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  1. #1
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    Squeezebox Audio and Power Mods: How, Photos, Experience

    While I am happily impressed with the Squeezebox2’s ease of installation and great sound, based on the various threads in this Forum and Tweakers’ Asylum, several mods were undertaken as explained in this post.
    [Please note that the CAPS in this post are not “shouting”, but rather, are simply to make the links easy to find.]


    First Mod: Substituting a linear power supply (principally because it was cheap and easy).

    The supply substituted is a 5 volt 1.5 amp linear supply manufactured for an IBM Lexmark printer and is Model 7202C-3 PN1333561. This is apparently still available for $6.95 from Hosfelt at http://www.hosfelt.com/. To find it type its Hosfelt part number which is 56-534 in the “search phrase” box at the top of the page. This is a fairly impressive linear supply with a measured output is 5.04 volts DC and a 0.9 millivolt ripple!

    It has a fairly long outlet cord but the wrong end adapter. Either cut it off and splice on the last few inches of the squeeze box cord or order THIS CONNECTOR which is 2.5 mm by 5.5 mm by 9.5 mm long. Although there are a number of good suppliers on the net, I prefer Mouser as they have a large stock and no minimum order.

    When doing this make sure by checking with a meter that the center (inside of the barrel) is the positive (+) terminal. If everything is fine, the meter will read +5.0 or 5.0 volts. If it reads minus, -5.0 volts, something is wrong and you need to reverse the wire connection that was made!

    [These indented blue lines in this post denote additional information, details, or explanatory material that are available in its appended MS Word document
    …that is in the SBox Mod Detail Word97 doc + Audio Pass Calcs Excel97.zip file attached to this post]
    [--Inexpensive multimeters if you need one--]
    [--How to do polarity checks on the power supply--]



    Results for Linear Supply Mod: I am not sure converting to the linear supply made much, if any, difference. However, the audiophiles in the forum say it does help and it certainty didn’t hurt. In any event, the linear supply mod is so cheap and easy to do that there is no reason not to do it if you are going to fiddle with the insides of the Squeezebox.


    Second Mod: Using coupling capacitors to go directly from the DAC chip to the RCA audio outputs.

    This has been widely discussed and I wanted to give it a try, particularly if it could be reversed if it didn’t work out. Actually, this mod has also been discussed at length relative to another DAC in the Tweakers’ Asylum and is known as the “SWENSON MOD”! There is also a web page on it HERE.

    Basically the idea is to take the left and right voltage outputs directly from the PCM1748 DAC to the RCA output jacks on the back of the Squeezebox. In theory this avoids undesirable changes that might be introduced by downstream components and the output amplifiers, albeit at the expense of a slightly lower output voltage from the Squeezebox.

    In looking at the SQUEEZEBOX2 SCHEMATIC which Sean was kind enough to supply in an earlier discussion on this forum, it is clear that he optimum place to pull off the signal would be at the plus (+) side of the coupling capacitors C7 and C39, which are the left and right channels respectively.

    [--Comments on capacitor location--]

    To do the work the following steps were undertaken:

    Step 1: Remove the top of the Squeezebox, but not the board, by loosening the four T-10 Torx screws in the bottom of the Squeezebox2.

    [--Where to find a T-10 Torx screwdriver--]
    [--Which boards NOT to touch--]
    [--Avoiding mounting post locations when installing mods--]



    This picture shows that general area of the circuit board and overall modification that was done. Probably more useful is THIS MODIFICATION PHOTO which shows a 560kB high resolution image of the specific Squeezebox modification described in this guide.


    Step 2: Locate and remove C7 and C39 which were respectively at the end of the yellow and red arrows in the image below. (Please note that the image below is a low resolution posting image.

    For clearer detail please see this MODIFICATION PHOTO which is a 560kB high resolution image of the specific Squeezebox modification described here.
    As you can see, C7 and C39 are surface mounted so a bit of care is required.

    [--Types of soldering equipment and options for removing SMDs, costs, and personal rating of usabilities--]
    [--General issues involved in soldering on printed circuit boards--]
    [--Solder choices and recommendations--]
    [--Role of, and need for, flux. Flux and solder wick recommendations--]
    [--How to solder, things to do and not do including when using inexpensive irons, useful tutorials including NASA training videos, recommendations, etc--]

    C7 and C39 are the coupling capacitors between the left and right channels respectively of the DAC and the downstream audio amp to the RCA outlets. (Note: C7 and C39 are the numbering scheme for Squeezebox2; it is probably different for Squeezebox3! These, in any event, come from Pin 7 and Pin 8 which are the bottom two left pins of the PCM1748 DAC.)

