DIY Attenuation Adapters for CDPs

Discussion in 'DIY Discussion' started by BlueMax, Oct 23, 2003.

  1. BlueMax

    BlueMax

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    Amplifiers do not work well if the volume control is kept at very low levels. eg. 9'O Clock position.
    Input sensitivity of amps tend to be around 150-200mV into 50kOhms. Output by most CDPs is 2 Volts This overloads the amp input and quality suffer. Attenuation of the signal from the CDP is the answer.

    Attenuation adapters are available to purchase from one or two companies. They look like large phono plugs. They fit on the end of existing cables using a back-to-back female RCA adapter. Rothwell Electronics is one such firm. £39 / pair incl. P&P. 10 dB loss. However, 10 dB loss will not be sufficient in most cases

    You can make custom attenuated leads for a few pence to precisely meet your requirements. Use Metal Film 2W Resistors and a good quality RCA plug. There is an Excel spreadsheet that will enable to calculate the resistor values and attenuation you need at:
    http://www.tnt-audio.com/clinica/diyattenuation.xls
    It also has a useful a circuit drawing and an attenuation graph.

    Next task is finding the resistor values that are actually available to purchase. After some experimentation with various attenuation values, I found optimum results with:
    39 Kohm Metal Film 2W Resistor, Maplin part no. D39K, 2 off at 17 pence each
    12 Kohm Metal Film 2W Resistor, Maplin part no. D12K, 2 off at 17 pence each
    Other Parts required are:
    Phono Plugs, Maplin part no. AQ57M, £3.99 for 2 (or de-solder and use your existing phono plugs)
    Silver Solder, Maplin part no. DP52, £1.49
    'One Wrap' PTFE tape, RS Components part no. 314-9372, £1.40 (or use plumbers tape)

    Solder the one end of both resistors to the signal pin. Solder the 39K resistor to the signal lead and the 12K resistor to the barrel of the plug or the 'ground' part of the lead. Keep everything insulated with PTFE tape. Resistors are too big to fit inside the plug cap. So use heatshrink sleeving to protect. I also use self-adhesive aluminium tape before heatshrink to protect against RFI/EMI. Fit the attenuated plug at the pre-amp end of the cable.

    Resistor values above will give the following results:
    Attenuation: 14 dB
    Effective load resistance: 48,677 Ohms
    Attenuation factor: 0.1935

    If you don't want to modify your interconnect and want to make a separate unit, solder the resistors between the plugand a socket. There are two types of good quality sockets at Maplins. JZ05F/JZ06G (chassis socket) and FA93B/JH96E (inline socket). I used the chassis socket for the pair I made. Bend down the lug with a hole; then thread the resistor wire though the hole in the earth lug of the plug (AQ57M) and the hole in the lug of the socket. Trim off the excess wire. Make sure that the solder runs along the length of the wire where it makes contact.
     
    Last edited by a moderator: Sep 22, 2004
    BlueMax, Oct 23, 2003
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  2. BlueMax

    moz

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    Where will the attenuator be? On the source or amp side?

    Please post the sonic effects of such a "tweak".

    Would this be effective between cdp-->preamp or preamp-->power amp?

    TIA
     
    moz, Oct 24, 2003
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  3. BlueMax

    cookiemonster

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    My new amp has a 20dB attenuation selector switch built in. Man, this thing has loads of toys on it. :)

    The Rothwell's as you point out, with only 10dB are usually insufficient. I tried them for a while, and they only really made about 1hr difference on the volume pot.
     
    cookiemonster, Oct 24, 2003
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  4. BlueMax

    BlueMax

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    At the amp end.
    Improvement will vary from from one amp to the other. Attenuator will ensure that the preamp is not overloaded and works at its best.
    It is intended for use between the source and the preamp. That way it will affect only one source such as the CDP and not Tuner, phono, etc.

    I haven't tried it between preamp and power amp. I guess it could be used. But you will need to calculate the resistor values using that spreadsheet.
     
    BlueMax, Oct 24, 2003
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  5. BlueMax

    BlueMax

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    Is this new amp the vintage heavyweight you just bought?
     
    BlueMax, Oct 24, 2003
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  6. BlueMax

    cookiemonster

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    'tis indeed :) she's a beauty, and has more knobs than your local council office.
     
    cookiemonster, Oct 24, 2003
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  7. BlueMax

    moz

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    Thanks Bluemax,

    I'll try it out this weekend.
     
    moz, Oct 27, 2003
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  8. BlueMax

    technobear Ursine Audiophile

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    :lol: What, even Mendip District Council. Wow! :eek:

    Pictures please Cookie! :)
     
    technobear, Oct 28, 2003
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  9. BlueMax

    cookiemonster

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    [​IMG]
     
    cookiemonster, Oct 28, 2003
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  10. BlueMax

    technobear Ursine Audiophile

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    Mmmm, tasty! I used to lust over gear like that when I was a mere teenager. Of course, I'm older and wiser now. Or am I? I bet it sounds fab. What on earth do all those buttons actually do? I think we need an annotated picture :)
     
    technobear, Oct 28, 2003
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  11. BlueMax

    BlueMax

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    Another tip!
    The hole inside the Phono Plug cap is not big enough for the socket to pass through. So if you want something substantial to hold on to when removing or inserting the adapter; drill out the hole in the Phono Plug at the non-threaded end only with a 9 mm drill bit and file it down to tidy up. The cap is not long enough to enclose the phono socket also. So heatshrink is still required. Also remember to insulate both the resistors with Teflon tape to stop them coming into contact with each other or the plug cap.

    BTW. Cookies Pioneer SX-1250 Receiver is a beauty. There is an entire thread called 'Vintage Heaven' at
    https://www.audio-forums.com/as-rediect/showthread.php?s=&threadid=1422
     
    Last edited by a moderator: Mar 15, 2005
    BlueMax, Oct 28, 2003
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  12. BlueMax

    BlueMax

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    Was looking for the photo of Cookies Pioneer SX-1250 Receiver.
    It's gone!

    Where can I find it :confused:
     
    BlueMax, Mar 15, 2005
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  13. BlueMax

    zanash

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    some pics would be nice !
     
    zanash, Mar 15, 2005
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  14. BlueMax

    penance Arrogant Cock

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    what makes the difference is the quality of attenuator for volume, not the amplifier.
    A good (very good) potentiometer will not suffer from the problem so much, a stepped attenuator (ladder/shunt etc.) will not have the problem at all.
     
    Last edited by a moderator: Mar 21, 2005
    penance, Mar 20, 2005
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