Subs only powered by Class A/AB to augment my Zus

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#1
Hi y’all.
I’m very close to getting my sound as good as I can hope for. Room and power grid sorted, analog, digital, amps all sounding great. Cables, dedicated lines, balanced power, grounding, vibration isolation platforms all exemplary. My Zus that aren’t much loved by the taste meisters in the high end, continue to really talk to me.
Interestingly the last area that I’ve found has made a big difference is the absolutely correct settings on my onboard Zu subs.
So the other day, I really turned the wick up, raising the rafters in my roof space audio room, and it was instantly apparent I had my settings too high.
Adjusted down from 40Hz to 30Hz, and level from 5/10 to 3-4/10. And now things sounding so much more open, less opaque in mids, faster bass lines, and critically more open and airy treble.
Now this has got me thinking that going the whole hog to a pair of dedicated subs will take me further to an even more exemplary sound.
Esp w the possibility of siting the subs independent of the main spkrs.
But critically, I want to rid myself of the last potential weakness in the system, which is the 300W Class D Hypex N-Core amps internal to the Zus that power the 12” downfiring woofers.
Particularly relevant since the full range drivers and Radian tweeters in the Zus are powered by high quality 70W NAT Audio 211 tubed SETs, a league above those Hypex modules.

Ok, preamble over.
I’m concluding (rightly or wrongly) I should be looking for a pair of subs that
1- have a full set of crossover adjustments
2- Class A/AB, 300W at least, absolutely no Class D
3- would be as “reasonably” seamless w my Class A 211s to main Zus
Any and all suggestions welcome.
FWIW, my Zus go full range down to 40 Hz, indeed in my room close to 30Hz, so these subs will only be needed for output below 30-40Hz, the Zus are good for everything above this.
Thanks in advance to everyone who contributes.
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,337
129
63
Beverly Hills, CA
#2
Class D for subwoofer amps does not revolt me like it used to. I am okay with that now.

I think a pair of REL No. 25s (using the speaker-level input) would work very well!
 

Folsom

VIP/Donor
Oct 26, 2015
2,672
21
38
Eastern WA
#3
The only reason I would avoid classD specifically was if I were going to upgrade to servo, from non-servo considerations. Otherwise classD's dampening factor is rather useful.
 

Al M.

VIP/Donor
Sep 10, 2013
3,999
49
48
Greater Boston
#4
Yes, no problems with class D here either. I have 1800 W class D amps in my JL Audio subs, paired with class A/B tube amplification for the main speakers.

It's all about the quality, not primarily the typology. While you don't like your 300W Class D Hypex N-Core amps, Marc, the class D amps in my JL Audio subs are clearly superior to the class A/B amp in my old REL Storm III (which is a pretty good sub that I have been happy with for 17 years, but not excellent like my current subs).

To put the subs on an isolation platform for efficient de-coupling of energy from the floor, such as ASC SubTrap or equivalent, is by far more important than some purist and likely irrelevant considerations of amp typology.
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#5
Al, no problems on the isolation front. Stacore platforms, or even Symposium Rollerblocks are possibilities. Plus yr solution, and many others.
Re “purist and likely irrelevant considerations of amp topology” re Class D - maybe, maybe not
All I know is I wouldn’t let Class D near my main spkrs, and to allow some convergence w my Class A amps, I’d at least like the chance to consider Class A/AB subs.
That’s if they exist.
Hence this thread.
PS, It’s not that I don’t like my Class D Hypex N-Core pwrd subs, I’m curious if better is out there.
 

KeithR

VIP/Donor
May 7, 2010
3,098
66
48
Marina del Rey, CA
#6
its way easier to use Zu's active crossover with a driver that Sean has personally picked to match the FRD than guess on outboard subs because of their amps. i think you would be wasting your money, sorry.
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#7
Keith, I’m in contact w Sean. I don’t know if there is anything special about the downfiring 12” sub driver per spkr. If there is, and it carefully matches the 10” FRD, then I would be stupid to ditch it for generic subs.
In this case, my curiosity would be whether I can run off-board Class A/AB amps w Sean’s (or another) active crossover, keeping the Zu sub drivers and not replacing them.
 

