Amp not putting out enough Volts

I installed an Autotek ATA1000.4 amp and after testing it with my digital multimeter I can't get an output of anything more than 11.1 volts.

Amp Specs: 125w RMS per channel @ 4 ohms

The math:
125w X 4 = 500w RMS total
500w RMS X 4 ohms = 2000
Square Root of 2000 is 44.72 volts.

Process:
-all head unit settings to zero/flat/neutral
-head unit volume set to 75%
-unplugged all speaker wires connected to amp
-all bass boosters, HPF, LPF turned off
-amp crossovers are set to full
-multimeter connected to channel 1 + and -
-multimeter wont read any higher than 11.1 volts on these settings.

Am I missing something in my math or process or can I blame it on a defective amp??

 

A few thoughts:
1. Not sure why you're multiplying 125W x 4. If you are testing only one channel of the amp, you won't develop the full 500W unless it in mono mode. Are you testing it in mono-mode or one of the 4 channels separately?
2. You state head unit volume is set to 75%. What is the RMS voltage going into the amp?
3. What are you using as a reference signal? Tone generator or music? Redbook CD or other source?
4. The multimeter isn't presenting a 4ohm load to the output devices of the amp so the 4 ohm assumption isn't correct. It is probably much, much higher as multimeters don't like seeing a bunch of current. The multimeter manual might list it.

I poked around for the gain of that particular amp with little luck. I would check what the RMS voltage input and use that to compare to the output you're measuring as opposed to looking at the 11.1Vrms as an absolute.

The simpler test is to hook it up to the speakers and see if it goes loud.

 

Thanks for the input,

1. I am using all 4 channels. The amp has a gain knob for channels 1/2 and another for channel 3/4. So I should really be calculating for 250w for channel 1/2?

2. How would I measure the amp input voltage? Through the RCAs? I just followed the several videos available on testing with a MM (including ones from MTX and Sonic Electronix) and they stated turn head unit volume to 75%.

3. I played a 40hz test tone through Bluetooth from my phone to head unit.

4. Is it that for off that would make this little text completely useless?

What do you mean about seeing if the speakers go loud?

 

chances are that amp doesnt make 125W per channel. That is a MAX rating so it will most likely be a 40x4 or 50x4 RMS
Another way to check is by the fuse rating, it has a single 30Amp fuse. At 100% efficiency on 12v thats 360w total rms
Class ab amps id use 50-60%MAX efficiency so thats about 180Wrms / 4 = 45w-55w ish per channel. Your reading of 11v is about right

 

Be cautious about inferring amplifier rating based on fuse size. The fuse rating is a continuous rating (i.e., it can carry 30 amps forever) and most can handle much higher current for a shorter duration. For example, a simple 30A bussman cartridge fuse can handle 80 amps for 10 seconds and 150 amps for 1 second. Music is not continuous.

 

The channels may be tied by gain pot but it sounds like you are using them independently so the 125W is it. Found the manual and 125W looks to be the max rating (or MAXX rating, whatever the eff that is). You'd have to come close to clipping the front end of the amp to test for it and your MMR would have to be setup to catch the max and not RMS. http://www.autotekcaraudio.com/manuals/current/AutotekATAAmpManual.pdf

You would measure at the output RCAs of the head unit. 75% volume is useless as it is a relative number dependent on the magnitude of the recorded waveform and the actual output of the head unit.

Is it referenced to 0dB for CD Redbook or some other value?

Not completely useless. You've shown you have some amplified output as most head units put out 2 or 4V RMS.

Hook the amp up to the speakers and see if it plays music. I've never had an inclination to test car amps unless something is wrong (either distorted or dead output). I usually just hook them up and listen.

 

There are errors in the math. When calculating stuff like this, you can't take peak values to do the math. The 125w is a peak value, not rms. Look up the non peak value specs before doing any kinda math.

 

1. There is enough volts to introduce clipping when I adjust the gain pot. Even if the speakers are only receiving half the wRMS they can handle, can clipping still occur?

2. Is there a specific volume I should set when reading RCA output volts?

3. I'm not sure, it was just a video off of youtube. I'll download some tones to a cd.

4. The moment I turned the truck on after installation I had doubts on the sound. It was obviously there and sounded better than stock, but maybe I had to high of expectations. After a while I thought about if the amp was performing the way it was supposed to which led me to attempt testing its output.

The fronts are Polk DB 6.5" components and the rears are Polk DB 6X9's.

manethon,

Is it the non name brand amp that is giving me half of the stated power output? When finding an amp, are people just supposed to find an amp that has double the amount of wRMS their drivers need? I followed an MTX Audio video on this exact topic and it works for them. Is it just because they have more reliable amps? Any suggestions on amps for my speakers?

