Keeley C4 - LM13700 version

[MAO]

Sometimes I need to be reminded how great some of these pedals were/are.

I had a request for a Ross compressor, so I made up a LM13700 version of the C4. Sounds so good.

I started with Mark's layout from the main page and moved things around to accommodate the 13700. I also added polarity protection and some additional DC filtering.

I used tantalums for the 4 polarized 1u caps and the 10u.

I also used matched MPSA18 for Q1 & Q2 and matched 2n5088 for Q3 & Q4.  And then a 2n5089 for Q5.  Not necessary, but sound great so I've stuck with this combo through the years. (An early Mark Hammer suggestion)

BTW, the Attack control is wired up so CW is the quickest attack.  Use lugs 1 & 2 if you want it reversed like the original C4. And the Level can be 50k linear.

NOTE: Pins 2 and 15 of the LM13700 need to be lifted. I just cut those 2 legs off the socket and soldered the rest.

Verified

[Travis]

Great job, MAO! God bless the LM13700

Even though I haven’t built a pedal in a long time I still would love it if we figured out how to use the other half of the 13700 as an expander or something

[MAO]

Thanks Travis!

Agreed, and it just seems wrong to only use 1/2 of an IC

At one point was thinking maybe put both sides in parallel just to see what would happen, or maybe build 2 different CA3080 based compressors in one enclosure.

The expander idea is interesting.
Here's one Mark Hammer reworked using a 3080. Could be reworked for a 13700
Simple Downward Expander