Removing over

August 10, 2015
 by Paul McGowan

“I am feeling somewhat overwhelmed,” writes one of our commenters to yesterday’s post and it’s easy to see why. The dizzying array of design choices to reproduce music in our homes can be exactly that. And I was going to move on to another type of accessory but instead let’s try to remove some of the over from the whelm.

A DAC/PRE is an analog-centric product. A better anachronism might be PRE/DAC, though that sounds prehistoric. The focus of a product is important both to its design and the user’s understanding. If you take an analog approach and add a digital component, you wind up with a very different product and sound than the opposite: a digital approach with an analog component.

For example, take a 100% analog preamp and add a modular DAC in the far corner of its chassis – its output another position on the preamp input selector. Change nothing else. You now have what we are referring to as a PRE/DAC (or DAC/PRE). If you never engage the DAC input of the analog preamp then you would never know it is anything BUT an analog preamp. Little would have changed.

But now let’s turn the tables around and rearrange our example. Take a digital DAC with built in digital volume control and add one set of inputs labeled ‘analog’. The analog signal must first pass through an ADC (analog to digital converter) before it is accepted by the DAC. If you never place an analog signal into this input, you would never know it is anything BUT a DAC. Little would have changed.

The two scenarios are not semantic differences. The devices sound unlike each other and the distinctions are fundamental to the design.

I am not bashing either approach, merely pointing out contrasts exist.

I hope we’ve made some progress reducing the over from the whelm.

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9 comments on “Removing over”

  1. During periods where major technological changes are occurring in an industry, many competing ideas will find their way to the market, each one claiming to be “the best” and “the way of the future.” The overwhelming majority of these concepts fall by the wayside while others emerge as the new paradigm until they are replaced by something even better. An example of this was the innovation of video tape recorders. Original recorders using helical scan heads were open reel using several different tape formats. Two basic cartridge tape systems evolved, Betamax and VHS. Each had a variant, Professional Betamax and SVHS. The systems were incompatible with each other. Eventually VHS won out. When such a technology is obsoleted and a new replacement emerges, there is a period when those who were satisfied with the old technology will have a field day buying up unsold new stock in the old technology and used product from those who don’t want them anymore.

    And then there are people like me, pack rats who have to buy increasingly larger houses to warehouse everything they ever owned because they never get rid of anything and buy up whatever old unwanted junk becomes available that seems like an irresistible bargain. No you cannot buy any of the 3000+ phonograph records I own but never listen to including the 78s. They’re not for sale. One man’s junk is another man’s treasure.

  2. Paul, I know almost nothing about the digital realm so forgive a basic question. Almost every manufacturer of AC line conditioners claims to separate “nasties” of the digital signal devices from those with analog signals which might be passed by the power line connections.

    So how could a DAC/PRE or PRE/DAC pass or process the signal from both types within the proximity of the same chassis without harming or distorting the signal?

    1. Thanks and it’s a great question. One of the downsides faced by anyone designing more stuff in a box than just one device faces the problem of power supply contamination. That’s always the risk and careful attention must be placed – the upside is the lack of connectors and interconnects – and depending on the skill of the designer, hopefully the choices made outweigh the compromises risked.

  3. Any system which is so complicated as to be overwhelming is an incomplete system. It has a along way to go before it gels into something simple and elegant. Still it is not certain that it will be better than what it is trying to replace. Remember when solid state was introduce how its backers were claiming it to be the second coming, the hype and hoopla. Well it has taken more that fifty years for it to mature enough to at least sit in the company of the technology it was trying to replace. Is there a trait of masochism in humans who persist in jumping through hoops and go through endless contortions to get pleasure. Just a thought. Regards.

  4. Preamp stands for a function that amplifies the source signal! For an old school preamplifier having an integrated phono preamp the naming might be helpful. This kind of preamplification is not necessary at all for today’s high voltage source signals. Even the input signal from a phono preamp doesn’t need any further amplification. Thus the hole discussion about pre/DAC or DAC/pre seems most strange to me. I can only see two remaining functions: source selector and volume attenuation neglecting any kind of equalization. Both could be designed as passive components! I have such components from AKAI and MusicFirst Audio respectively. The latter can compete with the most expensive active ‘preamps’!
    Thus I can only see ADC or DAC with single or multiple inputs. DACs with or without volume setting. Why not dump the ‘preamp’ and focus on the core function?

    1. Hello paulsquirrel,
      I’m on your side!
      I too do not believe that one profits from a separate pre-amp today.
      I go even further.
      As I have mentioned in a previous post, I am sure and I know that even the phono signal can be handled by using a FPGA for analog/digital conversion and frequency equalization.
      One can believe me, I’ve done so many comparisons between ‘pure’ digital signal processing with an ADC/DAC and pre-amp-DAC combinations.
      I and my friends, who participated in these tests, had ALWAYS the same conclusion: One can forget the preamplifier finally.
      At the same time I am sure that a lot of people would not agree with my conclusion.
      Greetings from an old German =D

  5. I’m in full agreement with paulsquirrel and bernd about the need for a preamp in the chain, the only reason in my experience is the second harmonics which it brings into the sound that’s so beloved by us humans. Inspite of the fact that we profess to want accuracy, we prefer what sounds pleasing instead of what is correct. Less is accurate you were correct Paul in your initial assumption.

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