Does the BFD double as a line driver? (1 Viewer)

[jeff lam]

After firing up my crown ce100 last night I found that I may be a victim of the "sub output too low to drive my pro amp" club. I didn't have the BFD hooked up yet. I was able to get to referrence level with the gain maxed out and the sub level half way but I have a feeling once I cure the room peek at 40Hz it may change the referrence level. Anyway, I read that the BFD can be used with both -10dbv and +4dbu, so will it help drive the voltage level to the amp?

BTW, The old 100W receiver/amp I was using previously at half volume drove the tempest much louder than the 450W crown does at full gain. I guess I'm lucky to have a small room, I don't think I could get to referrence if the room was larger.

I also checked the specs for my sub output on my Yamaha receiver and it said: 4V @ 1.2Kohms Don't know how it would relate to the input level on the amp though.

 

[Anthony_Gomez]

Well, my crown k2 will reach max at 1.4V...so no wonder your yamaha could do it at 1/2 volume ( 4V @ 1.2Kohms ). The BFD doesn't seem to boost the signal as a preamp that much. I just solve the problem by setting the sub channel to +4db. Problem solved.

 

[jeff lam]

I'm still not understanding this. If all it takes to get 450W out of the CE1000 is 1.4V and my yamaha puts out 4V, why am I runing out of headroom real quick with my sub output? I guess I was just expecting a 450W amp to drive the tempest much harder than my old 100W receiver/amp. Why is it that my 100W receiver/amp can drive the sub harder?

For movies, its fine, but for music I want to boost the sub a little bit extra to get that added kick! What's the problem? Am I really getting full power from my Crown? If so, it's much weaker than my old 100W receiver/amp.

 

[Vince Maskeeper]

Quote:

And I'm unsure what is preventing you from making that increase... you mentioned a lack of headroom above, but never said exactly how you determined or in what stage the headroom problem was occurring.
I personally don't usually find any need to "boost for extra kick"- as I'm more of an accuracy guy as oppose to a show-off guy-- but if I needed to- I don't think I'd have any trouble- so I'm confused as to exactly what you are experiencing.
Are you getting full power from the crown? Dunno- there should be a clip light on the face of the amp- Can you make it clip? Disconnect the speaker from the amp, and feed a line level 50hz sine wave into your system- and see how high you have to turn the master before it clips.
Again- there is some confusion here because I'm hearing multiple complaints:
1) Not getting enough juice (although you can calibrate and seem to within tolerance levels, so I'm unsure where you have made this determination).
2) Running out of headroom (although you never mentioned lighting the clip on the amp, or any specific knowledge of headroom on the preamp stage).
3) Not hiting as "hard" (although no real data or explaination went along with that-- and more so if it is a simple volume issue this seems easily solved and somewhat moot as the whole point of calibration is proper SPL level).
-Vince

 

[jeff lam]

Vince,

I was hoping you would chime in and straighten me out. I guess my terms are not correct. I guess what i'm saying is, I can't get near the volume I used to get with my old receiver and that only put out 100W as opposed to the crowns 450W into 4 ohms. All levels the same on the receiver and volume the same. When I run the old receiver at half volume I get more output from the sub as I do with the crown with the input level wide open.

Vince, you know what I mean when I say gain maxed. Just because the terms aren't correct doesn't mean I'm confused.

BTW, when going through the amps mannual, they do NOT recommend running the amp wide open!!! The recommend to turn it up till it starts to distort, then back it off a little. So, I don't know which way to run it. I'll get the exact quote later.

BTW, I'll check to see how high I can crack it before the amp clips. I don't think it will be a problem, what I meat by running out of headroom is not being able to take it as high as I expected. At full reference volume runing sub calibration with VE, the max SPL I can get at the listening position is 90dB(sub level maxed, amp wide open) which is more than enough for my room but I expect that level to drop when I eq out that 40Hz peek. And what if my room was larger? I would only be able to max say about 80dB or less. Remember, this is with full reference volume and sub output maxed. I bet I wouldn't have a volume problem if I ran the PE 250W plate amp rated at 200W less than the crown. So I know I'm not just expecting too much.

Final word is NO, I may not need a voltage boost in my room, but it would sure make me feel better to know I can crank it up if I need too without running full reference volume on all speakers.

Just for reference: my old Def Tech Prosub200(midfi at best) would do 90dB with VE sub calibration at less than 1/2 volume too.

I will run it more tonight and come back with a clearer picture for you tomorrow.

