Don't install resistor R33 until after you have soldered in the op-amp socket on the bottom of the PCB. Otherwise it will get in the way of soldering pins 5 thru 8 of the socket. I would also recommend soldering R37 & D2 on the component side of the PCB. This will allow you to clip off the excess lead down to the surface of the PCB. If you solder these components on the bottom of the PCB the solder joints can get in the way of seating the op-amp socket all the way down to the surface of the PCB. If they are too tall the pins of the socket may not protrude thru the PCB far enough to solder them adequately.
Be careful not to make the solder joints for C4 (220pf) too large. These solder joints come extremely close to shorting against lug 1 of the "Mix" pot and lug 3 of the "Speed" pot.
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