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Thread: Impedance matching discussion

  1. #1
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 1,250
    I'm Chris.

    Default Impedance matching discussion

    When you read reviews on assembling a great system there is always a great deal of emphasis placed on impedance matching between components. I believe this is so each component can successfully drive the next one in the chain. If it cant do that, there is a general softening of the sound quality and reduction of bass.

    I am aware of a couple of facts

    1. Cables etc may add a bit of impedance, but for short runs they are not a big contributor.
    2. A high input impedance makes a component easier to drive than a low one. This shows itself in an obvious way where speakers of 16 ohm impedance are more easily handled than those of 4 ohm.

    So my first question is "Does a fully passive volume control contribute significantly to impedance, or can it be viewed as 'invisible' ?"
    Source
    SW1X Universal Music Server UMS I Signature with Power Supply Unit PSU I Signature
    SW1X USB II
    SW1X DAC III Special
    Audiolab 6000 CDT transport
    Amps
    Pre amps -- Hi fi Collective twin mono ladder stepped attenuator, with Charcroft Z-foil and silver wired. And First Watt B1 active no gain buffer.
    Power amps -- Welborne 45 SET monoblocks 1.8W / Decware Taboo 6W / Elekit 300B TU-8600SVK plus further improved components 9W / ICE Power 1000W
    Speakers
    Highly modified Endorphin P17 open baffle speakers containing both vintage and modern alnico drivers and paper cones. All silver wired - 8" Cube Audio FC8 full range drivers and vintage 15" Altec VOTT 416 bass drivers. All sat on Townsend Audio Podium seismic isolation platforms.
    BK Electronics XLS400FF Sub.
    Cabling
    Silver mains cables, interconnects and speaker cables by SW1X
    Headphones
    HRT HeadStreamer and SennHeiser HD650 headphones

  2. #2
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

    Default

    Its a bit of a soar subject this Chris, as there are many here that use passive preamps, which in my opinion; more often than not; hinder the signal more than help it, especialy at frequency extremes, its all about the Attenuator's ability; or should i say; its all about the source being able to see, and drive the input load of the amplifier correctly through the Attenuator, at diffrent volume positions, in order to maintain linearity of the original signal.
    Quote Originally Posted by bumpy View Post
    When you read reviews on assembling a great system there is always a great deal of emphasis placed on impedance matching between components. I believe this is so each component can successfully drive the next one in the chain. If it cant do that, there is a general softening of the sound quality and reduction of bass.

    I am aware of a couple of facts

    1. Cables etc may add a bit of impedance, but for short runs they are not a big contributor.
    2. A high input impedance makes a component easier to drive than a low one. This shows itself in an obvious way where speakers of 16 ohm impedance are more easily handled than those of 4 ohm.

    So my first question is "Does a fully passive volume control contribute significantly to impedance, or can it be viewed as 'invisible' ?"
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

  3. #3
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 1,250
    I'm Chris.

    Default

    Thanks Anthony
    There are a number of passives types available, for instance transformer based, ladder etc. Do you have any feeling which type present the biggest impedance issues?
    Source
    SW1X Universal Music Server UMS I Signature with Power Supply Unit PSU I Signature
    SW1X USB II
    SW1X DAC III Special
    Audiolab 6000 CDT transport
    Amps
    Pre amps -- Hi fi Collective twin mono ladder stepped attenuator, with Charcroft Z-foil and silver wired. And First Watt B1 active no gain buffer.
    Power amps -- Welborne 45 SET monoblocks 1.8W / Decware Taboo 6W / Elekit 300B TU-8600SVK plus further improved components 9W / ICE Power 1000W
    Speakers
    Highly modified Endorphin P17 open baffle speakers containing both vintage and modern alnico drivers and paper cones. All silver wired - 8" Cube Audio FC8 full range drivers and vintage 15" Altec VOTT 416 bass drivers. All sat on Townsend Audio Podium seismic isolation platforms.
    BK Electronics XLS400FF Sub.
    Cabling
    Silver mains cables, interconnects and speaker cables by SW1X
    Headphones
    HRT HeadStreamer and SennHeiser HD650 headphones

  4. #4
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,861
    I'm openingabottleofwine.

    Default

    With a transformer, the signal level depends on the turns ratio, whereas the impedance variation varies as the square of the turns ratio.

