TOFT ATB MASTER SECTION MODS:
I'm getting a bit tried of reworking these, that gummy RoHS solder is a pain in the a s s. So, go for it yourselves. For the master strip do this:
Change C39/42 to a ferrite bead. Change C40/41 to 150 pf NPO or polyprop. Bypass C38, 43, C1, C2, C6, C7, C62, C61, C60, C59, C3, C4, C57, C58 with a wire. Also bypass C50, C49, C18, C17, C36 and C37.
Add a 10 pf NPO cap across R88, R101, R13, R3, R2, R113, R122. Change C10, C15 to 22pf NPO ceramic. Change C25 and 26 to Panasonic FM 1000 uf 25V.
Add 100 pf NPO ceramic cap across R144, R151, R140, R141. Change R84, R85 to 2k ohms, add a 100 pf cap across them. Change C9, C8, C5, C11, C13, C16, C34, C36 to Panasonic FM or Nichicon HE 220 uf 25 V. Bypass with Wima MKP-2 .01 uf polyprop film caps.
Add local .1 uf mono cermic caps at each opamp's power inputs to ground, that's pins 4 and 8 to ground.
Change IC1 to AD8512A. Change IC2, IC3, IC4, IC5 to LM6172IN. Change IC12, 12, 14, 16 and 11 to LME49720NA.
That will drop that THD+noise spec to .003% at +27 dbu. CCIF IMD is even lower. It loves the red zone, it won't crap out. Elevated levels help pull the signal further from the noise floor. Stereo crosstalk improved from -58 db stock to -75 to -80 db modified on a 24 channel. The 6172 output drivers easily drive 150 ohms, the stock console with 072's cannot drive a load below 2k ohms without severe THD and level loss. 600 ohm transformer gear is easily driven with the 6172's and the headphones crank too with 100 ma output current available. The low end is flat to below 2 hz so no more phase shift. The top end bandwidth was also increased while noise was lowered. Removing 20 or so electrolytic coupling caps got the fog removed.
All mods were tested and confirmed on the Audio Precision System One. It sounds better than it tests too.
Enjoy.
Jim Williams Audio Upgrades
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