Flea and other mods to CDi...

[Bemused]

At 18v3 your meter is reading the average (maybe rms?) of the unsmoothed rectifier output. No smoothing capacitors in circuit.
At 25v0 your meter is reading the smoothed rectifier output, close, very close to peak voltage.
RMS is 0.707, Average is 0.636 of peak.
18v3 average implies 28v8 peak but now you have a little load so 15% regulation and there is your 25v0.
Seems OK to me.
I wouldn't think the difference of 0.018uF in the snubber would have any effect, 100R / 0.1uF is only an approximation.

Always good to have a thumbs up from Martin

 

[Dowser]

Yes. Remove the crystal and two tiny (33pf ish) loading capacitors adjacent, leaving the resistor between pins 10 and 11. Then feed your new clock in to pin 11 of the SAA7220. Tie the 0v side of your signal coax/ twisted pair as close as poss to the 0v plane here (e.g. to one of the 0v connections vacated by removing the loading caps)

Edit to add - bonus point while you have the thing apart. The SAA7220 sends the system clock (11.28Mhz) from pin 9 to the decoder upstream (which controls flow of data off disc, 'slices' it does the EFM and sends an I2S-format signal to the digital filter - the 7220). You'll find a low-value resistor adjacent which is connected directly to pin 9 of the '7220. Remove it, or lift the '7220' end of it, and feed this signal from the second output of the flea instead. NB you'll need a second SMD resistor of 47-10ohms on the flea pcb to use the second output.

PS suggest you see post 16 above and tweak the flea board values before you fit it.

Hi Martin

I have no resistor from pin 9 of the SAA7220 on my CDI - track seems to go straight to the SAA7310 SM chip (I assume the digital filter) - still safe to connect 2nd Flea output? I'm going to try I think - but it means lifting pin 9 of SAA7220 out of PCB...dangerous stuff!

Thanks, Richard

 

[martin clark]

No need if you're uncomfortable with risk of breaking the CDi

The 7310 is the decoder - I've put the datasheet up here which explains what it does: SAA7310

 

[Dowser]

Thanks Martin - it plays a CD after connecting both outputs - photos to follow after I've put it back together and confirmed it makes sound too

 

[Dowser]

I have music

Improvement is hard to explain - smoother somehow, more joined up, and I keep hearing delicate bits I never heard before. Actually very similar to when I moved from a modified RB250 to a Mission 774 arm on my LP12. Happy bunny!

I started this on my balcony at midday today and in direct sun and sweating - finished in dark at 6pm and about freezing temps. Damn! I really need to invest in some decent mounting hardware - I'm not really happy with how I've done it currently, and need to revisit at some point soon to ensure everything is bolted down properly.

I didn't fit the snubbers to stock bridge's, nor install stand-offs to start playing with OP caps, nor fit RCA sockets for the output - I was just too damn cold!

Thanks for all the support - photos;


Unmolested;

Measuring up where to place new bits - shortest run for flying leads for crystal without interfering with other bits;

I decided to move the bridge rectifiers over to the left a bit - I preferred having the transformer close to the original;

Pin 9 of SAA7220 desoldered and ready for pin removal;

Stock crystal and caps removed;

Super bodge for input of OP2 of Flea - no way was I going to try and wire it direct to the 7310 surface mount chip ;

Flea test mounted;

Everything wired up;

Cheers, Richard

 

[Bemused]

Looks like you had some success then Richard.
Cutting the leg is what I would have done, I've inadvertently lifted too many a pad in the past by pulling chips.
Silicone or hot glue is a quick but sure method of fixing stuff down.

Another Flea lives

 

[Dowser]

Thanks - yes, indeed. I'm very happy with the sound - somehow much more coherent; more detail - meaning I'm able separate individual notes much easier and am hearing new bits all the time on known recordings (all the way down to realizing what I thought was a solo voice previously is actually two tracks of same voice at different frequencies). Weird to describe though - it is somehow faster and harder...but also more delicate

I was a service engineer in my youth - have desoldered more chips in my life than I have eaten I think With dual layer I normally re-wet joint, solder sucker and then use freshly wetted braid to get it clean for removal - but is still a real pain on dual-layered PCBs, agreed.