 

[jeff lam]

Vince,

On a side note:

3) Not hiting as "hard" (although no real data or explaination went along with that-- and more so if it is a simple volume issue this seems easily solved and somewhat moot as the whole point of calibration is proper SPL level).

Correct me if I'm wrong but if what's important is proper spl levels at calibration, why is it that we use loads of power to drive subs? After all, a few watts can drive a sub to 75dB during calibration right? However this would not be ideal. Again, please correct me if I'm wrong.

 

[Vince Maskeeper]

Correct me if I'm wrong but if what's important is proper spl levels at calibration, why is it that we use loads of power to drive subs? After all, a few watts can drive a sub to 75dB during calibration right? However this would not be ideal. Again, please correct me if I'm wrong.

Well, it isn't so you can use 450 watts at all times.

The point of higher powered amps is accurate, CLEAN power. Headroom. That deal above where you used a 100 watt receiver amp-- you were using 50% of its power to get 75db with a tone. I would say that on any real bass peaks you were clipping/limiting it badly. I'd guess the amp spent most of its time slamming out squared peaks at 130 watts with 15% distortion. This usually results in really boomy sounding subs (like the cheap subs in cars)- which creates the illustion of "volume" because it is loud and throaty. This is not the goal.

The point of having the 450 watts is HEADROOM. 450 would only be needed for extreme millisecond peaks- and probably no even then in a small room. However- you know it will be clean power because at normal operating level you are only using 10% of the available power. You have tons of room to go up on peaks, and have clean peaks.

That's the point of bigger amps- it's not a volume game (well maybe it is if your a teen with a bassmobile)-- for those who are serious about audio, bigger amplifiers mean more headroom, means clean output up to the max of the system. This might mean that they never use more than 400 watts out of a 3000 watt amp--- doesn't matter. The point is that all 400 watts were clean and undistorted.

That's what you have right now- an amp that can be properly calibrated, and is only using a small portion of its power at normal operating level. When it gets real bass peaks during program material, it should have all the power to handle them without effort.

-Vince

 

[brucek]

Jeff,

As Vince has inferred, you're confusing some issues here. You're comparing the power levels of amplifiers when the issue is one of voltage swing required to drive an amplifier for full power output.

Either way, what you are suffering is simply not enough voltage from your preamp output to the sub power amplifier to drive it sufficiently. This is a common problem, particularly if you mix pro and consumer equipment. It has little to do with the impedance output of the preamp. This is considered a line level, high impedance connection where the input impedance of the subs power amp will be in the order of 50Kohms while the output impedance of the preamp will be in the order of 100 ohms. This is a voltage bridge type high impedance connection where the preamp acts as a voltage source and almost no current is drawn. We are not interested in power transfer in this interface. If the voltage swing is insufficient to drive a power amp to maximum power output then you need to simply boost the voltage level.

A BFD has a unity gain, so there's no joy there.

A perfect device for this application is a Paradigm X-30. It has considerable voltage gain with an appropriate high input and low output impedance. It has the added benefit of being inexpensive, well made, very low noise floor and you get two line outputs with a front panel volume control and variable phase and crossover if you want to use it.

Put it after your BFD and you'll have lots of voltage to drive your amp. I'm sure you can borrow one to test out in your system.

brucek

 

[jeff lam]

Vince,

Your points are very well taken. In my case, I always ran my sub a little hot anyway(as most people do) and never listen at even close to reference levels. To give you an idea of the level I listen to, my reference volume is -16 on my Yamaha receiver and I have never taken it above -35 for normal movie watching(APT). During tests and kicks, I turn it up to -30.

I totally understand what you are saying. You're right about me getting kicks about how great my sub is and then just bring it back to normal calibration level. In the end it always comes back to calibration levels.

BTW, for music I have always found the sub to be well below my preferred listening preference. I guess that's what years of car audio bass does to you. I like that added "KICK" on my butt when the kick drum hits. That is my only real concern. I'm not worried at all about movies. I would always turn the sub level down during movies.

So if I did need a Line level driver, would you still suggest the EBTECH line level shifter above others? I don't know what it is but there is just some added peace of mind when you don't need to run your sub at max to get proper calibration.

BTW, what do you call that when you run out of room to increase your sub level. Thats what I was referring to when I said "headroom". You know what I'm talking about, when you have your sub at max level and your amp wide open and you still can't get to proper calibration.

Also, my LFE pad is max for DTS and DD. Is this where they should be?

