So after a long period of no changes, following the removal of the dreaded muting transistors. I've had a long hard look at the curcuit and though quite complexed each incoming signal is buffer[?] via two sets of opa275 arround the switching section to feed to the eq section then to another opa275 and the chip vol pot then either to the bus [balanced output] or the phono sockets ... there suprisingly little in the way of descrete components in the signal path ....a couple of caps and a few resistors [more of which later] So having just recieved some samples opamps from TI I thought lets drop one in to see how they sound. First I remove the opa275 [the third one before the vol pot, ic50] and fitted a top notch socket. Dropped in the new opamp [opa2107] reassembled... sound before was ok but would never win any prizes a bit dull and undemanding slightly slow ? Well the new opamp is fast and lively better seperation[imaging] dynamics in spades [bringing it up to normal levels ?]... the units been on for half a cd and is still getting sweater ...... So what next ...... I don't feel inclined to drop all the opamps [20 ish] may be I'll do the two in the switching section ..... So what else ? well the little diode bridges look an obvious candidates for a schottky bridge [made from 11dq10's]. The two blocking caps 10uf 35v in the signal path before the cs3310 vol pot are to be replaced with a pair of huge 4uf 200v pio's that have just arrived ....if they will fit in the case. These are the size of a 4 stacked cream crackers as an a side a pair of these where shoehorned into the output of a entech 203 and have just turned a into a stonkingly good sounding dac. Its odd this dac was not fitted with dc blockers ? I also fitted shottky diodes and a dale vishay resistors too and a full suite of bypass caps to muse electrolytics. Sound before was ok a bit edgy and lacking in life, following the mods was smooth fluid agile. Infact better than my Quad 99cdp own dac [bugger]
