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Discussion Starter · #1 ·
Hi,


Just bought the AV20 and I am seriously considering the Gemstone amp. It has gotten good reviews here and elsewhere.


My setup is a 5.1, with no plans to go to 7.1. Live in a condo and the extra speakers would have no where to go. My question is, is there any advantage to still getting a 7 channel version? Such as bi-amping the front speakers? I know there was a thread regarding bi-amping months back, seem to think it was split on the issue. Any other reasons to go for the 7 channel version? Or should I just save the $500 and buy the 5 channel?


Thanks in advance for your advice.
 

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Here are some reasons to get the 7 channel:


1. They are in-stock and immediately available - the 5 channels are made-to-order and take a couple extra weeks.

2. A 7 channel amp will probably be easier to sell if you ever decide to do so.

3. The unused channels could be used to bi-amp your fronts as you mention, though any improvement would probably be marginal at best.

4. You may change your mind and decide to go to a 7.1 system later.
 

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One other possible reason.


(Does the Gemstone use 1 or 2 tranformers? Not "monoblocks", right?)


If you get the 7 channel version, it will probably be able to deliver greater power to each of the powered 5 channels than the 5 channel version. Asssuming it has (a) larger transformer(s), and that the amp is designed so that it's not the output devices that limit current output.


7x200=1400 / 5 = 280.


It's not that simple, but that's the idea. :)
 

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You can use the extra 2 channels to power subwoofers. You can either do a mono-sub with dual voice coil (one channel per coil) or drive a pair of subs. I would bet the Anthem has 4th order crossovers that should work well combined with the power from the Gemstone to out perform most plate amplifiers.
 

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If you have no plans to go to 7.1; and if your front speakers are not terminated for pasive bi-amp (two sets of terminals with jumpers) then I'd save the money unless your in a real hurry for it. My guess is both models have the same power supply, just to keep costs down, but you could check with Gemstone and find out.
 

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Quote:
Originally Posted by Kevin C Brown
One other possible reason.


(Does the Gemstone use 1 or 2 tranformers? Not "monoblocks", right?)


If you get the 7 channel version, it will probably be able to deliver greater power to each of the powered 5 channels than the 5 channel version. Asssuming it has (a) larger transformer(s), and that the amp is designed so that it's not the output devices that limit current output.


7x200=1400 / 5 = 280.


It's not that simple, but that's the idea. :)
According to SteveH, the 7 and 5 channel amps have the same size transformer, which arguably puts the advantage to the 5 channel in maximum output per channel.
 

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Quote:
Originally Posted by dsmith901
According to SteveH, the 7 and 5 channel amps have the same size transformer, which arguably puts the advantage to the 5 channel in maximum output per channel.
True if,

The demand load was so great to drain the main on-board capacitance and the on-board per channel capacitance.

Both the five and seven share identical Capacitance & amplifier/channel boards which include the same rated output devices.

The majority of amplifiers power supplies well exceed power requirements for the demand placed upon them given adequate available energy storage “capacitance’

The difference would be how much more the power supply actually is working.

The duty-cycle still would remain relatively low in either case.
 

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Discussion Starter · #8 ·
Thanks for the replys, so far it's about a 50/50 split in advice though :) .


With regards to Enigma's point, I have PSB Silver speakers which have two sets of terminals, but I not sure if the AV20 supports bi-amping. Anyone know for sure if the processor allows for bi-amping?


Thanks.
 

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Quote:
but I not sure if the AV20 supports bi-amping. Anyone know for sure if the processor allows for bi-amping?
Its not the processor that needs to support biamping, its your speakers.
 

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Discussion Starter · #10 ·
hmm ... perhaps I am under a misunderstanding of biamping (a very real possibility :) ).


But I thought that to biamp the amp need to have 4 of its channels 'feeding' the two front speakers (since there is now 4 speaker posts in play). But doesn't this mean that the front L/R pre-amp channels need to be sent to 4 channels on the amp? Therefore, doesn't the pre-amp need to be configurable to send the left and right channels twice? Other threads have mentioned that some people with 7.1 pre-amps and amps but a 5.1 speaker set up will do this. I was initially interested in this as well, but was told by the dealer that the AV20 did not have the software for this currently. It was far from a deal breaker for me.


If any of the above is wrong the please correct. Thanks. I hope I have not hijacked my own thread :) .
 

