Gain Setting with a DMM or OSCOPE!

[deathcloud]

So I have been in the other forums reading. And people say that setting the DMM is just a general ball park. The real way is to get an oscope and set the gain. Crazy huh. Here are some interesting quotes.

hehe, u know to get ohms you must have voltage and amperage present.

So, if you set your gains with speakers connected, then you will have impedance rise to deal with.

You won't know what the rise is unless you clamp one fo the 2 wires and take a voltage reading at the same time.

Pointless route to go.. an oscope is the most accurate way of setting gains on an amp.

And then...

There are several assumptions involved when setting the gain with a DMM and the voltage formula. These assumptions may or may not be accurate. As a result, your gain setting with the DMM may or may not be accurate. There is no guaranty clipping will not occur with the DMM method because, as stated, the DMM doesn't measure the shape of the wave....only the voltage.

The DMM method helps get the gain setting within the general ballpark so people aren't going crazy with the gain control. But in reality it's not an exact or accurate method.

woahhh my brain hurts. I thought DMM was the most accurate way.....

[stipud]

Well, the assumption you need to make with a DMM is that your amplifier makes the rated wattage at the targeted impedance. With PG amps this is a no-brainer, since they are all underrated anyways. An oscilloscope is far more accurate at being able to squeeze every last drop of available power out of your amplifier. You can visibly see when the waveform starts to clip, so you can set it exactly at the point right before clipping occurs.

Of course oscilloscopes cost hundreds of dollars and a DMM is something everyone has. You can get one for under $10, set your gains, and voila... your amp makes its rated power and should still have some headroom left.

[Eric D]

Like stipud said, you can count on PG amps to make their power.

The only drawback to the DMM method other than not getting max power from the amp is if something else clips, you would not know it. Many cheap decks clip, and if you have a signal processor between the deck and amp, you pretty much have to use an o-scope or you risk clipping.

Yes o-scope are way more expensive than DMMs, but they can be had on eBay used for pretty good deals. Especially if all you want it for is setting gains.

[bogart]

keep in mind that when you tune with a scope you are tuning for that setting and minor attenuation thru an eq or your hu's eq can drive the equipment past the clip point....so you want to go piece to piece and leave some room on each as all data formats are not equal and you will want to adjust stuff with different disks or mp3....a 3db gain at nearly any frequency will lead the system to clip if you tune it close

and when you do this you are creating a threshold that you don't pass....period....it is most often not ideal to tune your entire system in such a fashion....it is a very good idea to know where each component in you system is going to clip buy not alway ideal to make that point your target....infinite tinkering and equalization will still be required....

[ttocs]

I thought we covered this here already?

One big assumption is that all meters are equal and are used correctly. You know what happens when you assUme........

[k2f-gold]

hiya, a noobie q's but what's a dmm?

i've only done gain setting by myself by listening because I don't have any scope. is there anything not good or not good enough comparing scoping?

[bogart]

It is true...and we have...but unless your meter will read the pulse width and give you an indication of the notch in the wave it won't indicate the clipping threshold...mine will but I've never used the function really. All the scope is giving you is a target voltage or threshhold.....


I have tried this...it is a real peach of a pain and to me it created more elusive dragons then it was worth...in the end I tuned the amps for the highs by ear and made sure I was well under the clip point...set the subs up to be able to acheive their peak and dialed it all back from the hu...

Much like the triod guys...it seems to be point that could be beaten as the proverbial dead horse...

[Eric D]

I thought we covered this here already?

One big assumption is that all meters are equal and are used correctly. You know what happens when you assUme........

Your point here has absolutely nothing to do with the question at hand. The question is about using a DMM or an o-scope, not if DMMs are the same.

[joerg]

hiya, a noobie q's but what's a dmm?

i've only done gain setting by myself by listening because I don't have any scope. is there anything not good or not good enough comparing scoping?

To answer your first questition: A DMM is a Digital Multimeter

And to answer the second question: You did everything right because u adjusted your system the way you and your ears like it! As long as u are not a competitior in the highest classes of competition it makes no sense at all to use a DMM or a SCOPE.

[Eric D]

I don't think it has anything to do with being a competitor. I use an o-scope to set my gains so I never run the risk of breaking a speaker or an amp, and so far I never have.

All my non-competitor friends who set their systems by ear blow speakers or amps at least once a year. They somehow think that is just routine for having a car stereo.

[k2f-gold]

Can i know where should i scope/probe my setup if my HU is outputing 4V pre-out but my amp only having max 2V pre-out. Will this blow my speaker?

