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  1. #1
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    Squeezebox Touch Hardware Mods

    Hi there ! I just reach this board few days ago thinking to find what i was looking for, hardware modifications for the SBT.
    Is there anything here ?
    I just found few posts about this but not a lot....

    Hope there will be DIY enthusiats here !

    Cheers.
    Olivier

  2. #2
    Hi! I've done a fair bit on mine but the last time I tried discussing it on this forum, it turned into a bit of a nightmare argument over commercial mods and general perceived problems with suppliers which really only told 1 very biased side of the story.

    On my own unit, I have solid polymer caps on the SPDIF buffer chip, Main 5v, clock switch logic chips, both 5v DAC rails. Low noise regs for the DAC 5v and 3.3v. The 5v supply for the touch screen sense have been removed from the DAC rail and attached to the main 5v rail. I have a low noise linear PSU with 80va transformer and 44,000uF low esr smoothers. The DC blocking caps in the audio path have been removed. On the clocking side, I completely reverse engineered the clocks. I have 2 external low jitter clocks which are attached directly to the switching logic (buffer logic removed which made a significant difference). I'm now looking are bypassing the switching logic too! The clocks are temporarily mounted external to the touch (on the back) and connected via coax with grounded only at the source. I'm also running soundchecks TT3 but with the display enabled.

    The audio quality from FLAC and WAV is shocking!! by shocking I mean unbelievably good!!

    What are you thinking about and how far do you want to take it?????





    I should point out my wireless works fine with these mods!!!! (not that I'm currently using it of course!!)
    Last edited by UV101; 2012-02-19 at 12:50.

  3. #3
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    Great work. So I take it the boards that are installed are the low noise regulators, right?

    When you talk about bypassing the switching logic, what are you referring to? Getting rid of the functionality or putting it off on another board?

    As far as I know there are two chips involved, a clock mux and a flip-flop. If you are only going to play one family of sample rates you can get rid of the mux (and one of the clocks), but I don't see how you can get rid of the flop, its the primary method by which the low jitter clock is used, by reclocking the data coming out of the processor.

    I've done a lot of testing of different muxes and flops and found that the ones already in the Touch are the best sounding ones of all that I tried (and I tried a lot).

    There are actually two clock muxes, one for the "music" path and one for the "effects" path. If you are not using the effects at all you can cut the clock signal going to that mux thus decreasing the load on the clock source which does slightly help. (if you do that either remove the effects mux or tie the input to ground, you do NOT want to leave a floating input)

    Exactly how those clock boards get connected to the Touch is fairly critical. You can have a significant impact on noise and jitter by different ground connections. Using the shield on the coax is actually a very good way to do it. If it were me I would tie the shields on the two coaxes together and connect that to the Touch groundplane as close to the signal connections as possible. The power supply connection gets tricky. Its best if you have a separate power supply for the clock boards (not just a separate regulator, a complete separate power supply). With the two separate boards it gets a little tricky. I would put a very low impedance connection between the ground planes of the two boards, a nice wide flat braid would work or a strip of copper etc. I would connect the tied together braids from the two coaxes to the center of this connection between the boards. The "gnd" connection from the clock PS also connects to this point.

    This meets two important criteria for a good connection of an external clock: there is one and only one ground connection between the Touch and the clock board, and that the return current is in close, low impedance proximity to the signal. Using the coax shield for this, and tying them together meets this nicely. Because you have two clock boards it makes things a little tricky but by making a low impedance ground connection between them and connecting THAT to the Touch you can still maintain a really good connection.

    This doesn't mean that what you have now won't work, its definitely a significant improvement, but that by doing it this way you can make it even better. I once added clocks to a SB3 with long ribbon cable with no termination etc, the signal integrity at the far end was horrible, but it STILL sounded way better than stock.

    John S.

  4. #4
    The boards inside the unit are my low noise regs. The circuit is based heavily on one of the commercial designs but there are a few changes such as additional noise filtering on VREF. The layout of the positive reg has been designed so that an oscillator and cap can be fitted directly to the board itself effectively changing it into a decent clock. This is what is currently attached to the rear of the unit. I was supprised how well it works even with the clocks external on coax.

    The replacement PSU supplies 5v low noise regulated for the main player supply rail but it also supplies 11v unregulated to the 2 internal regs and clocks (drop out it about 5v for these regs).

    With respect to the clocking, The connectivity details are here. U14 is removed and the 24.576Mhz feeds into pad 6 and 22.579Mhz into pad 8. Pads 12&13 are linked to preserve the 2nd clock feed (presumably to the the "effects" area? John are you able to confirm this is the right way round?)



    The original clock digram I removed from the previous thread is here



    As the oscillators have an enable feature,I plan to try eliminating the Texus Instruments logic U15 & U33 and run the clock direct switched on as required likie this.



    I'll try changing the grounding arrangment on the clocks. Currently they are source gounded at the PSU. I didnt try with the gnd only at the touch end of the coax but I will try to see if there is any improvement.

    Cheers,
    Last edited by UV101; 2012-02-20 at 12:51.

  5. #5
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    On the taking out the mux and using the clock enables, it MAY work if the output is tri-stated when disabled. BUT you now have the capacitance of the disabled output in parallel with the load, this may or may not cause a problem.

    With this scheme you give up the ability to set the effects sample rate different than the music sample rate. Thats why there are two muxes in the first place. At it's worst this will just cause the effects sounds to sound strange. If you always have effects turned off it probably should not be a problem at all.