Thanks for all the help so far!

 

I'm well aware, it was a joint argument but in audio still gives a decent indication when used with other data.

 

Its not giving you 1/2 stated power nor is this an indication of an unreliable amp. The spec's clearly state 125MAX. Max wattage means absolutely nothing....

 

Yes. Clipping isn't just in reference to overdriving speakers. Overdriving the output of the head unit or the input stage or output stage of the amp can do it. That's why install instructions usually walk through setting the various gains of the head-unit and the input to the amp.

Just need to know what you are inputting to the amp and then what the amp is outputting. You're testing the gain of the amp so that's all you're worried about.

I wouldn't worry about it too much. You're more worried about knowing what the voltage is being presented to the input of the amp.

Never heard of the brand. Nowhere in the documentation does it mention the RMS output which is telling. They are marketing it a certain way catering to the max output which isn't dishonest but it isn't helpful. It sounds like it is working as intended. I'd spend a little time setting up the input gain to see what you can coax out of it or return it and find something else. I have enjoyed Alpine and Kenwood products.

 

I concur with others. Hook it up and set the gains by ear, avoiding the last bit of volume from the headunit. Listen for distortion from the drivers considering xovers are set appropriately. I never measure power and haven't blown a driver in decades.

 

The top drawing is of how I first connected the speakers to the amp. The sound was poor, did not go very loud and was a very unimpressive 125w RMS per channel.

Some will probably say something along the lines of "why did you hook it up the second way if you didn't know exactly what you were doing, you could/will blow the amp", but I wanted to try something. The amp is bridgeable.
1. Is the second drawing of how I hooked it up bridged? The sound is twice as loud and clear.

2. There is a "Mode" switch for 2 or 4 channels. If that is bridging in the second drawing should switch "Mode" to 2?

3. If this is bridging, does this change to 2 ohm?

4. Based on the 125w RMS per channel unbridged, how many watts RMS would be going to each speaker bridged?

 

1) its not 125 wrms, its peak wattage which is equal roughly equal to 50-60wrms
2) YEs you bridged it, but should be bridged to 4 ohms to be safe. 2 ohms may work though but will most likely overload the amp and see magic smoke
3) You actually bridged it to 2 ohms and you have now lost stereo = no differentiation between left/ right
4) ITs not 125wrms per channel unbridged.

1-4 see specs below

• Max Power Rating: MAX
  • 4 ohms: 125 watts x 4 chan. = roughly a 50-60x 4 wrms
  • 2 ohms: 250 watts x 4 chan. =
  • Bridged, 4 ohms: 500 watts x 2 chan. this is most likely 200wrmsx2

 

So how do I get back in stereo with the up I received in power from bridging? Get a quality amp that puts out more than the 50-60 wrms per channel?

 

another amp.... or run the rear speakers off your deck.... its only rear fill you know so its not vital and should provide enough fill from the deck

So bridge the front speakers for example

(FL) connected to Channel 1 + and channel 2 -
(FR) conned to channel 3+ and channel 4 -

 

You get what you pay for!

You bought a $65 amp, don't expect much from it.

 

UPDATE:

I was able to return the Autotek amp and purchased the Polk PAD4000.4 amp. At $230 I was expecting a much bigger improvement and it delivered. This amp is able to put out the correct amount of voltage that the amp was rated (per my multimeter) and subjectively through my ears. The Autotek wasn't putting out nearly the voltage it claimed.

It sounds wonderful now, but I'm curious if I can benefit from the HPF and LPF with my setup? I have Polk 6.5 components in front and Polk 6x9's in the rear. I have not been able to find anything about setting up filters for components or full range speakers together, only one or the other with a sub(s).

 

I'm totally missing something here... I spent 10 yrs working for Car Toys, the now defunct Magnolia Hi Fi (PNW local company) and <cough> Circuit City, and never once did I ever use my multimeter to test voltage coming out of an amplifier, or hear about any one of my fellow installers doing this.

What exactly is the point of this??

 

And yes, if you're running 6 1/2" components and 6x9's, turning the high pass filters on will absolutely help them sound better (they won't be playing the low frequency range that's intended for subs to reproduce). Look in the specs for each pair of speakers and they should have a recommended frequency range, and whatever the lowest number there is should be where you set your HPF... roughly speaking, I would say somewhere around 100-120 hz for the front components and maybe 80 but closer to 100 hz for the rears.