Add headphone tap to a Champ

[sluckey]

What would happen if I connected the resistor inline with the headphone signal instead? Would that affect the volume? Or something bad?

You should leave the 8Ω/25W resistor as is (like Rob's schematic). But you do need a series resistor (between the speaker jack and the headphone jack) to drop the volume and also protect those headphones. I see the Sony MDR7506 is 63Ω impedance and since you probably have the headphone jack jumpered for sound in each ear, the total impedance would be 31.5Ω. I would start with a 100Ω series resistor and experiment to find the value that drops the volume to a pleasing level. May have to increase or decrease the 100Ω.

A Champ amp is inherently hummy due to the cheap design. It was a student practice amp and the cheap 8" speaker did not reproduce the low frequency hum very well, so no need to spend money to improve. Fender wanted you to buy a bigger, hum free amp. There's an easy way to upgrade a Champ to lower the hum. Just add another filter cap and a choke. Cost should be under $25.

[glass54]

Last post by PRR is TOTALLY CORRECT. All of us were trying to guide you to get the best Headphone monitoring (and possibly most convenient) for your guitar and there is a lot of real life experience.
I personally have decades of experience with high end studios and engineering for Broadcast, so let me assure you that clean audio in headphone monitoring can really have its challenges, especially across multiple platforms.
All that aside, if you can achieve a headphone feed with attenuator and possibly Volume control go for it. Experiment, see what you come up with and enjoy your Champ. Let us know how you go as this forum is all about encouraging one another and leaning new things 
Kind regards
Mirek
Just noticed the post from Sluckey, this is what I meant by "achieving an attenuator"

[XYZGnomon]

You should leave the 8Ω/25W resistor as is (like Rob's schematic). But you do need a series resistor (between the speaker jack and the headphone jack) to drop the volume and also protect those headphones. I see the Sony MDR7506 is 63Ω impedance and since you probably have the headphone jack jumpered for sound in each ear, the total impedance would be 31.5Ω. I would start with a 100Ω series resistor and experiment to find the value that drops the volume to a pleasing level. May have to increase or decrease the 100Ω.

A Champ amp is inherently hummy due to the cheap design. It was a student practice amp and the cheap 8" speaker did not reproduce the low frequency hum very well, so no need to spend money to improve. Fender wanted you to buy a bigger, hum free amp. There's an easy way to upgrade a Champ to lower the hum. Just add another filter cap and a choke. Cost should be under $25.

Thanks! I'll probably do all of those things, plus maybe use shielded wire to the headphone jack or maybe even the entire signal path. It was a kit, so it's not like I'd be ruining a vintage masterpiece. I might even change my mind someday and put it all back to stock and build a specialized headphone-only amp. For now, I OBVIOUSLY am not an expert and I appreciate all the advice you fellows have given - even if I don't always sound like it.

[shooter]

IF you ever make the time;
you'll need a Marshall 4 X 12 cab
lots of space
Gibson guitar
your amp set on 10
start the guitar at 7
then play anything from 90's grunge to 70's hard rock, until your ears bleed


now go back and adjust for headphones   

[XYZGnomon]

IF you ever make the time;
you'll need a Marshall 4 X 12 cab
lots of space
Gibson guitar
your amp set on 10
start the guitar at 7
then play anything from 90's grunge to 70's hard rock, until your ears bleed


now go back and adjust for headphones   

I have an LP Special DC and the Champ goes to 12! 

[XYZGnomon]

I replaced the signal wire from the speaker output to the headphone output with a 10 watt 100 ohm resistor, and it's a more manageable volume and the hum has disappeared. It's almost perfect! I would be happy to leave it alone, except for that I'm not that kind of guy.

The only thing I would change is the volume range, but as it is now it gets too loud after about 3-1/2 on the dial - just like the speaker. Would it make sense to put another resistor before the speaker jack? If so, what value would make sense?

Or should I remove the resistor from the input jack, so that instead of a "high" input, a la input #1, it would be a "low" input, a la input #2?

Or something else?



Again, thanks for all the help on here!

