Class D Amps - Anyone else having second thoughts?

[NickyBass]

The PLX amps are all basically Class AB, and the higher-power models in that range (including the PLX1804) are also Class H.

Thanks for the reply.

 

[FromTheBassMent]

I'm so lucky. I don't really care for the characteristic qualities of tube amps that a lot of bassists desire. I had an SVT half for some years, and always struggled to get a tone out of it that I liked. I'd have other players show me "how to do it" by turning up the gain, and my response was always, "No, that's worse."

I love the sound of a tube amp for guitar. But for my bass tone I crave no grit, no grind, no fur... no overdrive, distortion or fuzz of any kind. I like my bass to sound clean. I play fingerstyle in musical genres that are relatively sedate, so I'm not battling Marshall stacks and double kick drums. I'm trying to blend in musically with acoustic instruments for the most part.

If I prefered tube tone to class D tone, I might have a bit of a challenge on my hands. But the first time I plugged into my Markbass CMD121P combo on the floor of GC, I instantly had a grin from ear to ear. Even with everything flat and no tweaking to my taste, that little amp had the tone that I crave... clean, warm, and not at all scoopy or sterile. Which is why I bought it on the spot. It actually warms up the sound of my EBMM basses compared to the Eden rig I had been playing before.

The fact that it's light and would fit in a Smart Car (if I had one) is simply an additional bonus. What I love about the thing is the tone. I'm not alone, as I have had many bass players and sound guys tell me after a show, "I can't believe that sound is coming out of that dinky box." I can hardly believe it myself!

 

[VroomVroom]

FWIW, even in the highly unlikely event that my Shuttle failed tomorrow, I'd run right out and buy another one. I've had well over a hundred gigs (most being four-hour gigs) on my Shuttle 6 with zero issues. I've treated my Genz reallly rough during that time as it is small and gets thrown into my gig bag and slammed around.

It's a lot cheaper if you don't have to have anything fixed in the first place.

As far as tone -- that's why amps have EQ sections. I get fantastic tone out of mine, and regularly get compliments from fellow bass players who want to see what I'm playing.

Yeah, that. I've settled on the Shuttle 9.0 for my main work...and have used it extensively since purchasing late last year. The 6.0 still sees use every day, although it's limited to rehearsals and small gigs for ensemble situations.

For me, the weight and small form factor would be non-issues if the sound and reliability weren't there. I dig the tone, and I've pushed both amps much harder (and for much longer) than originally intended, and I've not been disappointed. No second thoughts on my end, whatsoever.

 

[Bob Lee (QSC)]

So specific amp - speaker interactions, long discussed in high end and pro audio circles, do not really exist? I'm not fabricating this. Certain speaker types, such as electrostatics, have always been problematic for many power amps, price and / or topology notwithstanding. Speakers with severe dips in impedance, same issue.

Loudspeaker and amp can interact; if you're familiar with the term "damping factor" (as a ratio of load Z to output Z, not merely as a spec sheet number), that's a reasonable statement of the amp's immunity to that phenomenon. If the damping factor is, say, 50 or higher, interaction is going to be negligible.

Some loudspeakers are more difficult loads than others. Electrostatic loudspeakers tend to be capacitive loads, which are inherently more difficult for power amps, but they also tend to have high impedances. If they were somehow low impedance and capacitive, they'd be more difficult for amps to drive.

 

[seamonkey]

What might a player expect to pay for a replacement class D output section? That may be something to consider when making a new amp purchasing decision. Is a $599 amp still a great deal if it craps out and needs a $300 component replaced a few years later? Just like in owning a car, the true cost is what it takes to keep it on the road, not the showroom cost.

The question is more of does it break?

Class-d today overall is very reliable. Walter Woods, Acoustic Image, Hypex, B&O - all have it down pat.

Class-d in everything, cell phones, lap tops, hearing aid, TV's, home and car audio, ...
One reason it's taking over is because it is more reliable.
One reason it's more reliable is Class-d is high efficiency and has less heat. Longer battery life. And easier to fit into spaces other amps couldn't without big heat sinks.

 

[seamonkey]

Funny thing about class-d is the output devices are either on or off.
They are either clipping or they're off.
The waveform coming out the filter can clip just like a conventional amp, but just like any amp you can add feedback paths to handle this in a way pleasing to the ear.
GB has secret feedback technology they use.

 

[fdeck]

Funny thing about class-d is the output devices are either on or off.
They are either clipping or they're off.

It's more complicated than that, because the time period in between on and off is critical to designing a Class-D amp that is both reliable and efficient. Charging and discharging the gate of a power MOSFET at a few hundred kHz is no small feat.

The waveform coming out the filter can clip just like a conventional amp, but just like any amp you can add feedback paths to handle this in a way pleasing to the ear.
GB has secret feedback technology they use.

Chances are that at this juncture, all serious Class-D products have post-filter feedback.

 

[seamonkey]

It's more complicated than that, because the time period in between on and off is critical to designing a Class-D amp that is both reliable and efficient. Charging and discharging the gate of a power MOSFET at a few hundred kHz is no small feat.

They're still on or off.

Chances are that at this juncture, all serious Class-D products have post-filter feedback.

Doesn't mean you can't add extra circuitry to the feedback path to do special things.
Market differentiation.

 

[agedhorse]

Replacement costs of a complete power supply and power amp module is probably around 20-25% of the retail price of the amp (ballparking here). It's really worth repairing because that's not much different than the cost of repairing an equiv. powered conventional amp. Labor on a conventional amp repair can be very substantial so it's really a trade-off. I would have to say that in general, for a power amp failure, the cost of replacing a class D module would not be much different than repairing a class AB/G/H amp.

