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best used amplifier for around $800

2K views 8 replies 4 participants last post by  Dilip Chhetri 
#1 · (Edited)
I have polk lsim 707 tower and lsim 704c (center), planning to use it in living room for some music listening and to watch TV. Since I paid for the tower, would like to drive it full range. I came across multiple Amps in the price range that seem like good, but can't decide (read about damping factor, slit foil capacitors, amount of capacitance, need for high current capability, etc etc )
- parasound hca-2205a
- rotel rmb-1095
- emotiva xpa-5 gen2
- parasound a23 (lower price and power)
- anything else ?

... must have: 12v trigger or auto on/off

I'm currently using marantz sr5012 to drive them, seem like sounding OK to me ... but since this is my first time with speakers in this category, I have no idea how best can they sound.

Would love to hear peoples experience who used at least two amps with some tower speakers and liked one over other.
 
#2 ·
So the speakers are hooked up to your Marantz and you just can't get enough volume out of that without clipping and distorting? Otherwise, there's not a lot to be gained here adding an amp at least in that price range. I had emotiva xpa and hated it. The internal anthem was just as good sounding. I think the old onkyo I had was better. I think parasound makes some ok stuff but again, if you're not needing more power I don't think there will be any benefit. Just stick with the receiver.

I went with McIntosh amps due to the autoformer and tube-like nature of the sound of those amps. But the price on those are ridiculous and not near $800.
 
#4 ·
thanks. Volume is fine, but I have no idea if it's clipping or not able to drive as hard ... maybe bass is not coming out as fine . Impedance on this speaker can dip as low as 2.8 ohm (read some article) and I'm not sure if marantz can safely drive 4 ohm ... I don't find any spec for 4 ohm (it does 100 watts 2 ch at 8 ohm)
 
#8 ·
I thought maybe let's do some measurement (if anyone interested). Not sure how reliable kill-a-watt device is that I'm using for this purpose.

Connection: AC outlet -> kill-a-watt -> marantz sr5012 -> 2x Polk lsim 707
Note:
- I measure Watts and VA, and it seems VA=1.47xWatts in all cases (i.e. PF = 1.47)
- room size irregular living room, 20ft x 20ft x 9 ft
- for this setup, receiver volume 50-55 is comfortable listening level, and Volume 65 is little louder

Below are reading on the meter, and assuming 70% efficiency for class AB amplifier, per-channel consumption = Cn = (read - idle) * 0. 7 / 2

Idle Power: 73.4 Watt

Pink Noise:
At volume 55: 81.5 Watt (Cn = 2.8 W)
At volume 65: 91.0 Watt (Cn = 6.1 W)

Pure since wave: played frequency sweep and the consumption is very low at above 200 Hz, and it peaks at 25 Hz
@ 25 Hz, Volume 55: 102 Watt (Cn = 10W)
@ 25 Hz, Volume 65: 119 Watt (Cn = 16W)

Playing a sample song
At volume 55: 80 Watt (Cn = 2.3 W)

-----------------

So, it seem that on average, I need an amp that can put out 2.3 watt/channel and for low-frequency up to 16 Watt/channel.

Question:
- what about dynamic power
if average is 2.3W how much DB of dynamic power is needed.
This will solve the "power" requirement issue.

Now comes the sound quality.
- I heard you need good damping factor to get tight bass reproduction (and probably class-D amps are missing it)
- amps are rated using constant 8-ohm resistive load, and hence when we says amp-X is rated at 200W doesn't mean it performs similar to other amp rated same ... we need to consider the damping factor, how much current it can drive at low impedance, how it performs at high's (probably class D isn't good at that)
- there is some mention of slit-foil capacitors are good for high's
- amp's boast of how much capacitance they have ... how much is needed
- parasound always mentions current rating is important and they always states them, other manufacturer don't ... how important is it.

... with this it seem, 125W parasound a23 might be a option to chose rather than 200W beasts ?
 
#9 ·
to wrap up; after trying no-external-powered-sub, dual Polk HTS 10, single SVS PB1000 and single Hsu VTF2-MK5 ... I ended up with VTF2-MK5 and setting front speaker crossover to 80Hz (basically not using sub-woofer on LSiM 707) ... I could have saved $1000 by using LSiM 703 instead
 
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