I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
NFB is kinda bad for the distortion we prefer, but it's good for some issues.
Moderators: JMPGuitars, Daviedawg, Graydon, CurtissRobin, colossal, zaphod_phil
I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
Ok here is with the PI 12at7I said to switch to 12AT7 for a reason. Try it out and see what happens. If not better, raise the plate voltages.
NFB is kinda bad for the distortion we prefer, but it's good for some issues.
There is already 100pf theregeoff 1965 wrote: ↑Sat 01/09/21 7:41 amhave you tried a 47 or 100pf snubber across the phase plates?
Set up the PI so the voltages are on target to what I sent you with the 12AT7. You will need to lower your tail resistor, try 22K. This won't likely fix the problem, but it will be setup well for when the problem is resolved.
I have news. I put the signal from point x into the poweramp of the modern classic. Guess what? Fizz.JMPGuitars wrote: ↑Sat 01/09/21 8:52 amSet up the PI so the voltages are on target to what I sent you with the 12AT7. You will need to lower your tail resistor, try 22K. This won't likely fix the problem, but it will be setup well for when the problem is resolved.
Considering everything we've tried, it's likely the fault lies within the tubes or the OT. Either way, you should still try the snubber circuit. At this point I'm leaning towards a defective OT.
Thanks,
Josh
Are the preamp tubes new? Post some photos of your build.
Personally.. with these values now it's no more fizzy than my modern classic. It's also much more gainy. I'm going to try the CR on V1 like you proposed. Put 22k on the PI plates? Should I up the cathode resistors to lower the cathode voltages? Like 470K perhaps?JMPGuitars wrote: ↑Sat 01/09/21 9:24 amAre the preamp tubes new? Post some photos of your build.
Try adding a bypass cap to R3. .68µF to 2.2µF. You can also try increasing that resistor value to between 1.5K and 2.2K.
Did the changes.. but I can't test on volume because my daughter is asleep..JMPGuitars wrote: ↑Sat 01/09/21 10:32 am
No, 22K TAIL resistor. 470 ohm (not K) cathode resistor.
PI change:
PI-Tail.jpg
Preamp change:
V1-Input.jpg
Don't make any more changes until you listen to it at volume.
Played it. Sounds pretty fine that way. Fizz, but yeah...JMPGuitars wrote: ↑Sat 01/09/21 5:37 pmDon't make any more changes until you listen to it at volume.