Clean blend with clean volume/boost...Can someone look at this schematic

[bradberry00]

Hello all,

I am working on a modified big muff circuit and would like to include a clean blend circuit. One thing I would like to try is also including a boost/volume control for the dry signal, allowing the dry and wet signal to be at an (almost) equal volume. Starting with the B. Blender circuit, I simplified and added a gain/volume mod. Could you guys take a look at this schematic and tell me if it will work or not....I could be over simplifying this.



thanks!
-david

[Eddododo]

you may want to wait for a more qualified answer, but here goes...
to me it seems a little unideal; i would guess that the passive volume attached directly to the blend/output would have too interactive of an effect on the output of the circuit. I would even venture to guess that it would affect the output volume with the blend all the way 'wet'

what I would personally do is either put another simple buffer between the clean output and the blend pot, OR I would use a variable gain pot in the negative feedback of the 'clean' op-amp. I DO tend to go a little silly with these things, so perhaps there is a better solution [or perhaps there isnt actually a problem there at all]   

Depending on how adventurous you are, the b. blender can be a little simpler than it needs to be at times, so perhaps a similarly simple but slightly different topology is in order?
I have done some things using an opamp as a comparitor to blend the [inverted] dirty signal with a clean signal.. i had varying results because im a messy breadboarder

[bradberry00]

so I possibly just need to replace the 220k resistor with a 250k pot and ditch the passive volume?

does anyone know how many dB of gain I would get from this set up from Seanm.ca:

[dwmorrin]

http://www.geofex.com/Article_Folders/panner.pdf
Check out the article on geofex about panning.  On page 2, the bottom schematic is similar to what you're doing.

I didn't any errors in your schematic upon first glance, but I would consider the suggestions in R.G.'s article above.  The BLEND control is wired very differently, and you'll use the 2nd opamp for active mixing, which IME is much more satisfying, but it all depends on the application and your tastes.  Your blend is passive, and may wind up acting less than ideal due to impedance issues... whereas the active will sum the signals at a virtual ground.  When using opamps, take advantage of stuff like the virtual ground mixing.  If you were using discrete transistors, it'd be another story...
As Eddododo suggests, I would also consider making the CLEAN VOL control a variable gain control.  For various reasons, it is usually better to control the actual gain, than to "boost and throw away" with an attenuator volume.
The dual buffer is a bit overkill... but I get what you're trying to do with the boosted clean... but it seems like two buffers is too much.

[dwmorrin]

so I possibly just need to replace the 220k resistor with a 250k pot and ditch the passive volume?

does anyone know how many dB of gain I would get from this set up from Seanm.ca:

Gain = 1+(Rf/R1) where Rf is feedback and R1 goes from inverting input to Vref (4.5V here).
Gain = 5.54

[Kipper4]

the buff and blend pedal might be a better solution
about half way down the page here



http://www.beavisaudio.com/techpages/blocksfragments/

i used a switch for R4* jumper on one side , resistor on the other for choice depending on the circuit in the send ,return

[bradberry00]

Buff n Blend is possible, but because of the huge volume boost available in the big muff I fear the clean could just get lost at those high gain/volume settings. And I would prefer not to choke down that volume boost to match the clean.

but you are right....far easier to build.

-david

[bradberry00]

I just had another thought. Forgetting the volume/gain pot for a minute. Would this schematic work, using two g2 buffers? Do these buffers flip phase? If so, is there a way to get the wet and dry back in phase with each other?

[mth5044]

Those are some strangely complicated buffers.

Why not use the ROG splitter-blend. You can get rid of the phase polarity switch if you want to but replicating the 'red return' in place of all the 'green return' circuitry if you know whatever pedal you are putting in the loop doesn't invert that phase.

http://www.runoffgroove.com/splitter-blend.html

Use the information in the link to set up a boost on either of the opamp returns for your clean volume.

http://www.electronics-tutorials.ws/opamp/opamp_3.html

[bradberry00]

Cornish buffers.....I hear there is magic in all those components....

[bradberry00]

Ok I know I may seem all over the place with this...and I will probably build all versions, but here is another idea. Feedback would be great:

So using the run off groove split/blend as a starting point, would the following work and allow the stock volume to control the "effected" signal and the added gain pot to control "clean"? Attaching both to the output jack you would be able to fully control the clean and dirty mix, right?

[dwmorrin]

Yes, it should work.  Get to the breadboard already!  
I would probably stick two resistors on the outputs like this: (value not critical... 100Ω to 1k should be ok)