BFD Gurus - Need pointers (1 Viewer)

[MarkDesMarais]

Sundar-
One thing that you mentioned in your initial post is that you are driving the voice coils independently from two channels of your amp. I'm pretty sure this is a bad idea- I read not to do it right after I poofed the output stage(s) of the old receiver I was using to drive my Shiva. I think it has to do with the outputs not being identical, and the voicecoils fighting. Someone correct me if I'm wrong!
This has nothing to do with your signal level issues, of course!
Markd

 

[Sundar Prasad]

First the good news - things work just like I want them to. I opened up the BFD last evening and disconnected the ground leads from the case of the unit (there are 2 locations). I also put rubber washers between the metal transfomer mount locations and the case. Two problems solved - the hum through my sub has disappeared (a cheater plug would have worked equally well) and the transformer vibration hum has toned down a lot. It is still there if I take my ear close to the unit, but every transformer has some mechanical vibration - I am satisfied with the present state of things.
Terry: Louis may have had a bad transformer. My unit works just fine. In fact, if I switch on the BFD without the top cover, even the little vibration I can hear disappears (the top acts like a resonator).
Mark: I have been using the sub for over two months now with both channels of my NAD receiver driving it. Absolutely no problems even with nasty levels of bass. I can't see how one voice coil would fight the other when both of them see the same signal. I use a Y splitter to make 2 drive signals from one SW out. If there are slight differences in amplifier gain between the two channels, that should not cause a problem either since both signals are still in phase. The only important thing is that both voice coils be driven in phase for maximum power transfer. Phase differences will definitely lead to voice coils 'fighting'. I am not sure how they could blow the receiver's amps though - the voice coils are electrically separate entities, unless of course they short, and in that case I am hoping that the fuses on the NAD blow faster than the output stages of the NAD.
Geoff: The manual is not the best, however, the BFD is very easy to program. I will be posting a detailed note with tips on my BFD setup experience so that others may spend less time scratching their heads over some of the issues I have faced.
On a general note, since I have worked a lot with data acquisition rigs, I know how important it is to maximize the use of the number of bits available in your A-D converter. The more bits used to quantise a given voltage level, the better signal to noise ratio and dynamic range achieved, and lesser decimal truncation issues involved when doing DSP operations on the data. Consequently, the BFD does a better job if it sees as hot a signal as possible at its inputs provided there is no clipping at the A-D conversion stage, and no overflow at the D-A conversion stage after the signal level has been boosted at some frequencies (cuts are not a problem).
With this in mind, and seeing that typical listening level signals were getting to -30 dB max on the level meters of the BFD, I decided not to run the BFD connected directly to the sub out of the Denon 3300. Instead, the chain looks like this now:
Denon 3300 sub out ---> L-chan input of NAD 7240PE receiver
NAD L-chan pre-out ---> Input 1 of BFD (RCA to 1/4" jack from RadioShack)
BFD Output 1 (1/4" jack split to 2 RCA's from RadioShack) ---> Inputs of NAD L and R channel amps
This works extremely well. The BFD level meter now shows more life as it sees a boosted subwoofer signal. Peaks are up to -15 dB for most of the listening I will do and I still have enough headroom for the Haunting and U-571.
Contrary to what the manual says (and thanks to Deane for this), the In/Out LED on the BFD must be green for the filters to be active. I programmed two filters last night to supply some boost in the 25 - 30 Hz zone and they work!! This BFD is one fine piece of gear esp. for the price it can be had for.
I will post a note on my before and after BFD room response curves in a couple of days in addition to the promised BFD setup tutorial that other users may find useful.
Sundar

 

[Deane Johnson]

Glad to hear you got things going the right direction Sundar. I could never go back to listening to my sub the way it sounded before the BFD.
We'll be looking forward to your follow up posts.
Deane

 

[Geoff L]

Thanks guys, will be ordering soon.
Felt that this might be part of the problem. Fantasic that you all are working out much of my homework.
I hopefully will be able to make shorter work of the learning process threw cruising this thread.
Just a great piece of electronics, and at its price point, well just amazing!
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Smoothe