Tuning an Amp with a DMM?

[ahole-ic]

anyone link a proper (50-60 hz) test tone that hits at a volume close to the average recorded volume?
Also Ecrack, is there much difference in the accuracy of a cheap DMM and a more expensive one?

You can't know from price alone. I bought a cheapy extech, that is dead on with my fluke. You simply cannot gauge the quality of the reading on the purchase price.

 

[OmegaBunny 10+ year member]

I always turn the knob all the way up before tuning my amp. When I want less bass I can turn it down via the knob and then turn it back up when i want my bass back. As log as you have the knob turned all the way up when you set it then you'll be fine. Also the equation isn't hard to do.

Examples:

1 4ohm SVC @ 500 watts= sqrt (500*4)= 44.72

2 4ohm SVC @ 500 watts each = 2hom load =sqrt (1000*2)=44.72

1 d4 @ 500 watts= sqrt (500*2)=31.62

2 d4 @ 500watts = 1 ohm or 4 ohm load= sqrt(1000*1) = 31.62 or sqrt(1000*4) 63.25

1 d2 @ 500watts = sqrt(1*500)=22.36

Use this to find the impedance...

Subwoofer Wiring Diagrams

 

[i2ain2thunder 10+ year member]

I always turn the knob all the way up before tuning my amp. When I want less bass I can turn it down via the knob and then turn it back up when i want my bass back. As log as you have the knob turned all the way up when you set it then you'll be fine. Also the equation isn't hard to do.
Examples:

1 4ohm SVC @ 500 watts= sqrt (500*4)= 44.72

2 4ohm SVC @ 500 watts each = 2hom load =sqrt (1000*2)=44.72

1 d4 @ 500 watts= sqrt (500*2)=31.62

2 d4 @ 500watts = 1 ohm or 4 ohm load= sqrt(1000*1) = 31.62 or sqrt(1000*4) 63.25

1 d2 @ 500watts = sqrt(1*500)=22.36

Use this to find the impedance...

Subwoofer Wiring Diagrams

who in god's green earth runs at 100% gain......talk about clipping.

 

[OmegaBunny 10+ year member]

The remote knob not the gain

 

[i2ain2thunder 10+ year member]

I think I'm just getting more and more confused by what you are saying. is that a bassboost knob or a gain knob?

 

[ahole-ic]

who in god's green earth runs at 100% gain......talk about clipping.

He was ignorantly assuming (like he usually does) that all bass boost works like his does. He has a remote gain knob apparently. The gain on the amp is the maximum the gain knob can turn up to. Most people's bass boost is an active crossover basically... It is set to a specific frequency and boosts the hell out of it and the slope sharply falls off on either side of the peak. This means that when people set their gain that way, they are going to be incredibly disappointed when they turn their knob down, AND when they turn it up but listen to anything other than that narrow range of frequencies their bass boost is boosting. THAT is why bass boost is an epic fail and should be turned off when setting the gain (and the rest of the time as well).

 

[OmegaBunny 10+ year member]

LOL...

 

[OmegaBunny 10+ year member]

I set my gain with bass boost off and never turn it on.

 

[ItsAJeepThing 10+ year member]

bass knob NOT bass boost. If your bass knob is down when you set your gains with a dmm and then you turn it up you are raising the voltage past what you set it at. So you turn the bass knob (like in the above pic) to max then set your gains so you dont exceed what you set the gains at with the dmm when you turn the knob to max.

 

[Fiendstolemyamp 10+ year member]

bass knob NOT bass boost.

That's the thing, some bass "knobs" adjust the gain, some the bass boost. Depends on the amp.

 

[vector 10+ year member]

The moral of all of this is that the only really good way of setting gains is with an oscilloscope. Find someone with one with one that will do it for you or let you use one. You don't need anything special. Pretty much any working oscilloscope will do. Though I don't know if I would buy it, it looks like the steve meade distortion detector works just fine. (for that money I would order a crappy oscope, like this DealExcel: US$169.99 - Uni-T UT81B Oscilloscope 8MHz w/ USB vivid and LCD [18481]) You can measure each signal device for clipping as you set them up.

Unless your amplifier has a regulated power supply you will want to do all measurements with the load you are planning on running, i.e. with the speakers hooked up. Obviously you can do some damage to your mids/highs this way if they are not rated to handle that much power so I use a resistor at this point. However most people never come close to maxing their mids/highs so just measure this without a load knowing that they will never achieve a square wave/clipping.

I would highly recommend measuring any unregulated amplifier for subs with the subs connected however or a dummy load as your output voltage can change drastically with load. My subwoofer amplifier outputs 18 volts more at the same gain setting when the subwoofer is connected...

 

[vector 10+ year member]

On a side note I would be happy to do this for anyone here in colorado as I know scopes are usually very expensive, and most people don't need them that often. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[LosIsATool 5,000+ posts]

JL Audio - Car Audio Systems

 

[i2ain2thunder 10+ year member]

I've never heard of a "bass knob" I have a remote gain myself the way it operates...which I'm guessing is the way you guys are trying to explain to me (in different lingo) the remote gain knob acts as primary control of the gain when it is connected, however it can not increase the gain past the master setting on the amplifier. I don't do it your ways and maybe theres a benefit I don't know about but when I set the gain on my amplifier I simply do not have the remote knob connected as it is easy to disconnect when I'm back working on the amp.

In most cases setting the gain with a DMM is only a starting point for me. I set the gains the rest of the way with my ears for balance and loudness, because as we all know some speakers can take more power then rated as long as it is still clean and without clipping/distortion.

DMM is by no means very accurate I always think of it as a good starting point and a good reference point for RMS handling. Having an O scope is best but too expensive to be worth it for the avg car audio joe. Setting by ear is the best way for someone without a O scope, just make sure you listem carefully for distortion and use the DMM as a reference as to how many watts your subs are getting.

 

[OmegaBunny 10+ year member]

I use the remote because my wife doesn't like bass. It makes it much easier for me to turn it down when she's in the car, instead of going through my hu.

I bought a cheap oscope a couple months back but haven't used it yet. I'll use it when i start my new build. Plus I need to clamp my amps before kangaroux has a meltdown.