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.
The out put impedence is sufficently low for my phones which are 32 ohm. So I do not think I need any additonal impedence matching transformers but simply an attenuator, if that.
if I simply had a speaker a/b switch would that suffice? The low output Z of the amp, will provide sufiicent dampening for the phones, at 32 ohms I guess the phone provide anought load for the amp.
Am I missing something. I dont want to break my amp nor my custom Grado phones.
Cheers, Tony
P.s. maybe volume 4 of Morgan Jones book holds the answer ;-)
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.
The out put impedence is sufficently low for my phones which are 32 ohm. So I do not think I need any additonal impedence matching transformers but simply an attenuator, if that.
if I simply had a speaker a/b switch would that suffice? The low output Z of the amp, will provide sufiicent dampening for the phones, at 32 ohms I guess the phone provide anought load for the amp.
Am I missing something. I dont want to break my amp nor my custom Grado phones.
Cheers, Tony
P.s. maybe volume 4 of Morgan Jones book holds the answer ;-)
yeah, I'd aim a little higher - a 15 ohm parallel will give you 10 plus a bit ohm total load. Thats really just a matter of personal preference - Id rather the Z was set up slightly above the nominal since it has a nasty habit of going low at some frequencies. If you can get a frequency plot of your Grados that will make it a little clearer and your decision more fact-based!
Great points. I intend to build his into a small control box on the side rather than make any direct changes to the amp. I intend that the box will contain speaker output posts, amp inputs, a switch for phone to speaker, so I can keep teh phone plugged in, a fuse for the headphone circuit and the parrellel resistor.
Thank you all.
Thank you all.
Take a look here:
Headphone Adaptor for Power Amplifiers
If you decide to use a fuse, remember to connect the fuse(to your headphones) after the parallel resistor. Otherwise, if the fuse blows, your OPT will become unloaded and will arc itself to death.
Headphone Adaptor for Power Amplifiers
If you decide to use a fuse, remember to connect the fuse(to your headphones) after the parallel resistor. Otherwise, if the fuse blows, your OPT will become unloaded and will arc itself to death.
fuses only prevent fires - seldom "protect" equipment
serious amps have relays or output crowbar circuits to protect speakers - and by extension headphones that cost as much as speakers
a output transformer prevents DC from ever reaching the load
sensitive headphones may be better matched to a audio power amp with a power rated resistive divider
serious amps have relays or output crowbar circuits to protect speakers - and by extension headphones that cost as much as speakers
a output transformer prevents DC from ever reaching the load
sensitive headphones may be better matched to a audio power amp with a power rated resistive divider
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.
Sheldon
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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.
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.
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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