Adding Rolloff and Turnover Selections To Phono Preamp
I have an old pre-battery Radio Shack phono preamp that I decided to add different rolloff and turnover points to in order to use it as a standalone preamp for my 78 table. I know I could buy a Bugle (which I already have - not the pro - on my main table) or something else, but I'd really like for this to work since I've enjoyed trying to figure out how to make it work so far.
Which is does, actually flawlessly, using rotary switches with the different capacitor values for the different curves. Except - and this is where I'm lost - on the rolloff side, I can't get a "flat" setting. On the turnover side, I left one selection on the switch shorted and that gets me flat on the bottom end without problem. But with nothing connected on the top I get nothing, and with it shorted I get a dull, nothing above 800hz sounding signal. Everything else works as it should.
I don't have a schematic, but I'm hoping somebody here has fiddled with this unit before and can give me advice on how to get flat on the top end...I'm not sure I understand what's happening since it seems to me that shorted I should be getting what I'm after.
If any of this is too elementary go easy on me and remember I'm working on a $10 piece of equipment (which actually sounds pretty darn good.)