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You just hook up a Y cable from the channel outs that you want to bi-amp to your two channels of amplification.
 

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SRR is correct; there are really two ways of doing bi-amping.


If your speakers have separate terminals (as yours apparently do), then the simplist way to bi-amp is to remove the jumpers between the terminals; then use one amp channel for the woofers and the other for the mid/tweet (or tweet, depending on the speaker). The feed to each of those two amps (per channel; 4 altogether) is from the same output terminal of the pre/pro, using a Y-connector. So each of the two amps per channel is getting a full-range signal of the main left (or right) channel (assuming you're bi-amping the fronts). Once this full range signal gets amplified it is fed to the speakers. The internal pasive crossover is still there, and the inductors, capacitors, etc limit the freq going to the individual drivers. The normal setup would work exactly the same way, except there would be only one feed, which is jumpered at the speaker. Either way, once it leaves the speaker terminals and goes into the crossover network it is filtered for the appropriate driver.


So the bi-amping allows you to supply more power to the speaker by separating the power amp "channel" driving the woofer from that driving the mid/tweet. But you are still left with passive, high current filtering inside the speaker.


The more "old-fashioned" way of bi-amping is more complex and requires a special speaker set-up (such as most Linn speakers have), or actually modifying the speaker. The setup here would have the pre/pro output to a separate electronic crossover, which divides the signal by freq before being amplified, then sends LF and HF signals to separate amps (or amp "channels" in this case). These would feed the speaker drivers directly, with no internal crossover. As most speakers aren't designed for this, it's not generally practical. The benefits, though, are that you can eliminate all high-level filering (and in these modern times, you can use steep slope digital filters, as the NHT Xd system does). Thi s type of bi-amping (called "active") also eliminates the amp from amplifying signals that will be filtered out; for example if there is a very high output bass signal, the electronic crossover will filter it out of the amp going to the mid/tweet, where it's not needed, thus freeing up that channel of the amp to have more clean power available to drive the mid/tweet.


Personally, I'm not a huge fan of the first type of "passive" bi-amping, but I'm sure it does allow you to get more power from the amp to the speakers. For a 200 w/ch amp I just don't know if it's worth the trouble, unless you do a lot of 2 channel listening at very high levels (or have very inefficient speakers, very large space, etc). I admit, though, that I've never heard a set-up like this, so possibly there are other audible benefits.


The "active" type of bi-amping, as implemented by Linn (they use links in their speakers which allow you to eliminate the internal crossover from the signal path externally, and have external boxes for the crossover filter cards (they call those "Tunboks") has many advocates, and Linn speaker fans in general tend to swear by them (those I have heard, though not really in a critical comparision setting).


If you have the extra 2 channels available sitting there doing nothing; then, sure, why not hook them up in a passive bi-amp mode; but to buy an amp for that seems to me unnecessary.
 

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Quote:
Originally Posted by Enigma
SRR is correct; there are really two ways of doing bi-amping.



So the bi-amping allows you to supply more power to the speaker by separating the power amp "channel" driving the woofer from that driving the mid/tweet. But you are still left with passive, high current filtering inside the speaker.



.
I know this has been debated ad-nauseum, but I don't think this is an entierly accurate description of how a passive crossover interacts with the amplifier. The full band signal is not "transmitted" to the speaker. Once the high or low pass crossover is connected to the amplifier output, the crossover effectively becomes part of the amplifier circuit. It doesn't draw current for the frequency bands being filtered out as you suggest (Ohms law always applies, I = V/R). The stop band of the crossover creates a high R.


So, if you are driving your tweeters in a biamp configuration, the current draw for the low frequency signal will be very tiny, even though the voltage of the low freqencies may be visible at the speaker inputs (via oscilliscope). To say passive bi-amping is inefficent is like saying the 120v sine wave you see in your wall socket is an inefficent use of power when it isn't connected to anything. Put a voltmeter in a socket, it will say 120v rms, but with almost no current draw.



I have the Gemstone 7 ch amp, and I have my fronts passively bi-amped, and it does make a difference in the clarity of the treble, especially at high volumes. (Less sibilance, better imaging, etc.) The lower current demands of the treble signals allow operation in a more linear range of the amplifer (class A range?).


I wouldn't go out of my way to get two extra channels just to do this, but in the case of the Gemstone 5ch vs 7ch price, the improvment is worth it.
 
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