[lightspeed240]

OK, so Im hoping someone on here really knows their amplifiers and can help me with this one. In summary, is there any power/current advantage in running a multichannel amp with only two channels, as opposed to running the two-channel version of basically the same amp?

Specific example... I want to get a parasound hca-1000a for my mains. However, the multichannel version of this amp (basically,) the hca-1205, has twice the power supply VA and over twice the total capacitance, which would be expected since it is meant to drive 5 channels instead of 2.

So my question becomes, if I only run 2 of the 5 channels, is this power supply potential and capacitance going to be distributed evenly to just the 2 channels being used, or is it pre-distributed to all 5 channels? If so, it seems this would be a better performing setup, all-else being the same. However, both amps have the same per-channel current rating, so its seems this isnt the case.

The 1205 costs a lot more used than the 1000a, but I dont mind to spend more up-front and have the additional potential. I do not plan to ever run more than two channels from it, as I already have my desired setup on my center and rears now. I only need two more channels.

Thanks in advance!

 

[biomed_eng_2000]

Can your speakers be biamped?


You can then run 4 of those 5 channels.


Many many manufacturers gives specs of their multichannel amps driving less channels.


For example:

from http://emotiva.com/xpa5.shtm

5 channels - 8 ohm = 200 watts per channel


4 channels - 8 ohm = 230 watts per channel


3 channels - 8 ohm = 250 watts per channel


2 channels - 8 ohm = 275 watts per channel


1 channel - 8 ohm = 300 watts per channel


Perhaps Parasound let you know how their amps perform with less channels activated.

 

[MichaelJHuman]

In general, based on my experience, you would have more power available to the two channels when using a shared power supply.


Note that there's a limit to how much power it can put out per channel though. It can't amplify beyond the limits of the power supply rail.

 

[biomed_eng_2000]

Why not just buy a 2 channel more powerful version of the hca-1000a? Parasound makes plenty.

 

[DonoMan]



Quote:
Originally Posted by biomed_eng_2000 /forum/post/15481910


Can your speakers be biamped?

Useless unless your speakers have multiple woofers that you can amp separately.


What you want to do is bridge the amp - if it supports it.

 

[lightspeed240]

Hey guys, thanks for the responses. Let me try to clarify a little.


Biomed, Dono, yes, I can bi-amp my mains (Paradigm Studio/20.) However, the 20's dont have a terribly high RMS power rating (100 w/ch,) so I was afraid to bi-amp them using the 1205 (that would be 140 watts per driver, which seems "dangerous" to me.) I know you can never have "too much" clean power, but I need to protect them from myself

Also, my 20's measured out to 5 ohms of resistance on my meter (static,) so thats going to actually be more like 200 watts/driver, I would expect.

What are your thoughts on that?


Michael, I would tend to agree with you on the power supply and capacitance issue. It seems like a 140w/ch, 5 channel amp with 1.6 kVA and 100k uF capacitance would rock on just two channels, if its literally on a shared bus of some sort, but Im not an expert on these things. Thats a ton of reserve. The hca-1000a has 785VA and 40k uF, for comparision. But they are both rated at 45 amps peak per channel, so maybe they are rated with all channels driven?


I have an hca-750 for my center channel now, so I could get another 750 for even less money than the 1000, and either bridge them mono on each main (although thats 250 w/channel...yikes,) or bi-amp the mains with both, and get another amp on the center. Bi-amping would give them 75 watts per driver (presuming 8 ohms, but they are lower than that.) I would have to get yet another amp to power my center though

I dont know if 75 w/driver would be better than 125 w/speaker either.


BTW, my AV room is small and scaled accordingly, so Im not really that power starved now. Im just looking to get a little more oomph up front.


Too many amps, not enough time LOL Any input appreciated

 

[DonoMan]

DC resistance is not the same as impedance. To measure impedance, you'd need to sweep them with a signal of a known voltage, measure current and graph it out. While speakers are usually given a single impedance rating, it's really not an accurate depiction because impedance in almost every speaker varies greatly per frequency.

 

[lightspeed240]



Quote:
Originally Posted by DonoMan /forum/post/15486832


DC resistance is not the same as impedance. To measure impedance, you'd need to sweep them with a signal of a known voltage, measure current and graph it out. While speakers are usually given a single impedance rating, it's really not an accurate depiction because impedance in almost every speaker varies greatly per frequency.

Makes sense, I was just trying to estimate the power per channel. Even at 8 ohms, 140 w/driver would be a ton on my little 20's LOL

Ugh, decisions, decisions.

Any thoughts on which would be a better setup... running 2 hca750's on the studio 20's bi-amped (using the internal, passive speaker crossovers,) or the hca 1000 with 125 w/channel, with them single amp'd?

 

[DonoMan]

Bi-amping does little to nothing 99% of the time. You would be better off bridging or getting a more powerful amp. If you're getting a separate amp. then IMO 125w/chan is already a bit too weak to bother with.

 

[lightspeed240]

OK, so quick update on this. I decided to just go ahead and bi-amp them and listen for myself to determine the best setup.

I spent a long time comparing several different setups, including single and bi-amp'd configs:

- bridged rotel 2 channel amp (180 w/mono) on mid/bass and a small parasound in stereo (45w/ch) on the tweeters

- bridged rotel (180 w/mono) running single-amp'd to the speaker

- stereo parasound hca750 (75 w/ch) on mid/bass and the small parasound in stereo (45w/ch) on the tweeters

- stereo parasound hca750 (75 w/ch) running single-amp'd to the speaker

- stereo parasound hca750 (75 w/ch) on mid/bass and the rotel in stereo (60w/ch) on the tweeters


After all of these configs, I have to say there is little doubt that bi-amping the speakers was effective in improving sound quality. I think a major benefit was the ability to perfectly blend (to my ears) the level of the lows and highs using the individual amplifier gains. Also, there was tighter, more punchy bass and more a more spacious sounding midrange.

Remember again that I have small speakers and a small room, so I dont need a ton of dB to be enjoyable.

I will say that the best overall sound came with the 180w on the mid/bass driver, but I really dont want to buy another rotel to match this one in-order to run two mono amps on the mid/bass.

At this point, Im fairly certain that my final setup will consist of a larger, 2 channel amp driving the woofers and the hca750 on the tweeters. Now I just have to find the larger 2 channel parasound to match my other amps LOL