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Old 22nd July 2007, 12:59 PM   #21
awpagan is offline awpagan  Australia
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Jacco
A car saleman with a sense of humor
Would you really buy a car from him??

But the show is amusing.
Wouldn't you like to do the brand car what they do.......
and not pay for it..

Have you heard the Halcro DM58/68. I haven't
what's your impression of it or the topology?

I remember the only Krell i was really impressed with was the KSA50.
After that, yeh another Krell, lost it!
But that's me, my hearing..

allan
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Old 22nd July 2007, 01:31 PM   #22
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Good point indeed. How many supposed audiophiles are there that have heard a Halcro, or better still own one. A silly question I suppose on a DIY site, but in the big scheme of things quite valid.

If nothing else Bruce Candy has fired a big shot for the pro low THD camp. See below some of the mag review summaries. I can't find a bad one yet but I'll keep googling.


The Absolute Sound, Issue 129, April / May 2001

What’s Hot by Robert E. Greene

"with the ultra-low distortion Halcro amplifier, something of unusual purity emerged."


The Stereo Times
My First Trip to the CES by Henry Wilkenson

"Simply put, these amps are among the best that I have ever heard. They are extremely transparent, yet never hard or overly detailed. They display a relaxed and effortless quality, presenting the music in a way that made you forget about the system. These mono amps are something that you will be hearing a great deal about."

Stereophile, May 2001
Larry Greenhill on Accessories & Surround Sound

"they sounded so pure and beguiling as to almost defy description. (Upstairs) "

Halcro Review Extracts
Lead lines:
"Not Cheap but the very best never is"

"Leading the way to perfection"

"It was not only the best sound we have had in our listening room"

"NO ARTIFICIAL ADDITIVES (Used in TAS Ads)"

"The worlds only Super Fidelity amplifiers"

TAS - absolute sound review (Issue 71)
The Meaning of Zed

"My first impression was of vastly heightened dynamics, combined with extraordinary articulation of musical textures evident on recording after recording."

"The amp appeared to have limitless headroom.
Limpid & natural sounding with the Halcros – no hash, no glare, no glitter, nothing but air, delicacy and crystalline articulation."

"Miles own trumpet was palpably real. Reverberation, whether artificial or native to the recording space, was reproduced with startling precision. Black silences, the like I’ve never heard on an audio system. I don’t believe any consumer vacuum tube component holds an advantage over the Halcros. The more I listened, the more convinced I became that Halcro’s technical excellence represents the preferred approach to amplifier design. If you want the colorations, go to the other people. If you want diamond clarity and utter lack of blemishes or misbehaviour, go to Halcro. "

Stereo Review Harman Japan: 24 October 2001
THE BEST BUY - THE "STEREO" MAGAZINE (published by Ongaku No Tomo Sha)

Organiser: Ongaku No Tomo Sha
Panel of Judges: 14 Reviewers/Critics
Announcement of results: On the December2001 issue of the "Stereo" magazine



POWER AMPLIFIER - Over 1,000,000 Yen

Rank Brand Model Retail Price*

3 Total Received Points

1 Halcro dm68 (GM) ¥5,700,000 105.0

2 Accuphase P-1000 ¥1,100,000 103.0

3 Accuphase M-2000 ¥2,000,000 101.5

4 Mark Levinson No.436L ¥2,200,000 99.0

5 Mark Levinson No.335L ¥1,700,000 94.0

6 Mark Levinson No.33HL ¥3,700,000 93.5

7 Linn Klimax ¥2,400,000 80.5

8 Denon POA-S1 ¥4,000,000 78.5

McIntosh MC1201 ¥2,000,000 64.0

Mark Levinson No.33L ¥5,900,000 64.0

Mark Levinson No.336L ¥2,000,000 51.0

Niro PE-1000 ¥4,000,000 51.0

11 Mark Levinson No.334L ¥1,250,000 49.0

33 Mark Levinson No.434L ¥1,500,000 7.5

HALCRO dm68 Super-Fidelity power amplifier review
by the leading Hong Kong hi-end audio publication Audiotechnique, Issue 237, 2001.

"it has solid and sweet sound performance along with a great level of musical involvement, you will not regard it as a solid-state amplifier; on the other hand, its stunning dynamic contrasts, incredible transient response, and the distinct outline of each stereo image will definitely not make you consider it a tube amp."
Because it offers an ultra-quiet, almost "Pitch Black" super-low noise background, you will find much more never-before-heard details from your favorite CD collections than any of your previous similar experience.
details of harmonics of each instrument became exceptionally abundant, the different levels and three-dimensional sensation of the soundstage were also unprecedented.

I think dm68 is truly one of a kind--its extraordinary sound performance combining all the advantages of both solid-state and tube amps.

I exaggerated nothing. It really has a superb sonic performance so different from the others. But, the tremendous sound effects such as the life-like 3D imaging, pin-point focus and precise object location remind you continuously that they all benefit from the existence of dm68 and it’s the best sound that we have had in our listening room for the last three years. Searching my heart, I found no flaw in dm68’s superlative performance by any standard
it produces only 1,000 parts per billion (0.0001%) harmonic distortion at 20kHz at full power!

