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Topics - SemiConductive

#1
I recently picked up a Yamaha G50 Series III. Nice amp, glorious cleans. Solidly built.

BUT, it turns out the headphone jack doesn't cut off the speaker output. Odd, and useless for late night practice while the household sleeps.

Circuit diagram, click on it to zoom once you're there: https://i.imgur.com/E30dpvS.png

I'm thinking that I could just use a jack that switches the off the signal feed to the power amp when a plug is inserted into the headphone jack. On the schematic, there's a "T" junction where the signal splits and heads down to the power amp section and also up to C164, and IC109 to split into left/right legs for the headphone jack.

HOWEVER, I'm a newb. I don't know if it's safe to just cut that feed of the power amp signal, so I could use confirmation on that plan. Also, do I need to have a pulldown resistor and/or something else to prevent a serious "pop" on insertion?

Lastly, do they commonly sell 1/4" jacks that also have an independent switching function built in in addition to the more common the signal switching? I know I've seen that feature in some pulled Fender board mount jacks, but I haven't see other generic jacks for sale that have the feature. What's the industry name for that sort of jack?  Also, looking at the chassis, the jacks are definitely the isolated type with plastic housings. So it needs to meet that bar too.
#2
Circuit link below. Sorry for the poor quality. This amp was not popular and this is the best I've been able to find.

Background: I have some basic understanding of SS components and circuits. But I'm really a newb. Trying to increase my knowledge and perhaps mod this amp.

Signal comes in and through IC A / 4558 and moderated by the gain control POT 1. It then flows down into the other half of of the 4558, IC B (IC B is switchable by panel or footswitch through Q1). From there, the signal runs past a pair of Red LED clipping diodes LD1 & LD2. But, they are unswitched/directly grounded.

Are they always clipping? Or are the Red LEDs chosen because they only conduct over a higher gain signal coming through?

Possible Mod: What I'm thinking is that if the diodes themselves had a switch to ground that I might be able to get additional clean headroom with the primary gain control. But, I'm also thinking that by running the signal hotter (no clipping at all) that perhaps it is going to overdrive the poweramp... and maybe there's not much clean headroom to be added because of that (?). Perhaps the clipping is a "required limiter" or sorts?  Any danger to the other circuit components by switch-controlling the LED's?

Also, there's a capacitor C9 in parallel with the LEDs. Is it shown there simply for circuit drawing convenience in the schematic? Or would it need to be switched along with the LED's if I switch them?



EDIT: Schematic cleaned and waxed: Zoomable circuit diagram: https://i.imgur.com/WjfO8n1.jpg