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705x amp in bi-amped 3-channel mode?

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mikekohut

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Post Wed Sep 13, 2006 8:27 pm

705x amp in bi-amped 3-channel mode?

Wondering if anyone has done this, with a 705x, or any other 5-channel home theater amp?

I have 3 small rear speakers (B&W LM-1s) that will run off receiver power. I have intended to purchase an amp that will give me more power for music listening in 2-channel mode. However, I have also considered purchase of a 5-channel where one of the channels would drive my LCR600 center, and the other 4 channels would be used to biamp my B&W 604s.

Is this a reasonable idea? I am thinking for a little more money than a two-channel amp, or if I am lucky the same price, I could not only get some real center channel power, but I could delve into the world of bi-amping - something that I have never done.

Thoughts on this anyone?
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Chuck_K

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Post Tue Sep 19, 2006 6:34 pm

if i understand you correctly, then you'll need an active crossover to sepearte the highs and lows in the bi-amp configuration. imo - there is little to be gained by doing that with those speakers. your cost will also go up quire a bit - the last active crossover i purchased was over $300.
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Chuck_K

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Post Tue Sep 19, 2006 6:41 pm

if i understand you correctly, then you'll need an active crossover to sepearte the highs and lows in the bi-amp configuration. imo - there is little to be gained by doing that with those speakers. your cost will also go up quire a bit - the last active crossover i purchased was over $300.

i'm also not sure about your 'little bit more or about the same $$ than a 2 channel amp" statement either. a quality 5 channel amp with decent power capability can run a couple thousand $$ easily. i'd stick with a seperate hi power stereo amp for the b&ws, bag the bi-amp idea, and pick up a monoblock (or a lower power amp that you can bridge) for the center.

bi-amping is tricky. imo stick with the crossover the manufacturer engineered for that enclosure/speakers with the proper number of poles, phase response, crossove point, and matching. solid state power is cheap nowadays - there's little need to bi-amp for high volume.
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mikekohut

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Post Tue Sep 19, 2006 9:17 pm

Hi, Chuck!

And thanks for your thoughts. Your stated alternative to the bi-amping of a 5-channel (getting a two-channel and then a monoblock for the center)is probably the route to go, as I didn't realize that a separate crossover would be needed. I just figured that I the speaker's internal crossover would take care of that given that the speakers are bi-wire capable. Guess that was a dumb assumption. Still seems like it would work, but what do I know?

Here, though, is an example of an inexpensive 5-channel Carver amp, and I suspect they're not all much more costly than this (this model Carver that is - haven't checked Audiogon or Videogon lately):

http://cgi.ebay.com/CARVER-Premiere-AV- ... dZViewItem
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Chuck_K

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Post Tue Sep 19, 2006 9:31 pm

mike - you might be right about using the speaker crossovers. my case was different. i was using nht subs that had no crossovers, and high frequency panels (heath as1321) with the crossovers bypassed. you have a good point - didn't realize you planeed to slit hi/low within the 604s. what the heck - for the cost of that amp (and no active crossover) you might have a kick @ss system. now that i better understand - i'd have to say it's definatley worth a try!! 250W per speaker (125 for center) should be more than adequate. center is generally throttled down at least 3 db on my system because the speaker is physically closer to the listener, and doesn't need the full power. sorry for the confusion - i think you have a good plan!
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mikekohut

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Post Wed Sep 20, 2006 12:04 am

Chuck, thanks, again. Maybe somebody can give me the skinny on how easy it would be to bi-amp speakers with four connection posts each (speakers that are bi-wirable). Is it easy/possible? If so, pitfalls?

Below is a link to another amp that might be interesting. It is the same model, but even less money. I believe this amp has seperate volume pots for all 5 channels and thus I could tweak the bass and upper end (mid/tweet) for most pleasing balance? I believe that on each speaker the two treble speaker wires feed the midrange and up while the two bass wires feed simply the bass-only drivers.

http://cgi.videogon.com/cgi-bin/cl.pl?a ... 1151632575

Thanks, any and everyone who might have ideas/opinions.
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Chuck_K

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Post Wed Sep 20, 2006 5:02 pm

mike - It's real simple; just use a "Y" type RCA cable to drive a pair of power amp channels from a single (let's say right for this example) preamp out. then connect one pair (black-red) of power amp outputs to the hi frequency speaker binding posts (black to black, red to red). connect the other pair of power amp outputs to the low speaker binding posts. it doesn't matter if you switch hi/low around on the speaker ends, but do make sure you match black-to-black and red-to-red. the metal straps on the back of the speakers need to be removed - they are there to connect the hi/lo togather when driving them with a single amplifier channel. then repeat above for the left channel.

you don't really need seperate volume controls. the pair of speaker inputs by design like to see the same levels. seperate volue controls will only allow you to introduce a mismatch - less accurate hi/lo balance.
i don't recomend messing with seperate volume controlls - it's only going to make the hi/low balance less accurate than the manufacturer's design - which is usually matched internally for optimal flattness across the frequency band.
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mikekohut

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Post Wed Sep 20, 2006 8:37 pm

Thanks, again, Chuck-

I have already removed the metal piece on the pair of speaker terminals that you refer to, as I bought bi-wire cables awhile back.

