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Thread: DAC straight into power amp - not impressed!

  1. #11
    MartinT Guest

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    Quote Originally Posted by nat8808 View Post
    Essentially there is no difference between an active line stage in a pre-amp and the output stage of a source component... other than how it is designed and what it is specifically designed to drive!
    The key difference is in output impedance. A passive stage uses the source component output stage and puts the signal through a volume pot. So the output impedance is increased and is variable depending on the volume setting. This could potentially give changes to the sound according to the volume setting.

    An active stage sets the volume earlier in the gain stages and essentially has a low and constant output impedance.

    Your final point is a good one: a power amplifier designed for passive input will perform better with a passive stage. Watch the screening on your interconnects, though, as the higher impedance could allow noise and hum into the system.

  2. #12
    Join Date: Nov 2011

    Location: fuck off

    Posts: 2,033
    I'm fuckoff.

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    Even with a tvc line stage, my system sounds significantly better withone in than without, I was surprised at how much!

  3. #13
    Join Date: Jan 2008

    Location: nottingham

    Posts: 89

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    I run my M-dac full volume + 3 through a Audio Synthesis Passion passive preamp because to my ears that sounds better than M-dac direct to the amps.

    Running the M-dac full volume you are hearing it at its best and going through the passive the signal is only going through a single Zfoil resistor per channel.
    michell gyrodec with orbe platter - michell iso phono stage - sbt fed from synology nas or pc into
    young dac with palmer psu - passion passive preamp into wad valve amp

  4. #14
    Join Date: Apr 2011

    Location: Kingston, Surrey, UK

    Posts: 774
    I'm Alex.

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    Quote Originally Posted by nat8808 View Post
    The output stage of the source still had to be able to drive the power amp well though. Essentially there is no difference between an active line stage in a pre-amp and the output stage of a source component... other than how it is designed and what it is specifically designed to drive!

    I guess the 851 isn't designed in a way that drives your Conrad-Johnson sufficiently well.

    Of course, err.. opening up ALL possibilities, free thinking and all that.. perhaps you're experiencing something more neutral and your previous set up was slightly top and bottom heavy?

    I remember a famous speaker designer saying that that was many people's reaction to his speakers that he'd put so much effort into being completely flat responsed and neutral. As they came from other speakers accentuating certain extremes, they were hearing lack of sparkle and bass. Sticking with that neutral goal however, over time people adjusted their ears.. and now regard the designs as being neutral.
    Hi Nat,

    It well known that many speaker designers deliberately engineer a rising treble characteristic or exaggerated bass response and that some people have aclimatised to that, and so a speaker with flat response curve may sound dull or bass-light at first aquaintance and that time is needed to get used to the 'non-loudness' version

    My pre-amp has a pretty much ruler flat frequency response out to about 50k, so I don't think it is simple as that. The line-output impedance is 95 Ohms, which is pretty low, and will be able to drive the 100kOhm input of the power amp without any problems whatsoever. The output impedance of the 851c is <50ohms, which also suggests plenty of ability to drive a high impedance input too. I have read that this is typical in domestic audio, i.e. low output impedance/high input impedance - the load is essentially a bridging load and doens't actually load the source at all, and this maximises the voltage swing across the signal and ground of the power amp's input, with very little current flow.

    One area where the specs don't guide is highlighting at what frequency the output impedance is measured - if it varied significantly with frequency and between the source and pre-amp, then that could account for differences in frequency response. To be honest I don't think that is happening here as the 100KOhm power amp input resistance is so much greater than the source output impedance.

    ... which is all well and good, but I am left wondering why a pre-amp with a flat response sounds so different to a directly connected source given that the interface to the power amp is 'ideal' in terms of impedance. It actually sounds 'fine', but a bit bloodless, lacking in 'oomph'. I am just curious as to why this is... this is just a temporary arrangement while my preamp is away for a service. It will certainly be interesiting to see what I think when it is back in the system - I hope I like it!.

    Regards,
    Alex
    Technics SL1210| Jelco SA-750| Benz Micro ACE SM MC| Squeezebox Touch/MCRU linear PSU | Cambridge Audio 851C | High Resolution Music Streamer II+ / Linestreamer+ | Raspberry Pi 2/IQ-Audio DAC+ / Max2Play | Conrad-Johnson ET3 Control Amplifier| Conrad-Johnson LP125sa KT120 Power Amplifier| Avalon NP Evo 2.0 Speakers| Cardas Audio Quadlink-5C Speaker Cables and Interconnects| Finite Elemente Pagode Signature E-14 equipment support

  5. #15
    Join Date: Apr 2011

    Location: Kingston, Surrey, UK

    Posts: 774
    I'm Alex.

