[TenTec] OMNI VI+ & Heil Proset for K2

[OE3ZK Gerhard]

Hello 

Beeing a CW enthusiast I  bought a used Omni VI+ from USA. Works wonderful in CW (with additional 600 Hz INRAD Roofing filter).

Using it on SSB with my Heil Proset which is supposed to be optimized (whatever that means) for the Elecraft K2, I receive rather poor modulation reports. The audio frequency response is too low. 

The former owner says it worked wonderful with a Heil Proset HC5.

Any hints how to improve the audio quality?

73
Gert, OE3ZK