measuring amp outputs without resistive load?

[Slaugh 10+ year member]

hey i decided to unhook my subwoofer from the amplifier outputs and measure it's max voltage without any resistive load or anything, just plugging the DMM arms directly to the speaker out bornes..

it no matter how much i raise the volume, won't go over 70v... it sits right there at best... of course it was supposed just to be a silly experiment, but then i decided to plug in my subwoofer and i noticed that with or without it the amplifier will mark the same voltage at the same volume and shit, but i dotn have enough power supply to make it reach anywhere near those 70v (best it goes without cutting off is about 48v)

so here is the question: say i got the appropriate feeding to my amplifier... will it reach this 70v voltage with my subwoofer on? cos if yes, then this amplifier is a lot underrated cos it's rated at 600w RMS/4ohms@14.4v //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

i know it's not the right way to measure shit, but it's curious because it marks the same voltages with or without the sub on...

oh i tested it with my 4ch and i got insane result of 56v... that's massive being an amplifier that won't put out more than 80w rms per channel //content.invisioncic.com/y282845/emoticons/eyebrow.gif.fe2c18d8720fe8c7eaed347b21ea05a5.gif

hehe

Click to read more...

 

[thch 10+ year member]

for one, if you are just measuing voltage you are probably pushing things to clipping. especially if the DMM does peak detection and converts the result into and RMS value for a sine wave instead of actually doing a RMS detection.

as for the question, i don't understand. thus i will make an observation.

at lower power levels (up to the rated power output) you should get the same voltage on the amp's outputs if a speaker is attached or not. go beyond this point and things might increase if the amp has no speaker, but probably won't increase much if the amp has a speaker attached.

 

[Slaugh 10+ year member]

i want to know if i can have 70v output from this amplifier using a subwoofer

 

[Slaugh 10+ year member]

hmm?

 

[thch 10+ year member]

ok, i think the question makes some sense. firstly, you're probably clipping the amp, which accounts for extra power. if the unloaded output is noticeably higher then the loaded (with woofer) output then the amp is clipping.

you should measure the 12V input to the amp. if it is signifigantly lower with a woofer attached to the amp, you should be able to get more power by improving the charging system.

the amplifier is not a true "power" amp, but rather a voltage amplifier. it gets a signal of, say 2V from the HU. it then outputs, say 50V. if the signal from the HU reaches 4V, then the amp will want to output 100V. if the amp's power supply can only provide 70V, then the amp outputs 70V instead of 100V. this is clipping.

 

[Slaugh 10+ year member]

i know that it clips out at 70v... i ajusted my gains to clip with a 60hz test tone at volume 26 (out of 35)... but until that it goes up well, but it wont clip before 70v

im thinking this amp can do a lot more than the 600w rms advertised... maybe all i require is a beter feeding system

 

[helotaxi 5,000+ posts]

You need some load on it to really test it, and you need an o-scope to detect clipping. Until you have those two things you won't have a valid test.

 

[thch 10+ year member]

i know that it clips out at 70v... i ajusted my gains to clip with a 60hz test tone at volume 26 (out of 35)... but until that it goes up well, but it wont clip before 70v
im thinking this amp can do a lot more than the 600w rms advertised... maybe all i require is a beter feeding system

you don't actually need an oscope to detect clipping. you just have to have patience. actually, i've built prototypes for a device which detects clipping just as well as a human eye and oscope. if you really wanted, you could probably rig up a simple circuit for maybe $5 of parts to work with a decent DMM that would detect clipping, at least for one frequency. with a digital volume contol on the HU, you can also make differential measurements -- if you change between 26 and 27, the difference at the amp output should always be the same (in percent).

it is possible for an amp to do more then rated power. especially unregulated PSU amps.

 

[Slaugh 10+ year member]

yeah ive been thinking it's a little craze for this little A/B class rated at 600w rms amp with a 60amp fuse to build up the 1225w rms //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif (70v@4ohms)... and it gets quite hot if i play one bass test track tune straifht on knowing the voltages wont reach anything above 48v... again that was done with a subwoofer, not sure what the exact impedances were... when i have some fixed 4ohms resistance to measure it's output (and a good feeding system lol) i will try and see what wattage it can reach

so far i believe this amp is underrated... i do hope it is too