RFI

quote:

---

Does anyone have an explanation for this?

---

More cables acting as antennae, I would think. I used to have a real problem with the cables connecting my office system (which used to be in downtown Toronto).

You might want to try changing the position of the cables, cleaning the contacts, etc. Also, there's a chance that you've got a bad solder joint on one of your Hi-Cap sockets, which can often exacerbate RFI from cables. Have you got any spare SNAICs to experiment with?

-=> Mike Hanson <=-

quote:

---

Originally posted by Mike Hanson:
Also, there's a chance that you've got a bad solder joint on one of your Hi-Cap sockets, which can often exacerbate RFI from cables. Have you got any spare SNAICs to experiment with?

---

How common is this? Is there a way of telling? I may have this problem on an 180 input.

quote:

---

How common is this? Is there a way of telling? I may have this problem on an 180 input.

---

I've no idea how common this is. All I know is that it does happen occasionally. Electrically the connection is "OK", but it's not quite good enough to prevent RFI effects.

Since this can happen in the socket or in the plug, you should first try replacing the cable to see if that helps. If it doesn't, then I believe resoldering of the socket is the next step. I'm not an expert on this, though, and know about it only because it happened to me.

-=> Mike Hanson <=-

Very low power lines (like turntable signal wires) are more susceptible than high-power lines (like speaker cables). Then again, it might be the cables at all. However, I've found that RFI needs to be "received", which usually requires an antenna. Since antennae are generally usually long and straight, the arrow usually points to the cables.

-=> Mike Hanson <=-

i really don't know what's going on.

For example, my SNAIC4 between my 32.5 and 110 (at the time) caused bad RFI. The units were separated by about 30". If I let the cable hang straight down, the RFI was the worst. If I formed one 4" loop half way along, then it was much better. When I created two loops (at one-third and two-thirds), RFI was eliminated almost completely. BTW, the loops were created using a plastic cable tie. (See the attached image.)

I believe the reason this works is that the cable is acting as an antenna, and every antenna is designed to optimally receive a particular frequency, with others being near enough to work. (Think back to that crystal radio set.) The length of a SNAIC, stretched straight out, will match a particular radio frequency. By looping it, we're changing it into a bunch of smaller antennas tuned to completely different frequencies.

I don't know whether you'll be able to apply this theory to your prefix cable, though. Vuk had a real problem with his, and still does AFAIK. Or maybe he just got fed up one day, and killed that CB'er across the street .

-=> Mike Hanson <=-

[This message was edited by Mike Hanson on THURSDAY 23 August 2001 at 19:09.]

If that doesn't work make sure your system earth is OK - make sure the house earth cable is actually attached to the cold water pipe at the kitchen sink or wherever it goes. The RF should be drained off to earth via the cable shield.

If push really comes to shove, and the hi-cap to 52 lead is still causing problems, try moving the cable a little. You might get lucky and put the cable in null for signal thats giving you hassle.

Good luck.

In the UK I got some from Tandy -- very cheap and, if memory serves, they fitted most cables to around 8mm dia.

Worth a look-- they just clip over the casing.

PH

I had very severe problems with RF when I first got my Prefix, something I'd never experienced previously. The problems were AM radi station pickup, exacerbated late at night as the relevant band picked up.

The 112 pre has no binding post for the Prefix earth, so I originally tied it to mains earth, with little improvement.

Naim made a special adapter that fitted an unused input of the 112 to connect to which the Prefix earth lead could be connected. This connection emulates the binding post on your preamp.

This improved matters dramatically, but the breakthrough still occurred occasionally.

I now have a 4 pin DIN connector soldered to the earth lead (I chopped the earth tag off), so that the Prefix earth connects to the PSU (e.g. HiCap) 0V.

With this plugged directly into an unused output of either the SNAPS that powers my Prefix, or the Flatcap2 that powers my 112 the problems have totally disappeared.

If this is something you can try then you may find it works. It reduces the length of wire between the Prefix earth and the system earth, as it no longer has to pass through the SNAICS that connect the pre-amp to the PSU.

It will not affect the star-earthing in anyway, since the Prefix earth just acts as an screen to the Prefix electronics.

Poor electrical connections also act as RF detectors, so a quick clean may be in order.

Also, try RichardN's suggestion of wrapping the Prefix earth lead around the Prefix signal cable in a spiral formation as it exits the LP12. This was how I originally effected a cure, before the earthing solution above.

Your symptoms (i.e. disconnecting from the 52 earth tag improving matters, yet inducing hum) are identical to those I experienced.

The Prefix has some very high gain wide bandwidth electronics making the problems worse.

Andy.

Bruce