Setting gain with DMM

[fixinit]

Hey guys. I dialed in my amp's output voltage to 40v = roughly 750w with my HU at 2/3rds its max volume (38) @50hz. Here's the thing. I listen to my HU's volume around 15-20 max with quality CD recordings. At 15-20 volume, the voltage test at the amp obviously decreases exponentially, so that leads me to believe that I'm no where near my targeted output of 750w for the sub - more like half. In theory, shouldn't I be adjusting my amp gain to head unit at my personally chosen MAX listening level (20) instead of cranking the HU up 2/3rds (38)? Are their downsides to setting gain this way?

HU: JVC KD-R330 - Line-Out or Subwoofer-Out Level/

Impedance : 2.5 V/20 kΩ load (full scale) Output Impedance : ≤ 600 Ω

Amp: Power Acoustik PS1-4000D - 1700RMS @ 2ohms

Driver: MOFO-124x - 1200RMS

Wiring: KnuKonceptz Kolossus 4 gauge OFC

Links or comments would be helpful. I haven't been able to find anything too credible on this. Thanks.

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[Sguirrelfeather]

While I'm far from an expert, I'm sure the first thing most would bring up is the fact that if you accidentally went over your chosen max, you'll be putting out more wattage than you want. Your amp has lots of headroom, and it looks like your sub does as well, so a little above your chosen max should be fine, but is there a possibility someone else may drive your car and turn the volume well above your chosen? I'd also imagine there will be less adjustability, meaning you may find that a level of 10 is a little too quiet, and 11 is just a hair too loud for your desired listening volume at the moment. Otherwise, I see no issue with it...though I may be wrong. lol

 

[Jeffdachef 5,000+ posts]

Its better to set your gains by heat and ear with the gear you have. The multi meter method only works if you have a true to output rms amp. That amp only does around 400 actual watts after impedance rise if its lucky. Sorry to say.

You also need to analzye all your music on audacity to find out what test tone you would use to tune the amp along with creating such test tone. Sounds like you used a 0 db test tone which basically guarantees you being pigeonholed out of a lot of output. I dont trust the multimeter method too much to honest. Its a passive way of setting gains and that produces junk results imo.

With the ear and heat method its way better and safer imo. Play your hardest hitting song. Turn the gain up till it stops getting louder. Then back it off a notch. Then play music for 5 mins constantly monitoring the amp for changes in temperature or smell. If they stay cold, you can turn it up. If they get hot, turn it down. If they get lukewarm to moderately warm, then you are at a good balance.

Clipping doesnt directly kill subs and amps. Heat does. Manage your heat well will make your gear last long and give off everything it can put out. Each song will require different clicks of volume with the bass in each recording varying greatly. Keeping up with this is called active gain setting which ensures max output on any song along with keeping gear safe.

 

[fixinit]

Its better to set your gains by heat and ear with the gear you have. The multi meter method only works if you have a true to output rms amp. That amp only does around 400 actual watts after impedance rise if its lucky. Sorry to say.
You also need to analzye all your music on audacity to find out what test tone you would use to tune the amp along with creating such test tone. Sounds like you used a 0 db test tone which basically guarantees you being pigeonholed out of a lot of output. I dont trust the multimeter method too much to honest. Its a passive way of setting gains and that produces junk results imo.

With the ear and heat method its way better and safer imo. Play your hardest hitting song. Turn the gain up till it stops getting louder. Then back it off a notch. Then play music for 5 mins constantly monitoring the amp for changes in temperature or smell. If they stay cold, you can turn it up. If they get hot, turn it down. If they get lukewarm to moderately warm, then you are at a good balance.

Clipping doesnt directly kill subs and amps. Heat does. Manage your heat well will make your gear last long and give off everything it can put out. Each song will require different clicks of volume with the bass in each recording varying greatly. Keeping up with this is called active gain setting which ensures max output on any song along with keeping gear safe.

Thanks for the replies. After soaking this in a little bit, I think I know where you're coming from. I ended on turning up the volume on my deck (not amp gain as suggested) until my rear 6x9s stopped getting louder, then backed off a few dials (30 was the magic number). Went back to the [0dB] test tone and threw the gain to read low 40 something Vac which was about 50% gain. Then added another 10-15% gain.

Popped in a 'Bass Mix' CD and drove around town for 15 minutes at volume 18-20, pulled into a park then pushed a heavy hitting song 'yelawolf - trunk muzik' to 25 on the dial. Physically inspected the amp and it was bone cool. The sub was cool and didn't look or sound to be clipping. No dimming when I had my low beams and hazard lights on. Electrical system is stock '93 Camry 2.2 btw. So far so good.

As for the statement about my amp only pushing "400 actual watts after impedance rise" - I'm thinking that number is on the low-side according to my bleeding earbuds at the general tonal range of my preferred music after tests. I'm planning on getting accurate benchmark tests on this amp if I can find a shop who'd do that for a reasonable flat fee, then I'll share - without impedance rise - what she's capable of. Mind you, for trunk space and more so weight, I went with an enclosure that's nearly
For google search result giggles since there's none out there. Here's a photo of the Power Acoustik PS1-4000D board. I think the model was circa 2008.

View attachment 26555769

 

[hispls 5,000+ posts]

It's likely that amp won't make much more than 1500W. If you got 40V out of it, that's about right assuming it'll drive 1 ohm.

People really underestimate how little power it takes to get loud though since few people look at the impedance of their sub in the box. .

