If your preamp can tolerate say 20 mV DC (mine easily can), then bypass (pull signal from in front of) the coupling cap after the op-amp, usually a 47 ♟ or larger. In many cases, you'll find a very small DC offset out of the op-amp. Note that you really need a schematic to find these easily. Replace these with either Black Gate N or NX, NH non-polar electrolytics (Michael Percy) for large sizes (47 ♟) and/or use polypropylene caps such as Hovland, Auricap, or Solen (less expensive) for 1-10 ♟ values. Coupling cap mods - Many small electrolytic caps are in the audio signal path. Add local decoupling caps to gnd on +/- rails (many tuner have no decoupling at all).ĥ. Op-amp mods - Typical stuff, replace stock op-amp with new high performance unit (i.e., BB OPA2604, OPA2132, etc.) Gold plated socket allows swapping. Note: you lose muting, but it's worth it.Ĥ. This change alone was responsible for a huge increase in resolution in the mid and high frequencies. This was all bypassed, and instead CAT5 teflon twisted pair (one wire grounded at one end for shield) was used to go direct from the op-amp output, through 100-ohm resistor, to the fixed RCA jacks. In the KT-7500 (described below), the audio signal went through two switches, a relay, long board traces, around the power transformer, and then to the RCA jacks. Bypass muting relays, switches, board traces, old internal wiring, etc. Audio section signal routing - Bypass the external de-emphasis switches on the back panel. AC power noise filters will also help, either internal or external.ģ. Dedicated regulators for audio/mpx sections if you are really going all out. New "low noise" diodes, with snubber circuits, bigger better electrolytic caps with smaller bypass caps. Measure AC on chassis to outlet gnd with plug oriented both ways, mark plug for lowest noise. Power supply - Raise the transformer off the chassis with rubber grommets. When reinstalling the screws, don't re-tighten them so much as to crack the circuit board - just good and firm.Ģ. Second, clean the interface with Caig DeoxIT or another commercial electrical contact cleaner. First, remove the screws and inspect the board and frame for corrosion or dirt. Loose screws can cause electrical problems in the KT-7500 and other tuners. There are four screws that clamp the circuit board to the steel frame, which holds the power transformer and more. Return ground path - On the Kenwood KT-7500, there is a way to help ensure the integrity of the return ground path. General DIY Tips | More General Tips | Denon TU-800 | Harman/Kardon Citation 18 | Kenwood 600T | Kenwood KT-615 | Kenwood KT-815 | Kenwood KT-880D | Kenwood KT-917 | Kenwood KT-1100SD | Kenwood KT-3050 | Kenwood KT-5020 | Kenwood KT-5500 | Kenwood KT-6500 | Kenwood KT-7300 | Kenwood KT-7500/7550 | Kenwood KT-8300 | Marantz ST6000 | Mitsubishi DA-F20 | Philips AH673 | Pioneer F-90 | Realistic TM-1001 | Sansui T-60 | Sansui T-80 | Sansui TU-217/317/417 | Sansui TU-517/717 | Sansui TU-719 | Sansui TU-919 | Sansui TU-9900 | Sansui TU-D-99X | Sansui TU-X701 | Sony ST-4950 | Sony ST-A6B | Yamaha T-85ġ. We started with Kenwoods and branched out from there! Granted to quote our text so long as proper credit is given.ĮBay listings that quote us incorrectly or without credit may beįor those interested in modifying tuner audio sections, this page offers a few general suggestions, followed by specific information relating to many popular vintage tuners.
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