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Old 24th November 2010, 01:19 PM   #1
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Default Phone Preamp PSU

Hello everybody,
I'm building a new phono preamp and I'm now working on the PSU, attached there is a first schema.
Based on your experience what do you think about it ? Moreover, since my brother has a lamp shop, I would use 2 lamp transformer (pri 220V sec 11,5V 4A) but I don't know how these can work. So... any suggestion or comment??

Thanks
Francesco
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Old 24th November 2010, 02:35 PM   #2
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by francoiacc View Post
Hello everybody,
I'm building a new phono preamp and I'm now working on the PSU, attached there is a first schema.
Based on your experience what do you think about it ? Moreover, since my brother has a lamp shop, I would use 2 lamp transformer (pri 220V sec 11,5V 4A) but I don't know how these can work. So... any suggestion or comment??
I have no direct experience with back to back transformers, such as you have shown. But I've seen a number of schematics doing something similar. Conceptually, I don't see any problem with it other than some loss of efficiency. Actual noise performance will depend on construction of the transformers.

Sheldon
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Old 24th November 2010, 03:11 PM   #3
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I would add another choke and cap.
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Old 24th November 2010, 03:22 PM   #4
DF96 is online now DF96  England
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Use Duncan's PSU Designer (free download) to model it and see how much ripple you get. Or estimate using a calculator/spreadsheet.
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Old 24th November 2010, 04:54 PM   #5
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I'd suggest adding Salas HV Shunt regulator: Simplistic Mosfet HV Shunt Regs .
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Old 24th November 2010, 05:50 PM   #6
Sheldon is offline Sheldon  United States
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Originally Posted by DF96 View Post
Use Duncan's PSU Designer (free download) to model it and see how much ripple you get. Or estimate using a calculator/spreadsheet.
I guess you'd model it as a 220/220 transformer to get an approximation. Not sure how you'd account for the filament draw or the copper losses in the 12V windings.

Sheldon
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Old 24th November 2010, 06:26 PM   #7
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I would use uf4007's or similar fast diodes instead of in4007's to reduce noise
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Old 24th November 2010, 07:12 PM   #8
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You can connect electr. cap 22 uF between diods and 100 ohm.
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Old 24th November 2010, 07:26 PM   #9
DF96 is online now DF96  England
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In series a cap here will block DC. In parallel a cap will negate the benefit of the resistor and increase peak currents. Which one do you mean?
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Old 24th November 2010, 07:45 PM   #10
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Regarding the diodes I think I'm going to use the BY399, I've found them in a small shop close to me! They are fast recovery type therefore less noisy.
Joshua what is Salas HV Shunt regulator ??
Attached is the heater supply schema with 338K regulator, the zero is raised from the ground in order to reduce any hum due to ground loops.
I did some simulation with psu designer, and modeling the two transformer as a single 220/220 I've a good output without ripple. But this is only a simulation.. it doesn't sound!! My bigger concerning is about the transformers, any experience about using lamp transformer like this??

TRASFORMATORE ELETTRONICO 12V 60W x DICROICHE su eBay.it Trasformatori e Raddrizzatori, Elettronica ed Elettricitą, Audio, TV, Elettronica

thanks
Francesco
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