For example, my subs wired up to .7 ohm are generally between 3 and 7 ohm dipping only as low as 1.3 ohm at the lowest point.

 

[Jeffdachef 5,000+ posts]

As for the statement about my amp only pushing "400 actual watts after impedance rise" - I'm thinking that number is on the low-side according to my bleeding earbuds at the general tonal range of my preferred music after tests. I'm planning on getting accurate benchmark tests on this amp if I can find a shop who'd do that for a reasonable flat fee, then I'll share - without impedance rise - what she's capable of. Mind you, for trunk space and more so weight, I went with an enclosure that's nearly
In a bench resistive load then it will make around 1k ish or it might die since its not meant to be on 1 ohm resistive load vs 1 ohm nominal loads.

In the real world, not much more than 400, most likely even less. I bet none of the shops around you have a 5000 dollar amplifier dyno to run a proper resistive load test. Bet that you'll even have a hard time finding one that has a fluke clamp meter knowing how to do a proper clamp test along with an oscope to see if your signal is clean or not....

Btw if everything is still cold, You got some ways to go with the output. You dont use a 0 db test tone, thats just fking yourself over. unless you use audacity to analyze your music, you shouldn't be using test tones. here's a tutorial on audacity, leave on annotations

 

[n2audio 5,000+ posts]

Pretty sure that was one of Power Acoustik/Lanzar/some other cheap brands (?) ~1200w boards.

~700 @ 2 isn't a stretch IMO.

But setting the gain at 0dB will give you a LOT less than optimal power output since you rarely see music levels at even -2 or -3. It's often suggested to set them up with -3 or even -6dB tones.

My by ear settings compared to -3dB usually come out pretty close.

 

[Jeffdachef 5,000+ posts]

Pretty sure that was one of Power Acoustik/Lanzar/some other cheap brands (?) ~1200w boards.~700 @ 2 isn't a stretch IMO.

But setting the gain at 0dB will give you a LOT less than optimal power output since you rarely see music levels at even -2 or -3. It's often suggested to set them up with -3 or even -6dB tones.

My by ear settings compared to -3dB usually come out pretty close.

that depends man. If you take a look at my youtube video on checking music with audacity, modern rock needs around -9 db test tones and classic rock is around -15 db. its gonna be a different setting for every music. Hence passive gain setting feels pretty useless

 

[fixinit]

Pretty sure that was one of Power Acoustik/Lanzar/some other cheap brands (?) ~1200w boards.~700 @ 2 isn't a stretch IMO.

But setting the gain at 0dB will give you a LOT less than optimal power output since you rarely see music levels at even -2 or -3. It's often suggested to set them up with -3 or even -6dB tones.

My by ear settings compared to -3dB usually come out pretty close.

Yeah, it's an 8 year old PA amp. I'm surprised I was able to get the thing working as well as it is atm after gutting the board from the case. Time will tell if it holds up.

that depends man. If you take a look at my youtube video on checking music with audacity, modern rock needs around -9 db test tones and classic rock is around -15 db. its gonna be a different setting for every music. Hence passive gain setting feels pretty useless

I finally got around to your yt upload and this dB stuff makes a lot of sense from a tuning angle now. I'm under the impression that the "safest approach" to setting the gain for every music genre on the planet would be with a 0dB test tone so not to put too much strain on the alternator when peaks hit. If it's too low for classical or rock or too much for dubstep or rap, adjust the HU's equalizer accordingly. This brings me to another point. I ditched the HU's loudness off and turned it [dirty power] on again then reset my amp's gain. This has already helped my behind-the-wheel control when I'm flipping from CDs of choice to talk radio or even Pop radio stations.

 

[Jeffdachef 5,000+ posts]

Yeah, it's an 8 year old PA amp. I'm surprised I was able to get the thing working as well as it is atm after gutting the board from the case. Time will tell if it holds up.



I finally got around to your yt upload and this dB stuff makes a lot of sense from a tuning angle now. I'm under the impression that the "safest approach" to setting the gain for every music genre on the planet would be with a 0dB test tone so not to put too much strain on the alternator when peaks hit. If it's too low for classical or rock or too much for dubstep or rap, adjust the HU's equalizer accordingly. This brings me to another point. I ditched the HU's loudness off and turned it [dirty power] on again then reset my amp's gain. This has already helped my behind-the-wheel control when I'm flipping from CDs of choice to talk radio or even Pop radio stations.

to be honest, if you get a korean board sub amp, most come with remote gain knobs with built in clipping indicators and thats a very simple way of keeping it clean. People are skeptical but those knobs with clipping indicators are pretty spot on from all my tests with them. You can easily adjust to any music genre accordingly and get max clean output for all of them.

 

[fixinit]

to be honest, if you get a korean board sub amp, most come with remote gain knobs with built in clipping indicators and thats a very simple way of keeping it clean. People are skeptical but those knobs with clipping indicators are pretty spot on from all my tests with them. You can easily adjust to any music genre accordingly and get max clean output for all of them.

Does that apply to my 'Made in China' board because I've been thinking of getting a volume (BB) knob for christmas ($10?). I don't even know if the datalink connection works tbh. A gain/clipping knob within arm's length would be perfect!

 

[Jeffdachef 5,000+ posts]

Does that apply to my 'Made in China' board because I've been thinking of getting a volume (BB) knob for christmas ($10?). I don't even know if the datalink connection works tbh. A gain/clipping knob within arm's length would be perfect!

nope. Most china boards dont have it unless its a ct sounds one which shows voltages as well. Its a feature built into the amp not a universal knob.