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Flea and other mods to CDi...

Discussion in 'd.i.y.' started by Dowser, Apr 14, 2010.

  1. Dowser

    Dowser Learning to bodge again..

    So, 3 years after buying and fixing up an old Naim CDi I am finally going to mod it to see whether its performance can be brought closer to my LP12. Original thread is at http://www.pinkfishmedia.net/forum/showthread.php?t=33604 - I bought it faulty and with Les' help got it up and running for around £200 with a new laser to boot, it's the best CDP I've heard.

    Mods I intend doing are listed below and I, of course, have some questions :) ;

    1.) PFM Flea fitting - I bought a kit a couple of years ago, but never got around to assembling it. Recently bought a built one from Mus, just need to swap the crystal, hence the motivation to actually do something...

    I few questions though;

    a) I have a simple small encapsulated xer and a small bridge rectifier that was originally part of a white noise +/- 15v PSU kit which I intend using to provide a dedicated 30v supply for the Flea. How much difference does the quality of the raw supply impact the performance of the Flea? Should I use Schottky diodes and decent smoothing caps instead of the junk I have now? What sort of uF value for the smoothing is best, and any value in a RC filter (I have lots of 1 ohm high watt resistors)?

    b) Is there any value in my using the unbuilt Flea I have to power one of the other chips too? And how should I do it? Talking with Les when he helped me get it up and running initially he mentioned the NOS mod as being a big step forward - what does this actually do? Remove the 7220 chip form the cct? Rather than simply using the Flea to power another chip, and then look at further mods later, I'd rather do it in one go. Anyone been there, done that? Or suggestions for another approach, and use for a 2nd Flea as a regulator? How did those early adopters go power the TDA1541 with a Flea - did it survive? And can I hang 2 Fleas off the one raw supply I will be using? Should I put any additional filtering in too?

    2.) Schottky rectifier diodes in CDi PSU - I want to do this, but also probably need to if I want to fit the Flea raw PSU inside the CDi - see photo below, not a lot of space - if I use Schottky's they'll have a smaller footprint and hopefully a bit of juggling will give me required space for the Flea xer with bugged rectifier/smoothing. Anyone tried this in a Naim CDP, and what were results (and what Schottky's did you use - MBR2020s?)?

    [​IMG]

    3.) Smoothing cap replacement in CDi PSU - any recommendations for replacement smoothing caps (I remember Laverda using BHC T-Nets)? I guess if they are smaller that is good, but if higher value will give better results I can work something out I guess. Does anyone know stock value of smoothing caps in a CDi (I am being lazy, I know...)?

    4.) Tant replacement - I have 20 odd 10uf/35v tants from Les, and another 30 or 40 Wima 10uF little red jobbies. Does anyone know which tants I should target for replacement, or just do them all?

    5.) What else should I be doing while everything is apart? I intend to test after each mod to limit risk of a screw up causing grief, but want to get maximum benefit from having the thing in pieces (it's taken me 3 years to drum up the motivation to pick it apart!). One day I intend taking output from DAC straight through an unfiltered and simple discrete output stage - but this is definitely something I will do after all the above.

    As always, many thanks for any comments or advice.

    Richard
     
  2. martin clark

    martin clark pinko bodger

    Quick answers to the first half:

    a) Really, not at all. That said, making the raw smoothing CRC is nice to have becasue it keeps all rectification noise away from the board. Use the junk you have, but add at lleast 1R in each side of C-R-C (ie in the notionally '0v' side too, two reisors, two caps) and keep this close to the transformer. Since the flea draws <20mA these can be quite large resistors, say 10-22r, and regular 0.6w metal film types are just fine thermally.

    b) I am absolutely not a fan of NOS mods. It sounds fatter simply by completely messing-up the designed freq response (in a way that analogue filter realignment cannot correct), and it's a band-aid fix for poor clock/supply/decoupling practice hence popular with diyers.. ;) DO give the SAA7220 a better regulator than it has already - this is essential for best results. Two LM317s as a tracking prereg can work surprisingly well for this.

    2) You can get exactly the same benefit snubbing the existing diode bridges, which is a lot easier and possibly more effective. See Maplin part RG22Y, its 100nF in series with 100R in one package. Add one across the AC terminals of the bridge rectifier - it completely mops-up the reverse-recovery step/rining. Make it out of discrete parts if you want to experiment. Cheap and easy!