    As THIS PHOTO OF A REMOVED CAPACITOR indicates, the black plastic base is part of the capacitor.
    To continue with Step 2: To unsolder and remove C7 (or C39) do the following:
    • Flux the capacitor’s right pad
    • Heat the pad with a “wet” iron and tilt the capacitor left
    • Flux the capacitor’s left pad
    • Heat the pad with a “wet” iron and tilt the capacitor off
    • Flux and clean the pads with solder wick


    [--Detailed step-by-step directions and guidance--]


    Step 3: Cut Traces to RCA Right and Left Output Center Pins

    While removing C7 and C39 isolates the output from the DAC, we also need to isolate the RCA output jacks from the analog output amplifier and it’s various parts and filters. Originally the idea was to cut the center connection or to pull up R42/R44 or C44/45. However, the center connection of the RCA plugs is relatively robust and the area around the surface mounts is rather tight. Also, an auxiliary goal was to enable the maximum chance of restoration. A cut trace can be easily restored by cleaning off the ends and adding a drop of solder.

    The cut location is shown by the black arrow circles in the earlier MODIFICATION PHOTO. The right trace cut is clearly shown but the left trace is actually underneath the added wire. No special tool is needed to cut the trace, simply an ordinary Stanley utility knife. See the “TOOLS” PHOTO.


    [--Detailed step-by-step instructions to cut and monitor trace cut--]


    Step 4: Add Wiring for the DAC outputs at the left C7 and C39 pads

    The next step is to use the inlet (left) pads at C7 and C39 to wire additional coupling capacitors to the DAC Left and Right Outputs. To do this, two pieces of something like 24 to 30 gauge wire are needed that are 2.5 inches long. You don’t need to go buy anything special as it is likely already laying around: indoor telephone wire, a piece of Category 5 LAN cable, and old serial or parallel computer cable, etc.

    [--Importance of “good” wire stripper--]
    [--Need for a “third hand” clamp and options--]
    [--Detailed step-by-step directions and guidance--]


    (See First Reply to This Thread for Step 5, etc. continuation)
    Attached Files Attached Files
    Dick


    Squeezebox2 With Hossflet pwr supply and output cap mods. Squeezebox Touch
    Sansui QRX9001 quad Resoldered and recapped with Black Gates. Sansui QRX6001 quad Bought new. Recapped and driver board mods.
    Onkyo T-4711 and Sangean HDT-1X tuners
    Sherwood Newcastle CD-980T
    Four Axiom M22ti Four Large Advents Bought new. Reconed.
    Cowon S9



  2. #2
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    Continuation of Post

    Step 5: Connect the wire leads from the C7 and C39 pads to the new audio output capacitors.

    As illustrated in the photos, the selected coupling capacitors are a pair of 3.0 microFarad Dayton metallized polypropylene film capacitors from PARTS EXPRESS at $1.67.

    [--Lead and orientation ‘good’ practice--]
    [--Making the input lead solder connection--]

    The Dayton 3 microFarad film capacitor is 16.5 mm in diameter by 31 mm long (5/8-inch diameter by 1 1/4-inches long). Dayton is a reasonable quality house brand of Parts Express manufactured by Bennic as reported in this CAPACITOR MANUFACTURER GUIDE. Alternates might be the $2.25 SOLEN (3/4-inch diameter by 1 1/8-inches long) or the $14.95 AURICAP (15/16-inch diameter by 1-inch long). As discussed HERE, AEROVOX might also be an OPTION. Personally, I doubt that my aged ears can tell the difference between any of the these polypropylene film capacitors.

    [--Cautionary note about using larger diameter caps, size, Using dowels to premeasure fit--]
    [--Types of coupling capacitors (polystyrene, silver mica, polypropylene, electrolytic), suitability, cost, recommendations, suppliers, etc--]
    [--How an audio coupling capacitor works--]
    [--Calculating coupling capacitor resistance as a function of audio frequency--]
    [--What is Fo, Use of the High Pass Filter.xls bandpass spreadsheet calculator attached in the zip file--]
    [--What size of coupling capacitor is needed for Squeezebox, Recommendations--]
    [--Possible use of paired Black Gate 0.47μF 50V NX HiQ nonpolars if Squeezebox space is an issue, Where to order--]


    Step 6: Connect output leads from the new audio output capacitors to the left and right audio outputs …and… install 300 pF silver mica capacitor shunt across left and right RCA jacks.