    With the two clocks directly connected together I would probably put a small resistor on each output (say 22 to 47 ohms) and connect the other ends together, this will help isolate the oscillators.

    John S.

  6. #6
    Quote Originally Posted by JohnSwenson View Post
    On the taking out the mux and using the clock enables, it MAY work if the output is tri-stated when disabled. BUT you now have the capacitance of the disabled output in parallel with the load, this may or may not cause a problem.

    With this scheme you give up the ability to set the effects sample rate different than the music sample rate. Thats why there are two muxes in the first place. At it's worst this will just cause the effects sounds to sound strange. If you always have effects turned off it probably should not be a problem at all.

    With the two clocks directly connected together I would probably put a small resistor on each output (say 22 to 47 ohms) and connect the other ends together, this will help isolate the oscillators.

    John S.
    Thanks for the contribution John :0)

    In the diagram I had included a couple of 10r resistors to isolate the oscillator outputs. I knew it wouldn't be straight forward but I think it might be worth trying.

    I now understand why there are 2 mux (U15 & U33)chips. I couldn't work out why there were 2 independently switchable system clocks but now I understand.

    So what exactly does the effects clock do and when would it come into play? I see what you are saying with my conceptual clock, there would only ever be 1 clock feed albeit, could be sent to both area's.

    A couple of quick wins..........
    For those using the SB internal DAC, you can bypass the DC blocking output caps C88 & C91 10uF 16v SMT caps below the DAC which has been previously discussed elsewhere. I've removed mine and linked the pads. Another thing I have discovered is that the 5v SOT23-5 reg (U21) not only supplies the DAC with its 5v, it also supplies the sense side of the touch screen. On the front of the main PCB near the narrow screen connector, there is a 10r resistor (R179) this is the supply from U21 to the screen. It is possible to remove this resistor and connect the supply direct from the device input supply via 10r. The result removes the screen sense from the DAC regulator. I'm not sure how much of a audible difference this would make on its own but I would suggest it can only have a positive effect on the DAC supply.







    On the subject of PSU regulation, can anybody identify these components?
    I know they are 3.3v and 5v regs but I'm interested in the spec. I believe there may be significantly better low noise versions available with similar pin outs. The pin marked NR seems to be conveniently placed near to GND for some of the better spec regs that use a bypass cap on this pin for very low noise operation!



    I've got a few Nat Semi low noise regs on the way to try and hopefully a donor unit to fit them in!!! (eh Andy!!)

  7. #7
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    Big thanks to UV101 for rebirthing the SBT DIY thread!
    And additional thanks for all his offline help.

    I have now added the Fidelity Audio microclock, replacement cap on the main 5v digital rail, removed the optical spdif assembly and a hardwired a 75ohm cable and connector in place of the previous socket mod. The image below shows an early stage. The end result has much shortened leads and fits close to the main pcb.

    And a word of warning to any noob DIY-ers - this stuff is pretty tricky.
    I was without my SBT for almost a week because something wasn't working. Ended up not being my fault(!) but a bad cap which took a while for me to track down.

    Remember all of the images in these threads are many times actual size and can be misleading as to the actual scale of this work. See the second image below for one of the SMD resistors on my small lady-like finger for a better sense of what you will be working with. And look more closely - the connection points are those thin silver strips at each end, narrower than a fingerprint ridge. Magnification is mandatory.
    Last edited by HumanMedia; 2012-02-24 at 20:43.

  8. #8

    Wink Nice work

    Glad its finally sorted (although I prefered the option where you pay for me to do a house call with my scope!!)

  9. #9
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    Quote Originally Posted by UV101 View Post
    Thanks for the contribution John :0)

    So what exactly does the effects clock do and when would it come into play? I see what you are saying with my conceptual clock, there would only ever be 1 clock feed albeit, could be sent to both area's.
    When you touch the screen to push a button, select a menu operation etc a beep or blurp or some other sound gets played through the internal speaker, these are the "effects". There is a separate path for these sounds, with its own DAC (the Wolfson) and little amplifier and speaker.

    These sounds are stored in little wav files on the Touch. The sample rate of these is probably going to be different than the sample rate of the music thats playing through the main system so they had to come up with a means to give a possibly different clock to the effects DAC. Since they are still audio files they will have a sample rate in one of the standard families (related to either 44.1 or 48). The second clock mux selects the appropriate clock for what is playing on the "effects channel".

    The processor generates two signals, a clock select for the effects and a clock select for the music path. If you implement the "connecting the two oscillators together" scheme, make sure you use the clock select for the main music system.

    With the clocks connected as you propose the effects channel will always get the same clock as the main music system, which may wind up playing the effects either too slow or too fast. If you always have the effects turned off you will never notice the issue.

    John S.

  10. #10
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    Quote Originally Posted by UV101 View Post
    On the subject of PSU regulation, can anybody identify these components?
    I know they are 3.3v and 5v regs but I'm interested in the spec. I believe there may be significantly better low noise versions available with similar pin outs. The pin marked NR seems to be conveniently placed near to GND for some of the better spec regs that use a bypass cap on this pin for very low noise operation!

    I've got a few Nat Semi low noise regs on the way to try and hopefully a donor unit to fit them in!!! (eh Andy!!)
    I don't know what those are, but I have used LT1761 regs many times which will be pin compatible. You just add a 0.01uf cap between the NR pin and the OUT pin. With the LT1761 its important to not use a larger cap, if you use a 0.1 (maybe to try and get better low frequency performance) the regulator shuts itself down. (don't ask how I know this!) I like to use the Panasonic film SMD caps for this, they work really well.

    John S.

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