Inveterate meddling #105: stuffing ALW-Audio super regulators into a Naim CD3.5
Naim's CD players need little introduction - we're big fans. The CD3.5 and CD5 players from Naim are upgradeable by plugging-in an external PSU in one of varying flavours, from the humble (but good) SNAPS of yore through the Flatcap, Flatcap II and Hicap; you could even use a Supercap if you had more money than sense. The external PSUs solely power the analogue output stages of the player and leave the player's internal PSU running just the digital works inside the box. This brings two benefits: one, obviously-improved separation of digital and analogue power supplies; secondly, and more subtly, the offboard supplies deliver lower noise and tighter regulation through lower impedance which is key to maximising the potential of analogue circuits. On the CD3.5 and CD5 models the external supplies replace a 'link plug' providing regulated power to the two internal LM317 regulators situated adjacent to the analogue stages; here's the 'before' photo (152KB). One '317 powers all four opamps (two per channel) of the anti-aliasing filter, and the other powers the two opamps (one per channel) driving the output. Few who have heard the transformation the external PSUs bring could deny it's a worthwhile improvement: but why stop there? Better is better !
Better, in this case, comes in the form of Andy Weekes' Super-regulator boards which you can read all about here. Designed as a drop-in upgrade to better the performance of three-terminal regulators such as those used in Naim's *caps - where the implementation is far more subtle than first appears - it seemed logical to try using the SR boards to directly replace the LM317s inside the cd player. This would provide the lowest possible noise and impedance where it is needed most, regardless of whether or not an external supply is used, and without the internal 317s undoing all the good work wrought by a better offboard supply...
The guinea-pig player here is a CD3.5; there seems no reason why this arrangement cannot be retrofitted to a CD5 which is essentially the same design rearranged internally. All that is required is a space approx. 45 x 35 x 75mm to mount the SR boards in, and the fabricating of a small wiring harness. Finished it looks like this (68KB). Either way it's all a bit tight, so pay attention now...
Tools & Materials
What to do
1 Create a mount for the SR boards from a piece of copperclad PCB material
2 Remove - carefully! - the LM317s from the CD analogue stage
3 Connect up the SR boards instead
4 Plug in, turn on, quickly develop silly grin and a strange urge to bounce around the room.
How to do it
1 Unplug the player, and remove the cover - 1 screw and four plastic locking pins on the CD3.5, be gentle levering the pins out with a sharp edge.
2 Make up the SR boards if in kit-form and test both. If using the tracking-preregulator feature - and you should ! - the Super regulator output requires setting for approximately 17- 17.2v out. This allows sufficient voltage headroom for the SR boards to work properly even when running the player using the link plug, i.e. without an external *cap supply. Set all the thermal isolator bits to one side carefully.
3 Cut a piece of PCB material 70 x 30mm; drill four 3mm holes at 19mm centres down the centreline (Click on the drawing above). NB there is little margin for error here, +/- 1mm only. Less than 30mm wide is OK, but fiddly to connect to the harness later.
4 Cut two more small pieces (or use thin copper sheet) and solder to the main PCB to form an offset mounting hole 5mm from the end of new pcb board and approx 7mm above it. It's easier to drill the required hole first, then cut the pieces down afterward....This hole will mount the SR assembly in the CD3.5 located using the PCB screw nearest the disc tray (see photos).
5 Trial-fit the SR boards interleaved on the pcb, then mount the PCB as 4 above. Try to refit the top case to the player - the SR assembly should clear it by 3mm and the disc tray by approx. 2 mm radially; see side clearance photo.
6 If it doesn't fit easily, fix it now.
7 Set the SR rough assembly aside and set to freeing the main PCB from the CD player. In the CD3.5 this involves 4 main screws holding the PCB, freeing the rear panel link plug socket and undoing the heatsinking screws on the 6 voltage regulators near the big main capacitors on board. Keep notes on what fits where, how the mica washers fit etc. In the CD5 matters are complicated by the plastic isolator grommets used to mount the PCB. These must go back as you found them - it does affect the sound..
8 All this is just to get at the underside of the board to remove the two LM31s. Use a chisel bit, heat all three legs of the LM317 just long enough so that the piece comes away easily under gentle pull with the pliers. Do not overheat - the pads and tracks may lift from the PCB - but use plenty of heat for just long enough. It will pay you to find the right size chisel-bit, you are more likely to damage the pcb tracks by trying to use a regular bit heating the legs in turn.
If you are super-nifty with a soldering iron and chisel bit, this is possible -just - from above the board, skipping stage 7 above, but we cannot recommend it!
If you just dont care, use the sidecutter to chop the LM317s off, remove the Vadjustpins retaining the others for the harness connections.
9 Cut four 10mm lengths of 0.7mm copper wire and solder neatly into the holes left by both LM317s' Vin and Vout pins. The wiring harness from the SR boards will connect to these.
10 Trace the 0V return that the LM 317s are decoupled to, and find a convenient spot to add a 13mm copper wire stub to it (top of main PCB). This will become the 0V return and sense point for the Superregs
11 Refit the motherboard back into the CD player and take a break.
12Afterwards, check you've got everything back where it came from, and only two LM317s left over.
13 Re-read the super-reg manual and design your wiring requirement. Nominate one regulator and start planning the wiring: raw dc in (from copper pin at former LM317 Vin to Vin on SR board; 0v connection to copper rail added in 9 above; SR +Ve output; SR +ve feedback sense; SR 0v feedback sense - a five wire bundle for each SR board.
14 Refit the trial SR assembly in its final position and measure up for a neat harness from each board to the pins it will serve; add 3mm each end for soldering allowance. Pick some coloured wires, make up two bundles of 5 wires. Use heatshrink to bind together and/or heat and set at any bends required.
15 Dissemble the SRs from the copperclad and solder-up the SR ends of the wiring harness.
16 Check you got all the colours where you really wanted them!
17 Finally-assemble the Super reg boards to the copperclad using thermal washers and isolators on the screws. Check isolation is maintained between regs with a multimeter on the tabs of the LM317s, and to the copperclad itself.
18 FIx the SR assembly in place using the corner motherboard screw (CD3.5)
19 Solder the free ends of the wiring harness where they belong. Raw dc in (from copper pin at former LM317 Vin to Vin on SR board; SR +Ve and +Ve feedback-sense wires to output to former LM317 Vout copper pin; all 0v and 0v sense wires commoned together at the new copper 0v rail. Here is a closeup 'after' photo of these connections (73KB).
20 Have a coffee, check your wiring later.
21 Refit the link plug, power up the player and check +ve output from SR boards on the motherboard is what you expected. Remove power and refit top case.
Now, set the player up, plug in and enjoy!
The superregged CD3.5 here has been running faultlessly since the start of January; on the link plug alone it stomps a standard CD3.5 with Hicap...its a completely different animal.
© the twisted pair 2003