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Regulated DC PSU - Plain and simple please?
Regulated DC PSU - Plain and simple please?
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Old 15th June 2008, 05:49 PM   #1
GlidingDutchman is offline GlidingDutchman  South Africa
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Default Regulated DC PSU - Plain and simple please?

Hi there

Sorry for this dumb question but I need some pointers on a simple, regulated PSU that produces 0 - 12v DC.

It is a for a single ended amp that I built but a standard bridge rectifier induces too much buzz in the system

Thanx

Dewald
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Old 15th June 2008, 06:11 PM   #2
Mooly is offline Mooly  United Kingdom
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Regulated DC PSU - Plain and simple please?
Hi,
Do you mean a single fixed 12Volt supply. How much current does it need to supply ?
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Old 15th June 2008, 06:45 PM   #3
AndrewT is offline AndrewT  Scotland
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Default Re: Regulated DC PSU - Plain and simple please?

Quote:
Originally posted by GlidingDutchman
.......I need some pointers on a simple, regulated PSU that produces 0 - 12v DC.

It is a for a single ended amp that I built but a standard bridge rectifier induces too much buzz in the system.......
That symptom does not sound like it's the fault of the rectifier. I would more likely expect a wiring/construction fault.
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Old 15th June 2008, 08:03 PM   #4
GlidingDutchman is offline GlidingDutchman  South Africa
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Default Re: Re: Regulated DC PSU - Plain and simple please?

Quote:
Originally posted by AndrewT
That symptom does not sound like it's the fault of the rectifier. I would more likely expect a wiring/construction fault.
No, I dont think so as the amplifier circuit works just fine on the makeshift PSU from a PC and from the battery.

D

Mooley, I think a 15VA to 25VA system would suffice.

D
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Old 15th June 2008, 08:07 PM   #5
dave_gerecke is offline dave_gerecke  United States
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Hello GD, what are you using for filtering of the rectified DC. If you don't have a ground issue, as AndrewT implied, then you probably need more capacitance in your supply filter. Or maybe a CLC type filter.

Peace,

Dave
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Old 15th June 2008, 08:14 PM   #6
GlidingDutchman is offline GlidingDutchman  South Africa
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Quote:
Originally posted by dave_gerecke
Hello GD, what are you using for filtering of the rectified DC. If you don't have a ground issue, as AndrewT implied, then you probably need more capacitance in your supply filter. Or maybe a CLC type filter.

Peace,

Dave
Hi Dave

I have a single 63v - 10000uF cap on the supply rails as well as a propper rectifier bridge but the 50Hz buzz is terrable. When I switch to the old PC power supply the amp is dead quiet.

What regulator transistors would you recommend? I think it would be worth while to do a popper PSU for this amp... see attached.
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File Type: jpg class a se v04 amp - ss.jpg (12.1 KB, 861 views)
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Old 15th June 2008, 08:24 PM   #7
Andre Visser is offline Andre Visser  South Africa
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Hi Dewald

What is the transformer voltage and current ratings?
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Old 15th June 2008, 08:33 PM   #8
Nordic is offline Nordic  South Africa
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Hi Dewald...

It looks like a class A output... drawing about 0.6A

A start would be to look at doing a capacitance multiplier.... have a look at Rod Elliot's site...

Alternatively you could look at a fixed linear regulator like 7812 in TO220 package, good for about 1.5A up to 10V drop from supply rails...

Or with slightly better noise figures an adjustable reg like the LM317.

Download datasheets for both from google an read through it...

The regulated supply I posted on the Chipamp section recently is a step up, and with a nice 12VAC transformer a 12V zener and a hetsink that can deal with the 3W of dissipation, it should work sweet. It is a combination of a voltage regulator and capacitance multiplier...

Dewald's 15 to 25VA looks like enough headroom...

That circuit has an intrinsicaly low noise rejection, so you need a good supply. And will be pretty hard to get buzz free while shareing a transformer between channels
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Old 15th June 2008, 08:36 PM   #9
dave_gerecke is offline dave_gerecke  United States
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Hello Dewald, Andre Visser brings up a good point. If you are working the transformer too hard, this can contribute noise. It doesn't sound like you need more capacitance. Perhaps as Andre suggested, you should check the trafo. You could also go overboard and move the PS section into a separate case. This would tell you if you have an isolation issue. If you do decide to go with a regulated supply, for the voltage and VA rating you list, you should be able to use an LM317 or LT1085 regulator chip. You could build a regulator from discreet components also. If you take that route, I would use a 2N3055, easy to get, cheap, and handles a good amount of power.

Peace,

Dave

P.S. How is your ground setup? If possible, go with a star ground format, and isolate your safety ground from your circuit ground with a bridge rectifier or NTC, ala Nelson Pass Zen amps.
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Old 15th June 2008, 08:42 PM   #10
GlidingDutchman is offline GlidingDutchman  South Africa
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Guys

The transfo puts out 14.5V DC (Internal bridge rectifier) - this is a stand-alone "transformer" that I use in my workshop to power all kinds of stuff...

The ground scheme is not the culprit as the transformers windings are totally isolated.

I just think a simple regulator scheme will do the trick - dont you?

You say a 3055 ss? I have plenty of them in stock - how should I go about building a regulator?

D
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