CurtZHP
Well-known member
It's been a very slow, uneventful week at work. You know what they say: "Idle hands are the devil's workshop." So, here I am!
I found a fistful of Analog Devices SSM2015 chips. Apparently, these were pretty popular preamp chips in their day. I started kicking around building something around a couple of them. Then I started looking at currently available devices, like the THAT 1512. I guess my last two projects left me kind of "tubed out," so I'm leaning toward building something solid state this time around.
Most of the designs I see for these chips assume a capacitor coupled input, but what's the story with using a transformer?
So far, what I've scratched out on paper is something like this... Nothing new. Keeping it relatively simple, but leaving room for something more complicated, maybe....
Input-->(phantom power, maybe a pad)-->transformer-->solid state fixed gain stage-->(selectable HPF)-->level control-->second solid state fixed gain stage-->output transformer-->(polarity switch)-->output.
Trying to decide how much gain to have in each stage. My math could be wrong, but using an OEP input transformer like the one in the Gyraf G9, I was calculating 16dB of gain just in the transformer. The output transformer would likely cost me 6dB. So, then it would be a matter of figuring out how much gain in the active stages would get me to about 50-60dB. Or should I be looking strictly at voltage gain as opposed to dB?
What about giving the first stage selectable gain (five or six position switch), with the level control handling output level?
For about five minutes, I got really crazy and started thinking about a three band tone control and "single-knob" compressor stage before the final gain stage. (Those s.o.b.'s at THAT and their design notes!)
Please talk me out of this!
I found a fistful of Analog Devices SSM2015 chips. Apparently, these were pretty popular preamp chips in their day. I started kicking around building something around a couple of them. Then I started looking at currently available devices, like the THAT 1512. I guess my last two projects left me kind of "tubed out," so I'm leaning toward building something solid state this time around.
Most of the designs I see for these chips assume a capacitor coupled input, but what's the story with using a transformer?
So far, what I've scratched out on paper is something like this... Nothing new. Keeping it relatively simple, but leaving room for something more complicated, maybe....
Input-->(phantom power, maybe a pad)-->transformer-->solid state fixed gain stage-->(selectable HPF)-->level control-->second solid state fixed gain stage-->output transformer-->(polarity switch)-->output.
Trying to decide how much gain to have in each stage. My math could be wrong, but using an OEP input transformer like the one in the Gyraf G9, I was calculating 16dB of gain just in the transformer. The output transformer would likely cost me 6dB. So, then it would be a matter of figuring out how much gain in the active stages would get me to about 50-60dB. Or should I be looking strictly at voltage gain as opposed to dB?
What about giving the first stage selectable gain (five or six position switch), with the level control handling output level?
For about five minutes, I got really crazy and started thinking about a three band tone control and "single-knob" compressor stage before the final gain stage. (Those s.o.b.'s at THAT and their design notes!)
Please talk me out of this!