Modifying the MSB Link DAC

Daniel G. Wright
July 17, 2000

MSB Link III


 + Power Distribution
   - Filter Caps
   - Diodes
   - Regulators
   - Other Caps
   - Cut Outs

 + Output Stage
   - Op-Amps
   - Resistors
   - Capacitors
   - Cut Outs
   - RFI Control

 + Summary
    

 Power Distribution
   

Filter Caps

The main filter caps, 3300uf - 25V, can be replaced with higher quality Nichicon Muse or Panasonic HFQ or FAs. The new caps may be too large to fit in the case vertically, so you may have to lay them down.

The ceramic bypass caps for the main filter caps can be replaced with Relcap 0.1uf styrene film caps. You will have to drill two more holes to install the ground leads. The holes for the ceramic caps are about 1/8'' apart, while the new caps are about 3/4'' long. To avoid very long lead lengths, extra holes were added and the lacquer mask scraped off to make a small solder pad. You may look for Panasonic poly caps that might be similar in size to the ceramics to avoid this. Either way, ceramic caps have no business in the analog portions of the circuit. You can probably leave the digital bypass ceramic caps alone because the are good in digital circuits.

Diodes

Replace the three diodes next to the ceramic bypasses for analog L/R and digital (3 total) with Harris FREDs. You will have to bend the legs of the FREDs to make them fit, or possibly extend the leads with a bit of wire to make it work.

Regulators

The voltage regulators can be replaced with +/-15V versions. If you are using the stock power supply, you might want to limit yourself to the +/-12V regulators. Either way, these are a bugger to get out. Use desoldering wick and be patient. You might need to wick from both sides of the joints as the board is double sided.

Other Caps

You may also want to replace the 100uf caps on the analog side of the board with Elna Cerafines, Panasonic FAs, or Panasonic HFQs. The 10uf - 16V NP caps on the analog side of the board can be replaced with Black Gate NP electrolytics.

Cut Outs

Remove the three fuses, mustard yellow things that look like ceramic caps at the power input. Replace them with jumpers. I believe this fuse protection is redundant since the power supply is fuse protected. Don't take this for gospel, but I felt that they were not necessary and was told that they mess up the sound. You can use your own judgement here.


 Output Stage
   

Op-Amps

The stock Motorola op-amps can be replaced with AD827 dual op-amps. You can find these in Michael Percy's catalog for $9.50 each (ouch! - they are worth it).

Resistors

Resistors R19 and R22 are very critical. Instructions are given here for one op-amp section, but they are laid out identically, so you can figure out the other side. Verify with your multimeter if you have any doubts. R19 is 100ohm, replace it with a 75ohm Caddock or Vishay (Caddocks are about 1/2 the price and I can't see the benefit of paying more for the Vishay's). R22 is the feedback loop (NFB) of the op-amp and affects gain at the analog outs. If you are using a passive preamp or want more gain, then you can replace R22 (20kohm stock) with a resistor up to 40kohm, preferable Caddock. I had a spare pair of 39kohm Riken Carbon film resistors left over from my Jolida mods that I used with good results. R21 (480kohm) and R23 (1kohm) are probably the next two critical path resistors that can be replaced with Caddocks. The remaining resistors can be replaced with Roedersteins: R25 (10kohm) and R26 (480kohm). You may also want to replace the 100ohm resistor at the digital input with a Caddock 75ohm resistor.

Capacitors

There are two NP electrolytic caps that can be replaced at both op-amp sections. For one side only, they are C41 (1uf - 50V) and C49 (22uf - 16V). I replaced C41 with a Black Gate NP of the same size and C49 with a Nichicon Muse NP also with the same value. This procedure should be repeated on the other op-amp section also.

Cut Outs

Remove C40 and C56. They don't benefit the sound of the unit. You can also remove the resistors at the analog output RCA's.

RFI Control

Lastly, just because I was in a tweaking groove, I took small pieces of 1/4'' wide copper tape and created copper shields on the top and sides of each IC, except for the op-amp and voltage regulators. Including the DAC chip, this is 9 or 10 IC's. Then I carefully soldered a small piece of wire (24ga individual conductors from CAT5 cable) to the top of each shield, tied and soldered them all together and soldered a small 19ga pigtail to the bundle and wrapped it around the ground screw grounding them all to the chassis ground. This is intended to capture and drain any RFI being emitted from the ICs in the unit.


 Summary
   

These steps don't all have to be completed at the same time. If you are just beginning, start with the easier steps and as you gain experience, you can move to the more difficult tweaks. As far as getting the most bang for the buck, you should focus on the FREDs, voltage regulators, op-amps, and Caddock resistors. The rest can be done at your whim. This really transforms the unit for less than $100 in parts. Enjoy.

Daniel G. Wright
dwright@internetcds.com