Figuring Out WPC

Power13

So I have been shopping around for an amp and most manufacturers give a WPC rating for either 4 or 8 ohms. I'm using a set of SDA 2B's which are 6 ohm speakers. Is their any way to figure out what the actual WPC would be at 6 ohm's or do I just have to guess somewhere between the 4 and 8 ohm manufacturer listing. Or in the case of an amp I found on audiogon, the manufacturer only list 200 WPC at 8ohms but the amp can handle a minimum of 4ohms. So I am left wondering what the 6ohm rating would be.

Secondly I need to make sure the amp is a "common ground" amp. From what I've read most stereo amps are. But its not something manufacturers list anywhere and the only way to find out is measuring the impedance across the negative speaker outputs. This method isn't ideal when buying online. Any other ideas?

Also have people here had good/bad experiences with Audiogon and sellers on there?


Thanks for reading!

tonyb

A quick call to the amps manufacturer might tell you if the amp is common ground or not. Or you could just tell us what amp it is and maybe someone here has one and can tell you.

As far as the wattage thing goes, your putting too much emphasis on it. Lets say your amp is rated at 200 wpc at 8ohms. When you turn on your amp, it doesn't start pumping out 200 watts full bore all the time. It depends on speakers and what it takes to power them and volume. WPC will vary under different loads/circumstances. WPC also has little bearing on sound quality or even capabilities. Current as in peek to peek amperes will give a better window into how well an amp will deliver it's power and control your speakers drivers. Also amps vary in design and build, so one amp may double it's power from 8 to 4 ohm while another may only increase it's power by 50%. If the amp your looking at is 200 watts into 8 ohms and 4 ohm stable, you have nothing to worry about. My guess is though, the lack of a 4ohm rateing suggests a weak power supply. Just my opinion of coarse. What amp is it exactly ?

Power13

tonyb wrote: »

A quick call to the amps manufacturer might tell you if the amp is common ground or not. Or you could just tell us what amp it is and maybe someone here has one and can tell you.

As far as the wattage thing goes, your putting too much emphasis on it. Lets say your amp is rated at 200 wpc at 8ohms. When you turn on your amp, it doesn't start pumping out 200 watts full bore all the time. It depends on speakers and what it takes to power them and volume. WPC will vary under different loads/circumstances. WPC also has little bearing on sound quality or even capabilities. Current as in peek to peek amperes will give a better window into how well an amp will deliver it's power and control your speakers drivers. Also amps vary in design and build, so one amp may double it's power from 8 to 4 ohm while another may only increase it's power by 50%. If the amp your looking at is 200 watts into 8 ohms and 4 ohm stable, you have nothing to worry about. My guess is though, the lack of a 4ohm rateing suggests a weak power supply. Just my opinion of coarse. What amp is it exactly ?

Yeah I do realize that the actual power out put varies depending on the circumstance. I will definitely consider peak amperes as well. The amp I was looking at was a Rotel RB1080 here are the specs from the manual:

Continuous Power Output (20-20 kHz, < 0.03%) 200 watts/ch into 8 ohms
Total Harmonic Distortion (20Hz-20kHz, 8 ohms) < 0.03%
Intermodulation Distortion (60 Hz : 7 kHz, 4:1) < 0.03%
Frequency Response (+0.5 dB, -3 dB) 15Hz-100kHz
Damping Factor (20-20,000 Hz, 8 ohms) 1000
Speaker Impedance 4 ohms minimum
Signal to Noise Ratio (IHF A network) 116 dB
Input Impedance/Sensitivity 32 k Ohms/1.5 volt
Power Requirements 115 Volts, 60 Hz (U.S. version)
230 Volts, 50 Hz (European version)
Power Consumption 550 Watts
Dimensions (W x H x D) 430 x 139 x 400 mm
1715/16 x 51/2 x 153/4 in
Weight (net) 16.8 kg, 37.03 lb.

nooshinjohn

You have no worries with that amp at all. Just plug it in and enjoy.:cool:

teekay0007

Great amp, that will do everything you will want it to do, and then some - my brother has the same one.

Be careful exposing your hand (eg. your specific online buying plans) around here, or on any high-traffic forum, there may be snipers lurking. :loneranger: