I am using a Radio Shack's 273-1374 isolation transformer to feed audio to a SSTRAN transmitter. I am using the isolation transformer because of a bad ground loop hum. I am feeding a satellite signal through a computer then to the transmitter. All of the equipment is on the same electrical circuit. The spec's rate the isolation transformers frequency response at 300Hz to 5kHz. The audio doesn't have the "full" sound that I want.
I am using a Radio Shack's 273-1374 isolation transformer to feed audio to a SSTRAN transmitter. I am using the isolation transformer because of a bad ground loop hum. I am feeding a satellite signal through a computer then to the transmitter. All of the equipment is on the same electrical circuit. The spec's rate the isolation transformers frequency response at 300Hz to 5kHz. The audio doesn't have the "full" sound that I want. Is anyone else using this isolation transformer? Are there other options available?
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:
Broadcast Supply Worldwide has a 600 ohm transformer for $59.95. Here's the link: http://www.bswusa.com/proditem.asp?item=PUREFORMER. BSW ships the same day.
Frank
www.easthillradio.com
Specs here: http://www.shure.com/ProAudio/Products/Accessories/us_pro_A15BT_content
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Being from Radio Shack, it is quite possible that there is quite a bit of variability in quality betweeen different samples of the same component. They probably buy from different suppliers, even. Having said that, I am using one of those same transformers with my SSTRAN transmitter. Mine was purchased several years ago and was sitting in my parts bin.
Last year, I put one of those transformers in a test configuration. I used a PC sound card on the input and the output was attached to a few hundred feet of Cat5. I then used software to generate various audio tones. Using an oscilloscope, I compared the audio waveform coming out of the PC with the waveform at the far end of the Cat5. I wanted to see if there was any distortion or drop in signal.
I don't remember the exact frequency range I used, but it was much wider than the specs you quoted. I found no appreciable signal degradation in my testing.
I am using that same transformer to feed audio to my SSTRAN on the roof. I am feeding it OTR and music 24 hours a day. The transmitted audio quality is very good.
Now, I will be the first to admit that the transformers that others have mentioned are probably of higher quality and have better audio response than the Radio Shack part. However, remember that AM BCB signals are rather narrow bandwidth and far from high fidelity.
You mention that you are running a satellite signal through a PC before sending it to the SSTRAN. Are you sure that the problem is not related to that part of your configuration? Have you tried listening to the audio directly from the PC soundcard? If that is ok, try listening to the audio from the output side of the transformer directly (no SSTRAN hooked up).
As for the ground loop, are you using shielded audio cable? If so, is the shield connected at both ends? If so, disconnect the shield at one end and see if that helps.
Before you used the transformer, did you try setting the jumpers for the inductors on the power/audio lines in the SSTRAN itself? They are specifically there to help eliminate hum problems. As the manual says, if you don't need to jumper them in, it is best not to.
As I mentioned, I also use a PC to feed my SSTRAN and have no hum problem. The reason I am using the isolation transformer is not because of a ground loop, but because it provides a better match between my sound card and the Cat5 cable that I use (instead of expensive audio cable). This particular transformer is not quite the correct one for matching impedances in my application, but it is what I had on hand and it seems to do the job.
And buy a Ground Loop Isolator for $17. It has RCA in and out on both ends and is designed for higher fidelity. I've used them in several location with high success.
http://www.radioshack.com/sm-see-all-needs-and-wants--pi-2062214.html
WDCX AM1610 Part 15
John
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