Since dm68 has very low distortion in all stages, it’ unnecessary to make correction by applying feedback owing to the minimal accumulative errors. No compromise in component quality - it employs industrial grade components
The power supply of dm 68 features switch mode design
The switching frequency of dm68 is above 100kHz, in another word, far beyond the audible range. Ironically, all the test equipments have greater distortion than the amplifier itself. It’s truly a "real" sound. I have to say that I’ve never heard an audio component which can sound like this. It has sweet voice of tube amp, almost limitless frequency response, which is full of nuance and delicacy, hi-resolution reproduction similar to the magnifying ability of a microscope, and no matter what type of music or instrument it plays, the extending of ultra highs and attenuation of harmonics of the percussion instruments are both dealt in completely natural ways.
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Old 22nd July 2007, 07:25 PM   #23
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Quote:
Originally posted by awpagan
the show is amusing
yeah, after all the fuss overhere about the Halcro amps i did.
The beauty of this cheese place is that there's an audio palazzo at a 2-4 hour drive in any direction.
(don't know a more fitting word for these mega luxury shops)
Visiting at least one audio store on every trip i make abroad has become a tradition after doing that routine for +2 decades. The brand was/is not imported overhere afaik, i had to visit one in Paris for the 58s.

I'm not trashing B.H.Candy, i welcome any techn. innovation and see the existence of these amps as serving a purpose. For what it's worth, the Halcro 58 is a piece of art. But if i had my eye and wallet on a Veyron, it better do 250mph or the riot salesman will be in knee deep doodoo.

(anyone visiting Paris : Adagio, 10 minute walk from the Gare du Nord trainstation)
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Old 22nd July 2007, 09:09 PM   #24
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Hello

I think that the Halcro amp do take account of the memory distortion problems and correct it, but is that type of distortion are a so big problems ?

Here's a web page about it;

http://peufeu.free.fr/audio/memory/m...annoyance.html

At least it seem that the input diff pair transistor can be the problem.

Gaetan
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Old 23rd July 2007, 12:12 AM   #25
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Quote:
Originally posted by gaetan8888
Hello

I think that the Halcro amp do take account of the memory distortion problems and correct it, but is that type of distortion are a so big problems ?

Here's a web page about it;

http://peufeu.free.fr/audio/memory/m...annoyance.html

At least it seem that the input diff pair transistor can be the problem.

Gaetan
The consensus seems to be that Halcro acheives low distortion by applying big amounts of global as well as nested fb. However, I haven't personally seen a schematic.

- I'm not sold on the idea of cascoded current sources just yet. Particularly in the VAS where you would expect the Cdom to totally swamp any non linear VAS loading from a current source.
A good reason for cascoding the VAS is to load the LTP with an EF stage with AV=1, which negates the impact of the very non linear Miller capacitance.
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Old 23rd July 2007, 12:35 AM   #26
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As this turned to Halcro stuff, a video of the Logic series: here

In French, but it is nice to watch.
During the interview it's stated that the software of these models can be updated from the Halcro factory through the web.
(MS goes Oz)
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Old 23rd July 2007, 10:53 AM   #27
awpagan is offline awpagan  Australia
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Quote:
Originally posted by David Lewis


The consensus seems to be that Halcro acheives low distortion by applying big amounts of global as well as nested fb. However, I haven't personally seen a schematic.
Wouldn't large amounts of nfb slow the amp??



gaetan8888
"memory distortion problems"

Thermal drift ???
using the component within it's "sweet" spot. ?

allan
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Old 23rd July 2007, 12:31 PM   #28
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Quote:
Originally posted by awpagan


Wouldn't large amounts of nfb slow the amp??

According to Bruce Candy the output stage has a 1MHz bandwidth with feedback applied around it. I Gather that it uses Mosfets but I'm not sure in what configuration. Large amounts of feedback doesn't make the ampifier slower, but it's fair to say that it usually requires limiting the bandwidth at the input to avoid slew induced distortions or TIM. The major problem is stability and apparently that's an area that has been paid attention to. The amplifier layout more resembles a radio transmitter than a conventional audio amplifier (Candy quote) with individually shielded stages and global feedback applied via a terminated transmission line.
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Old 23rd July 2007, 12:31 PM   #29
AKSA is offline AKSA  Australia
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Why?

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Old 23rd July 2007, 02:02 PM   #30
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Default Re: Compensation capacitor Cdom

Quote:
Originally posted by sandyK
Matching the LTP devices for VBE and HFE, and then IDENTICAL current flow gives even better results. You need to simulate identical loading of the VAS , on the unloaded LTP side.
A close approximation in many cases, could be as simple as a
1% 22Megohm resistor from the tied base and collector of the current mirror, to the -VE rail. I am not using this method,but my.....
SandyK
I just tried this today in an amp where the current mirror is from the +ve rail with 330E resistors. I just put two 10Meg resistors in series from the tied Base/Collector of the current mirror to the +ve rail.

The sound stage is expansive and the energy from the amp is superb. This was already a well tweaked amp and it only got better. I am not sure about this, but the noise floor of the amp seems to have lowered and the depth perception is a little too much that it almost sounds unrealistic.

I also found that this type of loading does change the tone of the amp (or timbre of instruments) ever so slightly. The do sound a bit harder now as compared to very, very natural without the mod.

Is there a rule of thumb value for the loading resistor? Does this depend on the value of the current mirror resistors?

Another question is, which is the best place to put an offset trim if not somewhere in the LTP degeneration resistors?

Thanks.
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