    3) I used some small BC components, 10000uF /40 caps in my CD2 - they drop right in.

    4) A subject for another day. The wimas drop-in as coupling caps OK and sound pretty good.

    I would recommend you search out midcm1's CD2 mods thread - there is an awful lot shared between these two players except transport mech. Keep the current OP42 opamps. Better regs for the analogue stage can be fun though!
     
  3. Dowser

    Dowser Learning to bodge again..

    Cheers Martin, appreciated - that's NOS off the cards then :D Do you know what current the 7220 draws?

    On the C-R-C - you mean 2 smoothing caps across the bridge output, with a series resistor between them on both + and 0v lines.

    I check RG22Y thanks - my main driver here has to be to create space for the raw Flea supply.

    Thanks again for swift advice!
    Richard
     
  4. martin clark

    martin clark pinko bodger

    The '7220 wants +5v at about 200mA. It runs hot!
     
  5. midcm1

    midcm1 pfm Member

  6. Dowser

    Dowser Learning to bodge again..

    Many thanks midcm1 and Martin.

    midcm1 - any chance of resurrecting the photos? Shows how long I've been procrastinating, given I commented at the start of your thread...but my CDis cover hasn't come off since :)

    Richard
     
  7. Dowser

    Dowser Learning to bodge again..

    And midcm1 (what's your real name? :)!), is your CD2 PCB the same as my CDis? My comments on your original thread suggest not.

    Cheers, Richard
     
  8. midcm1

    midcm1 pfm Member

    Its Dom.

    The pcb is quite different however the basic concept is very similar. I'll try and put pictures back up again although can't use photobucket (any suggestions...must be free).

    See teddy pardos thread on his CDX2 mods. Basically they are all the same.

    I'm not sure if the CDi has a dual winding supply.

    What I've done my CD2 is quite drastic as I've cut tracks on the pcb and swapped some of the psu supply rails.
    My external PSU has separate +/-supplies for two superteddy regs powering the output opamps (I/V stage and filter which are isolated from the other circuitry that was sharing the original +/-18v supply), a supply for a Flea XO clock thingy, the original Naim supply powers just the digital things from one winding and the DAC via a Flea and accelerated teddy regs and 7220 via the original regs I think with perhaps more filter capacitance. Actually I might be feeding the 7220 of the other supply rail......to keep its noise off the rest.....
    I've also replaced all output stage resistors in the signal path with Dale RN60s and replaced the output caps with a wire link and removed all of the original Naim psu bits. The original Naim transformer runs two of Carls cap boards.

    Once you've worked out the required voltages for each stage (output opamps, dac, 7220, digital stuff) its easy to rejig the supplies. Really thats all I'd recommend is done, more isolated supplies with improved filtering. The resistor change was subtle but worthwhile as I had the bits. I also eliminated the output din socket and wire direct to the board so my signal lead is fixed. I thought this was a surprising improvement, but this could have been cos the socket was old.
     
  9. sam_cat

    sam_cat ʇɐɔ_ɯɐs


    Flickr. Very good and free.
     
  10. Dowser

    Dowser Learning to bodge again..

    Thanks Dom - I use fotopic.net, also free.

    Richard
     
  11. Dowser

    Dowser Learning to bodge again..

    Coming back to this - lazy ass that I am I never got any further than ordering some 10k uF/40v Kendeils and making sure I had all the bits for the Flea.

    However, having had to replace a couple of chassis suspension springs (I stupidly moved it from Ireland to Switzerland without transport screws - fantastic service from Naim who sent me 2 free replacements!), I figured I may as well swap out the smoothing caps too.

    Upon unbolting the originals, I find they are 15k uF/25v BHCs, rather than 10k uF items. So I'm looking for some alternatives - given the size reduction in caps nowadays, I can actually get 47k/25v Mudorf MLytic AG replacements slightly smaller than the stock BHC 15k items. Has anyone tried increasing smoothing capaictance in a CDI? There are 4 caps, fed by 2 NAP style heavy duty bridge rectifiers, so I do not expect any issues - just wondered whether anyone had tried.

    Why? I had good results increasing smoothing capacitance of my Croft Micro II pre - would like more of the same (although admittedly, no idea how much is due to new caps, and how much to increased capacitance...).