DaveyF

Well-Known Member
Aug 1, 2010
5,843
47
48
La Jolla, Calif USA
#8
I don't believe the class of amps that is driving the active sub is anywhere near as important as having the ability to have a) multiple subs in the system, b) being able to connect the subs to a speaker-level input and c) to make sure that the subs chosen are going to have a great chance of blending not only with the mains, but also with the room. ( Here's that old synergy thing again)
Also, what i found important is to have the cabling that supplies the amps signal as capable as the rest of the cabling in the system...and not to use the generic cable that comes standard with the subwoofer.
Set-up of course remains crucial and unfortunately is more problematic with the more subs you have in the room. ( As i recently discovered...but after many hours of fiddling, the subs are now dialed in).

All IMHO
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#9
Davey, my subs are integrated into the Zus, via a slot-in modules housing Hypex N- Core Class D 300W/ch amps powering 12” downfiring cones, one per spkr (chosen by designer Sean to be as close as possible in character to the speakers’ main full range drivers). I’ve upgraded things here with custom Lundahls transformers, SR Black fuses, Sablon Corona Elite powercords, and custom fitted ground posts to ground the amps to my Entreq.
The subamps indeed receive speaker-level input from my Nat amps.
 

DaveyF

Well-Known Member
Aug 1, 2010
5,843
47
48
La Jolla, Calif USA
#10
Davey, my subs are integrated into the Zus, via a slot-in modules housing Hypex N- Core Class D 300W/ch amps powering 12” downfiring cones, one per spkr (chosen by designer Sean to be as close as possible in character to the speakers’ main full range drivers). I’ve upgraded things here with custom Lundahls transformers, SR Black fuses, Sablon Corona Elite powercords, and custom fitted ground posts to ground the amps to my Entreq.
The subamps indeed receive speaker-level input from my Nat amps.
So, why are you considering augmenting the subs in your Zu's if you are so happy with what these can do??? If you're considering augmenting the mains...my post above still applies.
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#11
Davey, the usual mental noodling of the audiophile.
Maybe you’d disagree w me, but I just considered that these Hypex amps could be the weak link in my system, and that something higher quality might be interesting.
I’ll certainly leave well alone if this isn’t the case.
To be clear, I’m v happy w my sound. But could I be happier?
 

Folsom

VIP/Donor
Oct 26, 2015
2,672
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38
Eastern WA
#12
Davey, the usual mental noodling of the audiophile.
Maybe you’d disagree w me, but I just considered that these Hypex amps could be the weak link in my system, and that something higher quality might be interesting.
I’ll certainly leave well alone if this isn’t the case.
To be clear, I’m v happy w my sound. But could I be happier?
Can you describe the "weak linK" to us? What exactly is it that you want to get out of new/changed subwoofers?

From a technical standpoint the Hypex's are actually crazy good amps. That doesn't mean you are getting what you want, or that the whole integration is to the top of either the amp or drivers capability. Whatever upgrades you are wanting, it may not come in the package you're imagining like just amp swapping.
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#13
Folsom, actually I can’t relay any weaknesses. I’ve made major changes in upgrades to the Hypex to incl Lundahl transformer, and this, ahem, transformed things.
Additional attention to fuse and power cords have gilded the lily.
And my big discovery in only allowing subs output below 30Hz (instead of previous 40Hz), and at a lower level, means I’m finally solving the mids opaqueness issue where previously higher output from subs was smearing the mids.
This is finally clearing. I was just curious if a move to subs w Class A/AB would provide further audible benefits.
 

Leif S

[Industry Expert]
Feb 14, 2015
535
2
18
California
www.vonschweikert.com
#14
From my experience class D amplifiers work excellent on subs. I only use high level inputs because we have found the integration to be far superior than taking the signal from the pre. This way the sub amp sees the same signal the main towers see. It is important to make sure the class D high level inputs are cap coupled and that the negative binding post doesn't show continuity to the ground pin on the IEC or you can damage some brands of main amplifiers if they are bridged. Also, if you have the space you may want to try the subs at the back of the room aimed back at the main towers. This will equalize the bass pressure in your room and also keeps all that pressure from the subs from modulating the pressure from the main speakers. We have found also using high quality power cords on the sub amps as well as the signal cables to be a HUGE improvement to the quality of sound to the whole system. Also critical to be able to rotate the phase of the sub to truly lock it in.
 

