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Old 11th February 2012, 08:08 AM   #11
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Location: Auckland, NZ
well, its flat at that scale...
"It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
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Old 11th February 2012, 08:19 AM   #12
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Man, thats flat. 32 ohms fromdc to daylight, as good as.
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Old 11th February 2012, 03:07 PM   #13
Sheldon is offline Sheldon  United States
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Originally Posted by Roulston View Post
Thanks all.

DB, that circuit seems to be spot on.
Yes, you probably want a resistive divider. And you want it to reduce the output level to the loudest listening level you want - with maybe a little extra margin. This, not just for protection, but unless your amp is designed specifically for very low residual hum (and many single ended DHT amps are not), you are likely to have objectionable hum at low listening levels.


Last edited by Sheldon; 11th February 2012 at 03:12 PM.
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Old 13th February 2012, 09:48 PM   #14
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Don't use Rod Elliott's circuit as-is! It was not meant for a tube amp.

It would load your OPT secondary at 120 ohm instead of 8... not good! The load line would become almost horizontal and negative half-waves could go over maximum allowed dissipation.

Your amp is 10 watt; your headphones can take a maximum of 0.2 watt. You need at least 10*log(10/0.2) = 17dB of attenuation. Let's say 20, to be safe.

Use this calculator: T-Pad / H-Pad Calculator - Resistor Values for Attenuation . Imput impedance 8 to 10 ohm, output impedance around 120 ohm, attenuation - 20-23dB.

I would use R1 = R2 = 5 ohm/10w and R3 = 120 ohm/0.5w.

I don't know if a fuse is really necessary, but if you want one, use a 80mA fast blow.
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Old 14th February 2012, 03:18 AM   #15
ChrisA is offline ChrisA  United States
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Originally Posted by Roulston View Post
I have a small and very nice SET value amplifier that with only about 10 watts gives me all the SQ I need in my DEN.

However ther are times that for reasons of family harmony I would like to be able to listen via heahones instead. My study ajoins the master bedroom and my wife can clear be kept awake.

What you need is a resistor network that will provide an 8 ohm load to the amp. Unless the amp also has taps on the transformer for 16 ohm

A single resistor in parallel likey will not provide enough attenuation. You need an "L-Pad". this is two resistors in the shape of an "L". With a l-pad you can choose the attenuation and impedance independent of each other. The single parrale 10R resister will give close to 8R but will not cut the sound much.

Read this. It's not hard to make
L pad - Wikipedia, the free encyclopedia

Then you want to limit the power so your headphones don't get blown out. You can buy a kind of diode called a Transient Voltage Surge Suppressors. These cost about 25 cents and are just a special kind of zenier diode. They will clip or "limit" the voltage across your headphones and do nothing to the sound if the volume is reasonable. They came on all voltage ratings.

You can put in a fuse but likely it will not be needed if you have the above diodes.

About the l-pad, you can adjust the attenuation to the volume sounds the same as the speakers. So when you plug in the headphones you do not have to adjust the volume control. But you will just have to test with you ears. Look of a calculator like this.
L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin
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Old 14th February 2012, 07:54 PM   #16
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Zeners or TVSS diodes would just clamp the output voltage to square waves, which can kill the headphones.
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