Blocking Mains DC

regal · 24th December 2009, 11:54 AM

I have two problems with my 120V 60hz mains: Dc around 50 mA and a low frequency ~.05 hz oscillation p-p.5V. I am building a tube hybrid headamp that is very sensitive to passing DC (especially the low freq oscillation), obviously headphones don't like DC.

This schematic

Looks like what I need but I can't find a small 20H choke, anyone know where to look?

Magura · 24th December 2009, 12:04 PM

Simply use a small toroid transformer, using the primary as inductor.

Magura

AndrewT · 24th December 2009, 12:27 PM

the transformer model shown in the ESP circuit includes that 20H as part of the model.
You do not need to add that.

However, all mains voltage varies in frequency and voltage and interference including even harmonics (dc).
The transformer and rectifier converts all that to DC for your hybrid circuit.
The hybrid should be designed to run from any appropriate PSU.

DC blocking is required to save the mains transformer from saturating. It does nothing for the subsequent circuits.

24th December 2009, 11:54 AM	#1
regal diyAudio Member Join Date: Jan 2004 Location: MD	Blocking Mains DC I have two problems with my 120V 60hz mains: Dc around 50 mA and a low frequency ~.05 hz oscillation p-p.5V. I am building a tube hybrid headamp that is very sensitive to passing DC (especially the low freq oscillation), obviously headphones don't like DC. This schematic Looks like what I need but I can't find a small 20H choke, anyone know where to look?

24th December 2009, 12:04 PM	#2
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Simply use a small toroid transformer, using the primary as inductor. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

24th December 2009, 12:27 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the transformer model shown in the ESP circuit includes that 20H as part of the model. You do not need to add that. However, all mains voltage varies in frequency and voltage and interference including even harmonics (dc). The transformer and rectifier converts all that to DC for your hybrid circuit. The hybrid should be designed to run from any appropriate PSU. DC blocking is required to save the mains transformer from saturating. It does nothing for the subsequent circuits. __________________ regards Andrew T.

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