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Thread: Caiman passive output mod revealed

  1. #1
    Join Date: Feb 2008

    Location: http://www.homehifi.co.uk

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    Default Caiman passive output mod revealed

    I have mentioned the passive output mod a few times, and here it is.

    Please note that the Wm8716 DAC analogue output is only digitally filtered. The passive mod bypasses the analogue filter circuit based around the line output opamp in the Caiman. The MUTE circuit is also bypassed. So the DAC output can be a bit noisy in between tracks. This should not be a problem in most cases and on anything other than near full volume level. The mod is however easily reversible in case the results don't go with your system setup.

    Now, after the disclaimer, what does this mod do? Well, if you ever wanted to know what PRaT is all about, this is a good way to get an idea. On drum kits you'll very likely to feel a kick in the floorboards on decent volume levels. The back rest of your sofa should also produce a kick in your back. Guitar and piano will sound snappier. The effects are more noticeable on a responsive amp/speaker combination. If your system is more laid back, then the passive mod might be hard to distinguish from an unmodded DAC.

    The first thing to do is to identify those two tiny holes in between the ribbon cable. Use a PCB scraper of some sort to remove the track insulation so that the copper track is exposed around each of the two holes.

    Next, cut the signal pin on the left and right Fixed Output socket. Use a fine snipe electronic nose set of pliers so that you don't make a mess. Make sure that you cut the right pins! The pictures are not very clear, but an experience modder would know exactly which pins are visibly cut in the picture.


  2. #2
    Join Date: Feb 2008

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    The next thing is to fit a 47uF non-polarized capacitor between the point on the PCB that was scraped off, and the top side of the Fixed output socket. Make sure that you don't accidentally also solder back the cut pieces of the connector when you solder the cap to the connector!
    Do the above for both left and right channel.
    I advise the use of some sort of insulation over each leg of the caps. That will avoid any bare wire shorting against another part of the DAC. I left out the insulation in the picture so that the soldering locations are a bit better to see.


  3. #3
    Join Date: Feb 2008

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    This mod only works on the fixed output. The variable output and headphone amp are not affected by the mod.

    I have tried a number of different caps, both polarized and non-polarized. If you use polarized caps ( in case you want to try the mod but don't have any non-polarized caps) the negative end of the cap should be soldered to the Fixed output socket, and the positive end to the scrape on the PCB. A cap of 16V rating is the optimum. If you are rich enough, you can o exotic with one of the audio grade polypropylene etc. type of caps. 10uF/63V is the most I could afford to try. Maplin sells a 10uF/630V for 9.00 odd. If anyone tries them let us know if they are worth the cost...

  4. #4
    Join Date: May 2008

    Location: Surrey

    Posts: 5,567
    I'm Rob.

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    How does this mod alter the sound?
    I have the most wonderfully insightful and sublime hifi that it would embarrass me to put in writing exactly what it is.

  5. #5
    Join Date: Feb 2008

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    It doesn't alter the sound. It's the raw unexpurgated sound directly from the horse's mouth ( read: digital to analogue conversion process) so to speak.

  6. #6
    leo's Avatar
    leo is offline Circuit Junkie & DIY Room Forum Leader
    Join Date: Jan 2008

    Location: Notts UK

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    Default

    Nice! I'm sure some will be interested in giving this a go, its reversible incase you prefer it with the output op-amps.
    I'll have a scrounge to see what caps I have

    I'll stick the link to this thread in the collection of mods
    Cheers,
    Leo

  7. #7
    Join Date: Feb 2008

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    Cheers Leo.
    I wanted to add a 100nF cap across the 47uF in order to bring up any attenuated highs from variations in HF damping from the 47uF. But because the mod has no HF roll off filter in circuit, I decided to let the 47uF act as a bare bone HF filter without the 100nF. Others might disagree with that approach, so I mention it in case anyone wishes to try the 100nF in parallel with the 47uF.

    Important addition!
    The fixed output signal from the RCA sockets should be plugged into an AUX input on your amp. That's because the passive mod has a lower output by about 3dB compared to the opamp boosted output. You can use the signal in the CD input, but you'll have to turn your amp a bit higher in order to get the same average level as obtainable with the opamp in circuit.

  8. #8
    Join Date: Apr 2009

    Location: Chippenahm, Wilts, UK

    Posts: 586
    I'm Richard.

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    I have my 7510 running like this. I did at first change the surface mounted op-amps on the board, but this was MUCH MUCH better.

    Looks like it's time to do the Caiman too now it has the official seal of approval .

    Cheers Stan.
    Rich

  9. #9
    Join Date: Feb 2008

    Location: http://www.homehifi.co.uk

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    Just be careful with the neighbours . The raw energy that is coming directly from the WM8716 analogue pins output can make the earth move. Almost every time I use my passive modded Caiman the next door neighbour comes knocking on my door. I am not making it up. It's the honest truth.

  10. #10
    Join Date: May 2008

    Location: Surrey

    Posts: 5,567
    I'm Rob.

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    Quote Originally Posted by lovejoy View Post
    I have my 7510 running like this. I did at first change the surface mounted op-amps on the board, but this was MUCH MUCH better.


    Cheers Stan.
    Can you describe how it is MUCH MUCH better?
    I have the most wonderfully insightful and sublime hifi that it would embarrass me to put in writing exactly what it is.

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