J
jamme61
Member
I have 2012 xtc 101b I'm new to this amp but I love the stk Red channel sound
Setneck
Member
Before modding my amp I also liked Red Channel without post2004 gain mod, with bare 10k in 3rd stage cathode. But now I need to boost the overall gain a little, as I lowered the bias - therefore the gain - in 1st and 2nd stage. But still "Factory" mod is too much, especially as far as compression is concerned. So tweaked Cameron voicing, with .68uF cap instead od 1uF, is that amount of boost that is adequate.
That tweak was once invented by Brent, a moderator of old Bogner forum. He called it "Uber mod", as it sounded "Uberschall-ish" for him
. More about it here: http://bognerampforum.informe.com/red-c ... dt967.html.
As for the 20th Ann.
First of all, 1st and 3rd coupling caps (C1 & C14) values has been changed to 10nF (101B - 4.7nF) and to 2.2nF (101B - 22nF). By doing that the lows are coming earlier into the circuit (more nF's in CC - more bass going thru) and are being cut out after the last gain stage.
2nd stage's grid stopper was increased from 500K to 1M and added 330K voltage divider resistor before that, with added 2nF cap before 1M grid stopper. 101B has here 499K grid stopper resistor bypassed by 470pF cap (R112//C112), which is basically a regular treble-peaker like in 1959/2203.
Also 470pF bypass cap from 3rd stage's 500k grid stopper has been removed - less bass going thru.
The 2nd cathode was changed from 4.75K to 2.7K and is bypassed by 1.5uF tantalum cap, like in Classic. Structure circuit was removed.
Bogner also removed cold gain stage, changing 3rd stage's cathode from 10K to 2.7K, bypassing it also with .47uF electrolytic cap (sort of SIR '39 mod).
4th cathode 1K is now bypassed with switchable 1uF marked Vintage/Modern (the switched is placed where Structure switch in 101B is)
Plexi Mode values has been changed from 499K//470pF to 2.2M//100pF
B1 & B2 was reworked from 470pF|4.7nF to 150pF|1nF
Big part in overall 20th Ann to is Classic filtering and Sozo & Mojo Dijon tone caps. They are film-to-foil polyester caps, opposite to 101B's Wima FKP polypropylene caps. That make the distortion smoother and more middy.
Regards, Andy
That tweak was once invented by Brent, a moderator of old Bogner forum. He called it "Uber mod", as it sounded "Uberschall-ish" for him
. More about it here: http://bognerampforum.informe.com/red-c ... dt967.html.As for the 20th Ann.
First of all, 1st and 3rd coupling caps (C1 & C14) values has been changed to 10nF (101B - 4.7nF) and to 2.2nF (101B - 22nF). By doing that the lows are coming earlier into the circuit (more nF's in CC - more bass going thru) and are being cut out after the last gain stage.
2nd stage's grid stopper was increased from 500K to 1M and added 330K voltage divider resistor before that, with added 2nF cap before 1M grid stopper. 101B has here 499K grid stopper resistor bypassed by 470pF cap (R112//C112), which is basically a regular treble-peaker like in 1959/2203.
Also 470pF bypass cap from 3rd stage's 500k grid stopper has been removed - less bass going thru.
The 2nd cathode was changed from 4.75K to 2.7K and is bypassed by 1.5uF tantalum cap, like in Classic. Structure circuit was removed.
Bogner also removed cold gain stage, changing 3rd stage's cathode from 10K to 2.7K, bypassing it also with .47uF electrolytic cap (sort of SIR '39 mod).
4th cathode 1K is now bypassed with switchable 1uF marked Vintage/Modern (the switched is placed where Structure switch in 101B is)
Plexi Mode values has been changed from 499K//470pF to 2.2M//100pF
B1 & B2 was reworked from 470pF|4.7nF to 150pF|1nF
Big part in overall 20th Ann to is Classic filtering and Sozo & Mojo Dijon tone caps. They are film-to-foil polyester caps, opposite to 101B's Wima FKP polypropylene caps. That make the distortion smoother and more middy.
Regards, Andy
J
jamme61
Member
Great info thanks 
Setneck
Member
Mojo caps really made my tone. It is definitely more crunchy and smooth now, less "hi-fi".jamme61":2uegs9pb said:
IMO not possible without cutting the traces on pcb to separate it off the Structure circuit.jamme61":2uegs9pb said:
Regards, Andy
Setneck
Member
Keep trying and feel free to ask any questionsjamme61":b5o0a0tk said:
To me it totally kills poweramp's clarity and dynamics. The amp's response becomes totally sluggish. I have it on switch now and can compare the tone with and without the cap. The difference is like night and day. The switch is still there only because I had to drill a hole for itjamme61":b5o0a0tk said:
.That cap alongside audio dirty treble pot is mainly responsible for famous "blanket effect". It is completely gone in my amp after deleting the cap and replacing treble pot with linear one.
Regards, Andy
J
jamme61
Member
did you take out the whole board?
Setneck
Member
Yes, You got to raise the board to replace the pot. It isn't tough operation and it is really worth doing that. The amp responses much much faster.
To do so You got to remove preamp tubes, then remove knobs, unscrew the pots, then unscrew the pcb, disconnect loop wire and desolder wires that link powerboard with main pcb. Then You got to raise the pcb the way where the pots are pointing down to the chassis and the inner (back) side of pcb is raised. You will have it angled and there will be space to desolder the pot and replace it with linear one.
Tried to make it as clear as possible. Unfortunately have no pics of that but You could make it quite easy, as that is the only way to lift the pcb without trying to remove it off the chassis completely.
Regards, Andy
To do so You got to remove preamp tubes, then remove knobs, unscrew the pots, then unscrew the pcb, disconnect loop wire and desolder wires that link powerboard with main pcb. Then You got to raise the pcb the way where the pots are pointing down to the chassis and the inner (back) side of pcb is raised. You will have it angled and there will be space to desolder the pot and replace it with linear one.
Tried to make it as clear as possible
. Unfortunately have no pics of that but You could make it quite easy, as that is the only way to lift the pcb without trying to remove it off the chassis completely.Regards, Andy
Setneck
Member
Did the same once but that's one of the mods that was reversed. The amp was prone to go squealing very fast. I was hitting the chord and instead of sounding it was turning into squeal very quickly. Went back to 1000pf and the problem was gone.jamme61":zllipqbw said:
But that symptom was caused by other mods, which made my amp brighter (22nF PI output caps, 2.2nF 1st CC cap, raised cathode resistors in 1st & 2nd gain stage, custom Mercury Magnetics OT). In Your amp 500pf 2nd stage snubber should still prevent oscillations.
Regards,m Andy