Headphone Distortion

[morbank]

Hello All, this is my first post here and I apologize in advance for my ignorance and plead that you help right the audio wrongs I have made!

I'm using Nintendo's old Gameboy Color video game system with custom software (LSDJ) to sequence the Gameboys 4 channel internal synthesizer. I wanted to expand from 4 channels to 8 so I added a second Gameboy and enclosed them both in one case and hardwired sync and audio. And despite my ignorance this set up actually sounded really good (musical tastes aside)! Because the Gameboys default audio output is low and thin sounding I decided to hardwire the Gameboys outputs to an old analog Boss parametric EQ guitar pedal. And while this sounds great when connected to a loudspeaker the output is low and extremely distorted when used with headphones.

Below is a description of my blasphemes path (signal path that is):

-I've got two Gameboy Colors (lets call them GB-A and GB-B) each has a stereo headphone output.
-I bypassed both of the Gameboy headphone amps and combined the left signal from GB-A and the left signal from GB-B to make one left signal (GB-A/B Left) and then did the same for the right (GB-A/B Right).
-I then combined the GB-A/B Left and GB-A/B Right signals into one signal and hardwired it to the input of the mono input of the Boss EQ guitar pedal.
-I then split the Boss EQ's mono output signal into two (double mono?) signals and hardwired one to the left input of GB-B' s headphone amp and the other to the right input of GB-B's headphone amp.



What can I do to eliminate the headphone distortion?

I can provide more information, pics and schematic if necessary.
Thanks for reading,
-Clay

[Mooly]

The obvious problem just going off what you describe is that you can not combine any outputs directly.
An output is a "low impedance" feed and you can not just parallel them to combine them as each output "sees" the other a nearly a short circuit. They are fighting each other which may well cause distortion as th output stages are effectively overloaded !

Try adding resistors to provide a little isolation from each output. Value isn't critical, try 1k for example.
So thats four resistors inserted where you have written Lout Rout. That should help with distortion but I can't help but feel the overall sound will be a little odd to say the least mixing four outputs into one (phase issues etc).

[digits]

Being a guitar pedal it is also more accustomef to see a high impedance load on the output....

[morbank]

@ Mooly, I've added the resistors and they did indeed make a difference but the distortion is still overwhelming with headphones...

Would it work to mix the signals via a mixer? Do you know of a Mixer IC that I could integrate into my signal path?

[morbank]

@ Digits, So I am coming into the guitar pedal with a low impedance load and the pedal is designed for a high impedance load? Is it possible to correct the impedance miss match?