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Old 16th October 2010, 11:56 AM   #1
cr0wl3y is offline cr0wl3y  United Kingdom
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Default Powering a headphone amplifier with DC filament supply

Hello,

Building a pure valve (in the signal path at least - PSU is solid state) pre-amplifier/mixer and I am in two minds about whether to add a built in headphone out to it or not, for monitoring purposes. One option is to to take the signal from the "tape out" from each channel, mix it using resistors and feature an output with no further gain at the back, which will go into an external headphone amplifier.

Another option is to add the latter inside the mixer. Was thinking that I could use a simple 12-13V design and use the filaments PSU to power it.

The advantages of the latter option are obvious. What I was worried though is that adding more "stuff" to the heaters' power supply line could somehow affect sound quality. I am clearly ignorant about it so any views would be very much appreciated.

Before people suggest it, I am not interested in adding a tube-driven headphone amp to the mixer. Reason is simple - I never listen to music using headphones (unless I'm on the plane or in long train journey) and cannot justify the additional cost, time and space on my mixer this would involve.

Thanks,
Nikos

Last edited by cr0wl3y; 16th October 2010 at 12:02 PM.
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Old 16th October 2010, 01:18 PM   #2
Brit01 is offline Brit01  United Kingdom
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You're looking for a simple FET driven headphone circuit I guess. No experience in this but I believe they are very simple to build and may need 24+ volts to drive them.

There's a web site specific for headphone circuits. Off the top of my head I can't recall but I'm sure someone else will chime in.


You could use the 12volt filament supply with a voltage doubler to supply the FETs I'm assuming, as long as it has enough current.

What's the transformer you're using? Or haven't you got that far yet?
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Old 16th October 2010, 03:51 PM   #3
cr0wl3y is offline cr0wl3y  United Kingdom
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I have - the pre-amp is already built. Problem is I am not sure what transformer I am using, other than what the secondary voltages are. I salvaged it from an ancient valve amp that I picked up on ebay for next to nothing. No idea how to check its rating.
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Old 16th October 2010, 05:27 PM   #4
Brit01 is offline Brit01  United Kingdom
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This is the headphone site:

HeadWize Library - Projects

I'm not too knowledgeable on trannies.
I believe a good indication is the gauge of the secondary. How thick is the wire?
I have 6.3 and 12.6 heater tranny.

12.6 is 4 Amps and very thick wire. 6.3 is about 1.5 amps and much thinner.

Also have a 300mA tranny which has very thin wire.

But there must be a way of measuring the current rating.
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