SPMSU for heater supplies

ruffrecords · 11th July 2009, 05:36 PM

I am building an audio mixer that uses 9 pairs of tubes and the heaters take 12V at a total of 5.4 amps dc. I don't fancy building a single 6amp 12V linear regulator so as I see it I have a couple of choices.

1. Build nine separate 1 amp or 5 separate 2 amp regulators - a bit cumbersome but workable.

2. Use an off the shelf 12V SMPSU. I have looked at a few examples. Most seem to switch at around 25KHz and at rated current have about 200mV pp ripple on the output (content unspecified but I bet there's some 25KHz in there).

As a low cost, small size way of achieving what I want an SMPSU seems the way to go but this 25KHz power circuit worries me. OK, the PSU will be in a separate screened box some way from the mixer's sensitive circuits but still am am a little concerned.

Anyone have any experience of using SMPSUs for heater supplies in low level audio or any other comments or ideas??

Cheers

Ian

Enzo · 11th July 2009, 07:46 PM

18 12AX7s at .15A each makes 2.7 amps, so I assume you are using a different tube.

Heater current doesn't vary much, once established at a voltage level, is it really necessary to have it regulated?

If you are concerned with 200mv of ripple on your heaters, then slap an additional filter stage on the 12v coming out of that SMPS. Since one can make a darn quiet preamp with 6VAC on the heaters using good engineering practice, 200mv doesn't sound like much of a threat, after all 6VAC is nothing but ripple.

Lingwendil · 12th July 2009, 06:57 PM

You could use a 32 ~36v transformer, rectified, and and run the tubes in three parallel strings of three each with a resistor (or RC filter) in series with each string. That would let you use a lower current transformer, and less dissipation in a regulator. What circuit are you building, and what tubes are you using?

Zero Cool · 12th July 2009, 07:11 PM

I have interest in using a SMPS for filaments too. I need to run 20 tubes at 6.3v at 2.5 amps each! that's 50 amps of 6.3v. if anyone has info on a supply if that nature, please let me know.

Richard Ellis · 12th July 2009, 08:52 PM

I would look into parting out a full size automotive battery charger....perhaps one could run regulators for...lets say three per regulator. I would be leery of running it at full load however as most of these chargers have a low duty cycle. Besides the transformers of this size & rating tend to be very.."buzzy".
_________________________________________________R ick.....

11th July 2009, 05:36 PM	#1
ruffrecords diyAudio Member Join Date: Jun 2007 Location: Holt, Norfolk	SPMSU for heater supplies I am building an audio mixer that uses 9 pairs of tubes and the heaters take 12V at a total of 5.4 amps dc. I don't fancy building a single 6amp 12V linear regulator so as I see it I have a couple of choices. 1. Build nine separate 1 amp or 5 separate 2 amp regulators - a bit cumbersome but workable. 2. Use an off the shelf 12V SMPSU. I have looked at a few examples. Most seem to switch at around 25KHz and at rated current have about 200mV pp ripple on the output (content unspecified but I bet there's some 25KHz in there). As a low cost, small size way of achieving what I want an SMPSU seems the way to go but this 25KHz power circuit worries me. OK, the PSU will be in a separate screened box some way from the mixer's sensitive circuits but still am am a little concerned. Anyone have any experience of using SMPSUs for heater supplies in low level audio or any other comments or ideas?? Cheers Ian __________________ Ian

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11th July 2009, 07:46 PM	#2
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	18 12AX7s at .15A each makes 2.7 amps, so I assume you are using a different tube. Heater current doesn't vary much, once established at a voltage level, is it really necessary to have it regulated? If you are concerned with 200mv of ripple on your heaters, then slap an additional filter stage on the 12v coming out of that SMPS. Since one can make a darn quiet preamp with 6VAC on the heaters using good engineering practice, 200mv doesn't sound like much of a threat, after all 6VAC is nothing but ripple.

12th July 2009, 06:57 PM	#3
Lingwendil diyAudio Member Join Date: Apr 2008	You could use a 32 ~36v transformer, rectified, and and run the tubes in three parallel strings of three each with a resistor (or RC filter) in series with each string. That would let you use a lower current transformer, and less dissipation in a regulator. What circuit are you building, and what tubes are you using?

12th July 2009, 07:11 PM	#4
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	I have interest in using a SMPS for filaments too. I need to run 20 tubes at 6.3v at 2.5 amps each! that's 50 amps of 6.3v. if anyone has info on a supply if that nature, please let me know.

12th July 2009, 08:52 PM	#5
Richard Ellis diyAudio Member Join Date: Sep 2006 Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.	I would look into parting out a full size automotive battery charger....perhaps one could run regulators for...lets say three per regulator. I would be leery of running it at full load however as most of these chargers have a low duty cycle. Besides the transformers of this size & rating tend to be very.."buzzy". _________________________________________________R ick.....

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