Bridging or Biamping Marantz MA500 Monoblock Amps to Drive a Pair of Polk RTiA9s

Magice

Hi, I have 4 Marantz MA500 Mono Block amps and would like to use them to drive my Polk RTiA9s. The MA500s are bridgeable based on Marantz's owner's manual though, it does not show the total wattage output in bridge mode. I have read on a couple sights that the MA500 in bridge mode puts out 360watts into 8ohms. I have also read that in bridge mode the speakers should be in the 8 to 16 ohms loads which brings me to a concern with the RTiA9s. Though the A9s are rated at 8ohms, I read that the speaker configuration can result it 4 ohm loads which risk damaging the bridged MA500s.

Please provide your thoughts on the benefits / risks of using bridged Marantz MA500s to drive Polk RTiA9s. Would biamping the RTiA9 be a viable alternative yielding similar results? Thanks.

Dennis Gardner

Mono means 1 channel. You can't bridge 1 channel. That would be a bridge to nowhere.......

rooftop59

It looks like you could daisy chain them, and then remove the jumpers on the RTiA9s and run two sets of speaker cable one from each monoblock. But as has been rehashed on this form, the top set of binding posts is feeding either only the tweeter or the tweeter and midrange, while the bottom post powers the three 7 inchers, so you would be wasting a lot of power on the tweeter that only takes maybe 30 watts. Better idea is to sell all four monoblocks (they go for a good price on fleabay and audiogon) and buy one badass two channel amp like a parasound HCA 1500.

WilliamM2

Oddly, two MA500's can be bridged. See page 7:

http://us.marantz.com/DocumentMaster/US/MA500-OM-E_scan.pdf

Should be fine with speakers rated at 8 ohms. Just keep an eye on how warm they get.

Magice

Thanks for all the feedback, WilliamM2 in particular for the Marantz MA500 manual which clearly shows how to bridge the MA 500s. Clearing bridging these mono amplifiers is endorsed by Marantz. Is the general consensus that biamping, in this case using a dedicated 125 watts single MA 500 to service the Polk RTiA9 tweeter and midrange speakers, an overkill and waste of amp power to these speakers? Thanks.

Magice

Bridging in this instance is connecting 2 separate mono amps together such that 2 individual mono amps will act as one with increased wattage.

tonyb

Magice wrote: »

Thanks for all the feedback, WilliamM2 in particular for the Marantz MA500 manual which clearly shows how to bridge the MA 500s. Clearing bridging these mono amplifiers is endorsed by Marantz. Is the general consensus that biamping, in this case using a dedicated 125 watts single MA 500 to service the Polk RTiA9 tweeter and midrange speakers, an overkill and waste of amp power to these speakers? Thanks.

Manufacturers will endorse anything that sells gear, regardless of how it sounds. Bridging amps is usually not the first thought when sound quality is the goal. Most amps in bridged mode sound worse than when not. Plus in bridged mode, most amps won't like any dips in impedance below 8 ohm. Your A9's will dip below that.

Can you do it ? Yeah
Should you do it ? Only one way to find out, but my vote is no.

WilliamM2

tonyb wrote: »

Manufacturers will endorse anything that sells gear, regardless of how it sounds. Bridging amps is usually not the first thought when sound quality is the goal. Most amps in bridged mode sound worse than when not. Plus in bridged mode, most amps won't like any dips in impedance below 8 ohm. Your A9's will dip below that.

Can you do it ? Yeah
Should you do it ? Only one way to find out, but my vote is no.

It's common for all 8 ohm speakers to dip below 8 ohms, and people bridge amps all the time without issue. The distortion will roughly double to .1%, which still isn't bad.

Doubtful he needs that much power for though.

tonyb

Of course people bridge amps all the time, people also buy Bose speakers by the millions, doesn't mean they are in the realm of good sound. But....that's all debatable anyway. The only way to find out if it works for you is to try it yourself.

The A9's in spite of being an 8 ohm speaker will suck up as much power as you can throw at them. They will really open up with more quality current feeding them.

Magice

Thanks guys for the healthy debate and diverse perspectives.

FTGV

Magice wrote: »

Bridging in this instance is connecting 2 separate mono amps together such that 2 individual mono amps will act as one with increased wattage.

Yes one will handle the positive half of the output waveform the other the negative or inverted half.

WilliamM2 wrote: »

It's common for all 8 ohm speakers to dip below 8 ohms, and people bridge amps all the time without issue. The distortion will roughly double to .1%, which still isn't bad.

Correct the impedance is just a nominal or average rating.It can vary greatly with frequency.The issue is added thermal stress since a bridged amp will only see half the load so there will be increased current demands on the output section.If it is not running excessively hot then the load is suitable.As for sound quality a well engineered amplifier with closely matched channels should retain it's character when switched to bridged mode.(Some of the very best amplifiers utilize bridged/balanced output stages).Distortion will increase if there is poor gain and frequency response matching between the two channels being bridged.

It won't cost you any thing to experiment so give it a try a see for yourself.