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Old 20th February 2013, 04:57 AM   #711
sandyK is offline sandyK  Australia
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Originally Posted by abraxalito View Post
I have a hypothesis that the capacitance to the metal can with those parts is acting as a low-pass filter on the -ve and +ve inputs. Rather like how a feed-through capacitor works, so the SQ improves. A cheaper option would be to use an inductor and resistor passive filter on those sensitive pins, but its possible the screening effect of the can plays a part too.
Richard
You may be correct, but the metal can version gets warm enough when used with + and -15V rails, for many people to feel the need to fit a heatsink.
Considering that the internal chip is identical, then the poor DIP8 version must feel like it is wearing an overcoat !
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Old 20th February 2013, 05:29 AM   #712
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TI has started releasing reports about EMIRR (RF rejection ratios) of various of their opamps. If they ever do this for the LM4562 then perhaps they might notice a difference between the packages. My money though is on this part measuring so bad they will never release the report
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Old 20th February 2013, 06:03 AM   #713
owdeo is offline owdeo  Australia
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Originally Posted by Ian Finch View Post

Otherwise, a fixed pad at realistic impedances of ~200R might be closer to ideal. To establish or compare the audible effects of preamplifiers, or any devices, I think there should be a better reference device than just a preferred type. If it may only be an inexpensive 10 min. lash-up, why not at least consider it?

For that matter, digital level control is now incorporated in multi-ported DAC or DSP assemblies which connect directly to the amplifier without any traditional preamp. I think that removing the focus of criticism lets sense prevail rather than concerns about undetectable IMD effects or certain opamps sounding better. If only the essential analog output devices of the DAC are present, just as with CD, Digital Media players etc. then preamplifiers and the necessary measurements to demonstrate the superiority of particular types become largely irrelevant. i.e. We can and should first know how no preamp sounds.
I don't think loading the output of the DAC opamp with 200R is likely to give good results, and certainly not an example of what the sound of "no preamp" is like. Whatever impedance attenuator you choose is going to be a compromise one way or the other.

As for level control in the digital domain - you are kidding aren't you?! You want to throw away those bits? You are suggesting this could this be better than having a preamp in the system?

The sound of no preamp... sounds like some kind of Buddhist quest to me
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Old 20th February 2013, 06:16 AM   #714
owdeo is offline owdeo  Australia
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Originally Posted by abraxalito View Post
To help with further pattern forming, have a look at this paper I discovered a few weeks ago (if you haven't seen it already) : http://www.diyaudio.com/forums/analo...ml#post3330996
Thanks - pretty heavy stuff though! I also recently read Walt Jung's paper on opamp input degeneration or lack thereof.

What I don't see is where all this RF is coming from in a typical living room. Perhaps some remaining switching artifacts from the upstream DAC that aren't filtered out by its output stage active filter. But all the designs I've tried those opamps in have passive LP filtering at the input. Hang on though, the Self '96 design doesn't...
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Old 20th February 2013, 09:33 AM   #715
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Have tremendous respect for Doug Self, if it wasn't for his work I would have never started in this insane hobby. However over the years I have learned that his foundation is essential for the quest for better measuring audio designs, but the human concept is missing. It is the designers willing to take chances that often end up hitting the mark, any monkey with some knowledge can design for low Thd which is consistently done with heavy negative feedback, and many components. Until we have implants in our brains to receive audio there will always be imperfections, of course the thd is important in a distribution aspect but I guarantee the amp with 1 percent h2 could sound even closer to the source than .0001 percent. I did the blameless thing, always left me wanting on the musical front .
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Old 20th February 2013, 10:19 AM   #716
Bonsai is offline Bonsai  Taiwan
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I've built two preamps using this device, and it's single equivalent. I've measured the one design on an AP and the results are very good. I also built (on Veroboard) an experimental class A buffer using the 4562 as the driver to a discrete output stage and measured that on an AP. I listen to the preamps regularly and they are very open with great sound staging. So when people tell me so and so opamp is no good or I sounds bad I always wonder about their implementation.

I have a 200 MHz band width analog cope and a 1GHz DSO. You'd be amazed at the things you see that just don't show up with a 20MHz scope, or in some cases, builds where the individual has no access to decent equipment.

I'm not going to get into an argument about the sound of opamps (and they do sound different), but I am very skeptical about some of the comments. It's like the story about the PGA23xx devices. . .
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Old 20th February 2013, 01:44 PM   #717
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Originally Posted by owdeo View Post
.....As for level control in the digital domain - you are kidding aren't you?! You want to throw away those bits? You are suggesting this could this be better than having a preamp in the system?

The sound of no preamp... sounds like some kind of Buddhist quest to me
Aren't we being just a tad melodramatic?
I won't to go into the increasing pivotal role of DSP or even electronic volume controls in the recording and production of digital media,
as you are obviously sold on Analog controls in your domestic environment. I just don't buy the analog arguments any more, even from my
own, sometimes inconclusive listening tests, and some have been with quite expensive gear; well beyond my budget.

If you are more interested in discussing the possibilities than investigating the differences between the preamps, that's fine, no problem.
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Old 20th February 2013, 01:53 PM   #718
Mooly is offline Mooly  United Kingdom
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This was quite informative regarding digital volume controls,
Rocky Mountain Audiofest 2012
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Old 20th February 2013, 02:13 PM   #719
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Quote:
Originally Posted by owdeo View Post
What I don't see is where all this RF is coming from in a typical living room. Perhaps some remaining switching artifacts from the upstream DAC that aren't filtered out by its output stage active filter.
Common-mode noise via mains transformers is one - capacitively coupled between primary and secondary windings. Common mode pick-up of airborne RF on the shields of interconnect cables is another.

Quote:
But all the designs I've tried those opamps in have passive LP filtering at the input. Hang on though, the Self '96 design doesn't...
RC passive filtering only gives 20dB/decade filtering. Say typically there's a pole at 200kHz to maintain 0.1dB flatness at 20kHz. Then your rejection is only 40dB by 20MHz. Many DACs nowadays have OOB noise in the 100kHz to 3MHz range which barely gets attenuated under such schemes. But IME the main noise issues concern the noise on grounds - then the RC filter is actually making matters worse by providing a low impedance path for ground-borne noise to enter the opamp's input.
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Old 21st February 2013, 06:34 AM   #720
owdeo is offline owdeo  Australia
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This was quite informative regarding digital volume controls,
Rocky Mountain Audiofest 2012
Thanks Mooly - an excellent presentation on both subjects. I think he could have taken into account more with the comparison between D and A volume controls that quantisation noise is going to be far more objectionable than thermal noise, so the analogue control still comfortably reigns supreme even if you happen to have a DAC with twice the resolution of your source to avoid throwing away bits.
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