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Thread: The Khozmo Mkii Stepped attenuator

  1. #21
    Join Date: Mar 2012

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    Having just contacted Arek, he does indeed produce a series-type stepped version which would by far the more universally usable. I'll be trying a few Khozmo series-type mono's in the RFC passive.

  2. #22
    Join Date: Feb 2008

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    He does, I have had a few, they are very well made.
    Quote Originally Posted by Reffc View Post
    Having just contacted Arek, he does indeed produce a series-type stepped version which would by far the more universally usable. I'll be trying a few Khozmo series-type mono's in the RFC passive.
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  3. #23
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    I now use the Series version in my Croft. It's a green body. I've not looked back to be honest.

    Sounds superb.
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  4. #24
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    At the risk of ruffling a few feathers, let me explain why I think shunt attenuators are a bad idea.

    1) The input impedance is all over the place and the output impedance isn't as low as it could be. That may or may not be a problem, but it should be taken into account and included in the wider design decisions. Using a shunt attenuator as a drop-in replacement for a conventional pot may lead to problems.

    2) The rationale for using the so-called shunt configuration is based on a flawed concept of the "the signal path", in my opinion. The flawed argument goes something like this: "an attenuator is formed by two resistors, but only the top resistor (aka the series resistor) is in the signal path, with the other resistor (aka the shunt resistor) being less important because it is only shunting the "waste" signal to ground."
    This is totally wrong. Consider for example a 6dB attenuator. This could be formed by two identical resistors, and it usually is. However, it could also be formed by two identical capacitors, or two identical inductors. It could even be formed by a complex collection of resistors/capacitors/inductors in any series and/or parallel combination as long as the top half the attenuator is identical to the bottom half. Accepting the truth of this (and it's about as fundamental as it gets in electronics) should be enough to convince anyone that the so-called "shunt" resistor in an attenuator is just as important as the "series" resistor. The essential thing is that the two impedances (upper and lower) are identical.
    I chose a 6dB attenuator because is makes the principal blindingly obvious (in my opinion), but of course the same holds true for any other level of attenuation.

    So, if we accept that the shunt resistor is no less important than the series resistor the whole rationale behind the "shunt attenuator volume control" is shown to be flawed and the disadvantages outlined in statement 1) above have no counterbalancing advantages.
    So, that's my argument. Feel free to point out any errors I may have overlooked.
    Last edited by RothwellAudio; 10-11-2016 at 12:15.

  5. #25
    Join Date: Mar 2012

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    Quote Originally Posted by anthonyTD View Post
    He does, I have had a few, they are very well made.
    Good to know Anthony. I'll be ordering a few of them I suspect.

    Agree with Rothwell's post above. Don't see any real advantages at all of shunt attenuator designs, just drawbacks. For me, having input impedance varying, and output impedance being higher than it needs to be are my main issues with the design.

  6. #26
    Join Date: Oct 2012

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    Quote Originally Posted by RothwellAudio View Post
    At the risk of ruffling a few feathers, let me explain why I think shunt attenuators are a bad idea.

    1) The input impedance is all over the place and the output impedance isn't as low as it could be. That may or may not be a problem, but it should be taken into account and included in the wider design decisions. Using a shunt attenuator as a drop-in replacement for a conventional pot may lead to problems.

    2) The rationale for using the so-called shunt configuration is based on a flawed concept of the "the signal path", in my opinion. The flawed argument goes something like this: "an attenuator is formed by two resistors, but only the top resistor (aka the series resistor) is in the signal path, with the other resistor (aka the shunt resistor) being less important because it is only shunting the "waste" signal to ground."
    This is totally wrong. Consider for example a 6dB attenuator. This could be formed by two identical resistors, and it usually is. However, it could also be formed by two identical capacitors, or two identical inductors. It could even be formed by a complex collection of resistors/capacitors/inductors in any series and/or parallel combination as long as the top half the attenuator is identical to the bottom half. Accepting the truth of this (and it's about as fundamental as it gets in electronics) should be enough to convince anyone that the so-called "shunt" resistor in an attenuator is just as important as the "series" resistor. The essential thing is that the two impedances (upper and lower) are identical.
    I chose a 6dB attenuator because is makes the principal blindingly obvious (in my opinion), but of course the same holds true for any other level of attenuation.