LL21

Active Member
Dec 26, 2010
10,585
9
38
#15
From my experience class D amplifiers work excellent on subs. I only use high level inputs because we have found the integration to be far superior than taking the signal from the pre. This way the sub amp sees the same signal the main towers see. It is important to make sure the class D high level inputs are cap coupled and that the negative binding post doesn't show continuity to the ground pin on the IEC or you can damage some brands of main amplifiers if they are bridged. Also, if you have the space you may want to try the subs at the back of the room aimed back at the main towers. This will equalize the bass pressure in your room and also keeps all that pressure from the subs from modulating the pressure from the main speakers. We have found also using high quality power cords on the sub amps as well as the signal cables to be a HUGE improvement to the quality of sound to the whole system. Also critical to be able to rotate the phase of the sub to truly lock it in.
Very interesting...thanks. We have good success doing this where the big Velodyne is in the back corner facing the big Wilsons which are in the front. We do use a Sablon Audio power cable. When you say high level input vs 'from the pre'...in order that the the sub amp sees the same signal as the main towers do...can you explain if what we are doing is actually what you are suggesting?

Right now, the CJ GAT 2 preamp has 2 sets of outputs...we run one to the Gryphon Colosseum to drive the Wilsons...and the other set of outputs goes to the Velodyne. I think this means the Velodyne IS seeing the same as the main towers...but just in case, thanks for any clarification on what you are advising.
 

DaveyF

Well-Known Member
Aug 1, 2010
5,843
47
48
La Jolla, Calif USA
#16
From my experience class D amplifiers work excellent on subs. I only use high level inputs because we have found the integration to be far superior than taking the signal from the pre. This way the sub amp sees the same signal the main towers see. It is important to make sure the class D high level inputs are cap coupled and that the negative binding post doesn't show continuity to the ground pin on the IEC or you can damage some brands of main amplifiers if they are bridged. Also, if you have the space you may want to try the subs at the back of the room aimed back at the main towers. This will equalize the bass pressure in your room and also keeps all that pressure from the subs from modulating the pressure from the main speakers. We have found also using high quality power cords on the sub amps as well as the signal cables to be a HUGE improvement to the quality of sound to the whole system. Also critical to be able to rotate the phase of the sub to truly lock it in.
+1

Although I don't think an AB amp in the subs is a bad thing at all. However, Class D is also fine in that application.
 

spiritofmusic

Well-Known Member
Jun 13, 2013
6,509
108
63
E. England
#17
Davey, it’s been instructive to get fairly uniform feedback that Class D is just fine for subs even if not my choice of amps for main spkrs.
I’m working at getting a bespoke star ground/chassis ground system that will take a lot of the noise/grunge created by the Hypex modules (I’m informed Class D can be pretty polluting).
My remaining q is whether Hypex N-Core powered integral subs, utilising custom Lundahls transformers, are on principle inferior to the kinds of Class D amps in standalone subs like Rel, JL, Rythmik etc, or on a par/just fine.
 

cjfrbw

Active Member
Apr 20, 2010
2,172
7
38
Pleasanton, CA
#19
I have an older Von Schweikert 10 inch sub and it's literature selling point is that it is Class AB and not D. However, Class D sub amps have probably improved since then and they are subject to quality variation as much as any other.

One of my Class D sub amps (Martin Logan) went out, and I replaced the amp with an external Class AB, and I like it better, seems to sound more robust and "pulsive" in spite of lower nominal power rating.
 

DaveyF

Well-Known Member
Aug 1, 2010
5,843
47
48
La Jolla, Calif USA
#20
Davey, it’s been instructive to get fairly uniform feedback that Class D is just fine for subs even if not my choice of amps for main spkrs.
I’m working at getting a bespoke star ground/chassis ground system that will take a lot of the noise/grunge created by the Hypex modules (I’m informed Class D can be pretty polluting).
My remaining q is whether Hypex N-Core powered integral subs, utilising custom Lundahls transformers, are on principle inferior to the kinds of Class D amps in standalone subs like Rel, JL, Rythmik etc, or on a par/just fine.
Marc, I think you will always get a different presentation with stand alone subs vs integrated subs. If for no other reason than the various placement options that stand alone offers.
While I am agnostic as to the type of amp that the stand alone utilizes, my current REL pair both utilize class AB. In order for the sub to have a more powerful active amp, I fully understand the logic behind class D...since some of these subs are able to hit 500 Watts or even more, tough to do with class AB...due to heat, size etc.,
 

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