cap multiplier is not going to be capable of delivering instantaneous current in this fashion, but then is that going to be a requirement given that the amplifier will draw a constant current?

Has anyone who has connected large post regulation caps had problems with the regulators shutting down, etc?

HDTVman 15th August 2001 03:08 PM

If the amp. has constant current draw then a large well of current is not required, just clean DC. Still, always over design the power supply. If you need 5 amps DC build it to deliver 7, 8 or even 10 amps. This means the transformer, rectifiers and a very large cap on the input to the regulator (your deep well of curent). Make it very fast, use hight speed series pass transistors. Use a stable reference voltage (a correctly done zenor diode reference is fine). Use a high current gain configuration like a darlington stack so that the base current in the zenor circuit stays within the zenor regulation range.

This is a brute force type of regulator NOT some feedback type which I agree would sound bad.

Bruce

grataku 15th August 2001 03:14 PM

Jason
you can always try to increase the time delay of the regulator to try and charge the capacitors more slowly. You can do that by building a simple regulator using extra power amp transisors, a zener and a few other components instead of LT1084 Usually power transistror are more sturdy than regulators. That's what I am doing for my 30W HIRAGA amp (which I am testing today!! eh eh eh! ;-)). You can build an adjustable version to compensate for the slightly different characteristics of the zeners.
The capacitance multiplier has to be one of the biggest scum in the history of electronics. If you can see past the misleading name what the circuit is doing is reducing the ripple by dropping the voltage. Since there is NO way to get something for nothing, the energy storage (ie physical "capacitance") is NOT really there.

Jason Hubbard 15th August 2001 05:23 PM

Cap Multiplier
 
I knew that a cap multiplier circuit only gave "virtual" capacitance and had no stored energy and therefore already excluded it in favour of a regulator/big cap design.

I am also a little more enlightened (thanks Geoff) regarding the current requirements of the output devices for an SE amplifier running from dual voltage rails which has strengthened my desire to use a really big regulated supply.

I was considering soft starting the post regulator caps by ramping up the adjust pin on the regulator over a few seconds, the pre-regulator caps could be slow fed via a thermistor or two in the supply line to the toroid.

Still don't know if the regs will holds out with that amount of capacitance on the end of them though...

HDTVman 15th August 2001 10:54 PM

Don't all linear regulators reduce hum by dropping the output voltage below the ripple, or does magic come into play here?

Isn't the goal of any good power supply;

1. Very low output impedance at the frequency specturm present in the load.
2. More than enough current reserve to supply the load's needs.
3. A stable voltage output.

I have used Zenor referenced, cap filtered, non-feedback, series pass type power supplies with 100 to 500 watt RF power amps for years. They work better than any other type I've tried. Unless you spend a lot of money on a HP or Lamda.

Yes, you do need a big cap but it goes in front of the regulator to provide the extra current required when the transformer reaches it's limit.


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