    As illustrated in the MODIFICATION PHOTO , the C7 pad capacitor goes to the “left” J3 RCA output; the C39 pad capacitor goes to the “right” J4 (RED) RCA output. The 300 picoFarad (pF) SILVER MICA CAPACITOR shunts across the RCA outputs is to filter out residual DAC high frequency out-of-band noise.


    [--Step-by-step instructions--]
    [--Coupling capacitor orientation, Lead trimming and insulation--]
    [--Soldering coupling capacitor output leads to center conductors of RCA output jacks, Use of flux--]
    [--Purpose of silver mica capacitor first order shunt filter, Out-of-band noise from DAC above Nyquist frequency--]
    [--Possible use of High Pass Filter.xls bandpass spreadsheet calculator attached in the zip file--]
    [--Soldering silver mica capacitors to center conductors--]
    [--Fluxing and soldering silver mica capacitor shunts to RCA connector bracket grounds--]


    Step 7: Double check that there are no shorts between the newly installed audio coupling wiring and to the existing board and components. Then, reassemble the top to the Squeezebox using the Torx screws.

    Results for Direct Output Capacitor Mod: Even to my non-audiophile ears, the bass after the mod is definitely cleaner. Moreover, the midrange and high end sound, and the “soundstage” appear more precise. There was only a minor reduction in apparent Squeezebox output level (about five degrees more setting on the volume control needed to get the same loudness). Thus, in my opinion this direct output mod is worth doing, particularly if you can do it yourself for under $10 in parts and a couple of hours of labor.


    Appendix Notes:

    Note 1: Coupling Capacitor Choices
    As illustrated in the photos, the selected coupling capacitors are a pair of 3.0 microFarad Dayton metallized polypropylene film capacitors from PARTS EXPRESS at $1.67. The Dayton 3 microFarad film capacitor is 16.5 mm in diameter by 31 mm long (5/8-inch diameter by 1 1/4-inches long). Dayton is a reasonable quality house brand of Parts Express manufactured by Bennic as reported in this CAPACITOR MANUFACTURER GUIDE. Alternates might be the $2.25 SOLEN (3/4-inch diameter by 1 1/8-inches long) or the $14.95 AURICAP (15/16-inch diameter by 1-inch long). As discussed HERE, AEROVOX might also be an OPTION. Personally, I doubt that my aged ears can tell the difference between any of the these polypropylene film capacitors.

    Before investing a lot of dollars in an expensive, invariably larger diameter polypropylene capacitor than the Dayton, you should note that there is not a lot of height under the Squeezebox cover. Thus, you need to make sure any alternate will fit. Simply go the local Home Depot equivalent and buy a wooden dowel of the intended capacitor’s diameter (25.4mm = 1 inch). Then cut two pieces to the appropriate length and make sure you can find a space inside the Squeezebox lid! One option might be to drop down in size to 1 or 2 microFarad unit if fit for something like the Auricap is a problem. For detail see the Excel 97 audio band pass spreadsheet calculation named High Pass Filter.xls which is part of the attached zip file described in the next paragraph.

    Since the Squeezebox3 apparently does not have a lot of room, you might want to use the “Cadillac” of a smaller physical size electrolytic capacitors. This would be two sets of Black Gate 0.47μF 50V NX HiQ’s that are non-polar and 4mm diameter by 7mm long where each pair is arranged in an L-Canceling configuration. This would yield a 0.94 microFarad electrolytic coupling capacitor that some audiophiles might rate as good as a polypropylene film capacitor. For more information on this somewhat unique capacitor and configuration see the bottom of page 7 of the MICHAEL PERCY AUDIO CATALOG and the sidebar on page 7 of the Squeezebox Mods Detail document. This is a Microsoft Word97 document contained in the attached zip file which is SBox Mod Detail Word97 doc + Audio Pass Calcs Excel97.zip The sidebar starting on page 7 of that Word doc also has additional details about coupling capacitor selection and options:

    Note 2: Alternate Squeezebox “Audiophile” Cable Output (Also avoids trace cuts on board)
    Although I personally doubt that anyone can hear the difference between the existing relatively high quality RCA output jacks on the Squeezebox and $15 to $40 fancy audio alternates, direct cable output as part of this Squeezebox audio mod is also an option. This may also make sense if you are uncomfortable cutting the Squeezebox board traces to the existing center RCA outputs at J3 and J4 as in the earlier Step 3.

