Class G Amplifiers

[deanhorn]

I have not seen any reviews lately of Creek components, so I visited their website. They are a British company known for their very good, affordable integrated amps. Well, they have gone more upscale and have a new integrated amp for about $8000. But, what struck me was that the amp section was class G.

I know a few other companies use class G such as Arcam and Parasound (the New Classic amps). I did some research and this is a simplified explanation, but class G amps use class A for low power and then use a secondary power supply when more power is needed like a turbo charger. This is more efficient with less heat generated. And a lighter and smaller case with less heat sinking can be used. So, it has the advantages of combining class D and class AB amps.

For those more technical, I have some questions since class G seems to be an ideal amp technology.

What are disadvantages of using class G?

Why is not used more often?

Does it adversely affect sound quality?

[erospa]

See this brief article from Arcam

Class_G_the_ultimate_amplifier_technology_150714_A.pdf

Seems that class g is expensive to implement and not easy to get right. I think the story here may be similar to what we have seen with class D. Those first class D circuits and implementation of the circuitry, didn’t provide the sonic qualities associated with audiophile grade components. But fast forward to today and the best class D amps can certainly hold their own, if not quiet to my personal taste. I am sure the development of class G will be similar, but I suspect the end result, given that class A element of the circuit, might just outperform class D

[oceanrower]

Well Arcam A49 has got its first 50 Watts as pure class A and sounds like class A (perfect and great at low levels) When given a transient or extra power is needed the 200 extra watt kicks in. In 4 ohm it is 400 watts. In 2 ohm it is 800 watts.

It is a very clear open detailed neutral sound with great highs and deep thunderous bass. Lots of details in bass (capable of many simultaneous bass rhythms) and very detailed midrange.

Piano sounds like piano with lots of tone colors. It is airy and can disappear completely leaving only music in a nice 3D soundstage.

Many says it is one of the best integrated amps available. The power amp part is often called “worth twice the price” and its power amp as a separate box, the Arcam P49 was given the highest purchase recommendation I Stereophiles sum of the years best products. This remarks was given in the highest sound/price class, giving a hint at its more high end than expensive hifi.

If you pay 3 times more you will only likely get a bit more depth, not that the A49 is lacking depths as it is.

I think you already knew this, just looking for more confirmation

BHK 300 has got a bigger sound (A49 sounds big though), and more midbase (might have to do with different dacs and different listening rooms). Both has got almost unlimited control

BHK 250 and 300 are an upgrade from A49, but the A49 delivers way above Arcams brand value. Arcam has made two “unlimited research projects,” both resulting in very high performance high value products, the D33 DAC and the A49 amp.

I have no experience with other manufacturers class G. Arcam was bought by Harman and it’s technology might be spread within the Hartman group

[oceanrower]

A comparison win Pass Labs 60 and Parasound Halo, both monoblocks.

The conclusion is great for USD 5 000 but there are better if you are willing to spend a lot more.

The A49 can be had for USD 2000 today and there are a few brand new ones going for approx 3000.

https://www.stereophile.com/content/arcam-fmj-p49-power-amplifier-page-2

[owlsalum]

The idea of a ‘variable supply’ isn’t necessarily new. There have been variants that actually seek to improve the efficiency of Class A. While it’s not necessarily a ‘secondary supply’ for the purpose of efficiency, Krell came up with ‘sliding Class A’. That twist also monitors the dynamic envelope and ups the bias to the output stage when needed to maintain the amp in Class A. And drops the bias as the dynamic envelope dictates. As I might expect in marketing literature, ARCAM takes some license with ’ wildly inefficient’ without mentioning sliding Class A that, granted, may not achieve the efficiency of Class G. But nevertheless seeks to improve Class A efficiency without cross-over or notch distortion at any output level up to rated max. ARCAM is a tad sketchy about the cross-over distortion characteristic of its Class G during the ‘boost’ mode. I still think ARCAMs marketing not withstanding, well done deep bias Class A/Class AB topology is the best compromise I’ve ever heard. That is the basis of the Pass X-series amps.

[chrisj1948]

I have an Arcam Solo Movie 2.1 which has an 80W Class G amplifier which runs as Class A for the first 20 watts. It did sound cleaner than the previous Denon Class AB amp on that system. Switching in the higher power transistors for heavy lifting must introduce some additional distortion but it is well away from the famous ‘first watt’ region and is not readily perceptible. I have always had a weakness for Class A but it is very impractical for all but the smallest amps, and Class G seems a good compromise.