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Old 12th April 2013, 08:19 PM   #731
rsavas is offline rsavas  Canada
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Default "A low-noise preamplifier with variable-frequency tone control"

Cool, I guess I have to make an order for this one & the vinyl-trak phono design as well.
Actaually, i would like to automate the tone control, using something like a dac, vca, epot, any suggestions? I wonder how this would impact performance. The way I see it, a tone control is a necessary requirement for a pre-amp design. But it is only needed to make up for some deficiency, usually in the source material. In that, the source is probably compromised in some way, so adding a little distortion (assuming that the tone control has some) is of little consiquence.
Using a tone control such as this, are normal HP & LP filters also required in a pre-amp design? Maybe only a rumble filter is necessary!
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Old 13th April 2013, 01:22 PM   #732
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Originally Posted by Carl_Huff View Post
As promised earlier in this thread Jan Didden has published Doug's "A low-noise preamplifier with variable-frequency tone control" in his Linear Audio magazine. My copy will soon be in my mail box!

See details here: Linear Audio magazine
Is it something like Massenburg's parametric equalizer? If it is than I must admit that it is much more attractive proposition than ordinary tone controls with fixed turnover frequencies.
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Old 13th April 2013, 02:47 PM   #733
rsavas is offline rsavas  Canada
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Default Is it something like Massenburg's parametric equalizer?

No it is a variable frequency design having a HP & LP section
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Old 13th April 2013, 03:27 PM   #734
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Originally Posted by owdeo View Post
Good points thanks - food for thought. So if this really is the main cause of disappointing SQ from many opamps that look good on paper, you could say we're stuck with needing to use RF resistant opamps (or discretes) as there's no convenient way to prevent these kinds of noise getting in completely. Perhaps use of additional LC filters in the power supply would help with mains noise, and using balanced interconnections should sort out noise picked up on cable shields, but what can you do about DAC OOB noise...
JFET op amps are generally more RF-resistant in the critical input stage. That may be why some prefer to use them (even though they typically do not have as low noise and distortion as the best bipolars).

Cheers,
Bob
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Old 13th April 2013, 05:03 PM   #735
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Originally Posted by Mooly View Post
This was quite informative regarding digital volume controls,
Rocky Mountain Audiofest 2012
I found this disappointing, because he skated over some critical areas in what is fundamentally a sales pitch for ESS. This made me distrust the other section of his presentation which was about perceived differences in SD DAC performances ESS claim to have documented in blind testing.

The 2 principal things that he neglected to mention are:-

1) that digital controlled IC analog volume controls probably can meet the performance of any discrete or mechanical attenuator, a point he was forced to concede when pressed at the end of the volume control presentation, and

2) that low-jitter clocks do NOT require to be locked to any 'transport clock' since it has become economic to store data purely in solid-state memory.

This is not that different from what I observe amongst the majority of participants here, talented people perverting their skills to provide less and less plausible justifications for performance differences which are not demonstrated to be audible.

You all proceed as though the audibility of these features can be taken for granted. You hang around here in your cozy little blinkered group effectively congratulating each other on the profundity of your expertise because you know that the likelihood of your being taken to task for it is small, but to all of us who retain our critical faculties with respect to the evaluation of evidence it's still just a load of redneck noise.
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Old 15th April 2013, 08:19 AM   #736
owdeo is offline owdeo  Australia
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Originally Posted by Bob Cordell View Post
JFET op amps are generally more RF-resistant in the critical input stage. That may be why some prefer to use them (even though they typically do not have as low noise and distortion as the best bipolars).
Thanks Bob. Seems plausible, though having tried the OPA2134 and the OPA2604 in the same design (a simple series feedback line amp), I thought the 2604 sounded very good, while the 2134 was very disappointing. Only my opinion of course . From the datasheets there appears to be some significant differences in their topologies, so I wonder if there isn't more to it than just the extra RF resistance due to fet inputs.
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Old 5th May 2013, 11:12 AM   #737
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Originally Posted by Ian Finch View Post

Judging sound quality? I can't see much room for the usual implication there of a little sweet distortion, when absolute lowest
distortion is the design goal. That suggests zero sound quality to me, much as Owdeo discovered at the conclusion of his build.
I am tempted to call this one of the great truths of audio electronics. From now on I shall call it Finch law after the first man who formulated it in such clear way.
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Old 5th May 2013, 07:22 PM   #738
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Originally Posted by ivanlukic View Post
.....call it Finch law after the first man who formulated it in such clear way....
I'm not sure about any credit there, ivanlukic. I obviously trod on toes with the comment but as you suggest, a lot of people would have arrived at a similar conclusion long before me.
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Old 7th May 2013, 07:30 PM   #739
redjr is offline redjr  United States
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I've been sucked back into this thread recently and have spent some time re-reading the posts and I'm only up to page 49! Beyond the basics I'm not knowledgeable at all about the electrons and how they travel and what affects them. I just know good sound when I hear it, without questioning how it's produced, or the minutia of detail that ultimately shapes it.

I will admit, that I always prefer to put the science first - as a starting point to understand what should affect the sound - or not. Since we can never re-create the original recording in terms of time and space, a mentor once told me more years ago than I care to remember, all we have is the ability to try and recreate the 'illusion' of the recording.

So having said that, I've never understood how any level of distortion - whether introduced into the circuit by design or not - is a good thing or helps to more accurately re-create that illusion. Perhaps that's just my naivete about how noise make things sound better. If one wants to introduce noise into their personal listening experience all you need to do is listen to any recently recorded Pop CD! I've found that some of my older CDs from the 80's sound soooooo much better than the current crop of available CDs. I know that is a broad-brush statement and I'm sure there are some 'good' recordings out there, but I've found it almost unbearable to listen to the last 2 CD's I've purchased. And I don't believe it's all because of my golden ear of yester-year is loosing some of its luster. But I will admit some of it is.


I've built the new DS pre-amp and what I can say is it has revealed the short-comings of my up-stream equipment. This project was probably over the top for my needs, but I looked at it more from the standpoint of a DIY challenge and to get my feet wet with one of Doug's designs. Needless to say, I picked a comprehensive project! All I can say is it far exceeds my expectations and provides me with wanting to upgrade the rest of my gear down the road to match it's level of performance.

That's my latest ramblings on this topic.
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Old 8th May 2013, 04:00 AM   #740
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redjr,

read this:

Wired 7.01: The Revenge of the Intuitive
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