    This alternate essentially involves: getting the cables, cutting to desired length, stripping the cut ends, connecting the center to a newly installed audio coupling capacitor output lead, connecting a 300 pF silver mica capacitor across the cable, grounding the cable shield, etc.:

    The cable pair can be RCA male or female pair or stereo plug / cheap or expensive, etc.

    [--Step-by-step details are in the attached SBox Mod Detail Word97 doc + Audio Pass Calcs Excel97.zip file attached --]


    Note 3: Non-removal of Audio Output Amplifier
    Various other direct audio output Squeezebox mods have concurrently called for removal of the (U10 in Squeezebox2) NJM2041M audio output amplifier (next to J3 and J4) that feeds the Squeezebox RCA jacks. This was not done with this mod as the input capacitors C7 and C39 have been removed (at the amp’s input end) and the traces have been cut (at the amp’s output end) to the Squeezebox RCA center output jacks. This effectively isolates the amps existing inputs and outputs. Thus, the audio mod rationale for removing this amplifier does not make sense to this author. With both the inputs and outputs cut from the 2041 amp, it is difficult to see rationally how this audio amp, even left in place, could possibly affect the fully isolated output from the newly installed, completely isolated coupling capacitors.

    Thus, I do not feel removing the now fully isolated 2041 audio output amp is necessary because of the way this mod is done. However, if you are determined to remove it anyway there are only two real options: 1. Cut its leads with a nipper or 2. Use a Chip Quik SMD Removal Kit. With either option, use a magnifying glass and a great deal of care. Also check very carefully for inadvertently introduced shorts between its pin pads and elsewhere as that may well be an irrecoverable error.
    Dick


    Squeezebox2 With Hossflet pwr supply and output cap mods. Squeezebox Touch
    Sansui QRX9001 quad Resoldered and recapped with Black Gates. Sansui QRX6001 quad Bought new. Recapped and driver board mods.
    Onkyo T-4711 and Sangean HDT-1X tuners
    Sherwood Newcastle CD-980T
    Four Axiom M22ti Four Large Advents Bought new. Reconed.
    Cowon S9



  3. #3
    Senior Member ezkcdude's Avatar
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    Thanks, for sharing your DIY experiences!
    There are 10 kind of people in the world - those who understand binary and those who don't.
    ShinyMetal
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  4. #4
    Senior Member opaqueice's Avatar
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    Thanks for the thorough and detailed post!

  5. #5
    Senior Member Wombat's Avatar
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    Isn´t 3üF for the output a bit low? I use 10üF Black gates in my DAC as lowest recommended value and i didn´t test lower values. I don´t have the knowledge to know why. Can anybody explain?

  6. #6
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    Hi Wombat,
    Isn´t 3üF for the output a bit low? I use 10üF Black gates in my DAC as lowest recommended value and i didn´t test lower values. I don´t have the knowledge to know why. Can anybody explain?
    Depends a bit on the input resistance of the connected device. See the High Pass Filter.xls spreadsheet in the zip attached to the original post. With a 50,000 input resistance to an amplifier, a 3 microFarad cap would have an Fo (down 3dB or equal to a 50% frequency pass) at 1.1 Hertz. Supposedly anywhere between Fo of 1 to 5 Hertz should be fine for HiFi coupling. However, if you have the room and $, I suspect there is no reason not to err on the large side. (Anyone feel there is an acoustic issue with a larger than needed cap?)

    However, I suspect it might be better to have a 3 to 5 mF polypropylene than a 10 mF electrolytic (even if the latter were a Black Gate). But I could be wrong.

    Regards,
    Last edited by dickmc; 2006-05-06 at 18:05.
    Dick


    Squeezebox2 With Hossflet pwr supply and output cap mods. Squeezebox Touch
    Sansui QRX9001 quad Resoldered and recapped with Black Gates. Sansui QRX6001 quad Bought new. Recapped and driver board mods.
    Onkyo T-4711 and Sangean HDT-1X tuners
    Sherwood Newcastle CD-980T
    Four Axiom M22ti Four Large Advents Bought new. Reconed.
    Cowon S9



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