Try putting the coax ground strait to the buss bar, at the same spot the input stage goes to the buss.
Re-connect the line you crossed out.
Cross out that little line going from the coax to the input stages cathode resistor.
Re-connect the line you crossed out.
Cross out that little line going from the coax to the input stages cathode resistor.
Or,
- disconnect the line from the coax to input stage gound.
-connect that little line strait to the ground buss
-Remove the strait line from RCA to ground buss.
- disconnect the line from the coax to input stage gound.
-connect that little line strait to the ground buss
-Remove the strait line from RCA to ground buss.
Yes!
Except, connect RCA ground to the same spot on the buss that the first stage connects to buss.
Give it a try, see how it goes.
I will try it tomorrow. Never had problems without the grid resistor, but I have a couple of yummy Dale 1K brown ones to stick there anyway. Thanks. Will let you know.
Jeb-D. said:
Jeb-D. said:
salas said:
Did that. Zzzz got worse. Grid stoppers in, too. Now it won't stop even if I pull one channel out.
Sorry to hear that. 🙁
Some other stuff you can check if your out of ideas:
-Is the coax ground of each channel grounded at the same point on the buss bar?
-Are your RCA jacks isolated from the chassis?
-Where did you ground your 120K(from the schematic) grid pull-down resistors? They weren't included on your last drawing.
-Is there any difference in noise depending upon which channel you pull out?
-Check your input resistance of each channel with a multimeter(with the amp off). It's easy to cut into the inner jacket when stripping shielded cable and not notice.
-Does the noise dissappear if you detach the input cables from the circuit?
Some other stuff you can check if your out of ideas:
-Is the coax ground of each channel grounded at the same point on the buss bar?
-Are your RCA jacks isolated from the chassis?
-Where did you ground your 120K(from the schematic) grid pull-down resistors? They weren't included on your last drawing.
-Is there any difference in noise depending upon which channel you pull out?
-Check your input resistance of each channel with a multimeter(with the amp off). It's easy to cut into the inner jacket when stripping shielded cable and not notice.
-Does the noise dissappear if you detach the input cables from the circuit?
I solved it. 😀
It dawned on me that there seems to be no flaw in the GND logic but TOO LONG an exposed return. The actual distances force that. So I used shielded cable (the core carries the GND return of the first stage, the shield is tied to it at the buss bar end only). I wanna thank all the people that followed this thread, (especially SY, arnoldc, and Jeb-D). This amp is a workhorse KT88 that sounds particularly complete, and it goes without saying that it may be freely copied by DIYers.
Regards, Salas.
It dawned on me that there seems to be no flaw in the GND logic but TOO LONG an exposed return. The actual distances force that. So I used shielded cable (the core carries the GND return of the first stage, the shield is tied to it at the buss bar end only). I wanna thank all the people that followed this thread, (especially SY, arnoldc, and Jeb-D). This amp is a workhorse KT88 that sounds particularly complete, and it goes without saying that it may be freely copied by DIYers.
Regards, Salas.
Attachments
Here is how it is finally wired. No zzz, no hum! Input stage grid stoppers are out again because there was no oscillation to fix but they cut some bass slam. With this Audio Note OPT it takes a 560pF parallel cap to the 1k feedback resistor for compensating the usual 10kHz Sq wave ringing. I had ceramics on hand, but I will look for some silver mica to affix there permanently.
Jeb-D. said:
Thanks Jeb. I post here the rest of the PSU bits (including the Giaime Ugliano's Mosfet Maida reg that I use for input and drivers). Just for completeness, since the thread dragged towards the design too. Also rearing the amp's ugly face (to catch up on Zen Mod commenting sooner or later). 😉
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