some dc-dc converters are bad beasts, about ripples ..... just as suggestion, place some 100nf or 220nf ceramic capacitors in parallel to all the electrolitics ones (electrolitic capacitors are not very efficent against high frequency spikes, due to their internal reactance, so ceramic ones in parallel helps a lot, sometimes)
The better combination can be: 100/220uF standard + 1/2,2 uF tantalium + 100/220 nF ceramic in parallel ..... capacitors have not a high cost, after all
..... also, using some counter-wired bobines or C-L-C pi-greek filters can help too ..... like the one that you already have placed on the output of the head ..... if you have occasion, try to complete it (adding another capacitor also from output and GND, and paralleling them with 100nF ceramic ones) ..... same thing for the one on the dc-dc inputs, and usinf the same on the dc-dc outputs, you probably end taking away 90% or more of these spikes .....
EDIT: sorry, i just had another idea ..... ground loops also, sometimes, contribute to link ripples and spikes where you don't want them ..... decouple the inputs and outputs of the dc-dc converters, coupling the grounds only on the signal side, and place a RF trap on the inputs of the converters ..... something like this, at the end:
Sorry for the bad drawing, i just sketched it on-the-fly
..... and, also, use good size wires (i know that there's no high currents in the circuit, but is always a good thing to use wires of a decent size for wire-up power sections, like, 0,5mm dia, at least, especially for the input of the dc-dc converters)