    It is possible to design 'constant impedance' resistive attenuators; but they are much more complex than simple L-pads, as in conventional potentiometers, whether discrete step or continious.
    Barry

  5. #5
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

    Default

    Where passive attenuators are concerned Chris, the ideal would be one that maintains its input, and output impedance at all useable volume positions.
    Then you have to take into account the affect the cablings capacitance, reactance, and resistance has on the signal at diffrent frequencies, when combined with the attenuator, the input source, and power amps impedance.
    Quote Originally Posted by bumpy View Post
    Thanks Anthony
    There are a number of passives types available, for instance transformer based, ladder etc. Do you have any feeling which type present the biggest impedance issues?
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

  6. #6
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,861
    I'm openingabottleofwine.

    Default

    Quote Originally Posted by anthonyTD View Post
    Where passive attenuators are concerned Chris, the ideal would be one that maintains its input, and output impedance at all useable volume positions.
    Hence a 'constant impedance' design. The question to ask is what value of impedance should one choose? Should it be the geometrical mean of the output impedance of the source and the input impedance of the amplifier?
    Barry

  7. #7
    Join Date: Feb 2008

    Location: South Wales

    Posts: 9,151
    I'm NotTakingLifeTooSeriouslyTheseDays.

    Default

    Quote Originally Posted by Barry View Post
    Hence a 'constant impedance' design. The question to ask is what value of impedance should one choose? Should it be the geometrical mean of the output impedance of the source and the input impedance of the amplifier?
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
    Nikola Tesla



    Its now a conspiracy theory to believe that the Immune system is capable of doing the job it was designed to do.
    A fish is only as healthy as the water its swimming in ! [Dr Robert Young]


    www.tubedistinctions.co.uk

    Matthew 5:10

  8. #8
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 1,250
    I'm Chris.

    Default

    Thanks, I can understand the variables in the discussion but don't have a feel for the scale of the contribution from the passive.

    Lets use an example.

    A DAC is capable of driving an amp with an input capacitance down to say 10K. If the amp has a variable input capacitance down to near 10K, could the passive take it over the cliff into undesirable mismatching?
    Source
    SW1X Universal Music Server UMS I Signature with Power Supply Unit PSU I Signature
    SW1X USB II
    SW1X DAC III Special
    Audiolab 6000 CDT transport
    Amps
    Pre amps -- Hi fi Collective twin mono ladder stepped attenuator, with Charcroft Z-foil and silver wired. And First Watt B1 active no gain buffer.
    Power amps -- Welborne 45 SET monoblocks 1.8W / Decware Taboo 6W / Elekit 300B TU-8600SVK plus further improved components 9W / ICE Power 1000W
    Speakers
    Highly modified Endorphin P17 open baffle speakers containing both vintage and modern alnico drivers and paper cones. All silver wired - 8" Cube Audio FC8 full range drivers and vintage 15" Altec VOTT 416 bass drivers. All sat on Townsend Audio Podium seismic isolation platforms.
    BK Electronics XLS400FF Sub.
    Cabling
    Silver mains cables, interconnects and speaker cables by SW1X
    Headphones
    HRT HeadStreamer and SennHeiser HD650 headphones

  9. #9
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,861
    I'm Dennis.

    Default

    This was alluded to on another thread recently.

    The general rule is that for maximum voltage transfer*, which is the objective in one audio component feeding another, the source Z should be about 1/10th of that of the load Z.
    *Power transfer not being a consideration in this scenario, but it is in transmission line situations.

    Trying to design a passive to meet this, and with a constant O/P Z must be a real challenge, and it doesn't matter if the source Z goes very low, but that is unlikely.

    With passives, (although I haven't tried to design one, but have designed many attenuators), the range of solutions may well be quite wide, the greatest problem AFAICS being trying to avoid a high O/P Z.

  10. #10
    Join Date: Jan 2008

    Location: Gerrards Cross

    Posts: 2,991
    I'm Tony.

    Default

    I love impedance matching, no seriously its is the holy grail of getting circuits correct imho

    That is why we now own a 13.5Ghz vector network analyzer, virtual probing capability on the scope plus a TDR unit for more in-depth looking at back plane, transmission lines. We can also de-embedd the cabling, individual components and circuit board vias. With capability up to 40 Meters. Its great for truly very accurate impedance analysis of the full circuits. For example, for the amplifier output, through the speaker cabling, x/overs and back to the amp wonderful device.
    Coherent Systems
    Real high end sound with musicality not hifi

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