summing two signals together

[acehobojoe]

I've been working on a split overdrive that will sum the signals together and so far so good! 

It sounds great, I just need to figure out how to evenly sum the two overdrive signals together.

so far, I've just tried creating a junction with nothing in between. That creates some fuzzy sound that I'm sure has to do with the signal of the bass side leaking to the treble side's op amp. Don't know what to use to sum them. just so I'm clear, this is what it looks like :

Guitar ---> split transistor signals (2 bs170s) -----Bass cut (treble) - - - - - - op amp - - - diode clipping
-----treble cut (bass side)  - - -- - - - - op amp -  - - - (gain boost)   

I want to bring the two signals together to have the bass and high's effected in different ways. I'll be looking at some graphic eq pedals to try and make sense of this all 

[ubersam]

Try a couple of resistors to tie the outputs together, then take the summed output from the junction of the two resistors. Something like this:
                  6.8k
BASS OUT --/////--
                           |-- SUMMED OUTPUT
TRBL OUT --/////--
                  6.8K

[acehobojoe]

Thanks. Why do you think it needs resistors like that?

[armdnrdy]

Without seeing the whole intended circuit...it's kind of difficult to know exactly what you need.

Google "summing amplifier"...that might help give you some ideas.

[acehobojoe]

yea, here's my schem, so far. there's a few things I changed, but the "spirit" of it is still the same 

http://i.imgur.com/WfcmIdv.png


from what i can tell, the diodes in a clipping feedback circuit are basically a summing amplifier. I may need a 3rd op amp.

[PRR]

Two outputs, tied together, will usually "fight".

I have a speedy short-leg dog and a lumbering long-leg dog. If I use a 16 inch "Y" on the leash so I can walk them together, it's pretty crazy. With more slack (two separate leashes) it is a little more manageable.

Active circuits often *force* their output to be what you told it to be. Two active circuits tied together will "fight" violently (your "fuzzy"). Sam says to use two resistors- this gives "slack" so each can do its own thing correctly, and the mix appears at the resistor junction.

[acehobojoe]

Very nice way of explaining it

I'll be sure not to use on of those "Y" leashes.

[blackieNYC]

Pan pot!  25-100kB.  Becomes a sort of tone control.

[armdnrdy]

If you look at the Quadra Fuzz schematic that R.G. posted in your original thread...you will see how the four different fuzz sections were summed.

I think...for what you're trying to do...that drawing is a pretty good example to reference from.

[acehobojoe]

Perfect, thanks. Is there a way I can add more headroom to my op amp? I guess I could just change the supply to 18 V. Would that work? Perfect, thanks. Is there a way I can add more headroom to my op amp? I guess I could just change the supply to 18 V. Would that work?

I just want a little more room before that op amp clipping. The JRC 4558D I'm using has a short lived fuzz when you push it hard. As far as I know, the tl072 or something similar will sound about the same, but I might experiment with some other op amps I have.