Alright well I had thought to try and filter the signal to clean it up and decided to try a series resonant circuit that would only allow 440 to travel through 

I knew I had some inductors laying around so I grabbed one that said 15 mH (praying this stands for milli and not micro)
Next I measured it and got 13.24 mH (again praying this is milli and not micro)

With that I cracked open an old book and started looking for the calculation which I found and inserted the value of 440 for f and 0.01324 for H then solved for C not having any idea what number I would come up with.

And I was quite floored with the result

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That's pretty crazy that I just need a 10 uf capacitor  so I'm damn lucky or damn WRONG

Oh well nothing better to do than hook it up and try

I went back and checked the math ➗


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Hi, anyone got the scheme for this one? Would be much appreciated.

Alex

Quote from: phatt on October 04, 2026, 07:45:00 PMWell sounds like you have a cracked solder joint on the 390 resistor which is intermittently connecting
Yes you will need to resolder it, better still (as G1 mentioned)replace it and lift it off the pcb which will reduce the heat transfer back down to the solder pad. (also bend it away from the regulator will help)

Cracked solder pads are Caused by the constant thermal cycling which fatigues the solder.

I think I've been looking at the wrong Schematic, I just found the right one, yay
Yes the Regulators do get hot hence the heat sinks are added.

thanks. the issue is the resistor solder joints were loose yesterday and the amp wouldnt work. today the resistor was firmly seated and the amp worked fine. also the voltage regulator 113 was significantly hotter than the other 2 or 3 around it.

my question is, could a bad relay that doesnt engage cause the buildup of heat at the voltage regulator/resistor? today the relay was engaging every time i turned the amp on though, so no issues today. but maybe some days it doesnt work? i dont know.

Well sounds like you have a cracked solder joint on the 390 resistor which is intermittently connecting
Yes you will need to resolder it, better still (as G1 mentioned)replace it and lift it off the pcb which will reduce the heat transfer back down to the solder pad. (also bend it away from the regulator will help)

Cracked solder pads are Caused by the constant thermal cycling which fatigues the solder.

I think I've been looking at the wrong Schematic, I just found the right one, yay
Yes the Regulators do get hot hence the heat sinks are added.

so yesterday the amp didnt work at all. today no issues. i believe the resistor is fine actually, but the voltage regulator gives off a ton of heat (compared to the other voltage regulators). this issue is intermittent though, not sure why the amp would work fine one day and not the next.

however yesterday i noticed the resistor in question was loose at its solder joints and perhaps disconnected, probably from the heat of the voltage regulator? today though , even after the amps been on awhile, the resistor was seated firmly in place, not loose.

is it a bad voltage regulator? or something else? i apologize for all the qeustions

The 390R resistor is supposed to run hot, it supplies current to the relay coil, that is why it is a higher wattage component than a lot of the smaller ones.  Measure it to see if it has changed value, it is probably still in spec. If it has drifted out of spec., replace it and raise the new one off the board a bit so it can dissipate heat better.
The heat from that resistor may be part of the reason the caps in that circuit go bad.  Replace them.

Nice post!

Quote from: g1 on October 02, 2026, 12:01:24 PMIn this case, the relay is also used to when protection circuits are triggered, so it is best to keep it in use rather than bypass it.
It is most likely capacitors in the circuit need replacement, specifically the ones mentioned in post #2.

thanks for your help..

https://imgur.com/gallery/yamaha-g100-112-iii-burnt-capacitor-MRPKIYX

i think its the cap thats at 2p 390. theres some heat coming off of that area, so much that it makes the cap loose after a few mins. also IC113 gets hot, probably from the cap. hoping i can just replace the cap. Are you able to determine the value of the cap? i could look it up but i'd like to double check with you if you dont mind. unless you think i should replace IC113 as well?

edit : burnt resistor... 2 pin 390 ohms.
edit : yesterday the amp wouldn't make a sound, like the relay wouldn't make a clicking sound, guessing because the resistor was prongs were melted, not sure. today the amp works fine, the resistor never loosened after awhile, but IC113 the voltage regulator was still hot. i'd like to remove the PCB and look underneath to see if i can notice any burns spots. but i'm wondering if its just a faulty voltage regulator?

But I had to take a look

Assuming that a guitar creates a signal with voltage without batteries or power supply I wanted to take a look

Especially since I now have a BNC to phono jack cable hey let's take a look

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Now strum (one string only) a bit and try to grab a pic on the scope

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The messy "waveform" shown is only one of a myriad of varieties obtained in mere seconds 

I can only observe that what comes out of a guitar is much enriched with lots of components and artifacts vs a simple sin wave or something from a generator 

Each little harmonic or vibration is probably fighting for survival cancelling each other out and stuff 

I then remembered I had a frequency counter from when I was playing with some old CB radios so I thought ok let's see 440 but I didn't manage to get anything useful out of it

Maybe it would help to read the manual

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I played whack a mole with all buttons and settings and couldn't come up with anything

In this case, the relay is also used to when protection circuits are triggered, so it is best to keep it in use rather than bypass it.
It is most likely capacitors in the circuit need replacement, specifically the ones mentioned in post #2.