I've been playing with a TC-750 preamp.
I found this guide on modding it: https://www.superbestaudiofriends.org/index.php?threads/tc-750-phono-pre-amp-continued.150/
I've removed the 220pf input caps (circled in green in my included schematic), as I don't need any additional capacitance, I rely on whatever is provided by my cabling. I do have a couple of test records with pink noise, and I can confirm my response is very flat (+/- 1db) out to the limits of the album and my ADC (typically 20k).
In one of the comments, someone mentioned they removed the 1k input resistors (circled in red). I had tried this but thought I was getting more noise. As it turns out, my noise may have been induced by power/cabling issues. But, I did put them back in.
My Q before I try removing them again is, does anyone know what function they may provide, and whether removing them is indeed something that may reduce noise?
TIA for any help.
I found this guide on modding it: https://www.superbestaudiofriends.org/index.php?threads/tc-750-phono-pre-amp-continued.150/
I've removed the 220pf input caps (circled in green in my included schematic), as I don't need any additional capacitance, I rely on whatever is provided by my cabling. I do have a couple of test records with pink noise, and I can confirm my response is very flat (+/- 1db) out to the limits of the album and my ADC (typically 20k).
In one of the comments, someone mentioned they removed the 1k input resistors (circled in red). I had tried this but thought I was getting more noise. As it turns out, my noise may have been induced by power/cabling issues. But, I did put them back in.
My Q before I try removing them again is, does anyone know what function they may provide, and whether removing them is indeed something that may reduce noise?
TIA for any help.
I did not know Beavis drew hi-fi.
NOTE that C7 and R9 are on there TWICE. It may work but is probably an error.
Follow the bias path. From C2 E it runs to C7, then R7 to C2, then out to the cartridge. Two low-pass filters inside a NFB loop is marginally stable. Especially at high gain. Which is what we need here. The typical symptom is a huge subsonic peak, like 13dB at 0.5Hz. Which reacts badly with LP warp.
R1 damps the resonance some. Damping is also provided by cart resistance and general gain. I have used 4.7k there to soothe an unhappy preamp. (I have also tried insane values for C7, also series resistors there, without conclusion, ended up at 2*6,800uFd.)
NOTE that C7 and R9 are on there TWICE. It may work but is probably an error.
Follow the bias path. From C2 E it runs to C7, then R7 to C2, then out to the cartridge. Two low-pass filters inside a NFB loop is marginally stable. Especially at high gain. Which is what we need here. The typical symptom is a huge subsonic peak, like 13dB at 0.5Hz. Which reacts badly with LP warp.
R1 damps the resonance some. Damping is also provided by cart resistance and general gain. I have used 4.7k there to soothe an unhappy preamp. (I have also tried insane values for C7, also series resistors there, without conclusion, ended up at 2*6,800uFd.)