Power amp for Axe-Fx 3 / FM3 / FM9

Greg Ferguson said:
The issue is not so much the class of the amp, it's the power reserve of the amp when it's running loud and is hit with a transient.

IIRC…
  • Class AB tend to be heavy and big because they're not as efficient so they have beefy power-supplies. The power-supply has big capacitors, that, when charged, are just waiting for a "chug" or a hard-hit clean chord.
  • Class D are much more efficient so they can usually get away without that beefy power-supply. The problem then becomes the amp has no reserve when it's being pushed hard so the dynamics are lost, so then they scale up the size of the amp. From what I remember, the class D amp needs to be rated about 4x the wattage output of a class AB to stay clean.
  • Tube amps, whether they're guitar heads or power-amps for PA, break up differently than solid-state, whether they're Class AB or D. Tubes will gradually slip into clipping and their harmonic order is more pleasant to hear. Solid state will usually clip instantly when overloaded, like a fuzz pedal, which is a nasty sound especially when it comes from a amp and cabinet that we expect to be crystal clear because it's supposed to be reproducing the sound of a modeler. Again, for solid-state we'll need that power reserve, whether it's in the power-supply or in its wattage rating.
  • I'm very suspicious of pedalboard-mounted class D amps because they don't have the reserves I want to recreate the sound cleanly. I've had my EV-PXM12 cabs keeping up with a FOH system that was peaking at 110dB. That is stupidly FREAKIN' loud and the EVs are rated for peaks of 129dB so they have some reserves. I don't think class D amps sized for pedal boards will do that simply because of the way power demands go up as the volume increases.
We have to be aware of the games the manufacturers play with ratings and how much we'll need, and a little dose of skepticism is probably good too for those times when you find yourself needing to go 1 more.

Just my $0.02.
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I don't think you need 4x the power for a class D amp as you would with a class AB amp. If the amp can put out a true 200W into a 16 Ohm cabinet then it has enough power to mimic a tube guitar head. The problem is that many amplifiers marketed for this application do not have that much power output despite their marketing claims (which typically list peak power rather than continuous power).

I agree that a major concern with a power amplifier's performance is having sufficient stored energy available to reproduce the dynamic transient peaks. Lower quality amplifiers will only have enough stored energy to maintain their rated power for a few milliseconds and then will drop off in power significantly (see the video for a demonstration of this).



There is nothing fundamentally inherent to the class AB or class D designs that make either topology superior in this regard. Either can be implemented well or implemented poorly. That said, class D amplifiers are very often designed with the goal of reduced weight and cost. Achieving those goals comes with the tradeoff of poor performance. Some ratings to pay attention to include THD, damping factor, and continuous power. If the manufacturer does not supply these ratings then I would conclude that the amp is not good.

Class D does require a filtering network to remove the switching noise that the design imparts, so in that sense class AB is superior. However, if done well, the switching frequency distortion should be outside the range of human hearing so as to be imperceptible.

The bottom line is that there is no substitute for quality design and components.
 
chumbucket said:
Yeah, it's not a road amp but I'm sure it would survive in the right case. Sounds great though. I prefer it to my tube power amps and my MOSvalve.
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I am intrigued by this power amp. What would you say makes it stand out compared tube power amps you have used? Do you play high gain stuff? Thanks!
 
mtb said:
I am intrigued by this power amp. What would you say makes it stand out compared tube power amps you have used? Do you play high gain stuff? Thanks!
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I found that my tube amps were decent but they're noisy, hot, and the sound changes as you get louder. With the class AB amps, it's more linear but you still get the punch of a tube amp. The tone I get at low volumes is still there at louder levels. At that point, it's just speaker compression that changes tone. The MOSvalve is good too, but it's got a noisy fan, and the Avantone is convection cooled. Silent and powerful. Super low noise floor.
If you're not playing at band or stage levels, you can get by with a class D, but I don't have any to recommend.

Yes, I play high gain as well. No complaints. Find a good guitar cab that you like with tube amps and run with it. I hardly ever play through monitors or headphones anymore. The 4x12 is much more satisfying to me.
 
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I've been looking at those CLA amps now, @chumbucket. Does your CLA100 get loud enough in a band setting? I'm in a loud band and it's not an option to turn our drummer down (nor do we want to). I guess if you're using a 4x12 and going bridge it's probably good.... I use stereo 2x12's so maybe I should go with the CLA-200.
 
chumbucket said:
I found that my tube amps were decent but they're noisy, hot, and the sound changes as you get louder. With the class AB amps, it's more linear but you still get the punch of a tube amp. The tone I get at low volumes is still there at louder levels. At that point, it's just speaker compression that changes tone. The MOSvalve is good too, but it's got a noisy fan, and the Avantone is convection cooled. Silent and powerful. Super low noise floor.
If you're not playing at band or stage levels, you can get by with a class D, but I don't have any to recommend.