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    Ok, now I'm seriously confused... I added some Rothwell 10Db attenuators at the power amp input, and it is sounding quite different again (and quite a bit better).

    Mid range has opened up, and the treble is cleaner and better defined. Mid-bass is also less opaque - bass textures seem much cleaner.

    Happy now, but haven't got a clue as to what is going on!
    Technics SL1210| Jelco SA-750| Benz Micro ACE SM MC| Squeezebox Touch/MCRU linear PSU | Cambridge Audio 851C | High Resolution Music Streamer II+ / Linestreamer+ | Raspberry Pi 2/IQ-Audio DAC+ / Max2Play | Conrad-Johnson ET3 Control Amplifier| Conrad-Johnson LP125sa KT120 Power Amplifier| Avalon NP Evo 2.0 Speakers| Cardas Audio Quadlink-5C Speaker Cables and Interconnects| Finite Elemente Pagode Signature E-14 equipment support

  6. #16
    Join Date: Aug 2009

    Location: Staffordshire, England

    Posts: 37,779
    I'm Martin.

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    Play some varied material and see if those Rothwells give you any issues with distortion. Not always noticeable with some music but I have always had issues when I have tried to use them even though at first things sounded superficially better.
    Current Lash Up:

    TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.

  7. #17
    Join Date: Apr 2011

    Location: Kingston, Surrey, UK

    Posts: 774
    I'm Alex.

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    Martin,

    I've checked for any form of distortion with some recordings that I know well and I'm sure that it's as clean as a whistle. What kit were you using that caused that issue?.

    Regards,
    Alex
    Technics SL1210| Jelco SA-750| Benz Micro ACE SM MC| Squeezebox Touch/MCRU linear PSU | Cambridge Audio 851C | High Resolution Music Streamer II+ / Linestreamer+ | Raspberry Pi 2/IQ-Audio DAC+ / Max2Play | Conrad-Johnson ET3 Control Amplifier| Conrad-Johnson LP125sa KT120 Power Amplifier| Avalon NP Evo 2.0 Speakers| Cardas Audio Quadlink-5C Speaker Cables and Interconnects| Finite Elemente Pagode Signature E-14 equipment support

  8. #18
    Join Date: Aug 2009

    Location: Staffordshire, England

    Posts: 37,779
    I'm Martin.

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    Quote Originally Posted by AlexM View Post
    Martin,

    I've checked for any form of distortion with some recordings that I know well and I'm sure that it's as clean as a whistle. What kit were you using that caused that issue?.

    Regards,
    Alex
    I've tried them with all sorts - too much to list - to try to resolve gain issues and never got a good result. Some people swear by them, I know. If they are working for you that's great it is an easy fix to what can be a big problem.
    Current Lash Up:

    TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.

  9. #19
    Join Date: May 2008

    Location: A Strangely Isolated Place in Suffolk with Far Away Trains Passing By...

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    I'm David.

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    Older amps and some modern ones are DESIGNED to just have a pot in front with no line buffer. Many modern ss amps NEED an active line buffer to feed them. TEC do a very cheap one (well under a hundred quid) which would easily do as a spare, although it won't have the cachet or 'personality' of a more expensive model.
    This is one area where some technical expertise is required if very variable results aren't to be experienced I fear.
    Tear down these walls; Cut the ties that held me
    Crying out at the top of my voice; Tell me now if you can hear me

  10. #20
    Join Date: Apr 2011

    Location: Kingston, Surrey, UK

    Posts: 774
    I'm Alex.

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    Thanks All - it was just my curiosity more than anything.. The direct connection into the power amp works well enough for now. Hopefully my preamp will be turned around quickly and normal service will be resumed...
    Technics SL1210| Jelco SA-750| Benz Micro ACE SM MC| Squeezebox Touch/MCRU linear PSU | Cambridge Audio 851C | High Resolution Music Streamer II+ / Linestreamer+ | Raspberry Pi 2/IQ-Audio DAC+ / Max2Play | Conrad-Johnson ET3 Control Amplifier| Conrad-Johnson LP125sa KT120 Power Amplifier| Avalon NP Evo 2.0 Speakers| Cardas Audio Quadlink-5C Speaker Cables and Interconnects| Finite Elemente Pagode Signature E-14 equipment support

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