[ttocs]

after 15 yrs of installing for a few different shops I only had the occasion to pull out a scope half a dozen times. The only time it really justified the time was in high end, multiple amplifier situations and a couple of times were we had multiple subs, all driven by their own bridged amp. Every other time I have done it, including on my own systems was by ear. Once you have it fairly zero'd in, it might still need small adjustments from time to time but I find it hard to believe that almost any system can't benifit from an occasional adjustment here-or-there. Even when you tune it with a meter, you finish the tuning by listening and making any final adjustments that make it sound better to you and that is the most important thing. So as stated above, meters are a good ballpark finder but your ears should be the final judge.

[Eric D]

after 15 yrs of installing for a few different shops I only had the occasion to pull out a scope half a dozen times. The only time it really justified the time was in high end, multiple amplifier situations and a couple of times were we had multiple subs, all driven by their own bridged amp. Every other time I have done it, including on my own systems was by ear. Once you have it fairly zero'd in, it might still need small adjustments from time to time but I find it hard to believe that almost any system can't benifit from an occasional adjustment here-or-there. Even when you tune it with a meter, you finish the tuning by listening and making any final adjustments that make it sound better to you and that is the most important thing. So as stated above, meters are a good ballpark finder but your ears should be the final judge.

You only find scope use in high end shops, not a place like Best Buy, so I have to agree with you here.

[ttocs]

I started at best buy 15 yrs ago and they would not know how to say oscilliscope, let alone what it does.

The prices have come down but they use to be too expensive for most mom-and-pop shops to even own one. When I was out in Az all the shops had them but again rarely needed them.

[KUB3]

I've never used anything other than ears. But then I don't think I've ever pushed my HU past 3/4 volume, with low-ish amp gains too. I guess all this is more of an issue if you push your system hard. I guess it becomes critical if your into SPL

[Eric D]

If you set your gains using an o-scope, it will actually be much quieter than a system set by ear with 95% of the people out there. Ears don't hear distortion as early as you can see it on an o-scope display. This is the reason systems set with an o-scope seldom blow speakers or amps. SPL guys often run their equipment well into clipping for max power, so they could care less about an o-scope unless they wanted to see just how much clipping they were running.

Nearly every system I have checked with an o-scope which was set by ear (friends systems and some customer systems), was at least 3db into clipping. In the case of many of these systems, they would fry tweeters routinely.

[KUB3]

I'd be interested to read a link on exactly what to do... I guess it must have been covered loads

[joerg]

Any clue how accurate those clipping leds on the MS amps are?

[Eric D]

The clipping LEDs on MS amps are very accurate. If you play a sine wave with no speaker connected and turn the amp gain up until you see the light come on, then back off a bit, you are right at the limit. When the light just comes on the amp is slightly into clipping.

When you hook your speakers back up and play some loud dynamic music, you can check again for the lights blinking. If they do, your load is drawing down the amp's rail voltage and it is clipping. You would then need to back off a bit more on the gain.

But, all of this is really crap if your deck has a clipped output, or your signal processor is clipping the signal before it gets to the amp.

[KUB3]

But what if you never go above 3/4 volume on the HU. Surely it won't be clipping at all...

[joerg]

The clipping LEDs on MS amps are very accurate. If you play a sine wave with no speaker connected and turn the amp gain up until you see the light come on, then back off a bit, you are right at the limit. When the light just comes on the amp is slightly into clipping.

When you hook your speakers back up and play some loud dynamic music, you can check again for the lights blinking. If they do, your load is drawing down the amp's rail voltage and it is clipping. You would then need to back off a bit more on the gain.

But, all of this is really crap if your deck has a clipped output, or your signal processor is clipping the signal before it gets to the amp.

Thanks for info! Those clipping LEDS always were my only indicators when i adjusted my systems. But i always had all my speakers hooked up and played something called "pink noise". My headunit was a P9 with it´s processor. So is this a way to go on then?

[oldskoolmseriesfan]

Fuck I hate pink noise, I always had a hell of a time tuning with that shit! Stupid bass cd's

[Eric D]

Pink noise it not usefull for gain setting. You need to use a sine wave. Make sure to not have speakers connected to your amp, as a sine wave can kill them quick. I use 1kHz for most full range amps, and 40Hz for Class D bass amps.

[oldskoolmseriesfan]

Pink noise is used for setting tweets isnt it? Its been so long I cant remember.

[Eric D]

It I were setting a tweeter amp I would use a 10kHz or 20kHz sine wave to look for no clipping. And again, without the tweeter connected to the amp.