Class D

[Haywood]

Am I the only one who thinks newer generation Class D amplifiers are the best thing since sliced bread? They are small, efficient, affordable, and sound good to my ear. I also LOVE that you can now get multi-channel amp boards with built-in DSP for building speakers with active crossovers. I already bought one for a set of bookshelf speakers I'm planning to make.

The speakers in my office run off a Fosi 50x2 integrated amp with a line-level subwoofer output. My porch speakers run on a simpler 50x2 Fosi. I recently bought a third one that also has a built in subwoofer amp with variable crossover and gain. That last one is going to drive the Overnight Sensation bookshelf speakers I'm building, along with an 8-inch Boston Acoustics subwoofer that has a dead amp board. Every one of these was under $150 and all of them have Bluetooth.

I think they offer a lot of exciting options and I'm not sure I will ever feel the need to buy another Class AB amplifier again.

 

[MakeMineVinyl]

Class D is efficient, economical, and doesn't take up much space. They will undoubtedly overtake conventional amplifiers in time.


Sounds like a rather boring future to me. Efficient but boring.

 

[Haywood]

Class D is efficient, economical, and doesn't take up much space. They will undoubtedly overtake conventional amplifiers in time.


Sounds like a rather boring future to me. Efficient but boring.

I disagree. This is fantastic for folks who want active crossovers, which have real advantages. I am looking at building a pair of new primary listening speakers later this year using two 100x4 DSP amplifiers. That DSP is a powerful tool, because it contains a PEQ as well as a crossover. It provides a ton of tuning capability. It also allows ongoing tweaking. The crossover settings can be saved as a file and applied to multiple speakers. They can be changed at will during the design process, which is a lot easier than tweaking a passive crossover. I think this is extremely exciting for speaker builders.

 

[Haywood]

I forgot to mention. These little DSP-driven amps are super configurable, because you can bridge any two channels. I bought a 30x4 amp for $64 that I can run as 30x4, 60x2, or 30x2 + 60x1. They can support up to four programmable attenuator knobs that can be assigned to a variety of functions ranging from volume and tone controls to crossover frequency. They also have built-in Bluetooth, as well as line-level inputs.

 

[MakeMineVinyl]

I disagree. This is fantastic for folks who want active crossovers, which have real advantages. I am looking at building a pair of new primary listening speakers later this year using two 100x4 DSP amplifiers. That DSP is a powerful tool, because it contains a PEQ as well as a crossover. It provides a ton of tuning capability. It also allows ongoing tweaking. The crossover settings can be saved as a file and applied to multiple speakers. They can be changed at will during the design process, which is a lot easier than tweaking a passive crossover. I think this is extremely exciting for speaker builders.

Aside from the efficiency and small size, what is the draw in terms of sound quality? (And note that I am on the engineering design team for two brands of class D amplifiers). DSP can be used with any amplifier technology after all - class D has nothing to do with DSP or anything related to DSP. I use active crossovers with tube amps - hardly cutting edge. Also, out of band spurious noise is a byproduct of class D, and I have seen this to be up to a volt. Not much gets written about this deficiency, but I certainly don't want 400kHz garbage going to my tweeters. To eliminate this high frequency noise completely would require highly complex passive filtering on the output of the amplifier rather than the single inductor currently used in all class D amplifiers. A filter more complex than what we have now would impact source impedance and ultimately, damping factor. So the compromise is to let the noise through.

The fact that they are small and efficient doesn't excite me, and in the end, that is the only difference between them and conventional amplifier classes. Any amplifier class can be 'configured'.

 

[Haywood]

Aside from the efficiency and small size, what is the draw in terms of sound quality? (And note that I am on the engineering design team for two brands of class D amplifiers). DSP can be used with any amplifier technology after all - class D has nothing to do with DSP or anything related to DSP. I use active crossovers with tube amps - hardly cutting edge. Also, out of band spurious noise is a byproduct of class D, and I have seen this to be up to a volt. Not much gets written about this deficiency, but I certainly don't want 400kHz garbage going to my tweeters. To eliminate this high frequency noise completely would require highly complex passive filtering on the output of the amplifier rather than the single inductor currently used in all class D amplifiers. A filter more complex than what we have now would impact source impedance and ultimately, damping factor. So the compromise is to let the noise through.

The fact that they are small and efficient doesn't excite me, and in the end, that is the only difference between them and conventional amplifier classes. Any amplifier class can be 'configured'.

I agree that you can use an external DSP and do a full active crossover with conventional amplifiers. That is a given. The advantages here are size and cost. I can attain 200Wx4 with DSP and Bluetooth for $172 per speaker. Buying 8 channels of traditional Class A/B amplifiers would cost at least several thousand dollars, plus the cost of a miniDSP or something similar. In other words, it is extremely expensive to do it the "old" way.

If I am building money-is-no-object truly high-end speakers, the traditional approach is obviously preferable. The magic here is that I can apply the advantages of an active crossover to more affordable speakers. As soon as I finish my garage workshop and finish the speaker kit I bought, I am going to build a pair of very affordable active bookshelf speakers with active crossovers. We are talking about speakers costing around $250 in parts. That could never be accomplished using traditional methods.

The new main speakers I want to build should come in at around $1800 in parts, roughly $500 of which is DSP amplifiers and power supplies. Each speaker will have a Morel tweeter flanked by a pair of 5.25" Seas midranges in an MTM configuration with a 12" SBAcoustics woofer filling out the bottom end. There will be 200 watts of dedicated power for each driver and I expect the results will be vastly better than anything I could otherwise accomplish at that price point, but I could be wrong.

