Hello
Wondering how Roger did his switching and avoided input to input cross talk.
I have been working on a home built preamp project for quite a while Curcio Daniel, circa 1985.
Trying to duplicate the RM5 input and tape out switching, I am using my RM5 as a benchmark.
I am using two rack chassis, power supply and preamp.
Even built a mute curcuit similar to Rogers and even went as fas as a custom 3 lead led that changes from red to green with in/out of mute using Rogers mute curcuit.
Went with the same off/on/play idea as in the RM5, except in my version "on" switches a solid state relay that turns on the fillament/B+ transformer.
I get input to input low level crosstalk. for example I can hear the tuner when switched to tape 1.
Alot of preamps just short the other inputs totally eliminating the input to input interference, but in the RM5 this is not done,
since the RM5 also has a selectable tape output.
I have tried different switches, grayhill and shallcross. tried alternating wafers for each input, tried switching signal and earth ( 2 wafers for each channel)seperated signal carrying wiring, the cross talk seems to be happening at the switch.
I have tried coax and twisted pair for wiring from the input jacks to switches, just cant seem to hit the RM5 benchmark.
If I eliminate the tape out switching, and just use a switch that shorts all unused inputs all is fine.
I have built many amplifier's over the years, but the preamp has to be the toughest, I have worked out the grounding so there is no hum, no switching noise, just that input to input cross talk.
My RM5 is totally quiet input to input, how did Roger do it ????
Comments ?
bob
