I run a Part 15 FM radio station as a hobby and use an Aphex FM Pro 2020 analog audio processor. The air chain is simple (Computer w/ ASI audiocard > Processor > exciter's composite input), but I am getting distortion, mostly on anything with heavy bass; it is very noticeable. I am modulating right at 100%, and all the levels into the processor are just fine as well (all my audio is normalized to -9db; and the processor input is set to +4dBr). The exciter is a BE-FX 30. The exciter is in great condition and was checked by another engineer who got it tuned up and ready to go for me; so nothing should be wrong there. I suspect the audio processor. It is an Aphex FM Pro 2020, and it really hasn't had replaced on it besides for a few chips for the display. Like I said, anything with heavy bass like Hip Hop sounds very distorted. It's like if you took a regular song into Adobe and amplified maybe 6/7dB past 0dB. While I suspect the processor, I really don't know where exactly it's coming from. If anyone could help me identify where this distortion most likely is coming from, that would be great.
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Audio processor distortion?
- Thread starter RadioGuy1019
- Start date
Couple suggestions: I believe the Aphex 2020 had a bass enhancement feature. Make sure that's turned off. It a lot like the old dbx sub harmonic synthesizer, which took anything below 60Hz and created a +-30Hz harmonic. That old FX30 can't take low frequencies like that. The modulator of the exciter sees sub harmonics as DC offset (square waves).
Second; if you put the processor into bypass, but reduce the level to keep it from overloading the FX-30 input, does the distortion go away? If so, you could be overloading the input of the Aphex 2020. As I recall, you're better off running a lower drive input, then increase the input gain to no more than 10dB of limiting or compression in any band.
That could be BUT I just remembered I did a test where I listen to the audio input and output through the monitoring output it has and hearing the same distortion. What worries me is if that bass thing was the case, I’m upgrading to an Omnia 3FMT here soon, and I heard that thing has very heavy bass.
No unfortunately it doesn’t. I have also turned down the composite output just because to like 30/40% modulation and even though the audio was low, I could still hear the distortion.
I didn’t see anything like that under any of the Processing settings. I also checked various different areas and can’t find it
What happens if you bypass the processor altogether? That will isolate whether the distortion is in the processor or the exciter.
Are you using the stereo generator in the Aphex and composite into the FX-30?
It could be that there are dried-up capacitors in the processor or exciter audio sections that are causing the distortion. Either that, or the 5532 OpAmp in the composite output could be bad. I'd try to isolate which device is producing the distortion, then concentrate on troubleshooting that device.
Bad caps in the exciter PLL would do exactly that. It would try to "chase" bass mod and "correct" it. Sorry, I don't have an FX-30 manual to tell you much more, it's all from memory.
He went radio-silent, which usually means:
A. He identified the source and it's going to take some work ($) to solve.
B. The problem was caused by something involving the install.
The FX-30 is a good exciter if the electrolytic capacitors have been replaced. Not so much likely that the few big ones are bad but most certainly the small electrolytic capacitors for signal coupling and power supply are bad and need your help.
These and the big brother, the FX-50 can be modified to sound Amazing. The Continental brand of analog exciters were of the same DNA and, as I understand, designed by the same person and also among the best.
These and the big brother, the FX-50 can be modified to sound Amazing. The Continental brand of analog exciters were of the same DNA and, as I understand, designed by the same person and also among the best.
Was never a fan of the Continental 802A or B exciters. They had microphonic issues.
Yes, that could be reduced by not having it in the transmitter but in a separate rack. When the rubber mounting hardware for the modulator module dry rotted away that didn't help either.
Question for the OP. Why are you running a BE-FX 30, 30 watt exciter if you are a Part 15 operation?
Something doesn't smell right.
Something doesn't smell right.
Could it be a PIRATE!!! Arrrrhhh... Shiver me timbers!
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