Total posts : 68
The transformer might be effecting your transmitter audio frequency output. CD quality sound is 20HZ to 20 KHz, cassette tapes were around 200 Hz to 13 Khz and even AM radio can have a wider bandwidth than that transformer does (10 KHz, IIRC)
The other factor might be the frequency response curve of the transformer. It might have a bandwidth of 300 HZ – 5KHz but the dB roll off could be fierce at the top end. The higher frequencies (above 2KHz, for example) might be attenuated severely.
I used that transformer a long time ago and had a similar experience, although I liked the effect because my content was NOAA Weather Radio which has a bit of high end hiss, so the roll off was great.
There are definitely alternatives. Try getting an isolation transformer from an audio house with wider bandwidth and a flatter response curve.
Here’s the specs of a typical high quality unit: