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Old 6th August 2007, 11:03 AM   #1
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Default No transformer power supply

With the power transformer usually costing the largest part of an amplifier budget -- could it not be eliminated. If a fully regulated psu is built with proper isolation could not a mains supplied psu function as well. I am new to this, however it seems that a great deal of though goes into building a clean psu. By regulating the voltage to what ever is needed and using discrete components to clean up the signal -- would it be feasible.
 
Old 6th August 2007, 11:13 AM   #2
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With the power transformer usually costing the largest part of an amplifier budget...
Coffins are pricier.
 
Old 6th August 2007, 11:24 AM   #3
suzyj is offline suzyj  Australia-Aboriginal
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What would you use for isolation? Apart from a transformer?
 
Old 6th August 2007, 11:44 AM   #4
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high-tech switching power supply
3600Wattsrms whit a small transformer
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Old 6th August 2007, 01:34 PM   #5
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That is the point i am trying to make with this thread. If we have to clean up all of the noise from the rectifier and smooth out the ripple with large electrolytics why not just smooth out the initial mains power. If adequate fuse protection is used and good electrical design employed why would the circuit need to be isolated.
Their is already a huge source of current at the terminals of the electrolytics -- transformer or not. With a heavily regulated supply there is some amount of isolation taking place. I am not an electrical engineer i just proposed this idea as a learning experience. Is not that what we all proposed to gain from this forum -- input and knowledge exchange. Transformers are heavy, expensive, and generate large extraneous electrical fields. Most discrete components are relatively cheap, lightweight, and diverse. thanks for the input. I believe early on Nelson Pass used mains power in some of his amplifier experiments.

Tad
 
Old 6th August 2007, 02:03 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
the inside of televisions and inside a computer power supply are just like this.dangerous No body goes inside these while powered up unless they really know what they are letting themselves in for.
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Old 6th August 2007, 02:04 PM   #7
ilimzn is offline ilimzn  Croatia
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i am not sure you grasp the concept of a closed circuit (or current loop if you wish) in it's entirety, what it is that makes current flow from a source, and what a transformer actually does. Smoothing the mains supply is as easy/difficult as smoothing a different voltage obtained through a transformer - six of one, half dozen of the other type of thing. Some valuse scale up, others scale down correspondingly.
 
Old 6th August 2007, 02:08 PM   #8
ilimzn is offline ilimzn  Croatia
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Originally posted by AndrewT
Hi,
the inside of televisions and inside a computer power supply are just like this.dangerous No body goes inside these while powered up unless they really know what they are letting themselves in for.
Not entirely true. Actually, these days, probably not true at all. old tube TVs with series wired heaters and so called 'live chasis' were not isoplated from the mains, but everything on the case had to be isolated. Touching the chasis and earth could kill you.
Computer supplies are mains isolated, as are switching power supplies in Tv sets (and a whole lot of other appliances). They have a part that is connected to the mains, just as a transformer has a primary connected to the mains. You would not go poking around with the primary connection of a transformer under power, would you? Just the same, one would not go poking around the primary side of the switching power supply. The fact that a lot more is electronically going on there compared to a transforemer really makes no signifficant difference in how dangerous it is when tackled under power.
 
Old 6th August 2007, 02:28 PM   #9
AndrewT is offline AndrewT  Scotland
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Originally posted by ilimzn
Not entirely true. Actually, these days, probably not true at all. old tube TVs with series wired heaters and so called 'live chasis' were not isoplated from the mains, but everything on the case had to be isolated.
Modern TVs use a mains charged cap @ ~400Vdc direct off the mains to feed the PSU. There is no enclosing box to protect the finger poker.
The plastic casing around the TV is the isolation.

I would not like that type of supply in any of my power amps. Mostly because of all the conductive parts that exit/enter the amp to/from the outside world.
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Old 6th August 2007, 03:40 PM   #10
Eva is offline Eva  Spain
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For low and medium power audio (and signal processing), in consumer applications, where supply rails well below +/-100V are involved, I think that power supply mains isolation brings huge benefits and must be mandatory because the audio voltages are considerably lower than the mains voltages themselves, and the risk of being shocked is reduced to almost nothing.

However, in very high power audio, in professional applications, when rails well over +/-100V are involved and their center tap is earthed, power supply isolation brings little or no safety improvement because those voltages are as lethal as the own mains voltages. In other words, if you touch +/-150V or +/-200V DC rails (or even the output posts of such an amplifier) you will receive a potentially lethal shock no matter if the PSU is isolated or not. Note that DC is substantially more lethal than AC.

For example: At present I'm working in a very high power class-D module (professional use) with +/-208V rails and I dropped power supply mains isolation due to size and weight constraints. The audio signal is isolated instead, with the help of 0.01% max. THD special linear optocouplers (Agilent HCNR200). The case and the heatsink are earthed as usual. Such a design should pass safety approvals.
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