Very Low Input Levels - DSP1124

[Nutball]

Hello all,

I recently purchased a BFD DSP1124 and am having significant troubles getting the inputs levels high enough. I searched through the site and found a few similar experiences but I wanted to double check that my experiences don't imply a faulty unit.

In order to see any bars when following the level setting section of the manual (or BFD guide) I have to crank up my Receivers sub level to +10 (maximum). Without the BFD I was running -5. Even at +10, I still only see 1-2 bars during my typical listening level. If I crank the master volume I can get 4 bars.

I have verified that the BFD is displaying the input levels and not the output levels.

I checked my receivers specs (Yamaha HTR 5890) and its supposedly outputs a 2V signal level which should be fine for the BFD.

I have checked both channels on the BDF with no success.

The output level is very low as well. Even with the receiver at +10 and my subs gain maxed I am > 6dB below my typical levels (I typically run @80% gain on the sub with no BFD)

On top of everything, I have a significant amount of hum coming through the sub which is not there when I remove the BFD. Channel 2 is considerably worse. I had manually switch off the sub last night since it would emit a loud hum every 5-10 minutes even with the receiver off.

I have switched cables as well. I am now running XLR to rca cables on both the input and output lines.

I am considering ordering a line booster but am hesitant given the significant amount of humming I already have. I would figure the booster may make it worse.

Without a booster I can not use the BFD since the sub level is so low. The auto power switch on my sub won't even kick on without the volume cranked. (unless I uses channel 2, in which case the hum powers on the sub and won't let is shut off).

Does anyone else think that my BFD is faulty, or should i try to boost my signal and clean up the hum?


Thanks,
Nut

[brucek]

There's a few issues here.

It isn't that unusual to suffer a low input level to the BFD. Many receivers don't supply a signal that's high enough to provide a max signal - it's not really a show stopper.. If this was the only problem, you could live with the low level or you can (as you suggested) use a signal booster.

But, realize that the BFD is a unity gain device. If I feed it 1 volt, the output signal will be 1 volt (assuming there are no cut or boost filters engaged).
So, if your sub operates nicely with a particular signal from your receiver, then inserting the BFD in-line will have no effect on the SPL level of your sub.
It appears that this isn't your case, as you now are experiencing a low level to your sub.

The hum is another issue, this can often be corrected by opening the shield ground on the XLR connectors with no short on the 1/3 pins.

Anyway, I would work on the problem of output level being low first. Play a tone through your receiver without the BFD in place and record the level from your sub. Then insert the BFD and enable bypass and see if the tone is at the same level. Then turn off bypass with no filters loaded and be sure the tone is the same level. If all that works, there isn't anything wrong with the BFD. (be sure to have the switches in the -10dBV position).

brucek

[Wayne A. Pflughaupt]

Thanks for detailing your troubleshooting efforts - sure makes things easier for us. However, I notice that you made no mention of what setting you're using for the rear panel input level switch. My guess is that you have it in the +4 dBu position. You want it in the -10 dBV position.

The output level is very low as well. Even with the receiver at +10 and my subs gain maxed I am > 6dB below my typical levels (I typically run @80% gain on the sub with no BFD)

The BFD does not automatically reduce signal level at its outputs. That can only happen if there are multiple and/or severe gain reduction filters engaged. If that's not the case, then it could be assumed that the BFD is defective.

Regards,
Wayne

[Nutball]

Thanks for the speedy relies.

A few more notes:
I did have the BFD in the -10dBV setting (I have tried it both positions)

New results obtained with the test tones in my receiver.
freq: no BFD, BFD in Bypass
39 Hz: 72dB, 65dB
44 Hz: 71dB, 66dB
50 Hz: 72dB, 67dB
56 Hz: 74dB, 69dB
63 Hz: 74dB, 70dB
pink noise: 75 dB, 69dB

The master volume and gain on the sub were untouched for these measurements. Also note that these numbers are from an uncalibrated RS meter. I do have a better mic (Beyerdynamic MM-1) but I didn't think it was necessary for these relative measurements.

This testing lit up only 1 bar on the BFD's inlet meter (in -10dB mode: 0 bars in +4dB mode). There was a significant amount of hum coming from the sub when attached to the BFD which could be heard from the floor above.

Thanks,
-Nut

[brucek]

note that these numbers are from an uncalibrated RS meter

Matters not.

This testing lit up only 1 bar on the BFD's inlet meter

Note the IN/OUT switch has three modes.
GREEN LED ON: filters on - VU meters indicate output level.
GREEN LED OFF: filters off - VU meters indicate output level.
GREEN LED FLASHING: filters off - VU meters indicate input level.

in -10dB mode: 0 bars in +4dB mode

Note that the switch only affects the operating level of the unit, and has no affect on the signal level.

There was a significant amount of hum coming from the sub when attached to the BFD

Would be interesting to know if it's a ground loop, by testing it with a ground cheater plug temporarily.

New results obtained

You shouldn't lose ~5dB through the unit. I wonder if there is a problem with the power supply and the hum is derived from this, and the low level is a byproduct of it.
Tell me about your cables. Are they standard RCA to XLR with the pin 1 and 3 shorted?

brucek

[Wayne A. Pflughaupt]

Hmm... Well, if you're confident you had it bypassed (it's a no-brainer with the In/Out button after all) then it looks like it has a problem. Still, you might double check by selecting a preset and turning all filters to "Of" (off) and running your "No BFD / BFD in bypass" test again (no need to run the assorted frequencies - pink noise is fine).

The hum most likely is a separate issue, so be prepared to deal with it once you get things lined out. Most typically it's caused by the feed from cable TV or a satellite dish.

Regards,
Wayne


EDIT - I seem to be one step behind brucek on this thread- LOL. Certainly, check out everything he mentions.

[Nutball]

More info:

Low level info:
I verified again that the in/out switch was flashing to indicate that I was in Bypass Mode.

I also tried manually disabling the filters: no effect


Hum issue:
Tested ground cheater plug: No effect

Unplugged cable line from wall: No more hum!

For reference, with the cable line plugged in I measure (uncorrected) approximately 75dB @ 1m from my front firing sub.

[Wayne A. Pflughaupt]

I think I'd look into replacing it...

Regards,
Wayne