Analogue systems

> Thank you very much for your answer !
> I have seen price of the moogerfooger and it's a little bit pricey 
for
> me... I thing that the rs400 is a good solution.
> However, I read some articles on the Net and there is something not 
very
> clear for me : is a phaser the same as a comb filter ? My opinion 
is that
> a phaser is a comb filter with the delay controled by a lfo. Am I 
right ?

a phaser and a comb filter are different things.

a phaser shifts the phase of a signal, then mixing this
shifted signal with the inverted original signal.
this causes notches in the frequency spectrum.
the more stages in a phaser, the more notches you get.
all these notches have the same amplitude and are
"tempered". example of a 6-stage phaser: first notch 200 hz,
second notch 1000 hz, third notch 5000 hz.

a comb filter is delaying a signal by several milliseconds
(much longer than a phaser) and mixes it with the original.
this also causes notches, but these are different than those
generated by a phaser. you get more notches, they have different
amplitudes and they are not "tempered".
this means, that a comb filter is more a flanger than a phaser.

best wishes

self oscillate