WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
It's been a while since I posted my progress. I got going with LTspice thanks to PotentiallyIncorrect. I played around with the circuit in LTSpice and the actual build. I can't get to sound right where the sound is very bright with almost no bass as well.
This is not my first try to build a tube tape head preamp. I also build another schematic from the net that was designed by Mikkel Simonsen. Even though it sounds much much better than the Tandberg 64x circuit, it's still not comparable in FR with the build in the reel to reel's SS eq. So I build this schematic in LTspice in order to compare the FR between the 2 circuits. I have attached both circuits and their respective FR's. To me, both curves are vary comparable with each other with Mikkel's circuit producing about 2db less, but otherwise very similar within 1 or so db. But the actual sound difference is huge.
This led me to believe that the tape head impedance plays a huge role on how these preamps are built. I knew it plays a role but I thought it would be minimal like comparing hifi to audiofile differences. I could live with hifi if these 2 builds provided sound close to the internal ss eq. These 2 builds have been tested with the playback head of a Tandberg 10xd and Tandberg TD20A. Both heads also sound and measure quite differently from each other with the same build.
Going forward, I don't have the necessary skills to tweak these circuits to be compatible with and possibly compensate for the tape heads, unless it's something relatively easy that you guys can suggest to try. I know that some universal phono stages out there that are tube based like Tavish Design and others have switched input resistors and caps to accommodate different phono cartridges. Is a MM and MC cartridge that much different than a tape head? Can I use a similar approach or the whole circuit would have to be adjusted?