Yes, I play high gain as well. No complaints. Find a good guitar cab that you like with tube amps and run with it. I hardly ever play through monitors or headphones anymore. The 4x12 is much more satisfying to me.
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I currently have a LX-II…noisy (fan) and hot…😃😅 yup, you got it.
 
MicroMort said:
I've been looking at those CLA amps now, @chumbucket. Does your CLA100 get loud enough in a band setting? I'm in a loud band and it's not an option to turn our drummer down (nor do we want to). I guess if you're using a 4x12 and going bridge it's probably good.... I use stereo 2x12's so maybe I should go with the CLA-200.
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Yeah, it's definitely loud enough. I run it into a stereo 4x12 at 8 ohms a side. The 200 looks cool but too big for my rack.
 
We hear different frequencies differently depending on volume, the ab/d will not change this. Thats how humans hear. Dial in at the volumes you will be using. As mentioned, power amp modelling on/off is up to the user and not power amp specific.

OP still hasnt mentioned a budget as far as I can tell. What can you test drive? Start there.
 
Absolutely wouldn't recommend Matrix. Unless you get a killer deal
and have a solid backup. See the other threads about the Matrix service nightmares.
Mines been out for 2 years with no support, diagnosis or communication.

Do they sound good? Yes, and I know people here are using them with no issues.
But my 800 failed twice, the second time actually catching fire.
Repaired once, but after returning for post fire repairs, not a peep.

Shit service. At least an email to say it can't be repaired.
Now I'm out a 700.00 amp. No idea who has it or where it is.
If I had possession, I could at least take it to another tech.
 
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MicroMort said:
Soundwise? absolutely.... but with matrix out of business, it's less of an option for me now that there is no service/support.
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I keep seeing this pop up when people talk about matrix. I've never taken a piece of gear to get repaired by the people who made it. I've always just taken it to a local tech (if I couldn't fix it). is there something I'm missing? Like no schematics or parts being custom made so they can't be replaced?

and I'm coming to this from the world of vintage amps, 90s rack gear, and esoteric pedals. where you just had somebody fix it.

I mean... it's just a poweramp so your not expecting firmware updates or something? or to make sure the old editor works with your newer laptop (I'm looking at you FAMC). Or am I missing something? I'm not trying to be snarky. I'm legit trying to understand this fear I keep seeing as I'm thinking about picking up a Matrix.
 
bchulse said:
Absolutely wouldn't recommend Matrix. Unless you get a killer deal
and have a solid backup. See the other threads about the Matrix service nightmares.
Mines been out for 2 years with no support, diagnosis or communication.

Do they sound good? Yes, and I know people here are using them with no issues.
But my 800 failed twice, the second time actually catching fire.
Repaired once, but after returning for post fire repairs, not a peep.

Shit service. At least an email to say it's can't be repaired.
Now I'm out a 700.00 amp. No idea who has it or where it is.
If I had possession, I could at least take it to another tech.
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this popped up WHILE I was typing my message. so now I'm starting to understand.
but it also seems like this was Matrix service directly?
 
chumbucket said:
Yeah, it's definitely loud enough. I run it into a stereo 4x12 at 8 ohms a side. The 200 looks cool but too big for my rack.
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So you have a cla100 and Axe III in a rack? How heavy is it to haul around?

I currently have an FM3/ps170 but was thinking about going back to a rack with an FC6.
 
jski59 said:
So you have a cla100 and Axe III in a rack? How heavy is it to haul around?

I currently have an FM3/ps170 but was thinking about going back to a rack with an FC6.
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I've just gone back to using my Axe III rig with my JP2C head and FC12. I'm using some lower gain amp models in the preamp of the JP. I actually only just realised I could do this and I've had the axe since it came out lol. It now means I can sell my pedals again! lol. I went back to an analogue rig with a VP4, pedals and loop switcher but I prefer using my Axe for effects.

I was thinking of adding a Synergy SYN-2 and the CLA-100. I've heard good things about the CLA-100!
 
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CL1-100 weighs in at 14.8lbs which is 6.7kg

The Matrix GT1000 weighs in at 8.2llbs which is 3.7kg so around 3kg heavier. The Fryette LXII is around 12kg and that was quite heavy for me anyway. It did have 6L6's in it though!
 
Any thoughts on the Captor Reload II? It is a load box / re-louderer but the power amp seems to have some interesting features. 2U alas.
 
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