In Reply to: You're welcome posted by Ralph on August 10, 2017 at 11:20:51:
"Its a big deal getting rid of that output coupling cap!"
We're definitely on the same page on that point. I'm expecting this to provide an output Z of a few hundred ohms, and there won't be any phase shift or coloration from a large series cap.
About the opamp, I already have a few OPA445s on hand for this project. This device is rated to +/-45V, and that's what I need to handle the bias voltage directly. The followers will be 5686s in pseudo-triode. With this tube, the DCR of the cathode choke (~2,200 ohms) dictates a negative supply of roughly 24-28V at the bottom of the choke. With the cathode at zero, that will produce about ~12mA current into the cathode. To keep the cathode at zero, I'll need about -18V to -20V on the grid. So, I believe the simplest plan will be a +/-28V supply using a LM317/LM337 pair. That will provide the negative voltage for the tube, as well as powering all the active components and the output relays. Now, if I can just find time to start on the chassis...
Buy Chinese. Bury freedom.This post is made possible by the generous support of people like you and our sponsors:
Topic - Eliminating the Line Stage Output Cap - Triode_Kingdom 19:44:53 08/07/17 (12)
- RE: Eliminating the Line Stage Output Cap - hennfarm 13:47:37 08/09/17 (0)
- Servo Amp Isolation - Triode_Kingdom 13:19:34 08/09/17 (0)
- This is similar to the old Berning TF-10 - Ralph 10:47:46 08/08/17 (5)
- RE: This is similar to the old Berning TF-10 - Triode_Kingdom 12:12:58 08/08/17 (4)
- RE: Eliminating the Line Stage Output Cap - Caucasian Blackplate 09:20:03 08/08/17 (2)
- RE: Eliminating the Line Stage Output Cap - Triode_Kingdom 13:15:01 08/08/17 (1)
- RE: Eliminating the Line Stage Output Cap - used-hifi 13:40:38 08/08/17 (0)
- RE: Eliminating the Line Stage Output Cap - PakProtector 09:06:59 08/08/17 (0)
- RE: You're welcome - Triode_Kingdom 13:53:09 08/10/17 (0)