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Old 9th February 2016, 12:53 AM   #1
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Default Standalone Phono PSU, cable to carry AC or DC?

I am having to build a standalone PSU to remove the transformer hum that has plagued a recent phono build since the start (I tried to pack too much into a small enclosure).

The standalone PSU will house a transformer which is connected to a XLR jack which in turn will connect to the PSU input on my phono stage enclosure.

The question:

Should the XLR cable carry AC (12V-0V-12V) and have the rectifying done inside the phono stage?

or

Should the AC be rectified in the PSU standalone enclosure and then sent over the XLR in the form of DC (+12V/-12V) to be filtered and regulated in the phono enclosure?

or

Does it matter?
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Old 9th February 2016, 01:22 AM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by ChrisM91 View Post
Should the AC be rectified in the PSU standalone enclosure and then sent over the XLR
in the form of DC (+12V/-12V) to be filtered and regulated in the phono enclosure?
The RIAA circuit should be quieter with a DC input to the enclosure.

Last edited by rayma; 9th February 2016 at 01:25 AM.
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Old 9th February 2016, 01:40 AM   #3
kevinkr is offline kevinkr  United States
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Definitely go for DC to the pre-amp, eliminating any AC to the unit can only help make it quieter.
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Old 9th February 2016, 01:47 AM   #4
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That's what I was thinking but thanks for the confirmation!

So I will rectify it before taking it to the preamp. Any need to filter it at all?
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Old 9th February 2016, 01:50 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by ChrisM91 View Post
I will rectify it before taking it to the preamp. Any need to filter it at all?
Yes, filter with a CRC.
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Old 9th February 2016, 02:20 AM   #6
kevinkr is offline kevinkr  United States
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Absolutely as Ray suggests or CLC if you are feeling a little more spendy.
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Old 9th February 2016, 02:23 AM   #7
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I have a CRC - Regulator - CLCLC in the phono preamp.

You think I need more in the PSU box other than a filter cap?
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Old 9th February 2016, 02:31 AM   #8
rayma is offline rayma  United States
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Originally Posted by kevinkr View Post
Absolutely as Ray suggests or CLC if you are feeling a little more spendy.
To max out the benefit, also have two floating DC voltages (from two separate, isolated transformer secondaries),
brought into the RIAA enclosure as 4 wires, before connecting the two commons together.

Last edited by rayma; 9th February 2016 at 02:45 AM.
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Old 9th February 2016, 02:37 AM   #9
rayma is offline rayma  United States
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Originally Posted by ChrisM91 View Post
You think I need more in the PSU box other than a filter cap?
A rectifier and filter cap still has significant 120 Hz (and harmonics) of ripple. You want to keep that out of the RIAA box.
An RC or LC filter before leaving the power supply box can reduce that ripple by an order of magnitude, or more.
Remember how small the phono cartridge signal is.

Last edited by rayma; 9th February 2016 at 02:46 AM.
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Old 9th February 2016, 02:58 AM   #10
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Originally Posted by rayma View Post
A rectifier and filter cap still has significant 120 Hz (and harmonics) of ripple. You want to keep that out of the RIAA box.
An RC or LC filter before leaving the power supply box can reduce that ripple by an order of magnitude, or more.
Remember how small the phono cartridge signal is.
Ill add a 100uF-47R-220uF filter
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