Class A “class D killer” amplifier with THD less than -120dB

[Sokel]

You want us to guess which one it is?

Maybe this one?

 

[Geert]

Maybe this one?

Sorry, that's the 60V. This is the 75V :

To save others from Googling, it's an amp designed by one of the DIYAudio members https://www.diyaudio.com/community/...ee-pole-compensated-class-b-retro-amp.385080/. Schematics supplied in the first post.

 

[LKA]

actual schematic
I don't want to discuss the amp here, just show how easy it's to build a Class-D killer

 

[voodooless]

That is quite amazing, what a nice welcome

 

[DonH56]

This is a Class-D and Class-A killer, single-supply (output capacitor) 100W/4R amp that idles at 3W.

Curious: Is the rise in HF THD at high frequencies and lower power due to noise creeping into the THD measurement?

 

[LKA]

I'll open a new thread to discuss my Class-D killer amps (I have 3)

 

[notsodeadlizard]

actual schematic
I don't want to discuss the amp here, just show how easy it's to build a Class-D killer

BTW Elvee's Circlophone (https://www.diyaudio.com/community/threads/my-little-cheap-circlophone-c.189599/) kills any class D amp also.
But, to be fair, Class D is very good for subwoofers.

 

[levimax]

You don't have to use "Class A" to achieve great performance, just good engineering and attention to detail. @tomchr Nuerochrome AB amps with lots of feedback achieves great results. While I don't think issues with well designed Class D amps are audible a well behaved Class A or Class AB certainly comes closer to the "old school" ideal amp as a "wire with gain". https://neurochrome.com/collections/power-amplifiers

 

[Geert]

a well behaved Class A or Class AB certainly comes closer to the "old school" ideal amp as a "wire with gain

The problem is that these days we have a new requirement; the 'ideal amp' consumes no more power than it delivers to the speakers.

 

[mhardy6647]

This is a Class-D and Class-A killer, single-supply (output capacitor) 100W/4R amp that idles at 3W.

Quasi-complementary?

 

[ahofer]

You'd think Class D was deader than a door nail.

 

[fpitas]

You'd think Class D was deader than a door nail.

The reports of its death are greatly exaggerated.

 

[pma]

You don't have to use "Class A" to achieve great performance, just good engineering and attention to detail. @tomchr Nuerochrome AB amps with lots of feedback achieves great results. While I don't think issues with well designed Class D amps are audible a well behaved Class A or Class AB certainly comes closer to the "old school" ideal amp as a "wire with gain". https://neurochrome.com/collections/power-amplifiers

We need more measurements than the 1kHz spectrum - it is not so difficult to get excellent results at 1kHz with almost any approach, that is why this measurement is so popular and manufacturers show it. Namely, HF nonlinearity with respect to amplitude and level is of interest, as shown for example here. As stated in standards, to measure non-linearity at higher frequencies properly, we need appropriate measurement bandwidth, not limited to 22kHz or even 45kHz.

Care is necessary to ensure that the frequencies of significant distortion components do not fall above the upper frequency limit of the analyser.
For example, if the upper limit of the gain-limited effective frequency range is 30 kHz, and the highest significant harmonic is the fifth, the highest fundamental frequency for which a value of total harmonic distortion is valid is (30/5) kHz, that is, 6 kHz. If the highest significant harmonic were the third, however, values of total harmonic distortion could be stated for frequencies up to (30/3) kHz, that is, 10 kHz.
Some amplifiers produce a spectrum of harmonics including small but measurable harmonics of high orders. The highest frequency component of this spectrum, the amplitude of which is significant, may in general be taken as the highest harmonic whose r.m.s. value exceeds one-third of the total harmonic distortion at the same fundamental frequency. In some cases a different criterion may be necessary, in which case it shall be stated.

The class A amplifier is the only one where the feedback circuit does not have to correct cross-over or switching distortion, that both lead to rise of distortion at higher frequencies as a main reason. This sort of distortion is eliminated in class A amplifiers, though another sources of distortion may still exist.

Below are some measurements made on the PM-A4 class A amplifier, with 90kHz measuring bandwidth. Load 6.8 ohm is used as with this load the output stage remains in the class A for the whole range of output amplitudes.

"Usual" 1kHz distortion. The highest component H2 is at -129.7dB, however it just what is to be expected, at best, from the Topping D10s and E1DA Cosmos DAC used for measurements. So, we still do not know. According to IEC 60268-3, signal source must have distortion of -10dB lower than the DUT under test.

Distortion at 20kHz with 90kHz BW. The highest component H2 is of -108dB. Again, it is not sure if it comes from DAC/ADC or from the amp, but we may be sure that 20kH distortion is very low .

THD vs. power plots at 1, 10, 20kHz with 90kHz BW.

THD+N vs. power at 1, 10 and 10kHz. The plots overlap, are indistinguishable and are dominated by noise with 90kHz BW.

 

[fpitas]

Quasi-complementary?

The schematic I see in post #103 is full complementary. PNP and NPN output devices.

 

[fpitas]

Guess I don't understand how such a weak amp is a "killer" of more powerful amps. This come in actual high-powered form?

Speaking for myself and a few others here, us horn guys don't need more than about 5W on peaks. But we need an amp that is very clean at low power. My horns draw 20mW average at my loudest listening level.

 

[pma]

Distortion at 20kHz with 90kHz BW. The highest component H2 is of -108dB. Again, it is not sure if it comes from DAC/ADC or from the amp, but we may be sure that 20kH distortion is very low .

Frankly, there is still something that could have been improved. It is disclosed in THD vs. frequency plots measured with 90kHz BW:

The behaviour above 25kHz is not optimal and is probably related to handling of charge carriers in B-E junctions of output power transistors, though they do not operate in the switching mode. Up to the 25kHz, we are just at the noise floor of the sweep sine measurement. Stepped sine would bring better resolution - confirmed in the measurement below.

THD and THD+N vs. frequency measured by stepped sine method (much higher resolution). Please note the troubles just above 20kHz. Please also note that around 1kHz we have best results, so it is the ideal "marketing point".

 

[ahofer]

Speaking for myself and a few others here, us horn guys don't need more than about 5W on peaks. But we need an amp that is very clean at low power. My horns draw 20mW average at my loudest listening level.

Horns are one of the rare cases where audiophiles prefer the more (energy, not space) efficient solution. Spoiled, of course, by the accompanying class-A amp that has to be on all the time.

 

[fpitas]

Horns are one of the rare cases where audiophiles prefer the more (energy, not space) efficient solution. Spoiled, of course, by the accompanying class-A amp that has to be on all the time.

Well, that doesn't bother me if the amp does a good job. I have no intention of replacing the J2 until it dies, which may frankly never happen. If it does though, I'll get a class D amp and resistively divide the output, since I need about 10 ohms drive impedance.

 

[ahofer]

Well, that doesn't bother me if the amp does a good job. I have no intention of replacing the J2 until it dies, which may frankly never happen. If it does though, I'll get a class D amp and resistively divide the output, since I need about 10 ohms drive impedance.

Does it ”you a toe-tapping experience that other solid state amplifiers do not”?

Products – www.firstwatt.com

 

[fpitas]

Does it ”you a toe-tapping experience that other solid state amplifiers do not”?

Products – www.firstwatt.com

Lol! He is a salesman as well as an engineer. The J2 has about 0.008% THD, mostly second harmonic, where I listen. I doubt I'd hear any difference with another decent amp.