I have hot glue, but promised myself I must get a bit more professional to attain longer term resilience - when I moved from Ireland back to Switzerland I forgot the whole main PCB and mech are on a sprung chassis in the CDI - I couldn't find transport screws so just locked mech down with foam around lid, locked laser in place, threw it in the car and drove it here. I managed to break one of the suspension springs at back of PCB as a result. I reckon hot glue would also break under similar circumstances.

Cheers, Richard

 

[Bemused]

Yes what you hear is typical of the flea in my experience, of course a Flea is not just limited to clock duties and 5 volts!
And there is the fleas spiritual brother the ALWSR
I think my first diy dac had seven fleas in all.

 

[martin clark]

Richard - nice pics, glad it works after surgery

'smoother somehow, more joined up, and I keep hearing delicate bits I never heard before.'



And if you don't like it , we have other suggestions to play with

 

[Dowser]

Thanks both - I have a second Flea here, but am thinking of fitting into my office Marantz CD60. I do have 6 spare ALWSRs ready built though, and 2 STRs all positive only though.

Martin - interested in your input (plus, you are only 2 posts away from 10k ) - I'm thinking a dedicated supply for the SAA7220 comes next? Not sure if the regulators I have now can supply enough current though? You mentioned a dual based 337 design? And I also need to decide whether now is the time to move the transformer external to make more space for follow on mods. Separate supplies for analogue stages needs to come too - but I should also map out the current regulator strategy on board - Naim have not exactly been stingy with the regulators in the original design

Richard

 

[Mike P]

I found a dedicated PSU for the SAA7220 to be a very worthwhile mod on my old Arcam Alpha 5 project. One of these with a small transformer makes an inexpensive and versatile little PSU which works great:

http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=131572582324

You can tweak it up by fitting schottky 11DQ10 diodes, a bigger better cap and using a pair of red LEDs instead of the voltage set trimpot. Oh and ditch the film cap at the output.

This old pic gives you the idea.

Also for best results pay close attention to the decoupling of the SAA7220 (i.e. Oscon/surface mount ceramic).

 

[martin clark]

Martin - interested in your input (plus, you are only 2 posts away from 10k ) - I'm thinking a dedicated supply for the SAA7220 comes next?

Outboard psu not remotely needed! I have a CD2, which is effectively a more-refined-one-box CDS; and one of the more fun things to demonstrate is what can be achieved within the one box Some reading here that Mike has been one test bunny for, and which I ('felix') have yet to summarise for a Naim/TDA1541-cd player page or two on acoustica.org.uk:

http://www.audio-forums.com/threads/arcam-alpha-5-cdp-upgrades.110869/page-2

- Yes, I shall shortly boil it down to some basic ideas for play ..! Two, no, three, quick wins:
1. The dac-15vdc supply: Naim use an LM337: swap the lower R setting the voltage for 'two LM329 in series'. You'll get about -15.2vdc or so output, but that's negligible (and in tolerance of the dac) compared with the >30+dB improvement in psrr. More refinement is easily had...
2. 10uF of decent cap between the -5 and -15v pins of the TDA1541. Make sure the -5v reg (LM337) has at least 100uF from -Vout to 0v, and at least 100uF from -Vin to 0v. These caps are ideally not 'low -esr'. i.e a few tenths of an ohm ESR are useful, so biggish /even bigger & cheap caps are ideal!
3. Third easy win here - swap the volt-set resistor for the -5v LM337 reg for two green LEDs (=-5.1v out approx: the absolute DC voltage does not matter, esp when it is so quiet..)

 

[MJS]

I'm going to give these a go on my CDI, thanks.

 

[Mike P]

2. 10uF of decent cap between the -5 and -15v pins of the TDA1541.

3. Third easy win here - swap the volt-set resistor for the -5v LM337 reg for two green LEDs (=-5.1v out approx: the absolute DC voltage does not matter, esp when it is so quiet..)

10uF is the recommended value but I've found you can go up to 15uF without any problems. I use a 15uF Oscon SC between the -5 and -15v pins of the TDA1541 which works well for me.

