An interesting way of modifying an open reel deck is to take the direct output from the playback head and route it to an external, higher quality, preamp bypassing the internal one.
Bottlehead, located near Seattle, produces hand-made dedicated tube repro preamps.These units are intended for 2 track systems.
Their top end model, Tube Repro, features:
- XLR-balanced outputs +4dB
- RCA-unbalanced outputs +10dB
- CCIR EQ
- NAB EQ
Different custom EQ curves available on demand.
Another model, the Eros Tape Head Preamp, is available as a kit. To my knowledge this is the only tube repro kit available on the market as of 2012.
Bottlehead also sells upgraded replacements for mechanical parts along the tape path (Otari and Technics decks)
Visit their site here and head to the Reel To Reel section.