Of course, I look at reliability very closely and I would have to say that the class D amps we build have a very similar reliability rate compared with our linear stuff. That's by design and choice of vendors. This does not come atthe lowest price however, and that's the decision that we made going into it. There are plenty of other companies who may place low cost above high reliability so let them cover that part of the market segment.

 

[agedhorse]

Feedback can also be nested (pre and post filter) as well as other tricks used to improve stability under clipping conditions.

 

[fdeck]

They're still on or off.

No. There is a time period as the gate is being charged or discharged, that is brief but of nonzero duration, during which the conductance of the channel also goes through a similar transition.

At the end of the day it's still an analog circuit. There's a chapter in my old electronics textbook that is aptly entitled "digital meets analog."

 

[agedhorse]

No. There is a time period as the gate is being charged or discharged, that is brief but of nonzero duration, during which the conductance of the channel also goes through a similar transition."

Also known as the "danger zone" or "no man's land".

 

[gkbass13]

After playing through my Markbass F-1/Epifani ul 2x10 set up tonight, I have no regrets whatsoever after switching to class-d amps.

One trip in and out of a gig/rehearsal is a beautiful thing.

 

[Craig_S]

My MarkBass SA450 sounds great to me. I'd buy another MarkBass amp without question.

 

[arbitrary]

Like others, I love the new technology.

I've been gigging my Shuttle 6 nearly every weekend in crappy bars and festivals for over two years with zero issues, and great tone. Most of my gigs run four hours.

Holy crapolla bartdude. Has it really been that long? damn...

Likewise I've been gigging my f1 for just about the same time and no problems at all. I love my read preamp, but the f1 sounds great and fits in my gigbag.

 

[nostatic]

I don't happen to own a class D amp yet, but I would have absolutely no qualms at all about using a good one, especially one designed by agedhorse, Pat Quilter, or any other exceptional designer.

Tone? If you even half know what you're doing you can dial in the tone you want on any good amp, regardless of its class of amplifier circuitry.

You don't own a K-series?

I have a K8 and K10 - love them. I don't use them as a bass amp though, rather as PA and run vocals, acoustic guitar, keys, and Vdrums through them. They would work fine for bass in a smaller room though.

As for the tone, comments about "sounding good in a mix" are funny because I'll bet that most people couldn't tell the difference between SS and tube with the bass solo'd, let alone in a mix (listening, not playing).

 

[pnut166]

Your signature and the tone of your post, indicate your personal preference. However, I submit that in a double-blind test, you (or the rest of us) would not be able to distinguish a Class D from a Class A/B, or other amplifier topology, whether tubes or solid state devices were used. I imply of course proper gain-matching.

Nobody can discredit your opinion or perception. But, if you're talking about ability to produce an audio signal powerfully, nothing is more elegant than an amplifier than wastes less than 5% of the energy it draws as heat and weighs in the single-digits.

Tubes do look cool, and the topology of most tube amps results in a pleasing sound when overdriven.

The "hoopla" as you call it is because lightweight amplifiers than produce huge power are appealing. I see or hear no reason to lug my 80 lb SVT 2-Pro around when I can get more volume and a similar tone from my 4 lb Genz Shuttle 9. It's an easy choice.

Listen with the ears, not the eyes or the wallet. Switch-mode power supplies and efficient amplifier topologies are being adopted for much more demanding applications than audio. Their performance isn't even remotely questionable. As with everything else in reality, it is impossible and assinine to generalize to such a high degree.

A well-designed amplifier will sound good regardless of the topology. Choose your price point, weight, tone, and power to suit your preference, but don't miss out on potentially awesome equipment because of an ill-founded prejudice.

+1. Well said. If it sounds good, it sounds good. Period.

 

[xray]

We do... but not in the bass market. We have 3 tube amps in our guitar line for years that have been successful and also very reliable. In fact, we probably have as much or more experience with all tube platforms than most other manufacturers since we do both guitar and bass amps.

One problem (from a manufacturer's perspective) with an all tube bass amp is that they end up being large, very heavy and expensive if you want to sell a reliable product.

The other problem is the marketplace tends to be very focused on a specific platform such as the SVT. If it's not an SVT they are not interested. That's a tough nut to crack. Look at the variety of manufacturers who have introduced an all tube amp only to discontinue it within a short time frame.

The players have for the most part spoken, They are interested in compact, high performance and lightweight. That is why the industry is headed that way.



The Shuttle was focused on a specific player, one who was looking for a simple, straight ahead amp that was small, lightweight, inherently tone-friendly and powerful enough to gig with. It also had to come in at a reasonable price.

We have a lot of experience with all tube preamps, from our guitar amp section we have expended thousands of hours developing viable tube circuitry for guitar and bass but we will see what the market (as a whole) asks for and if the wide-spread interest was there we would certainly consider it. It's not because of a lack of experience. It's really Roger's call, and he's looking at many of the same issues I mentioned above.

Mucho gracias, Mr. Agedhorse, for the reply.

 

[xray]

Would it all of a sudden not sound good if you found out it was a class D?

Not at all. Meas's in a league by themselves.

 

[gkbass13]

Cool stuff, Agedhorse. I loved the shuttle 9.0 that I played through recently.

And after another rehearsal tonight, one trip in and out, I can't be more happy with my 5 lb digital head pushing 275(ish) watts into my Epifani ul 2x10. With my bass, gig bag, cables, cab and amp, my total load each way tonight weighed in at less than 55 lbs. AWEOME!

I know the recent discussion in this thread is more technologically involved than I am able to participate in, but as for practical, day to day use, digital amplification(and Neo speakers) is the best gear move I have ever made.