Frontstage amp bridged only 11.5 ac volts?

[Vecticus 10+ year member]

So I wanted to make sure I wasn't clipping my front stage so I did the research and after some math (thanks Ionakron) to see how much ac volts each bridged channel at 4ohms had to be, it came out to a little over 26. something volts. I flattened out all my settings, made sure bass boost and cross overs were set to zero and inserted a 20 minute Pink noise CD. I turned my HU to exactly 3/4 max volume (26 out of 35) and turned my gain all the way down. Multimeter showed 0.3 ac volts. I turned it halfway and it showed 5. something volts......I started thinking... I'm not even half way to the 26 volt mark and this amp is turned up half way. So i just maxed it out. Multimeter shows 11.5 volts maxed out. This amp bridged supposedly does 180 watts rms. The CDT HD 61's are rated at 170 or 175 watts rms. I'm stumped, aggrivated, and just ready to trash it all. Could definitely use some help.

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[maylar 10+ year member]

Pink noise is not going to register on a DMM. You would need an oscilloscope and convert the peak-to-peak voltage to RMS before making your power calculation.

Or, replace your speakers with high power 4 ohm resistors and use a 400 Hz test tone. Your DMM would be accurate at 400 Hz and the resistors would put the amp under load for a propper measurement.

 

[Vecticus 10+ year member]

Thanks a bunch, Dave. Unfortunately I don't have the money to purchase an oscilloscope. I understand what you're saying. The DMM doesn't put a load on the amp to get that accurate volt measurement. Where could I get some 4ohm resistors? Are they pricey?

 

[groundpound4200 5,000+ posts]

depends on the wattage rating. Is it really that important though? Do your ears need to hear exactly 26 volts for it to sound good?

 

[maylar 10+ year member]

Pink noise is a mix of all audio frequencies combined, a DMM simply won't respond to the high frequencies. You need a fixed single frequency.

You can get resistors from Mouser. Here's a link to 4 ohm 100 watts.

HL10006Z4R000JJ Vishay/Dale Wirewound Resistors - Chassis Mount

 

[trumpet 5,000+ posts]

The calculations depend on a sine wave test tone, which is a lot more demanding on an amplifier than pink noise. Pink noise is a much closer representation to music than sine waves. Play music while you adjust the gain, and you might want to set the head unit volume a bit higher. RCA voltage doesn't rise linearly, it's logarithmic. This means it rises sharply as you approach the last few numbers of the volume range.