Input level - compromise between bits or amp performance?

[Mikkel]

Forgive me asking (considering it has been covered - in some way - dozens of times before, as far as I can read) but it is about the usual input level settings for the BFD (1124p). I need your help to interpret the best solution:

When setting the input level of the BFD one can either calibrate for -10dBV or +4 dBu.

Using a rather loudy DTS cd with a lot of sound pressure down to 5 hz and the AVR volume at -25 I get the following results to achieve a -6 db peak reading on the input level meter of the BFD:

BFD at -10dBV: -1 sub out on the AVR
BFD at +4 dBu: +8 sub out on the AVR

What setting on the BFD should I use? My poor logic tells me, that going below reference (0 db) on the sub out of the receiver means losing bits while going above reference means driving the AVR harder thus losing precious watt that degrades the general performance of the AVR.

Am I completely off? (I'm not tech-able, so don't yell at me if I am... I'm a mere "hobbyist")

[brucek]

Am I completely off?

Yeah, you're looking at it wrong.

The BFD should be operated in the -10dBV position for most receivers.

Regardless of the plus and minus trim level from the sub-out of a receiver, there are no bits lost. This is an analog voltage interface. It's known as a voltage bridge connection where the source is acting as a voltage source and almost no current is drawn. You needn't worry about any 'watts' being lost since there is no power being developed.

The trim adjustment is offered to allow a fairly large range of line-out levels to be used to accommodate different receiving devices and to give a range for balancing among the other speakers.

brucek

[Mikkel]

Thank you very much, brucek. Your input is much appreciated.

[ironglen]

If Mikkel was forgiven, may I as well? Just purchased a samson pg2200 amp and I hooked it up to the onkyo 806 via rca-xlr cable and to my 10" sonosub to try it out-signal levels must be too different because the output in bridged was barely enough to drive the sub with gain at max. I tried the same connections with my old Pioneer AV sub-out and had the same thing...will a Reckhorn b-1 or Elemental Designs eq.2 provide the proper signal, along with providing low freq protection? I'd rather get the protection and possible eq ability if I must buy another device, but of course, I need proper signal level first. FYI, output from onkyo 806 works nicely with svs cs12. Specs are below-thanks for help in advance!

Onkyo 806 output level, impedance = 200mv/470ohms

Samson pg2220 input level, impedance =1.22V(+4dBu)/10kohms unbal, 20kohms bal

B-1 manual stated:
input sensitivity 0,1-10V/10kohm
signal output 10V

EQ.2 manual stated:
Gain - The gain on the eQ.2 is actually an attenuation dial; the maximum voltage of 2.5V is only reached when the knob is turned to Max
Also note if you are using a Pro-Amplifier you may need to boost the signal after the eQ.2 in order to have the proper voltage for your
amplifier

[brucek]

The 200mVRMS nominal output level spec on the Onkyo is definitely the problem, but isn't out of line compared with many other receivers. Generally, a receiver should have a nominal output level of -10dbV (315mVRMS), but since the expectation is that they'll feed a non-pro device, then the 200mv would be suffice.

The Samson is certainly expecting a higher pro-level with its nominal input level at +4dBu (1.24vRMS), so a line driver is called for.

I don't think the B-1 would offer any gain. I suspect it's unity gain and the input level control would be an attenuator. The 1-10v spec would be the range that it can operate in, with a corresponding 1-10v out. The boost would be only frequency specific.

The EQ.2 spells it out for you by letting you know that the input doesn't offer any gain. It would also likely be unity gain (1:1).

You would need a line stage. The ART clean box appears to offer gain and a subsonic filter (that unfortunately requires modification).

brucek

[ironglen]

Thanks Brucek, suspecting and having confidence are different things- as as you know, unnecessary equipment purchases are, well, unnecessary and wallet-thinning. I can solder, so I can handle a modification; I'll end up with a SSF which is good protection. Thanks for the link as well!

[ironglen]

Found the Samson S-Convert performs the same function as the ART Cleanbox- without the necessary capacitor mod to prevent low-end signal loss. Plus, I have the Samson amp, so I stuck with the same- and found it for less money to boot!