    Thanks, Richard
     
  12. laverda

    laverda pfm Member

    FWIW...I replaced the original BHC 15k caps with 10k T NET (4 poles) though fiddly to get in and configured)) along with the rectifiers for 20200 schottky's. Quite nice. Cant comment on higher uF (didn't cross my mind) as I'm well impressed with the T Nets. Their on drop in replacement.
    [​IMG]
    [​IMG]I have done much the same as midcm1 but with ALW S/Regs apart from the output stages didn't bother with all those resistors, though I have replaced the output opamp with a BB OPA627BP. I even kept the original 10uF tants.

    I did at one stage have a separate PSU with 4 transformers and loads of pre-regulation. But that was in the good old days......
    [​IMG]
    The little transformer on the back is for the flea

    I still love how it sounds.....6 years on....:)
     
  13. martin clark

    martin clark pinko bodger

    I think I'd rather go for similar or slightly more uF at a higher voltage rating - for less leakage current and a longer life expectancy since some of those raw rails run up towards 22-23v as it is. So 15-22K uF/35vDC is what I'd be looking for, depending on what will fit. In my CD2 I went from standard 2x 4700uF +2 x 10000uF /25v to 4 x10000uF/40v items (BC components) that fit snugly.

    47mF would work, but may in fact prove a bit 'noisier' - conduction period can't really lengthen, so the peak currents have to be higher... (no way of knowing without a test though). One way to address that is to insert a small impedance(s) between the AC input and the bridge, or between the bridge and the cap - but then you are into an entirely different PSU and all the joy^^^experimentation and measurement that brings.
     
  14. Dowser

    Dowser Learning to bodge again..

    Thanks Both - measurement with anything other than my ears rules me out :) I'll check 40 or 63v 22ks.

    Being smaller gives me more space for the Flea and its xer as a next stage - although I hadn't thought of bolting it to back of the case - nice one!

    Richard
     
  15. laverda

    laverda pfm Member

    One thing I did notice....IMO the Flea supply likes more than 21vdc min. as a min or put another way use a 0-18v transformer. My first Flea transformer was all I had in the bin a 0-15v jobbie resulting in just over 21vdc. It worked but the result was a thin/er sound than I anticipated. For a long time it pissed me off....
    Swapping the 15v for a 18v transformer realising over 26vdc restored my faith in martin clark...:) IIRC the supply can be anything from 21 to 27vdc but I haven't checked the build manual lately.

    Just my findings and thoughts.....I think its called giving it 'head room' I await clarification and or ridicule.
     
  16. martin clark

    martin clark pinko bodger

    Yes it does Graham, good call.

    ... it's the 10K/3.3uF in the input cap multiplier. Take it down to 1k-2k2, and use a bigger cap instead (tant or reasonable electrolytic). Original value tends to 'starve' the 7812 voltage reg resulting in higher than expected DC output z to the opamp. One of the many things I have worked at since (its a project over 6yrs now :eek: )
     
  17. laverda

    laverda pfm Member

    Cheers Martin,

    That pesky z.....I'll give the Flea a tweek (revise the multiplier) next time the lids off.......:)

    as always, you have ALL the answers to ALL our questions..

    Was there talk of a Flea II..;)
     
  18. martin clark

    martin clark pinko bodger

    No I don't, I may have suggestions, that may or may not work but hopefully won't release too much smoke.

    Flea 2? Once upon a time. In trying for something better, all the incremental bits in-between turned it into something else - more of a modest general-purpose reg board that can be simplified to a clock reg. Still fiddling, still learning on that front. (And no, there's no layout yet, that's on the to-do heap!)
     
  19. Dowser

    Dowser Learning to bodge again..

    Thanks both - relevant points given I have 2 dual 12v secondary xers in the parts bin (small 1.6vA & larger 30vA toroidal [that could be bolted to rear as above] - so 2 questions;

    - is higher VA beneficial for a Flea supply?
    - what can I use to drop the DC volts a bit - I can use a VBE I guess, but any benefit to doing so?

    Thanks, Richard
     
  20. Dowser

    Dowser Learning to bodge again..

    Oh, and looks like I'll need to go with 33k uF / 40v smoothing caps - Mundorf MLytic AGs.

    Richard
     

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