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Placing of attenuator plugs

Discussion in 'audio' started by paulfromcamden, Apr 9, 2021.

  1. paulfromcamden

    paulfromcamden Baffled

  2. Woodface

    Woodface pfm Member

    I get that they will ‘work’ but not sure whether it’s a good idea if that makes sense. It tends to be more of a problem with some more modern recordings, can be rather loud.
  3. Mike Reed

    Mike Reed pfm Member

    Funny thing, but in order to get the right attenuation and not being well endowed by mathematical/electronics brain-power, I started a thread on which attenuation I should look at. Ran to a couple or more pp with many sage people on here working out the maths for my particular situation/spec's. -20 to -25 dB was prescribed. Luckily I had a trial of -10 and -15 dB ones, which were well o.t.t. Ended up with -6dB; a perfect match (according to my pre.'s meters)

    'Doing the math' in this situation resembled specifying the length of a piece of string. No idea why, but i think it better to err on the side a caution; at least it will result in a reduction; maybe not quite enough, but s.q. is less likely to be affected, if at all (it was in my instance with the higher values).
  4. paulfromcamden

    paulfromcamden Baffled

    My understanding is that -10dB represents roughly a halving of perceived loudness - so I can see how it might be overkill if something just a smidgen too loud.

    Being in a flat means I'm a quiet listener (~60dB) so having a bit more travel on the volume control is very welcome.
  5. Woodface

    Woodface pfm Member

    On balance, pardon the pun, it’s probably not worth bothering with.
  6. miktec

    miktec unissued

    I used source attenuated leads (-10db) some years back to connect a CD player to my Quad 33/303 set.
    They gave me more travel on the volume knob - but at a price in terms of a slight loss in clarity and sparkle.

    Went back to plain leads and less travel ;)
  7. Bairnstorm

    Bairnstorm pfm Member

    I am using the Rothwells. I thought they were only £40 but picked mine up used. They work in my system although YMMV.
    Woodface likes this.
  8. paulfromcamden

    paulfromcamden Baffled

    I've heard others say something similar. I wonder why? And whether it's system dependant?
    Could the attenuators be messing with impedance somehow..?
  9. martin clark

    martin clark pinko bodger

    systems like the 33/303 - because they were designed for sources with really low level output compared with the 2-3vrms+ anything today can deliver - have rather higher 'gain' overall; also likely higher input impedance too, which itself, esp in conjunction with the higher source-impedance from a poorly-chosen value of passive attenuator, can be small added source of (Johnson) noise. possibly even hair of HF roll-off, with the wrong attenuator value, the wrong end of a long interconnect.

    So - you take a modern source, attenuate it a lot, feed it into such a system where you wind up the vol pot thinking 'that looks about right' - you loose stuff into the noise floor, because you've heavily attenuated the signal, fed it into a system with a noisefloor not as pristine as is possible today, then used the available internal 'gain' to amplify-up to yor desired output. Just feeding the hotter raw signal in, and attenuating the output with the system vol pot, even at markedly lower settings, might, might well... sound better, overall.

    There are a lot of 'ifs and buts' in the above - it depends on several aspects of whatever the older amp architecture is, and impedances involved etc - therefore also, quite a bit of maths or other direct measurement req'd if you wanted a more exact answer - but that is the essence of it: it depends...

    Pick what makes you happy.
    paulfromcamden and John Phillips like this.
  10. davidsrsb

    davidsrsb pfm Member

    Attenuation does depend on the source and load resistance. Usually this makes getting smaller attenuation values messy.
    The output resistance of an attenuator is fairly high, so putting it at the load end after the cable capacitance is best - this could be one of the causes of "loss of sparkle", the other being reduction in distortion.
    John Phillips likes this.
  11. John Phillips

    John Phillips pfm Member

    Be cautious with these. The first link has attenuators designed for 200 Ohm or 600 Ohm impedance circuits (see the first two paragraphs under the illustration). That's not normal for consumer equipment but is normal in professional equipment. The second link is for 200 Ohm only.

    If they are wired as I think, the 200 Ohm versions may have way too low an impedance for most consumer-type balanced interfaces to drive. The 600 Ohm versions may be OK in some consumer cases but probably not all. My ATC CDA2 Mk2 XLR outputs, for example, will drive 600 Ohms according to the Stereophile review. I wouldn't even try 200 Ohms.

    The Rothwell attenuators (I use the 10 dB versions) use impedances suitable for typical consumer kit with caveats as expressed in the above two posts.
    paulfromcamden likes this.

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