iampoor1
Well-known member
Recently Ive been reading alot of schematics, books, and articles to fill up all the missing gaps in my knowledge. Of course, its still like the grand canyon.
I recently came across an AD797 preamp project from http://diy-tubes.com/diy-kits/
http://diy-tubes.com/image/data/manuals/ad797-v1.0-en.pdf
I have a few questions and I would like to make sure that Im right for what (little) I already know!
R1/R2 are the phantom feed resistors. 6.8k very typical
C1/C2 are the DC/Phantom blocking capacitors. How do you calculate the value of these? I have seen 1uf, 2.2uf (like this design, 10uf, 100uf etc. I am presuming that a lower value will present less phase shift, and a smaller time constant for charging..? (Not sure if that would improve transient response? Or maybe I am totally wrong here in the first place)!
C3/C4 Provide a low impedance path to ground for high frequencies. They also create a low pass filter in conjunction with the source impedance.
R3/R4 set the input impedance and limit the open loop gain so that the preamp doesnt need a microphone attached to not oscillate?
C9-C16 are the bypass capacitors per the AD797 Datasheet
R5/R6 provide an output load in addition to what the preamp is driving. They are low to reduce noise and to allow plenty of current drive.
Now, the feedback network I dont understand. The 5k Pot R24 and R9/R7 create the feedback loop with a voltage gain of around 50 or 34db right? C5/C6 in conjunction with the feedback network set the frequency for this gain? Im not sure what C8/R10 and R8/c7 do, and why they are connected after the output resistors.
Please help me fill in the blanks. Im here to learn!!
PS: per previous recommendations...Douglas Self's small signal audio design is an amazing book!
I recently came across an AD797 preamp project from http://diy-tubes.com/diy-kits/
http://diy-tubes.com/image/data/manuals/ad797-v1.0-en.pdf
I have a few questions and I would like to make sure that Im right for what (little) I already know!
R1/R2 are the phantom feed resistors. 6.8k very typical
C1/C2 are the DC/Phantom blocking capacitors. How do you calculate the value of these? I have seen 1uf, 2.2uf (like this design, 10uf, 100uf etc. I am presuming that a lower value will present less phase shift, and a smaller time constant for charging..? (Not sure if that would improve transient response? Or maybe I am totally wrong here in the first place)!
C3/C4 Provide a low impedance path to ground for high frequencies. They also create a low pass filter in conjunction with the source impedance.
R3/R4 set the input impedance and limit the open loop gain so that the preamp doesnt need a microphone attached to not oscillate?
C9-C16 are the bypass capacitors per the AD797 Datasheet
R5/R6 provide an output load in addition to what the preamp is driving. They are low to reduce noise and to allow plenty of current drive.
Now, the feedback network I dont understand. The 5k Pot R24 and R9/R7 create the feedback loop with a voltage gain of around 50 or 34db right? C5/C6 in conjunction with the feedback network set the frequency for this gain? Im not sure what C8/R10 and R8/c7 do, and why they are connected after the output resistors.
Please help me fill in the blanks. Im here to learn!!
PS: per previous recommendations...Douglas Self's small signal audio design is an amazing book!