I'm going to buy a pair of Polk LSi9 speakers (used) today. I've auditioned them & a few other speakers. I liked JMLab Cobalt speakers also but the price on the Polks are VERY good...they were terribly set up in a J&R showroom, so I'm hoping they will sound a little better in my room. In any case, it's my starting point (they will replace a borrowed pair of Bose 301 Series II speakers) and either I'll like them or I'll transform into one of the many hopeful, energetic, curious upgrade/swap-out freaks as so many of you forum dwellers appear to be.
I have some questions regarding amplification power. My amp is a mid '80s Yamaha A-700 Integrated Amp, 100W per channel at 8 Ohms (this is going to be a 2 channel music system BTW) and some folks have commented that the amp might be a bit underpowered. I called Polk and spoke with a technician who told me the amp should be fine. I've read elsewhere on other forums of folks using these 4-Ohm speakers with an underpowered amp, and the amp goes into 'Protection Mode' or a light switches on warning about overload issues. To the best of my knowledge no such protection mode proper exists in my amp and no warning lights either. Sure, it has a fuse in it...but I believe that that's it.
Now, I do not know how my amp will perform until I get the system set up (the impression I get is that it will be borderline adequate). What potential risks does the amp face? Before any irreversible damage is done to the equipment is there anything I should keep an eye on and monitor? What about the speakers? How should I monitor them to prevent them from damage, anything to listen to or look for? Remember, I'm new to this and developing my ears, so even if a symptom seems obvious to you mention it as I may assume it to be business as usual! I will need to select a larger gage speaker wire to run these 4-Ohm speakers vs. the wire I have for my 8-Ohm speakers (assuming my current wire gage is not sufficiently oversized) correct? If I use undersized wires will this have the same result of using an underpowered amp?
A Meridian 508.20 CD Player (used) will be used as the source. Does the CDP face any risk of damage in being hooked up to the amp should the amp get overloaded or overheated?
The CDP will not face any potential damage from the four Ohm load on the amp. The speaker cable you have now is sufficient if you are running a 16 gauge cable.
What you need to monitor is something you cannot monitor easily. If the amp gets in trouble, it will go into either thermal run away or it will blow the fuse when it tries to draw too much current from the AC outlet. The fuse is not a problem; replacing it and lowering the volume will probably remedy that problem. Thermal problems however require monitoring the temperature of the output transistors. The best you can do is run the amp at the volume level where you normally listen and get an idea how warm the top of the amplifier gets at an eight Ohm load. The four Ohm load will probably heat the amp up a bit more than that. If the amp gets to the point it seems excessively hot, shut it down. As I indicated in a previous thread, it is not the impedance so much as the variation in impedance. From your reply Polk indicated the speaker is fairly kind in its impedance curve. The 3 Ohm load is not friendly to most amps, but the Yamaha will probably survive. It is not the power of the amp you need to be concerned with but instead the stability of the amp. Into a straight resistive four Ohm load the Yamaha will probably produce in excess of 150 watts. That is more than enough power to drive the Polks. The dip in the impedance is what you need to worry about as it creates a situation where the amplifier draws more current from the power supply and, in turn, from the wall outlet. This is where the danger lies with the Polk/Yamaha combination.
Ive run Yamaha at 4ohm loads and found them to work ok (no smoke). Brfore the run, you may want to consider offing the cover for a vaccum and cleaning. Inspect the solder joints, and replace the power cord. Some contact cleaner and a toothbrush will clear dust varnish from larger joints. Get some spray for the pot shafts on the controls.
I ran my same amp for 15 years of torture them dropped it down the stairs. Worked fine.