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Started by Tehu, January 25, 2016, 07:18:15 AM
Quote from: Tehu on January 25, 2016, 07:18:15 AMThis weed-end
QuoteHas anyone back engineered this "rhodie preamp"? Or are there schematics somewhere? All the components are painted black.
Quote from: sean on January 26, 2017, 12:44:59 PMhttp://www.potentiometers.com/select_Bourns.cfmhttp://www.mouser.com/Bourns/Are there any markings on the pots installed on the preamp?R.A. Gresco is probably still alive. Anybody in California know what he is up to now?
Quote from: sean on March 27, 2017, 02:40:02 PMVery nice job, Janne!It appears to be based on the tone control circuit designed by P.J. Baxandall and published in 1952 (originally with tubes).See http://www.learnabout-electronics.org/Downloads/NegativeFeedbackTone.pdf if you want to start with the original history. TI has a good application note showing how to build it with their op amps http://www.ti.com/lit/an/sloa042/sloa042.pdf.There is also a good writeup about using the circuit in a passive network with no amplification at http://makearadio.com/tech/tone.htm.You lose 20dB of signal passing through the Baxandall network, so you need the op amps to make up that signal loss.I will build it on a breadboard, and see how I like the sound and the crossover point.Your schematic shows really small values for C7 and C2, but your board layout drawing shows very reasonable 10uF value for C2. Is that just a typo on the schematic? Also, the 50K volume control should be an audio-taper potentiometer. (The bass and treble pots in the feedback network can be linear.)Sean
Quote from: DynoCzarus Rex on April 13, 2017, 01:32:52 PMI happen to have a Rhodie preamp as well that I plan to have installed in my '78 suitcase Rhodes at some point as the primary EQ circuit. Have never been very satisfied with the Janus EQ. Does the attached schematic have mods done to the original Rhodie preamp and is this frequency response the one of the modified Rhodie? Or is this an original Rhodie with no mods? I'm a little confused.
Quote from: sean on April 21, 2017, 04:03:04 PMWell, we can't yet confirm the component values in the original Rhodie preamp with 100% certainty.
Quote from: JanneI on March 27, 2017, 11:46:56 AMHere's my unverified veroboard layout. I figured that since I don't have much time I could just share this if someone likes to try it out. A wise move would be draw a pcb with 9mm alpha pots with same mounting holes as in mk1 panel.. Maybe I'll do it someday