Levels drop significantly with BFD

[aspeters]

Hi gang:

First off, thanks for posting so much good info about BFD & REW. I'm familiar with the basic concepts but am new to the tools used to apply them.

After reading a number of posts, especially the one below, thought someone might have additional insight.

http://www.hometheatershack.com/foru...gh-enough.html

I also run an Onkyo 7.1 reciever with LFE line outs, and a Velodyne sub. Definintely never had issues with power - until hooking up the BFD. It seems I also cannot get the sub to respond with more than a bar or two on the level meter without cranking up volume severly north of normal.

The BFD is running in bypass mode, I just reset the box to factory settings, cleared all filters from preset 4, and the button is pressed in.

What could be some causes of a 20-30db difference in output with only the BFD added?

Thanks for the help,
Andy

[Danny]

Have you got it set to pro audio levels (+4Db). For most home audio setups it should be set to -10db input levels

[brucek]

What could be some causes of a 20-30db difference in output with only the BFD added?

Disregarding the VU LED's on the BFD, are you saying that the voltage level getting to the sub drops when you insert the BFD in-line between the reviver and the sub?

Are you sure you have the BFD channel 1 and/or channel two input and output jacks correctly oriented? They are very confusing.

The BFD is a unity gain device with the filters disengaged, so you either have the cables incorrectly hooked up, or the BFD filters are actually on and not bypassed, or you have a fault in the cables or BFD.

brucek

[aspeters]

Ok so in the 3:00am thinking, I failed the basic concept of understanding stereo vs. mono, and was using 1/4" STEREO for the input. Rewired using only mono made a huge difference. Thanks for the thoughts though.

Although, as a result I've picked up a ton of hum, but looks like theres plenty on the forums to address that already. One quick question came to mind though:

Based on room config (and WAF), the sub is placed pretty much on the opposite end of the room from the reciever, and thus I have a long run of RCA carrying the LFE/Sub Line out signal. Since the BFD has introduced significant hum, would putting the device ahead of this long cable rather than after it make a significant difference in line hum?

Thanks again and cheers to good sound in lousy rooms.

[brucek]

Since the BFD has introduced significant hum, would putting the device ahead of this long cable rather than after it make a significant difference in line hum?

Not likely. The hum usually comes from cable TV ground differences. First see if it goes away when you unplug your cable TV coaxial.

brucek

[aspeters]

Ok, i'll have to say that after a whole bunch of reading on here (multiple posts on humming and building custom interconnects and rewiring the CATV ground cable...all out of my skill level), I'm still somewhat confused as to the difference between balanced/unbalanced and its relationship to grounding. Even checked out a primer on some other site and that helped a bit with the education but not how to solve the problem.

Rather than someone spending the time to do an additional physics lesson (which is welcome of course but not necessary), I would love more specifically a clarification on the 1/4" balanced vs the 1/4" stereo connector.

My Onkyo TX-SR602 has a subwoofer pre-out RCA jack (and I guess that not a balanced output??). The Velodyne CHT-10 takes stereo RCA line-level inputs (also not balanced??) and I've had good success with a 40' run of Monster RCA and Y-splitter. To insert the BFD between Onkyo and Sub I'm using a pair of 2 RCA to 1/4" mono cables (presumably unbalanced???).

Enter line hum (which will be checked later and perhaps attributed to either CATV or using multiple electrical circuits.) In mean time, question in my head is still around this "balanced" cable thing:

Is it possible/appropriate to use connect any/all of the receiver, sub, or BFD with "balanced" cables instead, and eliminate hum?

Thanks again for the explanations.

[brucek]

My Onkyo TX-SR602 has a subwoofer pre-out RCA jack (and I guess that not a balanced output??). The Velodyne CHT-10 takes stereo RCA line-level inputs (also not balanced??)

Correct on both counts.....

Is it possible/appropriate to use connect any/all of the receiver, sub, or BFD with "balanced" cables instead, and eliminate hum?

Not unless you are able to fabricate/modify your own cables.

Your receiver only supports unbalanced output. This is a single ended signal on the pin of the RCA connector, with the ground on the shield being used to complete the circuit.
The BFD only truly supports balanced connections. This consists of a differential input of a plus and minus signal into a differential amplifier. The shield of the balanced circuit is a cold conductor providing shielding only. It isn't part of the completed circuit.

