[tculverhouse]

I was reading through the gain structure article in this forum and noticed a reference to my very own DEQ - the Yamaha DEQ7 (picked it up for $30 at a Music Go Round).

Now, it was mentioned but not really explained what my optimal gain structure should be for an older piece of equipment like this. There was lots of talk about not needing to max out gains for 24 bit DEQs, but when the DEQ7 was mentioned, it sounded like I should be maxing out signal levels (assuming no clipping). For those of you not familiar with the DEQ7, it has an input gain control knob, input level selector for +4/-20 dB (yes, -20 not -10) and an output level selector of +4/-20 dB. My chain of equipment and gain structure is as follows:

Pioneer Receiver LFE Output (0dB) -> DEQ7 Input (-20dB) -> Input gain dial maxed out->DEQ7 Output (+4dB) -> AudioSource Amp100 at 50% (bridged).

I use the +4dB on the output stage of the DEQ because the Amp100 states an input sensitivity of 1.4 V (+4 dB). I am running an Anarchy Tapped Horn off of this system, and if I get real close to it I can hear the noise.

My question is this: Am I better to run my gains at maximum until the last stage (volume control on the amp)? Or is there another way I should set this up? I can still turn up my receiver's LFE output to +10 dB, and in doing so see no clipping at my usual listening levels. Thoughts?

The only scenario that (subjectively) lowers the noise seems to be:

Pioneer Receiver LFE Output (+10 dB) -> DEQ7 Input (-20dB) -> Input gain dial maxed out ->DEQ7 Output (-20 dB) -> AudioSource Amp100 at setting to hit SPL desired

 

[Jungle Jack]

Hello,
Often with theoreticals like this, I find that experimentation yields the best results. Ideally with sympathetic Ears willing to provide input. QED if you will. Whatever sounds best to you, is the right call IMO.
Cheers,
JJ

 

[Wayne A. Pflughaupt]

Welcome to the forum, Tim! Frankly I’m surprised that you’re having a noise issue with a subwoofer.

Now, it was mentioned but not really explained what my optimal gain structure should be for an older piece of equipment like this. There was lots of talk about not needing to max out gains for 24 bit DEQs, but when the DEQ7 was mentioned, it sounded like I should be maxing out signal levels (assuming no clipping).

Yes, it was an oversight not delving more into the requirements for older digital gear - sorry.

There are two main problems with lower bit-rate gear. One will be the potential for a higher noise floor than what newer 24-bit gear has. The second issue is poorer low-level linearity. This is probably more critical than potential noise, because, as I noted in Part 5, there’s a lot that determines a piece’s noise floor besides just its digital converters. Even a piece with 18-bit converters has the potential for a dynamic range of 110 dB. However, I don’t think there is a “fix” via trick secondary circuitry for overcoming low-level linearity in lower-bit converters.

The only scenario that (subjectively) lowers the noise seems to be:

Pioneer Receiver LFE Output (+10 dB) -> DEQ7 Input (-20dB) -> Input gain dial maxed out ->DEQ7 Output (-20 dB) -> AudioSource Amp100 at setting to hit SPL desired

I think you’re on the right track there, not with the output switch set to +4.

As you know, with the input switch set for -20 and the output for +4 you get a significant signal boost. However, with it comes a substantial increase in noise. As I noted in the article, there’s no free lunch when it comes to signal boosting: The component’s entire signal range is lifted, including its noise floor.

Ideally, with all filters bypassed, the EQ should be passing the input signal straight through with no increase or decrease in level (aka “unity gain”). Since I guess you have no manual (and I can’t find one on line) to tell what the unity gain setting is, the best way to check this is by using the voltage-measuring technique I described in Part 7: Using the test sine wave, measure the output voltage of first the Pioneer’s subwoofer output. Then add the EQ to the signal chain and measure again, and adjust its gain knob until the two voltage readings match.

If you’re getting objectionable noise with both switches set for -20, you should take a closer look at your equipment, especially the EQ and amp. If you can, try taking the EQ out of the loop (i.e. Pioneer receiver straight to Audiosource amp), and then with the EQ in the signal chain, but using a different sub amp. This would help you isolate which component (if any) is the source of the noise.

Regards,
Wayne

 

[tculverhouse]

Wayne -

Thanks for the detailed response! Something I forgot to mention is that I did have a ground loop issue, but have corrected that by sanding some of the paint off the Yamaha's chassis and grounding that to my cable splitter. It's possible I didn't completely solve that issue and that is the noise that I am hearing.

By the way, the DEQ7 has a bypass switch, so when I get peace and quite later tonight (ie. kids go to bed) I'll try bypassing and see if I hear the noise. If I do hear noise, I'd bet it's the ground loop issue.

Thanks again.

EDIT: I should note: the noise I hear isn't audible at the seating position. I have to have my ear maybe 6" from the mouth of the sub to hear it, so maybe I'm just being too picky