An
Introductory Guide to Subwoofers
Troubleshooting your
subwoofer, your amp, and the BFD
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1) I'm using the BFD (and or a pro-sound amp), now there's a hum in the system. What's the matter?
First I want to post a link to the
largest online resource I've found that deals with the topic of hum and ground
loops. It was written by Tomi Engdahl and hosted by blueguitar.org.
Note, this an 86 page .pdf file.
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The BFD and most pro-sound amps have quasi-balanced circuitry (XLR/TRS connections), and most people are using single-ended (RCA) interconnects. This situation greatly increases the chances of ground loops = hum. Using a 'cheater' plug (3 prong to 2 prong adapter) will usually take care of this situation. These adapters are controversial since they lift the ground-wire.
Those afraid of using cheater plugs, frequently try passive ground loop isolation devices. These are either baluns or transformers. These work for some people, but some designs can have the side effect of filtering out some audible frequencies.
Several of the pro-sound companies make active hum busting products. Ebtech, and Art Proaudio offer such products. I recommend trying these if the company has a 30 day return policy
DCI Specialty makes a low cost active hum buster.
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1) I'm using the BFD, there's hum from the sub, but no output. What's the matter?
Check all the connections and make sure you have everything wired up properly. Make sure you're using MONO RCA to 1/4" adapters.
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3) I'm using a pro-sound amp, the red "Clip" LED's are flashing on my BFD, and there's not enough output from my amp. What should I do?
Change the output setting of your BFD. On the back panel of the BFD are two small black rectangular 'Operating Level' switches. For home use, these are normal in the (-10 dB) setting. If with the (-10dB) setting there is insufficient output to drive your power amp, change the switches to the (+4dB setting). Changing these switches should be done with the power amp turned off.
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4) I have the BFD Operating Level switches in (+4dB) setting. I'm using a pro-sound amp. I have the gain turned up on the power amp, and LFE (sub) out level all the way up. But I the output from the sub is still lower than my main speakers. What's the matter?
Occasionally people run into a situation where they have a pro-sound power amp requires a higher input drive level than that supplied by the output of their pre/pro or the BFD. A device that can provide the necessary higher drive level is called a line level shifter.
This is the ART "CleanBox", it's a line level shifter. Here's a .pdf information sheet about it's operation. These devices cost ~$70 at pro-sound retailers.
A word of warning, this device rolls of the bottom end of the pass-band. It's roughly equal to having a 1st order filter. Here's a plot of the roll-off measured by Ilkka Rissanen. Changing 2 capacitors (C7 & C8) on the PCB fix this problem. One can add on resistors or replace with a higher value. Pretty much anything over .47uf is fine. Don't use electrolytic (polarized) caps
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There are other line level shifting devices available
1) The 124A
Audio Level Interface from Apex systems.
2) The Balanced Buddy from
Rane
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Specialty Devices
Chasw98 and I are developing a
utility box for sub owners.
H@LF = Help @ Low Frequencies.
Currently we're beta testing the PCBs, and will post more info as it's
available.
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5) I'm using the BFD, but it doesn't change the sound of my subwoofer. What's the matter?
The first thing to check is that there are filters programmed and stored in the unit. If there are, corresponding red LEDs on the front panel will be glowing.
Next make sure the filters circuits are active, If they are the green LED in the black In/Out button will be
on, as it is in this picture.
Finally, check to see you have the filters properly set. If the frequency has a decimal point in front of it, that's not what you want. The frequency setting of .20 is 200Hz, not 20Hz.
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6) I'm using a fan cooled pro-sound amp, and the fans sound like there's a jet taking off in the listening room. What can I do about this?
Under no circumstances should the fans be removed or unplugged.
The obvious solution is to move the
amp to another location. If that's not possible, frequently the fans
can be changed out with quieter fans design for PC's.
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To be continued.......
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