Hello Guys & Gals
I've been hanging around learning what I can, for awhile now. It's time I put my latest project out there, and get some feedback. I hope this is the right place.
Back in 93, I converted my Bogen, MX30A, into a guitar amp. Having removed 4, TM200 transformers, I thought some day I'll build a mic preamp. Last year I found a 6DJ8, and a 12AU7, in my parts supply at work. I haven't used a tube at work in 20 years, so with the manager's permission, I took them home and started to design a pre using those tubes.
My first design, was based on a Jenson schematic, with a cascode input stage. The Jenson input transformer, had a lower turns ratio than the TM200, so I thought the lower gain of the 6DJ8 would work well. The Jenson uses a 12AX7. Though the 6DJ8 was made for a cascode, I read that the cascode, worked well for RF, but not so well with audio. So I scrapped that design, and went with a simple cascade, with a gain control between gain stages. This is followed by a parallel cathode follower.
Wanting bells & whistles, I came up with way to switch input impedance. By changing the size of the grid leak resistor, It will change the reflected Z, plus it can be used with the Hi Z input when used as a DI.
I will be back with channel 2, it is completely different than CH1. After all variety is the spice of life.
Let me know if anything looks off, or if I'm just crazy(not that my wife needs confirmation).
I've been hanging around learning what I can, for awhile now. It's time I put my latest project out there, and get some feedback. I hope this is the right place.
Back in 93, I converted my Bogen, MX30A, into a guitar amp. Having removed 4, TM200 transformers, I thought some day I'll build a mic preamp. Last year I found a 6DJ8, and a 12AU7, in my parts supply at work. I haven't used a tube at work in 20 years, so with the manager's permission, I took them home and started to design a pre using those tubes.
My first design, was based on a Jenson schematic, with a cascode input stage. The Jenson input transformer, had a lower turns ratio than the TM200, so I thought the lower gain of the 6DJ8 would work well. The Jenson uses a 12AX7. Though the 6DJ8 was made for a cascode, I read that the cascode, worked well for RF, but not so well with audio. So I scrapped that design, and went with a simple cascade, with a gain control between gain stages. This is followed by a parallel cathode follower.
Wanting bells & whistles, I came up with way to switch input impedance. By changing the size of the grid leak resistor, It will change the reflected Z, plus it can be used with the Hi Z input when used as a DI.
I will be back with channel 2, it is completely different than CH1. After all variety is the spice of life.
Let me know if anything looks off, or if I'm just crazy(not that my wife needs confirmation).