Question Tape Cassette Recording

Jul 8, 2021
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Hi all, I have a repaired fostex x-15 cassette deck.

However lately when I play back my recordings and analysis them I can hear a clear frequency boost in the recordings.

When I Analyze these recordings in Izotope I can see the 10 frequency is clearly boosted.

What can I do about this? It is my power supply or leads?
Or something wrong in the unit itself?