Stereo to mono + Balancer

[Rebel_88]

 Hi all, I want to create a particular effect and I want to ask your help.
My idea is to take two different mono input and amplificate them with two different LM386 Amplifiers, after i want to balance the output so i can choose what should be more powerful on the output, at the end i want to transform the "Stereo" output to a mono output so i can put it in a chorus pedal. I have made a schematic but I'm not sure I'm using correct tecniques to get a working balancer and stereo to mono stage. Could you help me or tell me where to learn these two tecniques?
This is my schema (sorry i don't Know how to publish image on the forum).



R14 and R20 represent a stereo pot to crete the balance audio effect.http://www.angelfire.com/electronic/funwithtubes/images/Amp-Bal.gif
R21,R15,R22 represent a stereo to mono converter  http://www.flyingmonkeystudio.com/pics/summing.jpg

Are these resistors correct for my project or I have to change them?
Thank you for your help.

[PBE6]

No help to give (yet!) but I would be interested in the answer, I'm working on a blend control for a Big Muff.

[PRR]

> resistors correct for my project or I have to change them?

470 Ohm mix-resistors on a 20,000 Ohm pot.... the pot won't do much until it is within 2% of the end.

Generally loads should be larger than what feeds them. Pots are funny, but I'd go 10K-100K for the mix resistors, not 1/2 K.

Your '386 outputs are MUCH hotter than anything your chorus pedal can swallow. You need some heavy attenuation. At least 5:1. Given say 50K mix resistors you could make the load R22 about 10K.

R16 R17 R18 R19 do nothing for you.

Since you need attenuation anyway there is an alternate cross-fade scheme using a single pot.

[R.G.]

read "panning for fun" a geofex.com

[PRR]

> "panning for fun" at geofex.com

Yes, a good read.

http://www.geofex.com/Article_Folders/panner.pdf

Taking R.G.'s example ?, but noting that we want not "some gain" but an outright loss, and assuming that 14.14K == 15K for practical purpose, we get sumthin like this:



While R.G.'s opamp neatens math and curves, it complicates the build. I'd try it without, using low (non-zero) loading to mix.

The 15K at the end adjusts overall loss. You have 2V-3V out of the '386 and can't need over 0.2V-0.3V into your chorus. I think the values shown give 10:1 reduction with 8K output impedance, which may be in the ballpark. If too loud or soft, adjust to taste.

Your C3 C4 don't need to be anything like 220uFd (that was for speaker). With this >15K loading, 2ufd or 1uFd is more than ample for any audio.

[Rebel_88]

Thanks everyone for your answers. You are a great resource for a DIY community.
Sorry for my bad project, this is my first attempt on this kind of circuit and I didn't know a lot of things.
So following your suggestions i have made this other schematic.

Is this what you were telling me?
I have changed C3 and C4 and have changed the Balance circuit wit a 15k Pot.

I have to do other changes?
Thankyou for your time.

[Rebel_88]

Hi I have a new idea, in parallet to the output of the chorus i want to put the sound of a bass or a guitar, can I use this same circuit of  R15,R21,R22 to sum Bass with this effect? or i have to use a sum circuit with opamp to avoid an attenuation of the bass or the guitar playing?
Thank you for your patience.

[PBE6]

If I understand correctly, you want to blend both outputs (clean and chorus) together. R.G. recommended an inverting opamp mixer for my very similar project, see the "Adding a blend to Big Muff" thread for details:

http://www.diystompboxes.com/smfforum/index.php?topic=106787.msg967235;topicseen

[Rebel_88]

Hi, yes my project is this:
I want to play with bass and in the same time i want to load audio file on the schematic i have just posted. Audio files will go to a chorus and other stuff and at the end I will take this output and blend it with the bass and go to aBigMuff.
So you think this kind of circuit is good for me ? http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm is good?
I think i will use 22k resistors, is good for you?
Sorry for this annoying questions but i have a lack of knowledge about impedance load of audio circuits and so i have to ask everything.
I take this opportunity to ask if you know where i can learn more about impedance load of guitar pedal, amplifier and audio circuit in general.

[Rebel_88]

According to this site http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm I have create a schematic
But when i start  the simulation this is whati I obtain

If i zoom on the output signal i obtain

This is not what i was waiting for. According to the theory i should have:
Vout=-(Vaudio1+Vbass) because i choose all resistors as 10k.
What I'm doing wrong?
Thankyou for your help.

[Rebel_88]

Sorry I forgot to polarize Input and Opamp in the right way, now i have changed all in this :



In this last Green and Red Signals are Input and the Blue is the output, I hope this configuation is the correct one.
However if there is someone could tell me how i should learn more i'm glad to read all you give me.