John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Ferrite beads are clamped on right at the amplifier loudspeaker terminals when used as a fix. Two or three are enough to drop heterodyne noise to acceptable levels.

I use a steel enclosed chassis to hold eight channels of filters. Allows a bit more complex filter. I get around 20 dB of attenuation.

Most of the amplifier power supplies meet power factor rules and don't put as much noise back on the AC power lines as some of the older analog power beasties.
 
Last edited:
Ferrite beads are clamped on right at the amplifier loudspeaker terminals when used as a fix. Two or three are enough to drop heterodyne noise to acceptable levels.
So, nothing new under the sun ?
Class D amps are only good for low frequency channels in "active speakers".
It is there that we need power and benefit of the efficiency of Class D.
We can use a passive filter at much lower frequency to increase the switching frequency rejection.

And use a little linear amp for trebles.
 
So, nothing new under the sun ?
Class D amps are only good for low frequency channels in "active speakers".
It is there that we need power and benefit of the efficiency of Class D.
We can use a passive filter at much lower frequency to increase the switching frequency rejection.

And use a little linear amp for trebles.

I generally use at least 300 watts on the high frequency driver, often 600 watts, occasionally more. Less of course for smaller loudspeakers used close up.
 
I can think of a number of manufacturers who might argue with that. I guess you haven't heard a beolab90 or Kii3 to show what class D can do when fully integrated into the speaker. There are also currently two class D amplifiers in stereophile class A (along with JCs parasound JC1).

I like Stereophile, as it is one of the few publications that support their listening tests with comprehensive measurement data.

HOWEVER, Stereophile does not use blind listening testing regimen, nor does the reader know if the reviewer has received inducements from the product under review.

As it happens, I've worked on a pair of JC1 amps and happen to think that they sound very good indeed. I don't care much for the design, as it pertains to serviceability though. It is a pity they don't pay someone like me to warn consumers about potential problems they can experience, should their products ever require repair.
 
Tournesol, you make a lot of sense, when you have actually tried something. '-) For example, Class D amps have subtle and sometimes 'less than subtle' problems that keep them from being the best amps for the high frequencies. If Bruno does not make a 'perfect' Class D amp, probably nobody does.
Now, I am relying on your listening experience, which I suspect in this case did not require some strict double-blind test. You just had to listen to the Class D amp in hi frequency service, I presume. At least, that is how I would do it.
For the record, Class D is not really 'new', it has been tried and first exposed to the public in WW in 1965. We have been evaluating it, improving it, etc, since then, BUT it appears to not be perfect in every way, yet. Yes there is still room for linear amps in high fidelity audio.
 
I've listened to and measured a few Class D amps. Some are truly, spectacularly horrible. Some are pretty decent. I recently compared a Devialet 200 to a high end linear amp (not a blind test, unfortunately) or equivalent power output. The Devialet was very, very impressive, particularly when comparing the 6kg mass of the Devialet to the 52kg mass of the linear amp. Then, of course, the size and styling of the Devialet was something to behold. A glorious thing. That said, the linear amp was a superior sounding product (despite a 20 year age difference) when driving a 'difficult' speaker system.

When you drill down, there's a few 'gotchas' in the specs. The Devialet has a power supply rated for several kW, but a continuous rating of only 600 Watts. The linear amp has a power supply rated for a continuous 5kW (if you can find somewhere to plug it in!). Therefore, speakers that exhibit low impedance loads at LF can be expected to over-tax the Devialet. All that said, the Devialet represents a very interesting departure from the normal Class D products. It does sound quite decent indeed.

My opinion is that high end linear amp manufacturers that embrace Class D are on a 'death spiral'. They will not survive very long, as Class D amps are rapidly becoming commodity products.
 
Member
Joined 2002
Paid Member
That said, the linear amp was a superior sounding product (despite a 20 year age difference) when driving a 'difficult' speaker system.
When you drill down, there's a few 'gotchas' in the specs. The Devialet has a power supply rated for several kW, but a continuous rating of only 600 Watts. The linear amp has a power supply rated for a continuous 5kW (if you can find somewhere to plug it in!). Therefore, speakers that exhibit low impedance loads at LF can be expected to over-tax the Devialet
Hi Zaphod.
What was the 'difficult' speaker system used in your comparison test?

George
 
My opinion is that high end linear amp manufacturers that embrace Class D are on a 'death spiral'. They will not survive very long, as Class D amps are rapidly becoming commodity products.

Couldn't that comfortably be said about the entire industry? I mean, let's be honest, AB amps have long been commoditized and that hasn't stopped the field. It's a luxury goods market. Supercars are still getting sold in spite of how good (and ridiculously performing) many a sedan has gotten.
 
I like Stereophile, as it is one of the few publications that support their listening tests with comprehensive measurement data.
HOWEVER, Stereophile does not use blind listening testing regimen, nor does the reader know if the reviewer has received inducements from the product under review....................................................
In past decades, Stereophile did do some weekend blind loudspeaker tests. But their Golden Ear reviewers couldn't repeat their opinions on the second day, so the magazine found excesses not to do anymore blind tests. A magazine has to keep Golden Ear reviewers and advertisers happy.
 
Couldn't that comfortably be said about the entire industry? I mean, let's be honest, AB amps have long been commoditized and that hasn't stopped the field. It's a luxury goods market. Supercars are still getting sold in spite of how good (and ridiculously performing) many a sedan has gotten.

No and yes. I cite the example of McIntosh. McIntosh build ordinary Class A/B, but exceptionally well constructed amplifiers, hamstrung by the use of output transformers (autoformers) and styling cues from the 1950s. The company appears to be performing quite well. To my ears they sound very average. In 10 years, McIntosh will probably still be building the same products, whereas 80% of the expensive Class D amps will have long disappeared.

BTW: Your supercar analogy is not a bad one, but the high end of automobiles is still a leap ahead of ordinary cars. My daily drive is a Subaru Levorg (2 Litre). Basically, a WRX, with a bit more space. Reasonably quick and phenomenal handling. My mate's Ferrari makes my Levorg feel a bit like a Model T Ford. As well it should for 10 times the price. Same with audio. High end audio amps are still well ahead of mid-fi. In fact, one of the guys here uses one of my favourite old high end amps from 1977. It compares favourably with anything produced today. Can't say that about high end cars. My Levorg handles better and goes quicker than a 1977 Porsche. In fact, it's almost as quick as a Ferrari 308 GTB and most likely has vastly superior roadholding.
 
Member
Joined 2014
Paid Member
I like Stereophile, as it is one of the few publications that support their listening tests with comprehensive measurement data.

I should clarify. I mainly read Stereophile for amusement after the chimp has waxed lyrical about a product and then JA has to squirm away to justify measurements so bad it seems broken.

But my point was, if class-D is getting into class A, then its mainstream and can be considered a valid high-end technology in a good implementation.
 
I generally use at least 300 watts on the high frequency driver, often 600 watts, occasionally more. Less of course for smaller loudspeakers used close up.
Oh, I see, PA systems ?
I think class D is a big step in that matters. No need to focus on restitution of subtle details, there, but dynamic and clarity are right the DNA of class D, on my opinion. And tend to simplify the content, making-it more 'intelligible'. I would not imagine anything else.
 
Last edited:
Status
Not open for further replies.