[Melodica-Me]

Hi Joanna, what you need to boost the line out is one of two things, either a clean boost pedal such as the Keeley clean boost one (see below link)

https://express.google.com/u/0/product/5834338391078252548_7215117854783236720_12145?mall=WashingtonDC&directCheckout=1&utm_source=bing_shopping&utm_medium=product_ads&utm_campaign=1003833%20%7C%20GSX%20%7C%20DR%20%7C%20NA%20%7C%20US%20%7C%20en%20%7C%20Hybrid%20%7C%20PLA%20%7C%20~%20National%20(acq)&utm_term=4576854590519942&utm_content=Overstock%20National

or a D.I. box pedal (see link below)

https://www.sweetwater.com/store/detail/ParaDriverV2–tech-21-sansamp-para-driver-v2-di?mrkgcl=28&mrkgadid=2976716985&rkg_id=h-72f9b425278460c566fd5c6f91c5fbe5_t-1529884083&utm_source=Yahoo&utm_medium=PPC&utm_campaign=Guitars-Guitar+Pedals+%26+Effects&utm_term=para+driver+di&campaigntype=paidsearch&campaign=Guitars-Guitar+Pedals+%26+Effects&adgroup=Guitar+Pedals+%26+Effects&keyword=para+driver+di&placement=yahoo&device=c&matchtype=p&network=s

to boost the line level up

I use the Sans Para driver because of the EQ but not necessary. If you take your melodica to the local music store that has guitar pedals they usually let you try them out before you purchase.

Hope this helps.
Melodica-Me