The BFD allows the connection of an unbalanced circuit to its balanced circuits by shorting its minus and shield together, thus eliminating the advantage that the balanced circuit offers.

If you're able to fabricate your own cables, there is a trick you can play on the BFD, that others have had success with, but short of that you'll have to find other ways of eliminating the ground loop....

brucek

[Wayne A. Pflughaupt]

aspeters wrote:

Is it possible/appropriate to use connect any/all of the receiver, sub, or BFD with "balanced" cables instead, and eliminate hum?

What brucek said. To embellish a bit, a balanced signal path requires each component to have balanced outputs and/or inputs. At any point where you insert an unbalanced component into the signal path, the signal path then becomes unbalanced.

Regards,
Wayne

[aspeters]

So, now that I'm home and futzed with things for another evening, I'm happier.

- Hum was from CATV line - jack outside looked like it had a grounding connector, but not grounded anywhere.
- Changing AC outlet to match that of rest of system did not change anything.
- Using the BFD itself to tune out the hum worked fantastically well (most of the audible hum was around 160 & 320 hz.)

Room isnt perfect but its better. I was able to use some some +gain as well to smooth out some dips. There are still some frequencies in playing some music that seem to over-resonate, but I guess thats to tweak later. Graph of before & after posted. Thanks again.

[Wayne A. Pflughaupt]

- Hum was from CATV line - jack outside looked like it had a grounding connector, but not grounded anywhere.

Run a wire from that ground block to your electrical ground rod. You can get a clamp at the hardware store for the ground rod, if there isn’t one already there, that will accept the ground wire. I think the ground wire should be 10 ga. or so – I forget.

- Changing AC outlet to match that of rest of system did not change anything.

Not sure I follow. You mean plugging everything into the same outlet or circuit? I’ve never heard of “matching” AC outlets before.

- Using the BFD itself to tune out the hum worked fantastically well (most of the audible hum was around 160 & 320 hz.)

Wow, what a great idea! I’m surprised no one has come up with that before – despite the endless threads dealing with ground loops.

Regards,
Wayne

[aspeters]

Wayne A. Pflughaupt wrote:

Run a wire from that ground block to your electrical ground rod.

Unfortunately I'm in a townhouse with plaster walls & ceiling, and hardwood floors. Circuit breaker box is on the other end of the house, and I'm no electrician. Maybe it's worth a call to Comcast though. Someone mentioned that its technically illegal to not have the cable signal grounded?

Wayne A. Pflughaupt wrote:

You mean plugging everything into the same outlet or circuit?

Yes, plugged into same outlet. Plugged into an API PowerWedge conditioner, in fact. Still no difference.

Wayne A. Pflughaupt wrote:

Wow, what a great idea! I’m surprised no one has come up with that before – despite the endless threads dealing with ground loops. .

I swore I got that idea from some other thread on this site. Regardless, I'm now noticing a bit of hum at 60hz, so may have to get a hum redux box in any case.

Any preference to one that would be in the sub line-out path (Behringer Hum Destroyer) vs one thats along the CATV (Jensen VRD-1FF)?
Thanks.

[brucek]

Any preference to one that would be in the sub line-out path

There are very few isolators that actually extend their response low enough to be useful.

The only decent one that is designed for those low frequencies (that I know of) is the Jensen SUB-1RR. It has ridiculously good specs and won't affect your signal (except for breaking the ground loop through its transformer). The trouble is that it costs about $100......

brucek

[StephenP]

If you make a cable with a male rca on one end, going to the pin and ring of a stereo 1/4 inch plug on the other end it will break the ground loop (at least it did for me)

[muzz]

aspeters wrote:

Unfortunately I'm in a townhouse with plaster walls & ceiling, and hardwood floors. Circuit breaker box is on the other end of the house, and I'm no electrician. Maybe it's worth a call to Comcast though. Someone mentioned that its technically illegal to not have the cable signal grounded?

Thanks.

The Comast splitters are grounded to the cold water pipe in MY Basement(Comcast install).
AAMOF, I had some hum a few years back, I redid their grounding(loose), and it went away.
EDIT:
Ooooooooooops, I misread the quote above... I must be going blind...

I don't know if it's ILLEGAL to have it not grounded, but it obviously should be.

