Lead 12 Headphone Issues

howard453

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Hey, y'all! New Guy here.

I just bought a used Lead 12 Combo (1987, I believe) which I am loving! but I'm experiencing an issue when listening through headphones which has me very confused. There was an older thread on this topic but the fix in that thread (basically inserting the headphone plug only partway into the jack) is not working for me, sadly.

If the 1/4" stereo TRS plug from the headphones (Shure SRH240) is fully inserted into the "H.P./Line Out" jack on the amp the internal speaker mutes but I only get audio from the right earphone. If I insert the plug only partway into the jack (to the first "detent") which seems to be a very popular suggestion online then I get sound from both left and right sides in the headphones but the internal speaker does not mute.

Any suggestions? And if it's an issue with the jack itself what kind of jack (Cliff? 6 prong? 4 prong? PCB or solder?)

Any advice appreciated as this is starting to make me crazy!
 

SteelLucky

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Did someone add a speaker jack to the amp. If so the speaker jack must be isolated or it disables the speaker mute of the headphone jack.
 

PelliX

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Out of curiosity I checked a couple of schematics, and they list the line/headphone output as mono. Well, one channel, to be more precise, not mono split across both. Are you guys sure it actually has L+R output, i.e. the T/R/S jack is fully connected?
 

PelliX

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Manners first... Welcome to the forum! :welcome:

That I didn't do. I can switch that out easy enough. I don't use headphones so not really a big deal for me.

It's a 1/4" jack soldered to the PCB, I believe. I'm still not sure whether you're fighting a defect or a piece of design, though. :shrug:

If the schematics are to be believed it would explain what you're witnessing. You could most likely jumper that on the inside, provided it's a stereo jack.
 

jmp45

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Manners first... Welcome to the forum! :welcome:



It's a 1/4" jack soldered to the PCB, I believe. I'm still not sure whether you're fighting a defect or a piece of design, though. :shrug:

If the schematics are to be believed it would explain what you're witnessing. You could most likely jumper that on the inside, provided it's a stereo jack.

This is for reference for what I did for use with cabs. Isolated jack may fix the headphone use. This works fine for me, I don't use headphones with this amp.

l12_03.jpg
 

SteelLucky

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Nope. Half way in will give you sound on both headphone pads and should cut the speaker. All the way in is line out and will only have sound on one pad of your headphones. Mine has worked that way since I bought it new in 1984. That was until I soldered a switchcraft jack in for a speaker out. Quickly found out the next time I tried headphones that I messed up. Checked schematic and changed to an iso-jack and it has been working properly ever since.
 

FracStrat

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That I didn't do. I can switch that out easy enough. I don't use headphones so not really a big deal for me.
I hope you didn’t think I was saying that to you .. I could see that on the schematic..
My Shunt Jack with be in the Back Panel which solves the grounding issue..
I won’t be using the Headphone / Line jack either
 

jmp45

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I hope you didn’t think I was saying that to you .. I could see that on the schematic..
My Shunt Jack with be in the Back Panel which solves the grounding issue..
I won’t be using the Headphone / Line jack either

No Frac, we are good ;) I should do the same as you on this. I think I have some isolated jacks around somewhere.
 

FracStrat

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No Frac, we are good ;) I should do the same as you on this. I think I have some isolated jacks around somewhere.
I’m gonna install a 1/4” TS Shunt Jack ( Switches to Internal Speaker when not plugged in and bypasses the Internal when you plug in an External Cab )
Stuck through the wood back plate will auto isolate that puppy !!
 
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howard453

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Out of curiosity I checked a couple of schematics, and they list the line/headphone output as mono. Well, one channel, to be more precise, not mono split across both. Are you guys sure it actually has L+R output, i.e. the T/R/S jack is fully connected?
yeah, that's something I was wondering about myself...but then again I AM getting left and right when the jack is inserted halfway...
 

howard453

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Manners first... Welcome to the forum! :welcome:



It's a 1/4" jack soldered to the PCB, I believe. I'm still not sure whether you're fighting a defect or a piece of design, though. :shrug:

If the schematics are to be believed it would explain what you're witnessing. You could most likely jumper that on the inside, provided it's a stereo jack.
defect or feature? not sure yet! aargh! looks to be a stereo jack, Cliff 6-prong PCB...
 

howard453

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Nope. Half way in will give you sound on both headphone pads and should cut the speaker. All the way in is line out and will only have sound on one pad of your headphones. Mine has worked that way since I bought it new in 1984. That was until I soldered a switchcraft jack in for a speaker out. Quickly found out the next time I tried headphones that I messed up. Checked schematic and changed to an iso-jack and it has been working properly ever since.
exactly what mine does at the halfway except the speaker doesn't cut...tried cleaning the contacts, nogo, there's no other jack hooked up isolated or not...at this point I'm thinking defective jack or solder issue...
 

