Ideal Sub Amp Gain Setting - AVS Forum
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post #1 of 11 Old 11-29-2004, 08:13 AM - Thread Starter
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When calibrating a sub is there an ideal level of amplifier gain that you should strive to achieve? I seem to remember something about slew rates and the optimal gain of a feedback control system being about 70% or [ 1/SQRT(2) ]. It's been a while since I took a circuits course and I'm admittedly not an electrical engineer.

I've been using a PB10-ISD for about 3 weeks now and I have the gain set to 50% and I'm wondering if I should lower the level in my receiver so that I can up the amp's gain to ~70-75%. I doubt the adjustment would be audible but I think the amp would work more efficiently. Any suggestions?
-J
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post #2 of 11 Old 11-29-2004, 08:20 AM
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I can't tell you if this is the norm, but my installer has all of my amplifiers at max output. We adjust levels in the processor and EQs.

There are more than a handful of [op amps] that sound so good that most designers want to be using them as opposed to discreet transistors. Dave Reich, Theta 2009
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post #3 of 11 Old 11-29-2004, 11:12 AM
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I usually set mine up pretty high - maybe 75%. The thought is that you keep the signal higher up away from the amp noise floor.

I am serious...and don't call me Shirley.
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GIK Acoustics

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post #4 of 11 Old 11-30-2004, 06:26 AM
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I received the PB10 yesterday, and the manual states to set it 1/4 to 1/3 of a turn, which would be slightly less than half.
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post #5 of 11 Old 11-30-2004, 06:46 AM
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My amps are pro amps and are designed for such play. If SVS recommends starting at 1/4 or 1/3 of turn, I would start there. The amplifier may be problematic if set all the waty to the top. When in doubt, trust the manufacturers recommendation. There are reasons for their suggestions even though no explanation is given as to why.

There are more than a handful of [op amps] that sound so good that most designers want to be using them as opposed to discreet transistors. Dave Reich, Theta 2009
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post #6 of 11 Old 11-30-2004, 09:17 AM
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I"m running about 60%. bpape's point about keeping it well above the noise floor is a good one. I'd say anywhere over 50% if it keeps the receiver adjustments in range. But do start with the manufacturer recommendation and work from there.

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post #7 of 11 Old 11-30-2004, 09:33 AM
 
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Quote:
Originally posted by aeromorris
When calibrating a sub is there an ideal level of amplifier gain that you should strive to achieve? I seem to remember something about slew rates and the optimal gain of a feedback control system being about 70% or [ 1/SQRT(2) ]. It's been a while since I took a circuits course and I'm admittedly not an electrical engineer.

I've been using a PB10-ISD for about 3 weeks now and I have the gain set to 50% and I'm wondering if I should lower the level in my receiver so that I can up the amp's gain to ~70-75%. I doubt the adjustment would be audible but I think the amp would work more efficiently. Any suggestions?
-J


My receiver let's me adjust the subwoofer through my receiver plus or minus 10DB.

Set the subwoofer in the ballpark volume wise at 0 DB at the receiver, then calibrate up or down via the receiver. You want to keep the receivers DSP in the ball park of 0 DB. In other words, not at -10DB or plus 10DB for a setting.

That's about all that you can do!

--Bill
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post #8 of 11 Old 11-30-2004, 01:18 PM
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Quote:
I"m running about 60%. bpape's point about keeping it well above the noise floor is a good one. I'd say anywhere over 50% if it keeps the receiver adjustments in range. But do start with the manufacturer recommendation and work from there.
DMF,

What about if your cable leads are too long and you've adjusted your subwoofer amps gain to max position? Is there a possibility of getting noise because you're receiver is sending a too low level signal to the sub?
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post #9 of 11 Old 11-30-2004, 03:18 PM
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Not sure I get your question, Jorge.

You mean the sub amp increasing the noise from the amp? Hmmm. Not sure how to answer.

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post #10 of 11 Old 11-30-2004, 07:57 PM
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OK. Let me rephrase my point:

When you set the amps gain to the max position you're trying to be well above the subwoofer's amp noise floor, as bpape correctly stated.

Then your subwoofer's output will be too hot, so the receiver or pre/pro will adjust the magnitude of the low level signal that is being sent to the sub: the DSP will lower it down for sure.

I think this signal can be below 1 volt, so a long cable can pick up noise whose order of magnitude is not so low if compared to that low level signal. If this is the case, then there's no point in setting the sub gain control to any position above 50%.
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post #11 of 11 Old 12-01-2004, 05:43 AM
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Quote:
Originally posted by spider_bill_2003
My receiver let's me adjust the subwoofer through my receiver plus or minus 10DB.

Set the subwoofer in the ballpark volume wise at 0 DB at the receiver, then calibrate up or down via the receiver. You want to keep the receivers DSP in the ball park of 0 DB. In other words, not at -10DB or plus 10DB for a setting.

That's about all that you can do!

--Bill
I subscribe the same mind set as spider_bill and I have to set my VTF-2 (max extension) at a small slight twist higher than the absolute lowest sub amp gain to get the AVR to be autoset to even -1 dB. At about just under 1/4 sub amp gain the AVR is autoset at -8dB.

I can not reconcile the mind set that Bill and I use with the one to have the sub amp set as high as possible for my room (12x16x8) and setup. Another plus to me at having the AVR output as close to 0dB and not far into the negative dB settings is to keep the auto-on triggered well. At this low sub amp settings I have had no audiable noise or issues with the subwoofer.
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