 

[MakeMineVinyl]

I agree that you can use an external DSP and do a full active crossover with conventional amplifiers. That is a given. The advantages here are size and cost. I can attain 200Wx4 with DSP and Bluetooth for $172 per speaker. Buying 8 channels of traditional Class A/B amplifiers would cost at least several thousand dollars, plus the cost of a miniDSP or something similar. In other words, it is extremely expensive to do it the "old" way.

If I am building money-is-no-object truly high-end speakers, the traditional approach is obviously preferable. The magic here is that I can apply the advantages of an active crossover to more affordable speakers. As soon as I finish my garage workshop and finish the speaker kit I bought, I am going to build a pair of very affordable active bookshelf speakers with active crossovers. We are talking about speakers costing around $250 in parts. That could never be accomplished using traditional methods.

The new main speakers I want to build should come in at around $1800 in parts, roughly $500 of which is DSP amplifiers and power supplies. Each speaker will have a Morel tweeter flanked by a pair of 5.25" Seas midranges in an MTM configuration with a 12" SBAcoustics woofer filling out the bottom end. There will be 200 watts of dedicated power for each driver and I expect the results will be vastly better than anything I could otherwise accomplish at that price point, but I could be wrong.

There is no argument that class D amps are far more cost effective, efficient and easier to integrate into projects by a typical user. In the end, it really depends on the goals - do you want a simple solution which is out of the way and economical or are you more interested in interacting with the gear. I fall into the last group and get as much pleasure dealing with and looking at glowing tube amps as I do actually listening to music. That is why I said what I did about class D being more like an appliance, and many people want that.

The latest class D such as the Hypex 502 has created something of a problem with traditional power amplifier manufacturers - these modules are complete amplifiers which need nothing but a power cord and input/output connections. Still, we build multi-channel home theater amps (for Monoprice) using these modules with the value add being the chassis, protection/power management/soft start circuitry using a microcontroller, and power line filtering which eliminates the interference caused by multiple switching power supplies in the same chassis.

There is no question that class D is the future for the average user, but there is still going to be a place for tube amps and traditional solid state A/B amps for those people who are more interested in the hobby aspect of the gear.

 

[Haywood]

I get that. My sister-in-law is building a Class A integrated amplifier from scratch using kits for all the boards and doing all her own soldering and such. Sometimes they come with missing or wrong parts, but that is pretty easy to deal with. She's having a lot of fun with it and just finished the phono preamp board and the input selector. It is a pretty neat project. I am thinking about doing a build myself, but I will likely just use fully assembled boards. I was looking at some 200W Class A/B boards on Amazon for $137/each. Are things like that worth bothering with? I've even toyed with buying a programmable DSP board and installing it in a chassis with a few amp boards and a power supply to drive an active speaker. There are so many things I want to play with, but money is a bit of a limiting factor <sigh> and that is why these little all-in-one boards are so appealing to me.

 

[Haywood]

There is no argument that class D amps are far more cost effective, efficient and easier to integrate into projects by a typical user. In the end, it really depends on the goals - do you want a simple solution which is out of the way and economical or are you more interested in interacting with the gear.

I have a ton to learn here. I've been doing some more research and I can get a DSP board for a 3-way build for about $30 from Parts Express instead of going with an all-in-one amp/DSP. That opens up a lot more options. The questions is whether you have any recommendations. I could use Class AB amp boards instead of D or perhaps use AB on the tweeter and D elsewhere. The dilemma I'm having with the Class AB boards is I have no idea which designs are good and which aren't. Can you point me in the right direction?

 

[MakeMineVinyl]

I have a ton to learn here. I've been doing some more research and I can get a DSP board for a 3-way build for about $30 from Parts Express instead of going with an all-in-one amp/DSP. That opens up a lot more options. The questions is whether you have any recommendations. I could use Class AB amp boards instead of D or perhaps use AB on the tweeter and D elsewhere. The dilemma I'm having with the Class AB boards is I have no idea which designs are good and which aren't. Can you point me in the right direction?

I don't keep up on the market beyond the brand I work for, ATI, but I think I saw a review on a Topping amp which did well.

 

[Haywood]

I don't keep up on the market beyond the brand I work for, ATI, but I think I saw a review on a Topping amp which did well.

Thanks for pointing me in that direction. They make interesting stuff. Unfortunately what I'm looking for is the actual boards and components to build amps inside of my speakers. All good though. There are a ton of Chinese amp boards out there.

 

[bmwuk]

Purifi and hypex are making some great stuff

 

[Haywood]

I'm looking at a couple LJM options, such as the LJM L12-2 or L15.

 

[MakeMineVinyl]

Purifi and hypex are making some great stuff

The Hypex NCx500 modules are just starting to become available in quantity. They are Hypex's answer to Purifi.

 

[Haywood]

Those Purifi boards are about $500 each. At that price, I'd be better off just buying an amp. The point of this exercise is to build something that sounds great at an affordable price point. I've read some good things about those LJM designs and the boards are very inexpensive. Granted, the power supply will cost as much or more than the amp boards, but the total will be closer to $200/channel than $500.

Note: I am NOT building a cost-is-no-object high-end setup. I'm just trying to squeeze every ounce of value I can get out of somewhere in the general ballpark of $2K. I can use four channels from my Marantz MM9000 if I need to and just buy a stereo amp. I think it would be more fun to build something though.