The Yamaha SLG 120NW is a nylon string "stick" (bodyless) guitar. It has internal, battery powered effects / pickup buffering and provides a headphone output, along with the usual 1/4" guitar cord jack.
For some reason, the headphone out sounds distorted to me. I cant comprehend why. I hear it with headphones and when I use the headphone out to drive an external amplification system. Of course, the regular "guitar cord" output doesnt have that sound.
Why not just use the normal output? Well, the guitar has nice sounding ambient effects (for circa 2005) and they are in stereo. The regular cord output they decided to leave mono, with the convenience of having the electronics come on when you plug in the cord, taking the "ring" function away from a second channel out.
I was lucky to find and download the schematic for free no less and decided to have a go at comparing signals on the oscilloscope. The circuit runs on +5 and +10, versus +/-5 and I was lucky that my signal generator could offset far enough to get the signal symmetrical. The guitar has a little pickup buffer circuit board separate from the main PCB, which is fed +5, +10 two ground pins and the one for the signal coming back. I unplugged it and connected at the ribbon header to drive the main board with 400Hz and 1Khz.
I couldnt find any difference in waveform appearance up to and when driven into clipping, both the headphone out and guitar cord out went into symmetrical soft round top clipping at the exact same input drive level.
The op-amps are different. The headphone out uses two TLV2372, while the guitar level out uses a TL072. All 3 are fed from the same dual potentiometer volume control. Between the headphone op amp out and the connector is a 10 Ohm buffer and a mute transistor, grounded collector, 2SC3326. These apparently mute any turn on hash until the system becomes ready - for the headphone output only.
Ordinarily, I'd rip out the mute transistors just to see, but I'm reluctant to "molest" the guitar, in the event I want to sell it one day. I will however if that's definitely the problem. It's so disappointing to have this artifact on the output I'd like to use, to enjoy the reverb and chorus effect in stereo. Hopefully someone can help me to fix it - or at least understand why it's not obvious on the scope, yet I can plainly hear it regardless. Thanks!
For some reason, the headphone out sounds distorted to me. I cant comprehend why. I hear it with headphones and when I use the headphone out to drive an external amplification system. Of course, the regular "guitar cord" output doesnt have that sound.
Why not just use the normal output? Well, the guitar has nice sounding ambient effects (for circa 2005) and they are in stereo. The regular cord output they decided to leave mono, with the convenience of having the electronics come on when you plug in the cord, taking the "ring" function away from a second channel out.
I was lucky to find and download the schematic for free no less and decided to have a go at comparing signals on the oscilloscope. The circuit runs on +5 and +10, versus +/-5 and I was lucky that my signal generator could offset far enough to get the signal symmetrical. The guitar has a little pickup buffer circuit board separate from the main PCB, which is fed +5, +10 two ground pins and the one for the signal coming back. I unplugged it and connected at the ribbon header to drive the main board with 400Hz and 1Khz.
I couldnt find any difference in waveform appearance up to and when driven into clipping, both the headphone out and guitar cord out went into symmetrical soft round top clipping at the exact same input drive level.
The op-amps are different. The headphone out uses two TLV2372, while the guitar level out uses a TL072. All 3 are fed from the same dual potentiometer volume control. Between the headphone op amp out and the connector is a 10 Ohm buffer and a mute transistor, grounded collector, 2SC3326. These apparently mute any turn on hash until the system becomes ready - for the headphone output only.
Ordinarily, I'd rip out the mute transistors just to see, but I'm reluctant to "molest" the guitar, in the event I want to sell it one day. I will however if that's definitely the problem. It's so disappointing to have this artifact on the output I'd like to use, to enjoy the reverb and chorus effect in stereo. Hopefully someone can help me to fix it - or at least understand why it's not obvious on the scope, yet I can plainly hear it regardless. Thanks!
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