Sorry for the confusion, fixed it.

[brucek]

If you make a cable

The poster (aspeters) made it clear at the outset that making cables was out of his skill level, so we went down a different road...

brucek

[Blue Dude]

StephenP wrote:

If you make a cable with a male rca on one end, going to the pin and ring of a stereo 1/4 inch plug on the other end it will break the ground loop (at least it did for me)

I thought this was a good idea to try, but it didn't work for me. In fact, the hum got a lot worse. I also tried to use narrow filters on the BFD to kill hum, and that did work in a fashion. The main problem was that I had to use either half the filters just to get rid of the hum (and even then some harmonics got through), or two really wide/deep filters that encroached on the subwoofer's frequency range.

In the end, I engaged the subwoofer's built-in crossover set to its maximum of 120 Hz and that almost entirely eliminated the hum. What little was left is all but inaudible. I had to rerun REW to check the sub's response to the extra low pass filter but it was set high enough that little change was required. Yes, there is double filtering going on, but the end result is worth it, especially when the alternative appears to be buying yet another $100 piece of equipment (the Jensen transformer) to fix issues with the first $100 piece of equipment!

BTW, here are before and after graphs of the primary listening position. I didn't correct for everything, only those things that appeared in the graphs of all three measured positions. For instance, the suckout at 110 Hz disappears entirely only three feet away to either side. So does the hump at 40 - 60 Hz. I'd appreciate feedback. Thanks.

Before:



After:

[brucek]

I thought this was a good idea to try, but it didn't work for me.

So, you used a (Tip, Ring, Sleeve) 1/4" connector and only connected the tip to hot and ring to shield (ground) of the RCA, with no connection to the sleeve and you experienced more hum. Hopefully you were using a three prong grounded AC connection.

Others have had luck with the ART CleanBox ll transformer. It appears to have a fairly good low end response.

Anyway, as long as the hum is gone, that's what's important.

I think your response chart is great. It's hard to tell until you test it with the mains to see what happens around the crossover area. Just add the mains and do the same test and watch the crossover area for peaks or dips.

brucek

[Blue Dude]

Yeah, I made a wire exactly as you described and it made things worse. My sub doesn't have a three prong connector, so no help there. Everything is plugged in with the supplied power cords; no grounds are lifted. The sub is on a separate circuit from the rest of the equipment. Soon it will share a circuit, which may help.

I'll look into a Cleanbox, but I think I'll stick with this arrangement for the time being. I was afraid that having overlapping crossovers would mess with the sub output but it appears fine so far.

I'll rerun REW soon, maybe tonight, with the mains added and we'll see what it looks like. I haven't lived with this particular setup long enough to tell whether I'm satisfied with it as it is. There's probably room to tweak.

Thanks for the look!

[Blue Dude]

OK, now I may just go insane. Daddy got a SUB-1RR for Christmas to tame the residual hum left over in the subwoofer. I wasn't 100% satisfied with the solution so far but I was willing to go the distance. However, the hum was worse with the SUB-1RR in the signal path than without. I just don't understand what's going on here. Any takers?

[brucek]

the hum was worse with the SUB-1RR in the signal path than without.

Where did you install the SUB-1RR? After or before the BFD? If your ground loop is between the BFD and sub, and you installed it before the BFD, it will be ineffective.

brucek

[Blue Dude]

I installed it between the BFD and the sub. I haven't tried it elsewhere since the hum still occurs with no input to the BFD.

[brucek]

I installed it between the BFD and the sub. I haven't tried it elsewhere since the hum still occurs with no input to the BFD.

Mmm, doesn't make sense to me. With no input to the BFD, and the 1RR transformer between the sub and the BFD; says that the noise is in the signal from the BFD. Not really possible when it's disconnected from a source, so I would say you have some sort of fault in the BFD.... definitely not a ground loop.

Have you tried both channels of the BFD?

Perhaps the power supply is bad and the hum is 120Hz noise on the output.....

brucek

[Blue Dude]

OK, kept fooling with it. It's now between the receiver and the BFD and the hum is almost entirely gone. What little is left is imperceptible unless you have your ear practically on the sub. Why oh why does this work? I'm so confused.

[fibreKid]

I use a cleanbox II and it's between the AVR and the BFD. It pretty much cleaned up my hum as far as I can tell.