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Class D Amplifier comparision test
started on 17 July 2008, last update 8 September 2008

 
INTRODUCTION

In these last years there was a large diffusion of Class D amplifiers using the pulse width modulation.

from AES document High Fidelity Pulse Width Modulation Amplifiers based on Novel Double Loop Feedback Techniques (mirror)

The basic principle behind a PWMamplifier is shown in Fig. 1.The amplifier principle is also termed a digital power amplifier due to the digital operation of the power transistors or a class D amplifier. The audio signal is pulse width modulated by comparing it with a reference signal (carrier) which can be performed in either the digital or analogue domain. The resulting small signal PWM is converted to power levels by the power switch. Ideal switching elements operating either 'on' or 'off' is the secret behind the theoretical very high efficiency of the PWM based amplifier.

Many people have buy a T-Amp with Tripath chips and now they are happy.

So I have decided to build this complete test to compare many different technologies.

TECHNOLOGIES

photo company model Power Output current max Input impedance output impedence size (mm)
ICE Power by Bang Olufsen 250A 250W on 2.7ohm  with +50v 25A 8Kohm 5mohm 69 x 75
Tripath MOKS Fenice 100 with Tripath TA2022 got from Audioskeggia 90W on 4ohm with +-31v 4.6A 100k   100 x 130
NewClassD NCD04 400W on 4ohm 28A 5Kohm   38 x 100
Hypex UCD 180 OEM 180W on 4ohm with +-45v 10A 100k or 1K8 20mohm 67 x 73
Hypex UCD 180HG with HxR regulators 180W on 4ohm with +-45v 10A 100k 20mohm 65 x 65

These modules have different characteristics like the power but this is not important because I will compare only the sonic performances as full-range amplifier in normal domestic use.

The Hypex 180OEM can be used without the input buffer stage to increase sonic performances.
I have found on HiFifever forum the descrition to modify the common Hypex 180 modules, see http://www.hififever.com/forum/viewtopic.php?t=1772 (mirror)

POWER SUPPLY DESIGN

The power supply used is a classic configuration, 3 components: transformer, diode bridge and capacitors.

To get the best sonic performances and to have a true comparation test all the power supply use the same diode bridge and capacitors.

As capacitors I have choices one of the best components in the market: Mundorf MLytic (snap-in 22000uF 63v).

To begin soon the test as diode bridge as been used a 36MB160A by IRF but will follow tests with ultra fast diodes with soft recovery.

All the amplifiers use Nuvotem Talema Encapsulated Toroidal transformers with different power and voltages buy from RS-Components

1 x  RS 223-8904   0500P1-2-030K for ICEPower
2 x  RS 223-8796   0160P1-2-030K for Hypex
1 x  RS 223-8831   0225P1-2-025K for Tripath

 

For the NewClassD modules I have used at the begin a 600VA 37-0-37V R-Core transformer and after two custom transformers 0-42V  0-42V  500VA build by Canterbury Windings transformers and designed on my specifications with:

  • - Audiograde type  (10% less flux)
    - Electrostatic screen between the primary & secondary windings
    - An external GOSS band to further reduce stray field
  • - Potted centre
  • - Black Mylar film finish

MEASUREMENTS

In all my recent projects I insert some measurements using the Clio system by Audiomatica but I don't consider these important in this test because I am sure that the distortion of all these modules are very low and the frequency response is perfect as declared so only the sonic performances are important.

Probably it is interesting compare the residuals square wave of these modules but now I don't have a valid instrument for this measurement.

SONIC PERFORMANCES TEST 1

In all my sonic performance tests I always search to be sure of an objective result using many persons and these with different experiences.
This mean that the result here is not my personal and it is not subjective like many other test published online.

photo (click to enlarge) environment hardware software results (1 is the best)

This is the system set-up for the first test on August 24, 2008.
We were in my laboratory room.
Two of my friends with a lot of experience on music reproduction were present at the test. They always agreed on the grades given.
 
As digital source:
- My laptop PC
- Audiotrak Optoplay to create a valid 24bit toslink output
- FireStoneAudio Spitfire DAC modified

As analog source:
- Rega Planar 3 with Denon DL-103
- Bartolomeo Aloia VTPA (pre-phono) modified with all NOS Jan Philips vacuum tubes

- DACT stepper attenuator 10K

Interconnect cables:
-
SilverMIca Zero-One by Voodoo Cable (prefered here)
-
Tao Analogue Interconnect  by Q-Audio (here less transparent)

Loudspeakers cables:
- Van Den Hul
D -352 Hybrid  2 x 3m

- The my refecence Monitor 2

Messiah (Dublin Version, 1742) (Dunedin Consort)
Recit Comfort ye.flac
88KHz 24bit from LINN

Oreobambo
Blue Eyes Moon
Piano
CD
 
Porcupine Tree
We Lost the skyline
Drown with me
LP
1) NewclassD
2) Tripath
3) Hypex 180OEM
4) Icepower

The bad result obtain for the Hypex in this test can be caused by 2 factors:
- the capacitors was not the same of the others (BHC Slit-Foil T-Network instead of Mundorf MLytic) soon will be changed
- unbuffered input used to reduce signal path length
In the next tests will be used a different Hypex module
UcD180HG with different performances.

