La Scalas and RFI

[shakes]

I've got a pair of clean La Scala Industrials (chunky handles on the side, textured finish in black, 400 watt k-43 woofer), and am generally blown away with the performance (accuracy is right on and the output is highly musical, in spite of the rugged woofer). Unfortunately, in my last apartment, and now my new condo, I pick up a terrific amount of radio frequency interference (RFI).

The RFI has been appearant off two amps (both British integrated). I've tried a number of set-up variations in hopes of ameliorating the RFI, to no avail:

1. I've lifted the ground prong on my amp's power cord, to make sure I wasn't experiencing a ground-loop . . . still RFI. Even with no inputs (no components plugged into the amp, just int-amp and speakers), the system still receives rf

2. I've tried ferrite beads (split) around my power cord and my speaker cables, but no obvious reduction in RFI. May not be using the best beads, however. I've wrapped my speaker cables in tin foil - presumably, insufficient shielding.

I suspect the RFI enters my system through my speaker cables - when I switched from high-end stranded to Kimber, there was some relief. Also, the RFI is worse in my new downtown condo than my old suburban apartment.

Is this a problem with all efficient speakers? Is there a good way to combat this unwanted reception? Help, please.

[shakes]

oh yeah: the rfi does not attenuate with the volume controls on my amp. also, no mods to my LSIs; mono-amped.

[EJH]

I'm no expert but try unplugging a few other AC devices (lights, things with motors like a refrigerator...) Maybe the noise is caused by another source. Also, don't run speaker cables parallel to power cords. Signal should cross power at 90deg., in theory anyway.

[JohnA]

All high efficiency speakers will allow you to hear things like your RFI because of their efficiency. Millivolts are audible through K-horns, Belles and La Scalas that just would not be heard with typical speakers because of the 20 dB higher efficiency.

If you have that much problem, you are in a really intense RF field. If it is not sensitive to preamp gain it is most likely in the power amp or power amp section of your equipment. If you remove the speaker wires from the amp do you still hear it?

[WMcD]

[WMcD]

But seriously folks!

There is the theory that in some cases the wires act as antennae. The RF signal gets into the amp though some feedback loop and then is demodulated.

Let me suggest the use of two 0.1uF disk capacitors from Radio Shack. They are sold two in a blister pack, #272-135, at a cost of $0.99.

Wire one directly across each speaker output of the amp. This is to say, just as if the caps were little speakers. You can slip the leads in along with the speaker wires or use a banana plug, if your set up allows.

The reactance of the caps is too small to have a significant effect at audio frequencies. At R.F. though, they should short out any signal getting into the amp through the speaker wires.

Let us know how that works and more about what sort of RFI you're picking up.

Best,

Gil

[lynnm]

Good suggestion Gil and the cartoon is a hoot!

[shakes]

Thanks for all the speedy replies. I'm new to the Klipsch forums . . . you guys are really on top of things.

To answer a few questions:

- with no speaker wire in the amp, there's no noticable sound at all (my speakers are 'off', and don't seem to move at all)

- my speaker cables do come in contact with my power cords, an unfortunate consequence of a *really* cramped setup. i've considered conduits, to keep everything isolated, but have not yet settled on any product

- I've unplugged all the accessible appliances in my place . . . i too thought this was an issue of dirty power. still no luck

- i've heard about these discs, perhaps elsewhere in the Klipsch forums. I will pick some up, and let you know the outcome.

My fav audio dealer near toronto recently suggested jamming unwired rca connectors into the unused terminals of my amp - any thoughts?

Thanks again. Cheers all.

[lynnm]

I suspect that he is referring to using shorting plugs ( rca connectors with their signal and ground connections wired together ). This is usually only effective on the low level inputs ( unused phono etc inputs ). That may help but Gil's suggestion would likely be more effective overall for your situation as I think that as suggested your speaker cables are the main culprit here.

[shakes]

Ok, will do. Just to clarify:

- I connect one lead of the disk cap to the + terminal and the other to the - terminal on my amp, for each speaker output. (This wont short my amp?)

Also, my amp has two outputs per speaker (for bi-wiring) . . . should I be doing anything with the naked terminals? (also, could they contribute to my RFI?)

An aside: I've noticed that lots of people bi-wire their La Scalas (and KHorns, etc.). Is this a common mod, and is it worth opening up the x-over for? I have some experience building speakers and wiring simple cross-overs, but not enough to conceptualize the consequences of separate power to this system . . . what's the concensus on best x-over and setup for the La Scalas? Where do you place the electronics on the speaker, or is it all done outboard?

Cheers.

[JohnA]

A capacitor is 2 plates in parallel, so it is not a direct short. Based on the capacitance there is a frequency where the charge on one plate can influence the other one and the cap begins to conduct. The smaller the capacitance the higher the frequency. That is why the 0.01 cap Gil recommended works. It is only effective well above audio frequencies, where you have a problem. It is small similar to cable capacitance so the amp should not care. Watch for excessive heat, though, in case it goes into an oscillation (not likely).

You can use your second terminals for the cap, if you want. It shouldn't matter which pair you use. Tha correct connection is from + to -.

Shorting plugs in unused inputs can reduce noise, too.

[PAR69]

Another thing to try is to find out if the RF is coming in through patch cables, so unplug at the source end and select it on your amp then if you hear the noise then there is a source. Of course, you can then buy cables (build your own) using shielded cable to solve this.

Good luck

Paul

[artto]

Gil's advice with the disc caps is right on. And so is your dealer & Leo with the shorting plugs (RCA terminator plug).

I have several large radio & TV antenna transmitors within a few miles of my home. I've always used RCA terminators on the unsed inputs & never had any RFI problems.

Another thing you might consider is the potential source of the problem. RFI can be caused by such things as light dimmers, neon & fluorescent lights, even computers.

[shakes]

Thanks again for all the input. I've checked Radio Shack (.ca site) on the web, trying to pick up the disc caps online . . . unfortunately, all the Ontario locations appear to be 'sold out' (unlikely, right). This week, I'll head over to some of the pro electronics warehouses, see what I can pick up, and update this thread.

As an aside, since I first posted, the RFI has subsided significantly (spooky, since I haven't changed a thing). Probably the winter weather, interfering with my interference.

Response to two posts prior: I've tried unplugging my sources (dangling interconnects from the back of my amp), as well as having no sources/interconnects plugged in at all. The RFI is constant. Also, while switching between live sources, the sound cuts (as it should) on my Exposure amp, although the RFI persists throughout (also, not attenuated with volume pot). Suggests that sources are not the problem, correct?

[shakes]

My many-months-later update: after many system tweaks (including construction of shielded/grounded speaker wire - not at all effective) and a great deal of headache, I believe I've finally beat the best of the RFI (really, WE beat it!).

The RCA approach didn't help my setup at all, but the .01uF disc caps seem to have done the trick. Along with a couple split-beads, my system is now just about free of audible RFI. Alone, the beads make only the subtlest of difference; the caps alone seem to clear about 90% of the audible RFI. Together, I'm in business.

As an aside: does anyone think an L-pad on each speaker (pre X-over) might have worked as well as the cap-filter?? Maybe lower the efficieny into the 90s, quiet the whole system down. Might be a nice tweak for those running big horns off big amps in small places. My amp seems wide awake at listening volume with lots of headroom remaining, but I've heard bigger amps (solid state) that didn't open up for the La Scalas by listening volume. Just a thought.

Thanks again, everyone, for all your input.