PelliX

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exactly what mine does at the halfway except the speaker doesn't cut...tried cleaning the contacts, nogo, there's no other jack hooked up isolated or not...at this point I'm thinking defective jack or solder issue...

I'm pretty sure it's working as intended. Note that for the circuit to kill the speaker output, one of the contacts in the jack needs to be lifted by the jack forcing it aside. If your jack plug is a little on the slim side or has a differently shaped tip to others this can be the case. Here are a few thoughts in no particular order;

If you want to use headphones with it, an unbalanced dry mono signal isn't going to be very pleasing anyway. Sure, if you're OK with that, then how about simply getting (or making) a little adapter cable with a male 1/4" mono jack and a female 1/4" stereo jack. Wire the male's tip to both tip and ring of the female and plug your headphones into that. You can then insert the (mono) jack all the way and you'll get both sound from both sides of the headphones.
A better option in my opinion would be to run it through something else that can actively balance or even make the signal slightly stereo. If you have some piece of gear that can add a little stereo reverb to the input signal, it will sound a lot better over headphones.
I haven't looked at the PCB itself, but according to the schematic, I would be lead to believe that the ring of the female is actually isolated. You could presumably jumper/bridge it to 'split' the output across both tip and ring - which is effectively the same as my suggestion with the adapter cable - just you have to go soldering in the amp.
Lastly, although quite uncommon thesedays, there are headphones that can be switched between mono and stereo for these purposes...

EDIT: I'm not quite sure about this circuit, but it is after all a solid state amp. You might be able to simply disconnect the speaker to mute it. Most (beware, I said most, not all) solid state circuits are absolutely fine with this. I'll let someone with more knowledge of this particular amp weigh in on the matter.
 

howard453

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I'm pretty sure it's working as intended. Note that for the circuit to kill the speaker output, one of the contacts in the jack needs to be lifted by the jack forcing it aside. If your jack plug is a little on the slim side or has a differently shaped tip to others this can be the case. Here are a few thoughts in no particular order;

If you want to use headphones with it, an unbalanced dry mono signal isn't going to be very pleasing anyway. Sure, if you're OK with that, then how about simply getting (or making) a little adapter cable with a male 1/4" mono jack and a female 1/4" stereo jack. Wire the male's tip to both tip and ring of the female and plug your headphones into that. You can then insert the (mono) jack all the way and you'll get both sound from both sides of the headphones.
A better option in my opinion would be to run it through something else that can actively balance or even make the signal slightly stereo. If you have some piece of gear that can add a little stereo reverb to the input signal, it will sound a lot better over headphones.
I haven't looked at the PCB itself, but according to the schematic, I would be lead to believe that the ring of the female is actually isolated. You could presumably jumper/bridge it to 'split' the output across both tip and ring - which is effectively the same as my suggestion with the adapter cable - just you have to go soldering in the amp.
Lastly, although quite uncommon thesedays, there are headphones that can be switched between mono and stereo for these purposes...

EDIT: I'm not quite sure about this circuit, but it is after all a solid state amp. You might be able to simply disconnect the speaker to mute it. Most (beware, I said most, not all) solid state circuits are absolutely fine with this. I'll let someone with more knowledge of this particular amp weigh in on the matter.

some excellent suggestions there, PelliX! Many thanks to you and all the other Forum members who kindly offered advice, much appreciated. And yes, it does look like a design issue...according to Dave, a senior service engineer at marshall: "The ‘Lead 12’ (5005) has a MONO socket on the headphone output which is why you only get sound out of one side unless you pull the plug out a little. I’m not sure why it was designed that way, but that’s how it’s drawn on the circuit."

So there ya go. I'll figure out my best option since I do need a working headphone jack. Thanks!
 

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