headphone out for tube amp

[Papa Jim]

I thought this was a pretty cool thing I came across for anyone wanting to do this with their build.
https://robrobinette.com/RobinetteBox.htm

[Tony Bones]

I don't have a problem with resistive loads, but I think it's important to point out that those 5W 6 ohm resistors buried inside a closed box will not handle anything larger than a Fender Champ. Maybe not even that.

[Papa Jim]

It say's ANY amp.  You'd need to take that up with Rob.

[Tony Bones]

The laws of physics work the same in Rob's workshop as yours and mine. I think he might have meant this device to be used with a stereo hi-fi where you would turn up the volume only enough to get the desired SPL out of the headphones. Anyone that plugs this into a guitar amp and dimes it will blow those resistors and their ears.

If I were to build something like this into a guitar amp I would use a circuit closer to that at the bottom of Rob's page (Basic Speaker Amp to Headphone Adapter Box Attenuator) but use a 6 ohm resistor rated at least 3x and a 2 ohm rated at least 2x the maximum output power of the amp. That won't blow the resistors, but it will still blow your eardrums if you dime the amp. The solution to that is an adjustable L-Pad. The fixed resistor are just a fixed L-Pad. The adjustable one acts like a master volume so you can crank the amp as much as desired and then adjust the output for desired SPL.

Unfortunately, I have not found a jack that will switch out the speaker with headphones plugged in and completely switch out the L-Pad without anything plugged in. Note that Rob's box has a bypass switch to switch out the L-Pad but leaves the speakers connected all the time. This means the speakers are not only blaring even when you're wearing headphones, but it puts both the headphones (L-Pad) and the speakers in parallel as loads to the amp. Makes no sense to me, especially with a tube amp.

[Papa Jim]

Cool. I will take a look at that other circuit. Thanks.

[shooter]

archived but not tried, yet

[MFowler]

Jeff Bobber - Ask Amp Man put out this head phone circuit and I tried it and it worked well.