[glass54]

Try an L-Pad attenuator.
Don't need 10W resistors, 1 Watt will do.
10R in series with your 100R and put your headphones across the 10R resistor.
Note I said TRY 
You may have to experiment with the 10R value to suit your comfort level.
see for hints https://www.electronics-tutorials.ws/attenuators/l-pad-attenuator.html
Regards
Mirek

[sluckey]

I say again...

I would start with a 100Ω series resistor and experiment to find the value that drops the volume to a pleasing level. May have to increase or decrease the 100Ω.

[glass54]

As sluckey said, even simpler.
Sorry Sluckey, missed your detail in Reply 50 "You should leave the 8Ω/25W resistor as is (like Rob's schematic)"
No need for L-Pad, save that idea for another project  But I repeat, save some money as you don't need a 10W resistor in this location.
Regards
Mirek

[XYZGnomon]

I say again...

I would start with a 100Ω series resistor and experiment to find the value that drops the volume to a pleasing level. May have to increase or decrease the 100Ω.

And you were right! Let me rephrase my question:

With the new 100 Ohm resistor, the perceived volume I hear in the headphones matches the perceived volume coming out of the speaker at any given number on the dial, which was the goal. Does it make any sense to also reduce the signal before it gets to the speaker jack, so that I'm not using just the very bottom range of the dial in both the headphones and the speaker?

Frankly, I am happy as is, but I think it's weird that I'm only playing at 3 when the dial goes to 12. It's like only exploring the first ten feet of a cave. I want to get a flashlight and go deeper. Maybe there are some bear teeth I can dig up!

[sluckey]

If you want to set the volume knob to 12 and play through your headphones, you need to use a bigger series resistor. Or maybe you just need to use an L-Pad if you have room.

[XYZGnomon]

If you want to set the volume knob to 12 and play through your headphones, you need to use a bigger series resistor. Or maybe you just need to use an L-Pad if you have room.

I bought two of the 10 watt 100 ohm resistors. Would it damage anything if I put it in series right after the output transformer?

[sluckey]

If you want to set the volume knob to 12 and play through your headphones, you need to use a bigger series resistor. Or maybe you just need to use an L-Pad if you have room.

I bought two of the 10 watt 100 ohm resistors. Would it damage anything if I put it in series right after the output transformer?

Probably not.

[thetragichero]

you need your big resistor across the output transformer secondary as that is what is providing the proper load to your output stage

[XYZGnomon]

It's been a couple of years since I've done this mod, and I added the L-pad shortly after the last pic was taken. It now looks like this:





I have decided that the headphone idea was worth trying but I'm over it. The L-pad works exactly like I wanted it to, though - however it's just flopping around the cabinet. I don't currently work in a machine shop (I used to! ), so I can't fashion a bracket to mount it and I don't want to drill unnecessary holes for experiments. There really isn't any place on this chassis for it to casually live.

I think I have a couple of options:

1) Return the kit to stock and build or buy a separate attenuator box, or
2) Return the kit to ALMOST stock, but replace the second input jack with a switch that engages or disengages a simple attenuation circuit to drop the volume to bedroom levels at noon (6-1/2) on the dial.

I found this at https://www.emprizeamps.com/post_attenuators.html:



I think this would easily fit into the tiny Champ chassis. Do you see any red flags? Have you tried something like this yourself? Bad idea? Good idea?

[XYZGnomon]

I want to follow up with my last post, in case I have made my case unclear.

My goal is to lower the output, not any specific mod. If there is a better way to lower the output, whether it be by changing certain components or some other way, I would be happy to explore that too.

I am leaning toward returning the Champ to its stock configuration, and lowering the output some way other than making a pile of spaghetti inside this tiny chassis. I'd love to hear your suggestions.

[sluckey]

It's a bad idea to run the speaker output near the input circuit. In fact, those two power resistors are located in the worst possible place in that chassis.

Since you like the L-pad consider moving it. If that's a steel chassis just solder the back of the L-pad to the chassis (requires a big soldering iron/gun). Or, put a liberal blob of silicone rubber on the chassis and set the L-pad in that.

Or move the L-pad to the speaker cab. It's rare to see one mounted on the amp.