Audiogon challenge! Choose an amp for me.

chadh · « **on:** 12 Oct 2009, 02:12 am »

I'm currently on a quest to supplement my single driver speakers with stereo subwoofers. But I'm also determined to maintain a fully active system. In pursuit of this goal, I've bought an Audiokenesis swarm of subwoofers. And tonight I won an Audiogon auction for a Beveridge RM3 active crossover. The only part of the puzzle that remains to be filled is amplification for the subs. So I thought I'd set the AC bargain hounds on the case, to survey the current marketplace and find two great channels of solid state amplification, 100w+ /channel, at the lowest possible price.

The two options on Audiogon that struck me were the following ones:

Acurus 150 ($350 for the stereo amp): http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1259574047&/Acurus-A150-Amplifier

Marantz MA500 monoblocks ($260 for a pair) http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1259757098&/Marantz-MA500-monos-7-of-them

I don't need to purchase quickly. I'm really just looking for ideas on what might work well without spending much money.

Thanks.

Chad

doug s. · « **Reply #1 on:** 12 Oct 2009, 04:54 am »

if you can do w/60wpc (into 8 ohms; more into 4), then an adcom gfa2535 would be yust the ticket - this is a 4-channel amp - two 535's in one box - that sounds really nice, and usually sells for <$300.

doug s.

chadh · « **Reply #2 on:** 12 Oct 2009, 03:24 pm »

Doug,

Many thanks. Whenever I ask for advice on these things, I can ALWAYS rely on you to come up with great suggestions. If I haven't mentioned it before, I really appreciate it.

The good thing about Adcom amps is that they seem to be readily available. I'll keep my eye out for this one.

Just as a matter of interest, do you recommend this one specifically because it has four channels of amplification? I'm wondering whether I gain very much using one channel for each of the subs when there's only two channels of music, and little stereo information below 100Hz in most recordings. I had presumed I'd be better off with a more powerful 2 channel amp and then daisy-chaining the subwoofers together. But I'm open to all suggestions.

I should check what the impedance of the subs is. I'm not sure if they're 4 or 8 ohms.

Chad

doug s. · « **Reply #3 on:** 12 Oct 2009, 04:12 pm »

Quote from: chadh on 12 Oct 2009, 03:24 pm

Doug,

Many thanks. Whenever I ask for advice on these things, I can ALWAYS rely on you to come up with great suggestions. If I haven't mentioned it before, I really appreciate it.

The good thing about Adcom amps is that they seem to be readily available. I'll keep my eye out for this one.

Just as a matter of interest, do you recommend this one specifically because it has four channels of amplification? I'm wondering whether I gain very much using one channel for each of the subs when there's only two channels of music, and little stereo information below 100Hz in most recordings. I had presumed I'd be better off with a more powerful 2 channel amp and then daisy-chaining the subwoofers together. But I'm open to all suggestions.

I should check what the impedance of the subs is. I'm not sure if they're 4 or 8 ohms.

Chad

if you are gonna run only two channels of amplification, w/two subs on each channel, then for sure, you don't need a quad amp. and, running two 8 ohm subs in parallel off each channel will make the amp see a 4 ohm load. in this scenario, a stereo adcom gfa535 might be yust the ticket; here's one for $125:

http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1260484642&/Adcom-GFA-535-

now, if you want more juice, i have a nice hypex home-brew amp i'd like to see go away; 100wpc 8 ohms/180wpc 4 ohms. i took it in partial trade on a speaker deal, and i have no use for it. it's a great amp, and a killer sub amp. but, it would be ~4 times as expensive as the adcom.

doug s.

JimJ · « **Reply #4 on:** 15 Oct 2009, 05:45 pm »

Out of those, I'd go with the monoblocks

fritzspeakers · « **Reply #5 on:** 17 Oct 2009, 03:37 am »

Hi Chad- Check out this Behringer amp from PartsExpress.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=248-749

$200 new, free shipping & with a 45 day full money back policy if you don't like it. 160 watts into 8 ohms, 230 into 4 ohms & bridgeable to 500 watts mono. 1/4", balanced XLR's & RCA inputs with separate volume controls for each channel.

I've used these to power 2nd & 3rd zones & love this amp. I have several older Adcom 200 watt per channel amps that I've collected- 555's, 555 Mk11's & 5500's & think this $200 piece sounds as good (or almost, especially for a sub amp) for a brand new current model with a warranty. The cheaper stereo Behringer crossovers ($80) also work very well for what you want to do.

Fritz Heiler
FRITZSPEAKERS.COM

JakeJ · « **Reply #6 on:** 2 Nov 2009, 04:30 pm »

Hi chadh,

As an owner of a Swarm I send you congrats on your acquisition.

As to how you want to run them I would suggest you consult Duke about it. I did get the included Dayton sub amp when I bought my set but I also experimented with running them stereo with two enclosures per channel. I felt performance went down and I am under the impression that on some music the two channels ended up fighting each other. There would be less bass running them stereo as opposed to mono on certain discs that had stereo information that low in frequency. Since most music doesn't have low stereo content you may not notice it but once in a blue moon.

As a contingent plan you might look for amps that you can bridge to mono with the flip of a switch should you find the stereo application does not work out.

Just my .02

Enjoy,
Jake

chadh · « **Reply #7 on:** 2 Nov 2009, 08:44 pm »

Jake,

Thanks for your message.

I'm just wondering where you cross over to the swarm?

In my application, I'm looking to cross over at around 100Hz. I think most modern recordings provide only mono bass below around 80Hz, but have stereo information between 80 and 100Hz. While the stereo effect may not be audible at these frequencies, I think I'd feel more comfortable with stereo bass presentation when crossing over as high as I plan to. But your suggestion of finding an amp that is easily bridgeable seems like an excellent one.

Chad

JakeJ · « **Reply #8 on:** 2 Nov 2009, 10:30 pm »

I crossed at ~60 Hz to my Quad 988s when I had them set up. Currently I am using Genesis 501.2 speakers that have built in subs and you are right there is stereo bass easily down to 80 Hz and below in some cases.

I'm sure you are familiar with Duke's design premise in that multiple subs asymmetrically distributed in the room pressurize it equally and help reduce or eliminate room nodes. In my room I was not able to get the swarm to do that in stereo mode so I merely mention it as a caveat and to think about getting an amp that can be bridged in the event stereo doesn't work out for you.

Just a little more fat to chew on.

Good luck in your search,
Jake