BFD and hum...

[htnut12]

Chrisbee from another thread wrote:

Somebody has to ask (so it may as well be me): Why don't you use REW?

I have powerful computers, three for my own use and one for my lovely wife to use. Unfortunately they are HEAVY and wired with a gazillion inputs and outputs. Not the sort of thing I would move anywhere. So that would mean long runs of something to the AV items, and the Rat Shack. It would take me longer to set up the REW than to "tune" my IB with the meter and the Rane. And my 1124 BFD causes hum into the Nady Amps. As well the BFD has nothing below 20 hz where I need substantial boost.

I know I know cut everything else. Well I would rather flatten with boost and cut than cut alone. Eventually it is the same thing at the voice coil. It is just easier than trying to get into the arcane setup for the Denon receiver to boost the LFE there. If I try that I have to do all the EQ for six other speakers all the way up and down the spectrum. Don't think so. The Denon does about fifty or sixtey EQs for me automatically.

[brucek]

And my 1124 BFD causes hum into the Nady Amps

Even when using balanced connections with the ground lift switch on the Nady enabled?

brucek

[htnut12]

No balanced connections, the input to the BFD comes from an RCA jack on the receiver with an adapter to the 1/4 inch plug. 1/4 inch unbalanced from the BFD to the Nady. The BFD did not hum into a plate amp with RCA input, which had the 1/4 inch out converted back to RCA for connection to the plate amp. Hums like a mofo into the Nady lifted or not. I can reduce the hum by moving the BFD around up on edge etc. No way to keep it in a position that reduces the hum to a minimum. Still hum just at a low level. The Rane is so much better anyway with knobs. The BFD is not tweakadoodle friendly.

The Rane does not produce hum into the Nady Amp with unbalanced 1/4 inch connections.

[brucek]

1/4 inch unbalanced from the BFD to the Nady.

But the BFD has balanced out available and the Nady has balanced in available. Use it with a ground lift switch and the hum will be gone?

brucek

[htnut12]

I didn't know you could put in garbage and then change it to better than garbage. I will give it a try. I will be using the BFD for some duty or other just not to try and get low bass. There is a dearth of shops around me that have anything I can use in those XLRs. Maybe I can find some three band 1/4 to try.

[brucek]

I didn't know you could put in garbage and then change it to better than garbage.

I don't really understand that statement, but most of the hum created with BFD's is a result of a ground loop passing through to the subwoofer.

Subs enjoy amplifying that hum frequency and so the use of XLR (or TRS) with the use of a ground lift between the BFD and the sub itself usually remedies the situation.

Actually the best method is to connect the tip (+ve) and ring (-ve) and shield at the BFD end and then leave the shield disconnected at the sub amp end. The +/- difference signal is passed and since the shield is a cold conductor in a balanced interface, you have broken the pathway for the groundloop.

brucek

[htnut12]

brucek,

I think I understand the use of the balanced line between the BFD and the Nady. And yes a ground loop would be eliminated using the balanced line between the BFD and the Nady. I don't think it is a ground loop. I believe it is a field that is feeding into the circuitry of the BFD. I have five power cords in the vicinity. If I fool around enought with the BFD and move it around in space I can minimize the hum. A ground loop would be a constant hum.

My garbage in garbage out point is that if the "hum" is in some line that is pre BFD then how can the use of a balanced output take out the hum? That hum signal to the BFD is no different than a 60 hz tone in the source material.

In any case I will try the balanced line in between and I do know that a shield tied into ground at one end only is the way to go. (Gotta keep our explosives from going off in the Rocket Science business)

[brucek]

point is that if the "hum" is in some line that is pre BFD then how can the use of a balanced output take out the hum? That hum signal to the BFD is no different than a 60 hz tone in the source material.

Yep, fair enough. The overwhelming, number one problem with a BFD is usually a ground loop, so I thought that may be what your problem was...

brucek

[htnut12]

Truth be told brucek, I think it is the humongous toroidal transformer in the Nady Amp. I could try inserting the BFD into the loop from a different location in the room. Most likely when I install my second IB at the front of the room. Or when I get my new mains built with the drivers I won on Ebay yesterday for a woofer. Essentially going to wrap a box around my Klipsch speakers which will also provide for a woofer and make my lovely wife a bit happier with a blended in set of speakers up front. If it works out well I will do the center too.

I would trade that BFD for another Rane in a New York second. I missed the first one on eBay and could kick myself fifteen ways from Sunday.

Anyone want a nice as new BFD?