My sub is a radio transmitter.

[mashaffer]

I have a little AR 108 powered sub. It works fine except that when used with the radio (does not matter whether I use high or low level inputs or which of several receivers I use) it generates a lot of high frequency interference (hash). I assume that the switching supply is generating rf that is running down the connecting cables to the receiver.

Disconnecting the power or disconnecting the interconnect from the sub clears up the radio so it is apparently not transmitting over the air unless it has a cable for an antenna. I took it apart just to check for loose sheilding or anything obviously out of killter. The only thing noticable was slight discoloration of some insulation next to one of the larger resistors but it is not a huge amount.

This unit does not have a three prong cord. Would it be worth trying to run a ground wire from the system ground (CT of the secondary of the main power x-former) to the safety ground at the wall outlet? Could I possibly filter it out by using a choke in the input cables? Value? Exact placement in the circuit? Or would I be better off to just buy a new plate amp from parts express (under the assumption that the amp in the AR is garbage)?

I have it apart right now so I could probably check just about anything that doesn't require a scope.

mike

[Eva]

Try a common-mode filter, either in the mains cord or in the other wires.

[lndm]

Originally posted by mashaffer
Could I possibly filter it out by using a choke in the input cables?

If it comes to this, a ceramic capacitor across the input would be a better choice than a choke.

[mashaffer]

Tried the cap... no change... very frustrating.

mike

[lndm]

There are a number of possibles, too many to be sure. It could be radiated through the air, electrically or magnetically, or through your power lines. Try turning off all your household appliances. Try grounding the body of your transformer. If you ground your common rail as you mention in your first post, make sure the amp isn't already grounded elsewhere. The interference may be at your inputs or on the amp in general. Try shielding your low level interconnects and stages. In the end, where to stop it may be a question for a scope.

BTW, did you try as Eva suggested?

[mashaffer]

BTW, did you try as Eva suggested?

Actually I meant to ask what exactly a common mode filter was but I forgot to . Is this something that I could easily make out of parts bin stuff? From the name I assume that it somehow filters out any signal that is common to both leads of a cable.

mike

[lndm]

Eva will correct me if I'm wrong, but when I read that I thought of an RF filter in the power lead. The easiest is to purchase an IEC socket that has one in it, or a power conditioner. An RF filter usually consists of a capacitor each from active to ground and neutral to ground, and a couple of rf chokes in series with the active and neutral lead, and a capacitor from active to neutral. The caps should be mains rated (like X2). It may be best if you don't just jump into this without looking at the way others have done it, or maybe pinch a filter from a comparable broken appliance.