Hi!
i can buy an used Alesis Quadraverb GT from a local store next to me for 100€. Do you think it's a good processor to add to my gear? I'm searching reverbs and some special fx like guitar distorsion, ring modulators, etc..
It is a cool machine. Just got one here actually, well a Quadraverb Plus. Very nice reverb, the resonator is cool and the sampler is nice and grungy. Haven't tried the ring mod yet. Also very easy to figure out how it works- MIDI etc. You might need to clean or replace the pots, but that's no biggy. Everything else seems quite durable.
IIRC the distortion on the GT version was the cool sound for about 6 months in 1989 but it doesn't hold up now. Never tried it on a synth though.
Not sure what you mean by "clean"? The whole machine can be a bit noisy, but you can get around that by reducing its own input level and driving it from the outside (aux send if you're using a desk). Obviously there's a balance to be struck between overloading it and keeping the signal above the noise floor.
It's a great sounding reverb, works on anything. To give you an idea- Orbital and FSOL used this reverb quite a lot.