The details ear with NewClassD amp. was more high than my 845 reference amp. also if the sound is a little less natural.

The sound with Icepower is completely smooth with many detail lost.

The Tripath amp. have sufficient detail but a little metallic sound.

SONIC PERFORMANCES TEST 2

In this second test the UCD180HG with HxR regulator have replaced the UCD 180OEM to increase performances.

The UCD180HG  has been tested with 22000uF 63v Mundorf MLytic capacitors and with their original UcD supply HG Mono using high-speed rectifier bridge and Slit-Foil capacitors.

The dual power supply of the analog section for the IcePower has been upgraded with OS-CON and r-core transformer to try to increase performances.

photo (click to enlarge) environment hardware software results (1 is the best)

 

 

This is the system set-up for the test on 7 September 2008.
We were in my laboratory room.
Two of my friends with a lot of experience on music reproduction were present at the test. They always agreed on the grades given.
 
 
As digital source:
- My laptop PC
- Audiotrak Optoplay to create a valid 24bit toslink output
- FireStoneAudio Spitfire DAC modified with OP275

As analog source:
- Rega Planar 3 with Denon DL-103
- Bartolomeo Aloia VTPA (pre-phono) modified with all NOS Jan Philips vacuum tubes

- DACT stepper attenuator 10K

Interconnect cables:
-
SilverMIca Zero-One by Voodoo Cable

Loudspeakers cables:
- Van Den Hul
D -352 Hybrid  2 x 3m

- The my refecence Monitor 2 

Messiah (Dublin Version, 1742) (Dunedin Consort)
Recit Comfort ye.flac
88KHz 24bit from LINN

Vivaldi
I quattro stagioni
Concerto Amsterdam
Iaab Schroder
CD

Porcupine Tree
We Lost the skyline
Drown with me
LP

Emerson Lake & Palmer
Trilogy
From the Beginning
LP

1) NewclassD
2) Hypex 180OHG
3) Tripath
4) Icepower

The details ear with NewClassD amp. are excellent using the standard LM6172 op-amp. The test with the optional LM4562 give a more smooth sound but some details are lost and in this case there is less difference with the Hypex.

The Hypex HG with both the power supply: Mundorf MLytic capacitors or UcD supply HG Mono is a lot better than Tripath and Icepower.

To be sure of this result for the first two amps. I will schedule very soon another test with a different system.

After these good results with Hypex and NewClassD I will continue to use these amps. until there is this hot season and I will wait the winter before to reinsert  the vacuum tubes on my 845 reference amp.The

The NewClassD amp will be tested soon with the power supply board using 8 x ultra fast recovery diodes.

SONIC PERFORMANCES TEST 2 bis

photo (click to enlarge) environment hardware software results (1 is the best)


Here the NewClassD with new Canterbury Windings transformers designed on my specs.

This is the system set-up for the test on 21 September 2008.
We were in my laboratory room.
Another my friend with a lot of experience on music reproduction and owner of many electrostatic loudspeakers and reference amps. l was present at the test and we was always agreed on the grades given.
 
 
As analog source:
- Rega Planar 3 with Denon DL-103
- My Pre phono 2  considered in this test better than Bartolomea Aloia VTPA

- DACT stepper attenuator 10K

Interconnect cables:
-
SilverMIca Zero-One by Voodoo Cable

Loudspeakers cables:
- Van Den Hul
D -352 Hybrid  2 x 3m

- The my refecence Monitor 2 

Norah Jones
Feels Like Home
Blue Note

LP
1) NewclassD with original LM6172 opamp
2) Hypex 180OHG
3) NewclassD with OP627
4) Tripath
5) Icepower

 

SONIC PERFORMANCES TEST 3

In this test the best amplifiers will be compare on different loudspeakers.

photo (click to enlarge) environment hardware software results (1 is the best)


Here the NewClassD in the chassie

This is the system set-up for the test on 28 September 2008.
We were in the hobby room of a my friend with a lot of experience on music reproduction and owner of many electrostatic loudspeakers and reference amps. l was present at the test and we was always agreed on the grades given.
 
As analog source:
-
cartridge Supex sd900 super
- pre-pre Supex sdt77
- turntable Pink Triangle
- My Pre phono 2  considered in this test better than Bartolomea Aloia VTPA

Interconnect cables:
- SynchestraRef by Luminous Audio prefered to the Q-Audio and Voodoo cables.

Loudspeakers cables:
- MIT MI-1-650

Electrostatic loudspeakers Audiostatic ES-240 prefered by the owner to the Quad ESL57 and ESL63.

various LP of my fiend 1) NewclassD with original LM6172 opamp
2) Hypex 180OHG

To be sure of the result has been connected some minutes a traditional amplifier.
The sound of the NewClassD is better than the Albarry M
1008 considered very well by audiophile people.