You can find some on Ebay or on the french site www.leboncoin.fr , they cost between 400-800 euros. The problem is how they are because it's near vintage mixers and it's difficult to find spare parts or technical help.
The disco sound is a special filter on the DJ series which push the bass, a special kind of loudness. I don't have it on mine but I heard it on an another Freevox and it's a brilliant filter, it gives strong basses with a little bit echo.
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