    So, if we accept that the shunt resistor is no less important than the series resistor the whole rationale behind the "shunt attenuator volume control" is shown to be flawed and the disadvantages outlined in statement 1) above have no counterbalancing advantages.
    So, that's my argument. Feel free to point out any errors I may have overlooked.
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  7. #27
    Join Date: Feb 2008

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    I agree,
    Ie; Shunt type Attenuators.
    I tried them in a couple of preamps, but they just seem to sit on the dynamics, unless you played loud, the series version [IMHO] is great, especialy if your using them in the front end of a valve preamp.
    Quote Originally Posted by Reffc View Post
    Good to know Anthony. I'll be ordering a few of them I suspect.

    Agree with Rothwell's post above. Don't see any real advantages at all of shunt attenuator designs, just drawbacks. For me, having input impedance varying, and output impedance being higher than it needs to be are my main issues with the design.
    "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. #28
    Join Date: Jun 2016

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    ok, so that's at least two of you vouching for Series rather than Shunt type from Kozmo for use in valve preamps including Croft units. I note, "shunt types sit on dynamics"; was that when used in a valve preamp or ss ? I'd like to order the SERIES type, but it cannot be built with Takman REX resistors, which, I am advised, would have given a warmer sound, and, according to the manufacturer would also give "more bass--though slightly less well controlled" than the resistors fitted as standard. I want to avoid losing bass impact through my single driver horn loudspeakers, which, as many on the forum will know, can suffer from bass lightness. So, if I fit a Khozmo Series type unit, which ended up removing too much bass, does anyone have a sense of how to dial bass back in to the equation by tuning the Khozmo ? I could of course return to using the Black Beauty pot and be happy! Everything else in the system has been optimised for bass response through the horns, including placing them in room corners ! Any thoughts greatly appreciated.

  9. #29
    Join Date: Mar 2012

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    Quote Originally Posted by Paul4972 View Post
    ok, so that's at least two of you vouching for Series rather than Shunt type from Kozmo for use in valve preamps including Croft units. I note, "shunt types sit on dynamics"; was that when used in a valve preamp or ss ? I'd like to order the SERIES type, but it cannot be built with Takman REX resistors, which, I am advised, would have given a warmer sound, and, according to the manufacturer would also give "more bass--though slightly less well controlled" than the resistors fitted as standard. I want to avoid losing bass impact through my single driver horn loudspeakers, which, as many on the forum will know, can suffer from bass lightness. So, if I fit a Khozmo Series type unit, which ended up removing too much bass, does anyone have a sense of how to dial bass back in to the equation by tuning the Khozmo ? I could of course return to using the Black Beauty pot and be happy! Everything else in the system has been optimised for bass response through the horns, including placing them in room corners ! Any thoughts greatly appreciated.
    That's a joke, right?

    Just use the standard SMD resistors. If a resistor (or any other passive device) "removes bass" then there's something seriously wrong elsewhere or it's a faulty component. Its impossible for one resistor measuring "x" to affect FR of the bass any differently than another type/brand. That's not opinion, it's fact. As for resistors resulting in more or less bass control, that's also not possible. Bass control is everything to do with damping factor and nothing to do whatsoever with the brand of resistor being used. Just order the series SMD and it'll perform no differently to the posh one with more expensive resistors, except will result in a healthier bank balance.

  10. #30
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    I first used a Black Beauty, then a TKD and then I tried the shunt, had two of the Khozy's a mk1 and a mk2. The difference between the carbon pots and the Khozy shunt was pretty dramatic. I then moved to the series SMD version and found that to sound slightly better in my system. I honestly have no problem with the series version. It's a lovely bit of engineering for the price.

    With the shunt pots I used a few resistors, firstly the TAKMAN's then the ZFOIL's. I did on this occasion find a difference in sound with the latter winning. But I found the series version just as good if not better. Less harsh, nicely balanced sound.

    I do think there is a difference in sound between a conventional resistor and the ZFOIL design but this is the bit of experience I've had with said resistors.

    It's the same with conventional wirewound and the Duelund carbon pencil resistors in my crossovers. There is a difference there IMO but you pay for something that is small, very small and to some it would insignificant. So it's a 'choose ya poison' moment, if you feel flush then what the heck.

    The only thing I can put these changes down to is the design as in both of these cases they are quite radical in design.
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