B. BLENDER

Below is a schematic for a blender. It is used to blend the dry signal from an instrument with the wet signal from an effect (or an effect chain). It has lots of uses:

• to mix in some bass so that guitar oriented pedals sound better
• as a buffer for true-bypass effects
• for developing effects
• with the gain mod it can be a clean boost

Notes

• Almost any opamp will work.
• If too much signal is pushed through the opamps they will start to distort. For added headroom the blender can be run off 12V or 18V. Just make sure that caps are rated high enough.
• The 1M resistors basically set the input impedance. Depending on the opamp, you can use almost anything from 470k to 10M.
• All the .1uf caps can be replaced with a cap from .01uf up with no loss of bass.
• The 10uf caps are probably overkill also. But I buy them in bulk and they are very cheap.
• If the send and return jacks have a no connection terminal, they can be connected togeather.
• The only opamp that is absolutely required is OPa to prevent feedback.
• Here is a minimal FET blender.

Mods

There are about 867 mods that can be done to this pedal to make it more versatile. Here are some I have tested.

• Gain mod adds a gain control to the dry signal. As shown you get a gain of about 5. Replace the 2.2k resistor with 1k to get a gain of 10. This is a boost only, you cannot attenuate the signal.
• Volume mod adds an attenuator to allow the output volume to be reduced.
• An untested mod would be to add a filter ala the Bass Paralooper (see links below).

Perfboard Layout

gaussmarkov at the diystompboxes forum did a perfboard layout. Information is at his B Blender page. Here is a link to the thread that also has a picture of the final perfboard. Very nice job!

PCB Layout

Jari Oinonen sent me a nice email with a compact PCB layout as a PDF file and BOM.

Credits

• gaussmarkov for the perfboard layout.
• Jari Oinonen for the PCB layout.
• Jack Orman for all his buffer articles.
• R.J. Keen for his polarity reverser.

Links

• Paralooper at Moosapotamus. Another bass blender.
  
  
• Splitter-Blend at Runoffgroove. This is for blending two effects chains, but would be easy to mod as a dry/wet blend. Just use jacks with a NC for one or both of the chains.
  
  
• You can google Buff 'N Blend by Joel Purkiss. Very cool single transistor circuit. Unfortunately his site is gone and he specifically disallowed posting on other sites.

Back to Stompbox Stuff
Contact Sean MacLennan