Stereo to Mono

[MikeD]

Hi guys.  I'm not a guitarist, but I have a keyboard and an interest in electronics .  I already started building a tremolo filter based on the Electronics Australia schematic.  Now the keyboard I have has an annoying feature where it automatically pans the sound to the left/right speakers based on the note being played (bass notes pan left and treble notes pan right).  I'd like to avoid the hassle of working with stereo signals by mixing down to a mono signal and processing it from there.  Will a unity gain summing amp like the one shown on this wiki page work for me?

Thanks!

[petemoore]

  I don't know the power supply voltage.
  And assume the keyboard output is 'hot' compared to guitar.
  The headroom needed and the headroom that'd be available are both unknowns, hence how that would equate to power supply needs.
  Perhaps studying commercially available units, otherwise mixing board is a commonly used option.
  That is a strange stereo mix to not be able to get around for a keyboard.
  The link describes opamp applications but doesn't recommend any applications.
  As shown it looks like a summing amplifier, fit the right component values and it looks good from here. At a glance it looks similar to AMZ's Simple Mixer.

[Processaurus]

Hi, I think you could just make a passive "Y" cable assembly, if you didn't want to mod your keyboard to sum the two signals together.

To make a Y cable you'd connect the tip connections from the keyboard to a 1K resistor, and then tie the other ends together, with the output.  Connect all sleeves (Ground) together.

Keyboard L -----------VVVV-----.---- out
                                   1K       l                      
Keyboard R -----------VVVV-----'                                
                                  1K

It is curious there isn't provision in the keyboard manual for disabling the feature, or that they wouldn't have the two sides combine when there wasn't a plug in the R channel, as is traditional...

Edit: ASCII schematic got weird

[MarcoMike]

+1 on processaurus' idea... I was just about to suggest it, but he wrote it first (then I was not that sure this thing was ok, but now I am a bit more )

about the keyboard... what if you just connect the L output? In many devices L is considered the mono out... so maybe if you just leave one output "empty" the keyboard will send everything to the mono out...

[mac]

i did the same to mix my mp3 player L and R channels into one LM386/388 chip. works fine.

mac

[MikeD]

Hi, I think you could just make a passive "Y" cable assembly, if you didn't want to mod your keyboard to sum the two signals together.

To make a Y cable you'd connect the tip connections from the keyboard to a 1K resistor, and then tie the other ends together, with the output.  Connect all sleeves (Ground) together.

Keyboard L -----------VVVV-----.---- out
                                   1K       l                      
Keyboard R -----------VVVV-----'                                
                                  1K

It is curious there isn't provision in the keyboard manual for disabling the feature, or that they wouldn't have the two sides combine when there wasn't a plug in the R channel, as is traditional...

Edit: ASCII schematic got weird

Thanks Processaurus, I tried pulling the ring to ground and listening to the signal on the tip.  That seemed to solve my problem.  The instrument adapted its output so that the volume was uniform throughout the entire keyboard.

I'll keep your mixing schematic in mind in case I come across stubborn instruments in the future.