You'll find that the voltage drop across green LED's varies a bit from manufacturer to manufacturer. Two bog standard cheap 5mm red LED's got me closest to 5v and I prefer to run the TDA1541 slightly under rather than over voltage for longevity. LED's are cheap so I recommend you buy a few different types and experiment to find the best combination that gets you closest to 5v.

 

[Dowser]

Thanks both!

OK - then I try the above as next steps, sounds sensible (and looks like another forum for me to join - interesting thread!).

First I will sort better power for the saa7220 though - at the moment I'm using both 12v secondaries and full wave to power the Flea, when I'm sure one secondary would be enough with a bridge? I then have a slight beefier toroid transformer that is not much bigger, also dual 12v secondaries, that should fit in same space as current one - I use one secondary for Flea, and one for a dedicated saa7220 regulator - I assume I need 5v for it (haven't checked yet), and that I can dump the extra volts from 12v AC ok using that eBay 317 regulator?

Other current questions (need to go and read that other thread in full);
"10uF of decent cap" - Wilma 10uf film ok I assume?
Output caps: there are currently 10uF taunts in there - is it important for me to maintain this, or can I drop down to 2.2uF? Or will I need to change some Rs too? I still don't really understand the whole output filtering thingy

Cheers - not sure if the Flea burns in, but it is performing better and better to my ears. After extended listening using old CDs I used extensively when testing differences between DIY SE valve hybrid amps and ESL 57s & 63s back in Ireland, and feeling something was missing from an imaging perspective, I finally swapped out my XTC pre and power amps back to my Croft Micro II (lightly modded) and 211 based DIY hybrid SE monos - wow, the result was holographic and I stayed up late enough listening I got a complaint from a neighbor next day. More listening required - preferably with less imbibed

Richard

 

[Dowser]

Thanks Mike - noted on the LEDs

 

[Mike P]

For the output DC blocking coupling caps films are the way to go. If you have some 10uF Wima MKS they'd be a good place to start and I'm guessing they'll even drop straight in without any messing about. If the 10uF are physically slightly too large try the 4.7uF which have a smaller footprint. Polypropylene (rather than polyester) would be slightly better still but they tend to be very large and difficult to fit, I'd put the Wimas in an see how you go.

Yes the SAA7220 requires +5v.

Please bear in mind that when I started writing the Arcam A5 thread I was very new to all this so take what you read with a pinch of salt. My experience and understanding has moved on considerably since then! Of course the advice from Martin (Felix), Tenson (Simon) and Rob on that old thread is all spot-on.

For the cap between -5v and -15v on the TDA I suggest a 10uF - 15uF Oscon, the Wima cap will be a bit awkward to fit. This photo is of a Sony 227ESD which uses two TDA1541A DAC chips but you get the idea.

 

[Dowser]

Thanks - I have some nice 2.2uF films, and didn't really like the result of 10uF Wimas when I blasted them all over my NAC62 instead of tants (it got too polite), but loved it when I did the same to an AR A60 I rebuilt (except for 2.2uF at output). I still have stacks of Wimas, but am disinclined to use them for blocking in a Naim device

Other points noted, thanks.

 

[Dowser]

I'm listening again tonight, at very low levels - the resolution at low volume is stunning with the new clock!

Going to prepare a parts list to do separate 7220 supply and Above 1-3 mods as a next step - it is a pain to get at underside of main PCB on my Naim due to the suspension and the PCB being mounted to a chassis, so need to do as much as possible in one go.

Mike - your thread (I was already a member, God knows from how long back!) gives me lots of other stuff to think about, thanks. Need to review how Naim did the implementation on the CDi really, before progressing much beyond above.

Richard

 

[martin clark]

Richard,

In the CD2 Naim used two regs in series for the SAA7220; it draws about 200mA. Providing the raw dc supply is above 10v you can usefully reconfigure two LM317s as a tracking pre-reg to the benefit of the '7220. (cough, http://www.acoustica.org.uk/t/3pin_reg_notes4.html ). After that its down to finessing decoupling - or going for a better discrete reg... [my CD2 glows in the dark inside ]

And yes, I've noticed that the flea gets better after a day or so - built dozens of the things over the last decade and rather think its a one-time effect in the oscillator used; there's nothing on the reg part itself that would explain it (and you still get it if you take an existing flea and swap to a different XO).