Headphone out mod?

[lexluthier72]

Hey Folks,
Im wondering if there is an easy way to add a headphone out to a champ (5f1) circuit. OR, Does anyone have a simple headphone tube amp schematic/diagram? I did a brief search on this forum and came up short.
-Erin

[carlg]

Even the smallest of guitar amps is more than capable of driving a pair of headphones so you could make a little dummy load + headphone out for silent listening. I have one on my dummy load so I can hear the amp I'm testing if needed.

A champ puts out what, 8 watts? Let's say it's having a good day and does 10W. I think these had a a 4ohm out too, so you've got sqrt( 10W x 4ohm ) = 6.3V on the speaker output. Headphone impedance and power handling vary over a wide range so it'd be best for you to figure out the values for your headphones, but lets say you have 50ohm phones and they can only handle 200mW. How many volts does it take to drive 50ohm phones to 0.2W? sqrt( 0.2W x 50ohm ) = 3.1V max. So lets make the dummy load by dividing the 4ohm load into two 2ohm resistors. Each should handle 5 or 10 watts. At the mid point you know you're not going to see more that 3V so this would be a good place to pick up your headphone out. Adding a volume control might be nice, something like a 10 or 20 ohm pot across that bottom resistor of the dummy load should do the trick.

Hopefully that helps, if you have the impedance and power handling of your phones you can post them here.

[stokes]

Try using an L-Pad.Check this link www.webervst.com/lpad.htm Its got a calculator for the parts you need.Plug it into your output instead of the speaker and out to your headphones.

[lexluthier72]

Hey Guys,
Thanks so far for the suggestions.....I will most definitely try the l-pad....what kind of attenuation am I looking for? Its measured in Db....?
-Erin

[stokes]

I built one for my son about a year or so ago.Dont recall offhand exactly what I did,I'll take a look at it when I can and get back with the specs.

[lexluthier72]

Thanks. My other question would be, do I still need a dummy load to protect the output tranny?
-Erin

[carlg]

I should have made a drawing I guess That L-pad is the same as what I was describing, except the headphones would go where the speaker is. If the two resistors are appropriately sized they will provide the dummy load your amp needs and the junction between them will give the right amount of attenuation to safely connect your headphones. It will sound different through the phones because you don't get the color the speaker provides, but at least you can play at night without waking your granny.

You really should look up the info for your phones though. I used 50ohms as an example because cheaper portable phones tend to be low impedance, but they can be as much as 600 ohms.