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Old 25th January 2014, 11:02 AM   #1
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Default Fully Regulated first stages

Here is an idea

Many in many circuits use regulated power supply for the first stages of an amplifier up to the drivers ..benefits of the above are known .

Though in consumer hifi this is only happening in top models since it increases part count but farther more increases the cost of the transformer which is most of the problem .

Idea is like that :

in an integrated amplifier it could exist one trafo that will provide rails for the output for example 35+35 volts ( after the rectification ) while a smaller trafo could provide some 40 +40 ( after rectification ) for the first stages and fully regulated while a second step on the regulator could also provide 18+18 which is needed for the preamplifier ...

If PCb is made properly to host proper grounding and distribution the results could be really very nice ...

Opinions please ?
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Old 25th January 2014, 11:17 AM   #2
AndrewT is offline AndrewT  Scotland
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Yes, the extra transformer with appropriate windings could be used for auxiliary starting and monitoring equipment and for the dedicated front end supply.
This transformer could be permanently powered up when the rear located ON/OFF switch is ON.

The Front ON/Standby switch can use an isolated low voltage DC for "remote" powering of the main transformer.

This arrangement would also suit a "remote ON" facility triggered from a central location, i.e. when a Source is "turned ON", the whole system powers up sequentially and quietly.
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Old 25th January 2014, 11:24 AM   #3
laplace is offline laplace  Australia
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There are a few published amplifier designs/kits from Silicon Chip magazine that work like this and I recently built an older 100W version. It has a 35+35 300VA toroid for the main supply in series with a 12+12 20VA toroid, wired in a 12+35+35+12 arrangement. Final drive is unregulated ~50V (classic rectifier+caps) off the big transformer; everything before the final drive (differential amp, gain stage, etc) is running off linear regulated 55+55V, which gives it incredible PSRR.

I have a 3rd transformer for regulated 15+15 DC for differential line receivers, etc.
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Old 25th January 2014, 11:37 AM   #4
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Voltage doubler - Wikipedia, the free encyclopedia
Voltage doublers supplied by the existing secondaries, and then regulated might supply clean enough voltage/power to the input stages.

Dan.
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Old 25th January 2014, 11:37 AM   #5
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Interesting. I was wondering about doing a regulated front end for my BA3 if I ever get around to starting it, but I was thinking this was going to waste a lot of power if my front end was running lower voltage than the outputs. Putting in a second low VA transformer to do the job is definitely something I will consider! The idea of putting a low voltage traffo in series with the bigger one is even more interesting. Are there any downsides to that? I imagine it would make the job of the regulator harder than if it was a dedicated transformer...

Tony.
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Old 25th January 2014, 11:50 AM   #6
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Since i have been watching some power supplies for preamplifier where 18+18 volts is needed and they do regulate in two steps with LM 317 337 sets where the first set will regulate for example from 40 to 24 volt and while the second set will regulate from 24 to 18 or 15 depending on the application .

The total point is that if you manage to both provide extra regulated rails for the first stages and ultra clean power supply for your preamplifier then the all thing starts to worth looking at better .

Thanks for the input
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Sakis
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Old 25th January 2014, 11:57 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by wintermute View Post
Interesting. I was wondering about doing a regulated front end for my BA3 if I ever get around to starting it, but I was thinking this was going to waste a lot of power if my front end was running lower voltage than the outputs. Putting in a second low VA transformer to do the job is definitely something I will consider! The idea of putting a low voltage traffo in series with the bigger one is even more interesting. Are there any downsides to that? I imagine it would make the job of the regulator harder than if it was a dedicated transformer...

Tony.
series connected prevents that extra winding from performing any other duty. And since most small transformers come with just two secondaries they become dedicated to running at the supply rail voltages, rather than at Audio Ground.

BUT the big saving is in cost and size. Now you could fit two extra transformers.
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Old 25th January 2014, 02:11 PM   #8
Holgi is offline Holgi  Germany
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For months now I'm targeting the AS-44xx series toroids from Antek. Besides the power secondaries they provide additional 15V+15V 2A voltages which give you enough headroom to feed regulated Vcc+10V into the first stages.

The only pain is that shipping cost to Europe is some hundred bucks
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Old 25th January 2014, 02:17 PM   #9
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well you can have your trafos winded in Athens at any size quality and voltage needed The company is ISO/ TUV and CE certified and we have been working with them more than 15 years now their built quality is exceptional !

Their prizes are very fair and i expect snail mail to Germany to cost nothing

Still though this approach will suffer that at full power rails are modulated by the audio signal meaning that part of it may find its way to the first stages through the trafo .

I expect a second trafo to be the best solution for a hi end approach

Kind regards
Sakis
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Old 25th January 2014, 04:55 PM   #10
tvrgeek is offline tvrgeek  United States
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An independent winding or transformer would seem wiser. If doing a MOSFET driver or output, a boosted voltage on the VAS helps. Have you thought about the middle ground? Using a capacitance multiplier?

If you just try to put a regulator on the main rails, even with low drop out regulators, you have to maintain margins at load peaks. So that 60V rail may dip to 50, and you need another 5. 45V VAS? I don't think so unless you design the driver and output stage assuming 45V and forget the 200W amp is really a 100W amp. Maybe not a bad concept. for only the cost of a bigger than normal transformer.
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