What to use as a subwoofer amp

I am currently using a nad 218 to drive two SVS+ 20-39's. Do you think I am getting the most out of the subs using this amp. I know sub amps are different, but is that because manufacturers want to put everything within the sub, or are the class D and other types better for sub applications.
Hi Michael, I used to use an NAD 214 bridged mono to run a single 12" NHT Sw3P sub. Sonically, I felt this was slightly superior to the NHT's own SA-3 amp which is made to power the SW3P. However, eventually the NAD started to fail and when I contacted an authorized NAD tech he told me that running this amp in bridged mode was very rough on it.

Last year when I was looking into buying a Talon ROC 2002 sub I spoke to Mike Farnsworth about the amp powering the ROC. I mentioned I was using only a single channel of my Bryston 4B to power the NHT and he said the amp in the ROC couldn't compete with the Bryston. He said it wasn't the number of watts of the amp, but the quality of those watts and that the Bryston was very good with bass.

Speaking with Gilbert Yeung of Blue Circle and Kevin Allen one of his dealers at CES last month, they both were a bit incredulous as to how Brystons can perform so well when producing bass. The 4B I'm using is definitely much better than the NAD, and it never seems to tire. I'm sure running only the single channel is much easier on the amp than if I were running both channels to two separate subs. This is something I plan to do in the future and I'm sure the 4B won't have a problem.

From the little I've read of class D amps, they seem only suited to bass reproduction and overall aren't as good or as dependable as AB amps. They're just cheaper.

I've read good things about the 218's ability with bass, so going to a bigger amp might not yield the results you're looking for. Are you using it in stereo or bridged and hooked to the subs in parallel or series?

Good luck and happy thumping!
My original plan was to use two 214's bridged like you, but tech at NAD said it was a bad idea since the drivers are 4 ohm. I guess thay were right.
I'm running the 218 amp in stereo mode, parallel. The amp has only clipped once, and that was me trying to bring the house down. It doesn't seem to have any trouble under normal conditions, even under very loud conditions. It sounds like yours didn't give you any trouble at first, but over time it wore down the amp. I asked NAD if that would happen with the 218 in stereo,and they said it wouldn't be a problem, only if I bridged it. (this would be 1000 watts@4 ohms which is too much anyway)

Having said that, I guess my question is if a class d amp will give me more slam. Or, if a class d isn't as good as the 218, is there an amp in the $400 to $500 range which is better suited for bass?
look at a pro amp--qsc,crown
I would go for a Bryston.
Bryston is a great choice, because you can easily bridge it and get the most out of your amp. I use an old 4B for my passive sub.
I use an old Acoustat Transnova amp on my subs and it works great. Hafler makes more current versions of this amp that can be found fairly cheap. A 350W/Ch version went unsold on Ebay this week for $750.

Good luck.
Because of their wide pro use and good reputations, I did consider the Crown and Hafler 9505 Transnova amps as well.
My experience with Bryston's are that they don't work that well with low impedances. Other comments by reviewers in Stereophile also support my findings. Take these comment for what they are worth i.e. simply my point of view. Obviously, others have contrasting points of view / experience, so i may be in the minority here.

I would suggest looking for a a Phase Linear 400. This should set you back about $200 give or take. Upgrade the capacitors in the power supply ( 60 - 80,000 uF's is a good starting point ), replace the internal speaker wires and power cord with something heavier and change the binding posts if you feel the need. You will end up with an amp that is better than the Bryston for less money ( easily under $400 if you are handy ) AND you can watch the large back-lit meters swing to the beat of the bass : )

Not that i think that it means a lot, but many people equate a high damping factor with increased bass control. The Phase was rated at a damping factor of 1000 at 8 ohms. Since you are running a nominal 4 ohm load per channel, the damping factor would still be a very high 500 ( give or take due to production tolerances ). I will say that a lower damping factor simply means that the reflected emf ( voltage ) from a large woofer or sub-woofer motor can more easily influence or "modulate" the amplifier. As such, a higher damping factor is never a bad thing.

As to having 1000 watts for bass and thinking that it is "too much" power, you might be surprised. With bass heavy music and high volumes, it's not that hard for you to suck a big amplifier dry during long duration low frequency passages. In order to handle this, you need both high rail voltages, steady state current and a good amount of reserve power supply available on a dynamic basis. Bryston's use low rail voltages, have a good amount of current available but are not that hefty on power supply reserve. While you can increase the power supply reserve by adding capacitors, you can't get around the low rail voltages without re-designing the whole amp. The Phase has high rail voltages, a good amount of current available and a small amount of power supply reserve. As such, it is two-thirds of the way there with the last part of the equation easily corrected.

As a side note, both designs use bi-polar outputs and iron-core ( non "toroidal" ) transformers. Quite honestly, i find that a good sized iron core is far superior to a toroidal of equivalent power rating when it comes to bass impact and definition. As such, weight DOES matter when it comes to amplifiers as "old school" transformers have to have a lot of metal in them to really do what you want them to do. Sean
Since 1981 I have been using stereo subs. First of course with passive subs and then subs with internal power. Phase Linear 400 and 700 at that time where both ill defined and proved to be unstable. Dynaco 400 and SAE 3cm where much the better amps designed by John Bongorno, later of Great American Sound. The relativley small Apt Holman amp designed by Mr.THX himself proved to be a huge improvement over the much larger and more supposedly powerfull Phase Linear stuff. Apt was able to play louder and was more stable and tunefull at the same time. Last external power amp I used was a Krell Ksa150. Each of the two channels driving three 10in woofers. This was a 1.8 ohm load and was no problem at all for the Krell. This impedance load allowed the Krell to produce over 600 watts of true class A power. The Krell was the most tunefull of many amps I had used to power passive subs. First and foremost look for an amp that is stable with both low impedance and reactive loads, as well as having no current limiting. Remember rated power is not always what is claimed. If you cannot go the Krell go Bryston. The Bryston will exert much more control over a large and unruly moving object such as a subwoofer than will a noisy and unstable Phuzz Linear. Tom
The Kenwood L-07M monoblocks are some of the best bass amps out there, if you are lucky enough to find a pair. 150 watts.
Aragon amps should also be added to your list of high value high impact sub amps.. Tom