And so, wonder if you -- or anyone with experience on this issue out there-- think the bi-amping would actually reap benefits over simply straight 2-channel power. For example, 2 x 125wpc on each speaker in bi-amp mode versus 250 straight wpc per side. More power, headroom, or any sonic benefit that one might think of....??? :-k

I hear you on leaving the volume pots alone - makes sense - again, thanks for the thoughts.
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Chuck_K

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Post Thu Sep 21, 2006 2:55 am

i think it made a lot of sense years ago when tube amps with puney output power (they still are puney actually) were the limiting factor. like you say - this will in that case provide much better dynamic headroom and lower harmonic distortion because that amp doesn't need to drive as hard. imo - a 250 watt amp would give you the same performance as the bi-amped 125 2 channel amp provided the 125 watt amp (as part of a five channel unit for example) can ectually deliver 125 watts with all channels driven - more on this later...


solid state isn't nearly as much an issue. it's relatively affordable (as in my case) to use ss amps with no less than 200 watts per channel that allows me to play lload, and stay far enough away from the point where harmonic distortion becomes audible. carver has made some outstanding asolid state amps in this 200+ watts per channel category over the years. if, on the other hand you like to play load and favor amplifiers with less than let's say 100 watts per channel (like those silly tube amps), then you would benefir from bi-amping to jack that power up (and lower distortion).

at this point you can probably tell i'm not really a big fan of bi-amping or tube amps due to my passion for hi power solid state amps, and the fact that it's simpler (ie less wires). another negative to consider is that most 5 channel amps tend not to have beefy power supplies and sometimes spec lower power levels when all channels are driven. they usually share a common (whimpy) power supply which cannot take the hi load when all channels are playing load simultaneously. carver has done some parlor tricks with 'power steering' - but its just that...since most people are buying them to save space they tend to skimp on the power supply.

i'm all for seperate stereo amps and raw, unrestrained power. you can play loud, no distrotion and simple. but everyone that looks at my setup is immediately taken back by the number of pieces! so i guess if your trying to save space or satisfy the female in the house who thinks audio equipment should be heard but not seen then a 5 channel unit would be a plus.

like i said in an earlier post there are 5 channel amps that deliver hi power (all channels driven) with excellent performance (200plus watts per channel - all channels driven and low distortion) but i think your looking at well over $2K for these units (anthem and adcom come to mind).

my past fond memories of 4 home made 125 watt swtpc 'universal tiger' power amps and speakers without passive crossovers worked really well with a heath active crossover and biamping, but those days are well in the past...high quality solid state power is now much cheaper, and computer aided speaker cabinet and passive crossover designs that are matched are much higher in quality.

sorry for the verbose rant
Last edited by Chuck_K on Fri Sep 29, 2006 4:21 pm, edited 3 times in total.
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mikekohut

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Post Thu Sep 28, 2006 9:09 pm

Okay, I see what you are saying and your verbosity -- to an extent, Chuck -- was necessary. :) From what I understand, the 705x 5 x125wpc RMS amp is quite a champ. I am thinking 125 for my center and 2 x 125 for each front (stereo) speaker if I were to biamp - for creative purposes if nothing more, or maybe if I got a good deal on a nice condition 705.

Anyway, I am just trying to think of creative ways to power my 6-channel system and make sure I'm giving my front stereo speakers what they need to really cook cleanly. I am also wanting to be sure the center gets some juice, too.

My choice combinations (that I am aware of) if I go all Carver power:

1) A-753x - hard to find 250wpc 3-channel
2) AV-705x - 5 x 125wpc w/2 channels bridged and the remaining channel driving the center (if bridging this amp is even possible?)
3) AV-705x - as described above (bi-amp) w/remaining channel for center
4) 2-channel stereo amp along with either a tfm-6cb or 15cb in mono mode for the center
5) AV-806x (run 3-channel if this amp is bridgeable?)

My surrounds are rather small (B&W LM1s mounted to the wall) and thus while more power for the three of them would be better, the priority on giving them their own amp is low right now (they are rated 100wpc RMS and the receiver is rated at that).

I don't have a wife right now so the number of pieces isn't a factor. :)

Any ideas welcome....
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garcianc

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Post Thu Sep 28, 2006 10:43 pm

Here's one additional all-Carver combination. I have been running a M1.5t / AV505 combination for a few years in my home theatre with excellent results. I later added a Sunfire True Sub Mark IV. My M1.5t drives my main speakers, and the AV505 drives the front and rear speakers in my 7-speaker system.

Due to a complicated set of dramatic circumstances, I just added an Outlaw 7125 amp (that's 7 x 125 wpc) to replace the AV505 which was on an extended vacation adventure to Gresham, Oregon.

Since I don't want to depart from my beloved M1.5t driving my mains (particularly for stereo listening), I now have two spare channels in my system. I briefly considered using one of the additional two channels to bi-amp my Polk Audio CSI-5 center speaker but I felt that introducing more connections and wires to the mix was asking for trouble.

IMHO, bi-amping is an acceptable complexity in two-channel audiophile systems but for multi-channel home theatre setups, I am not convinced it's worth it. After chasing down one too many buzzes and hums, I subscribe to the KISS principle.

I could use the extra channels to setup separate listening zones - my wife would probably like that better.

I hope that gives you some food for thought.

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