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Old 6th January 2015, 02:13 PM   #1
yaka24 is offline yaka24  United States
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Default Question about powersupplies in integrated amps

Hi I'm planning on building a lm3886 but would like to include a phono preamp inside as well.

How can I handle the power supplies so I don't have 2 power cables plugged into the amp? I currently have a chipamp built with this transformer
Avel Y236503 160VA 22V+22V Toroidal Transformer

and will look to repurpose it in the new build. For the phono preamp I was thinking of something simple such as this: Velleman K2573 RIAA Stereo Phono Preamplifier Kit
which requires :
Specifications: Required power supply: 10~30 VDC regulated (not included) Current consumption: 5 mA (typical) Equalization curve: RIAA standard Input impedance: 47K Input signal: 5-10 mV PCB dimensions: 1-5/8" x 2-1/4".
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Old 6th January 2015, 02:35 PM   #2
AndrewT is offline AndrewT  Scotland
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Put the phono pre-amp as close to the TT arm exit as you can manage.

Then take the amplified output at "line Level" to a convenient volume control location and finally take that Buffered "line level" output to the Power Amplifier located at the Speaker's terminals.
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Old 6th January 2015, 03:31 PM   #3
yaka24 is offline yaka24  United States
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I get that part of it.. My confusion is how I avoid having both an IEC Cord and DC Jack BOTH being plugged into the chassis.
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Old 7th January 2015, 06:54 AM   #4
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The DC socket has an integral leaf switch for such purposes, on the barrel contact.

Gajanan Phadte
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Old 7th January 2015, 02:43 PM   #5
yaka24 is offline yaka24  United States
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Sorry! I'm still a little confused....

SO I have to keep the power brick for the Phono Preamp inside the chassis? and use the integral switch how?
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Old 7th January 2015, 10:07 PM   #6
infinia is offline infinia  United States
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I would add a little power supply regulator like this Series Voltage Regulator | Series Pass Regulator | Tutorial
use a 15V zener and a 60V npn transistor, connect the input to the chip amps + V rail at the big cap. and the output to the Vellman.
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Old 7th January 2015, 10:46 PM   #7
infinia is offline infinia  United States
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here a better pre amp than the Vellman requires 2 for stereo. Hi-Fi RIAA Phono Preamp
use a pnp transistor with the same circuit I linked to above to supply the -15 V.
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Old 8th January 2015, 04:13 AM   #8
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Quote:
Originally Posted by yaka24 View Post
I get that part of it.. My confusion is how I avoid having both an IEC Cord and DC Jack BOTH being plugged into the chassis.
You have to elaborate the statement so that we understand clearly. More details, the better.

Gajanan Phadte
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Old 8th January 2015, 02:01 PM   #9
yaka24 is offline yaka24  United States
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Quote:
Originally Posted by infinia View Post
I would add a little power supply regulator like this Series Voltage Regulator | Series Pass Regulator | Tutorial
use a 15V zener and a 60V npn transistor, connect the input to the chip amps + V rail at the big cap. and the output to the Vellman.

This is very helpful. Thank you.
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Old 8th January 2015, 02:10 PM   #10
Mooly is offline Mooly  United Kingdom
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Such a low current consumption means you can use a very simple shunt regulator (which has excellent performance) consisting of a series resistor and zener diode (of say 18 volts) to ground, fed from the chip amps positive rail.

Super simple and great performance.
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