what kind of power specs should i be looking at if i'm going to get a 2 channel amp? should i be looking at the specs for 4 ohm or 8 ohm?
ie - 200w x 2 @ 8ohms / 400w x 2 @ 4 ohms
In general I get very careful with any advertised "double down" power output specs because I think most of the time they are just hypes/marketing tricks. Under ideal condition when there is no voltage drop, increase in losses or change in efficiencies due to increase in current, if you half the load resistance (8 to 4 ohms) the power output should double but in the practical world you get all sort of losses and there is the well known voltage drop that increases with current. If you have an older design Adcom power amp you will know what voltage drop means every time you turn it on (lights dim).
Most well designed/made power amps would spec something like 200W into 8 ohms and 300 to 350W into 4 ohms. If their marketing department wants to appeal to the audiophile group that don't have much background in physics/EE, they could easily turn it around and spec the same amp as 175W into 8 ohms and still 350W into 4 ohms, hence "double down" and those audiophiles will say, wow this one doubles down, it must be a better amp..
That's the specs from an Adcom GFA-5800. Would that kind of power be alright, or is that overkill?
Any power you don't ever use can be considered overkill, but you never say never so to me the more power the better as long as you can afford it and have room for it.
Peng, I noted that you wrote to find something like: 200w x 2 @ 8ohms / 300w x 2 @ 4 ohms
Any ideas? I appreciate your responses.
I said that because I knew you could easily get a two or three channel amp with that kind of specs, e.g. Emotiva, Outlaw, Parasound, Adcom.
I know people will tell you some how a 125WX2 UPA-2 will open up your speakers when your mid range 125WX7 AVR will not. I don't believe an UPA-2 with a little 300VA transformer will do much better than any mid range AVR in 2 channel output. The fact is, most 125WX7 mid range AVR will have a much larger P/S transformer and HTM lab measurements consistently show that those AVRs, e.g. most Pioneer Elite models, Marantz AVR6000 series or up, Denon AVR3000 series and up, Onkyo 800 series and higher etc., will deliver >200WX2 at 0.1% distortion.
Even the lower models such as your 667 should be quite comparable with the UPA-2 in two channel applications. Check out the following lower end models lab measurements:
http://hcc.techradar.com/node/5986
http://www.hometheater.com/content/pioneer-vsx-918v-av-receiver-ht-labs-measures
http://www.hometheater.com/content/yamaha-rx-v663-av-receiver-measurements
The last one, the RX-V663, predecessor of the 667:
"This graph shows that the RX-V663’s left channel, from Multi input to speaker output with two channels driving 8-ohm loads continuously at 1 kHz, reached 0.1% distortion at 166.7 watts and 1% distortion at 190.7 watts. Into 4 ohms, the amplifier reached 0.1% distortion at 218.0 watts and 1% distortion at 245.9 watts."
Now that was for 1 kHz, so for 20 to 20,000 you may get less, say 10% less, still pretty decent compared to the UPA-2. By the way, sooner or later, more forum member will remind you that doubling the power will only get you 3 dB increase in volume, such increase will be noticeable but certainly no where near being twice as loud.
Anyway, it is up to you to believe in science or Placebo. My suggestion is, if you want your investment to make an audible difference, go for at least something like a XPA-2 or 3.