 

[Shawn Solar]

yeah, I tend to agree with the other guys. If it was a voltage problem you wouldn't get loud bass period. You would have to max the levels on the amp,the lfe output, and the master volume and still not get any loud bass. If that were the case then you could say it was a voltage problem. I actually went through the exact same thing with my pro amp. I first hooked my sub(BP 1503) to my anthem 2-ch amp and got decent bass. So I thought 1200watts would be even better so I hooked it up to my pro amp. well I had to turn the lfe, the amp gain and the external crossover gain all the way up. I then cranked the volume on my reciever and it didn't even come close to the levels the 350watts into 4ohms the anthem put out. Things got even uglier when the limit light started flashing on the pro-amp.

 

[Kerry Hackney]

Jeff, I think the gentlemen at SVS have a product coming that will solve this problem for you. They are bringing out a "blackbox" that will be in the sub-out stream that includes, line boost, phase adjustment and rumble filter. There is a thread in the sub section where Tom talks about it. Gotta love those guys..

 

[Patrick Sun]

IIRC, there exists some device that will convert from the home/pro devices (-10dbv and +4dbu) and I think was around $70 and available at music gear stores. Does anyone else remember this sort of device?

 

[jeff lam]

Pat,
Vince once recommended the EBTECH Line Level shifter in a previous post a while back. I'm sure that would cure any voltage difference problems. Was just checking with Vince to see if he would still recommend this device.

 

[Patrick Sun]

Ah, okay, yeah, I think the name now strikes a chord and the price is right inline with my sievelike memory.

 

[Donnie Miracle]

Jeff,

Don't feel alone. I am in the same situation. I have a Yamaha 5280 paired with a Samson 1000 amp and SVS 20-39CS+ sub. I can barely get the sub calibrated with the Avia test disk even with the Samson amp gain all the way up and the sub line-level of the Yamaha all the way up (at 0dB). When I say calibrated I mean for movies. Bass for music is totally inadequate due to the "consumer" receiver to "pro" voltage/impedance problems. I did buy a Radio Shack SA-155 pre-amp for $60 that did totally fixed the problem EXCEPT...... with a fairly loud hum. The SA-155 is known to be noisy and I will be taking it back but it did fix the problem.

I am also interested in whether the BFD would be able to add "overall gain" or voltage to the sub line-level output or what ever is needed to fix our problem. SVS is working diligently on a nice audiophile grade auxiliary box that will fix our problem and have some other nice features. I believe it is estimated to be in the $99-$149 price range when it becomes available. For that price (BFD for $135)I thought IF I could fix the problem AND get a nice EQ at the same time I would like to do it. I have read where one person hooked up an ART351 and that fixed his sub line-level deficiency.

It was stated in an above post that the BFD has a "unity gain". I'm not sure what that means. So my question would still be:

Does the BFD have a feature that would correct deficient sub line level output from a consumer grade receiver that is being connected to a pro grade amplifier?????????

Anyone have a definitive answer? (I'm sorry if the "unity gain" post answered this question and I just didn't understand.)

Thanks for the info everyone,

Donnie Miracle

 

[jeff lam]

Donnie,

I'm afraid the BFD won't help boost the voltage level but it can help out a lot with room response. I hooked mine up last night and was playing around with it. It's a complicated peice of equipment for first timers, that's for sure.

I indeed did have a full 10dB peek at 40Hz and when I brought it down, my calibration level also went down. I was also running tests with the sub level output and found there is major distortion on the sub output if it is maxed out. With this being the case, I surely don't want to run max output on my sub level. I'm pretty sure I'll need a line driver when all my filters are set up on my BFD.

 

[Vince Maskeeper]

Also, my LFE pad is max for DTS and DD. Is this where they should be?

Yep... that's right.
Again, I'm suprised to find out that the BFD doesn't have an overall gain setting that allows a little goosing (most any EQ I can think of off the top of my head does)... guess I'll have to get one of those puppies and play around a little.
-Vince

 

[jeff lam]

Well, the main reason I suggested it is that it is one of the only ones I've actually ever used myself. If you can go to your local Sam Ash and they have something else, by all means try it out!

Vince,

Did you find the EBTECH LLS to work well for your application? Did you have any complaints about it?

 

[brucek]

Donnie,
Donnie said:

It was stated in an above post that the BFD has a "unity gain". I'm not sure what that means. So my question would still be:
Does the BFD have a feature that would correct deficient sub line level output from a consumer grade receiver that is being connected to a pro grade amplifier?????????
Anyone have a definitive answer? (I'm sorry if the "unity gain" post answered this question and I just didn't understand.)

By the statement "unity gain" I meant that the BFD will pass an equal voltage level from its input to its output. It is not a line amplifier. So 1 volt in will be 1 volt out. When a filter is entered the amount of gain and cut on the output voltage will center around the input level.
Jeff,
I agree with the recommendation not to overdrive the sub output of your processor to satisfy your sub amplifier. In fact, when you include a BFD in this chain, then you have to first consider the level input of the BFD and ignore the sub amplifier.
The important setting to start with is getting the input level to your BFD properly set using its LED readout and ignore the SPL levels of your system. Once this is accomplished, then you can freely adjust the SPL level of your sub with the subs own amp setting. If that requires a line amp after the BFD to reach the proper voltage levels to obtain the SPL you desire for your sub, then so be it.
Then set up your filters and readjust the SPL level of your sub amp if necessary with its own volume again to get your +10dB above mains or whatever end SPL level you like.
I wrote a technical review of the BFD for Sonnie Parkers site http://www.troycable.net/~snap/bfdinfo.htm at:
http://www.troycable.net/~snap/brucekreviewofbfd.htm and I included a section on how important the input level to the BFD is for obtaining your best levels. I reprint that section below regarding BFD level set up, if you're interested. I think it applies here.
quote:
------------------------------------------------------
I want to comment on subwoofer output level from your receiver/ preamp if that's ok. When setting up the input levels to the BFD you have to remember it isn't a normal fixed line level situation. Consider the output of a CD player for instance. It is a line level that has a varying output depending only on the music being played, but it still has a fixed maximum line level output that isn't passed through a volume control. This line level would be very easy to match to the input of the BFD because it's predictable. This unfortunately isn't the way we're using the BFD. We are feeding it a line level signal that is affected by our preamps volume control. See the problem? I can play a DVD at a very low level or a very high level and the BFD will be fed different "maximum" inputs. One of the problems with ADC's (analog to digital converters) is that they tend to become fairly non-linear and rather ineffective at low input levels. They operate best if they are fed a signal which has a maximum that is just below their maximum input level. This ensures that the maximum signal does not clip and the quietest signal gets properly evaluated and assigned the appropriate low order bits to correctly represent its actual level when converted back to analog by the DAC. This is where quantization error (noise) exists, at these low levels.
Your goal then, is to decide what the probable maximum listening level will be for your volume control of your receiver or preamp while playing a bass heavy disk like U-571 or TPM and then set the "subwoofer output" level of your receiver to where you see the red LED's lighting up on the BFD. The BFD does not clip when the red LED turns on, but it does clip with a signal slightly greater than that. I've done quite a few bench tests on mine and I found the red LED turns on at about 1.5volts peak and the output begins to clip at about 1.6volts peak (+4dBv). This is the case when you use the operating level sensitivity switch set at -10dBv (which is the only setting you should use).
Yeah, I know the book says the max input level is +2dBV (1.26volts peak) but my measurements show this is when the yellow LED turns on and you still have quite a bit of headroom right up to +4dBv before clipping occurs.
Anyway, once you have this subwoofer output level set, then you know the maximum sent to the BFD will be a maximum signal that it can tolerate and you'll know normal levels will be in the linear region. Now you can set the output level of your subwoofer with its own volume control to whatever level you enjoy.
Note that the BFD IN/OUT switch will enable and disable your filters with its’ light "ON" and "OFF" respectively. In these two conditions the LED indicators are showing the BFD's output level. But, if you push and hold the IN/OUT switch and it begins flashing, you bypass the filter section completely and the LED indicators are showing input level. This is the condition to set it up in and that I am discussing above.
----------------------------------------------------
Anyway, I will again recommend a Paradigm X-30 control unit to solve your line level problems. It provides excellent control for a sub.
brucek

 

[Vince Maskeeper]

Did you find the EBTECH LLS to work well for your application? Did you have any complaints about it?

Nope, worked fine. Different application- but same basic idea. I'm assuming it should work in this situation as well-- as long as the headroom is there it should be fine.

Bruce,

Although your info about digital conversion is generally true (full word length at greater input level, less than linear performance at lower levels)-- were you able to get any concrete data on this particular unit? Every A/D is different, and I'd be curious to see some quantitive figures on decent operating range... or specifics on where the error floor for a resonably simple signal featuring only 80hz and down would fall as far as input level.

I've thought about splitting the signal and then running it into a PC analyzer as a stereo signal and having it compare the two. I don't have one on hand though- so I hoped maybe you had saved the work for me and could let me know if you ended up with any concrete figures on this issue.

-Vince