BrentSP
Active member
I've had it for about a week and a half and have to say my impressions are that its the best XTC of the XTC lines. Mine is the metal grill and looks dead sexy with the gold faceplate. I went back and forth on EL34 and 6L6s. EL34s have never disappointed so went that route and glad I did. I pulled the chassis of course to see what was going on under the hood and how it compares to the other XTCs
Clean channel: Its been changed a little but not much. Its probably my favorite clean of the XTCs. It’s closer to the shiva Clean channel now (not exact) but with a gain control and 3 band EQ and the bright switch has a different value from the shiva. Great headroom with great break up when cranked. Boost is a little better and is a bit more of a gain/grit boost than a volume depending on how you have the controls set. Really nice sounding.
Plexi mode: Wow, very nice Reinhold. Still not near as good as Friedman's Smallbox plexi channel but its vastly improved. More gain and boost is now functional. Still very dark for a plexi even with the B2 on but again still an improvement.
Blue channel: Was a bit shocked that this channel was designed with less gain on tap compared to the 101B but in return you get a very open, vibrant, chewy crunch with a boost to get it up into JCM800 plus. I really like what was done, just wish it had a tad more gain available. Anything above 3:00 on the gain becomes bloated and boomy. I don't like that, the 101B isn't that way but the Classic was also.
Red Channel: Huge improvement over both 101B and Classic. The classic while such a nice sounding amp, the red channel gave me fits because of the amount of low end in that channel that is difficult to dial out without effecting blue. Its just right for the blue but too much for the red.......with shared tone controls. The 101B has a nice red channel if its pre-2004 but can get a little congested at times also. 20th Red is clear, crisp, fat, searing with a chewy middle and tight bass. With B2, M mode, I have to keep the gain at 11:00 or else its too much. With B1 I can raise it to noon or so. There's a crap load of gain on this channel but can be tamed by going to V mode on the structure, which is closer to the 101b. It can be aggressive and rude or soft and polite. Has much more gain available compared to Friedman HBE (without SAT or C45).
Here's a quick explanation of how cathode resistors and caps work in a tube amp. The resistor dams up the gain flowing through the signal path, lower the number/value (ex. 2.7k) the more gain passes through. Higher the number/value (ex. 10k) the less gain passes through. The value cap chosen will boost certain frequencies. A big cap like a 250uf would boost high and low frequencies. A 1uf cap would boost only mid to high frequencies filtering out the low end. So with that said....every gain stage has a bypass cap boosting frequencies (if in M mode) and gain unlike the other XTCs. For you that are in the know of the R12 mod. The 101B and Classic R12 via the red channel cathode has a single 10k, no bypass cap..........the Post 2004 has a .47uf and 2.7k in series, paralleled to the 10k on the board. The 20th replaces the 10k entirely in favor of a 2.7k and bypasses it with a .47uf boosting a crap ton of hi mid and high frequencies. Also on both the 101 and classic the last gain stage is a 1k resistor with no bypass cap. On the 20th that is vintage mode on the structure. When switched to Modern mode it engages a 1uF (SLO/Cameron) bypass cap again boosting gain but in the more thicker mid range frequencies.
The excursion or resonance switch is redone with different values. 101B and Classic has a 470p boosting low mids with L and M giving you different variation of how much boost and T with no boost. The 20th is a little different. It has two choices of frequencies to boost with T being no boost. M is .0047uf like Soldano, Friedman, Cameron (I've seen Cameron using a .0022uf also). Boosting the low end. The L is something I haven't seen before. Its value cap is .01uf which is boosting the really low frequencies. The result is a massive subsonic almost 3D undertone. I like it. But with that said I tend to use M more than anything. Still a nice touch.
The coupling caps in between the stages (particularly the 1st stage) are bigger (.01uf 20th compared to .0047uf 101B and .0022uf Classic) allowing more bass to travel through the preamp (still not as big as JCM800 .022uf coupling caps) but is counter acted sorta speak with more high end, openness through out the preamp. To big of a cap with more bass can sometimes result in boomy congested tone. He has it dialed in right. One thing left untouched on the XTC line is the 1st gain stage (cathode, plate, grid) of the lead channels. Its the signature tone of the XTC and if changed wouldn't sound like an XTC. It's reminisce of the 67/68 plexi first stage where its pushing a lot of gain in its first stage compressing the signal.
Power amp is borrowed from the Classic 50/50uf filtering which is classic late 60s to 80s Marshall.
Damn good amp. Would I personally change anything on it. Yeah possibly. A little more gain on the blue and a little less gain on the red but that's about it. Its near perfect the way it is and I can certainly live with it.
XTC 20th using a 412 Greenback loaded cab via UA Ox.
Leads were with a Friedman BE100.
Guitars were both Charvel SoCal w/ Duncan distortion and ProMod w/ Duncan JB.
https://soundcloud.com/brentsp/ua-ox
Clean channel: Its been changed a little but not much. Its probably my favorite clean of the XTCs. It’s closer to the shiva Clean channel now (not exact) but with a gain control and 3 band EQ and the bright switch has a different value from the shiva. Great headroom with great break up when cranked. Boost is a little better and is a bit more of a gain/grit boost than a volume depending on how you have the controls set. Really nice sounding.
Plexi mode: Wow, very nice Reinhold. Still not near as good as Friedman's Smallbox plexi channel but its vastly improved. More gain and boost is now functional. Still very dark for a plexi even with the B2 on but again still an improvement.
Blue channel: Was a bit shocked that this channel was designed with less gain on tap compared to the 101B but in return you get a very open, vibrant, chewy crunch with a boost to get it up into JCM800 plus. I really like what was done, just wish it had a tad more gain available. Anything above 3:00 on the gain becomes bloated and boomy. I don't like that, the 101B isn't that way but the Classic was also.
Red Channel: Huge improvement over both 101B and Classic. The classic while such a nice sounding amp, the red channel gave me fits because of the amount of low end in that channel that is difficult to dial out without effecting blue. Its just right for the blue but too much for the red.......with shared tone controls. The 101B has a nice red channel if its pre-2004 but can get a little congested at times also. 20th Red is clear, crisp, fat, searing with a chewy middle and tight bass. With B2, M mode, I have to keep the gain at 11:00 or else its too much. With B1 I can raise it to noon or so. There's a crap load of gain on this channel but can be tamed by going to V mode on the structure, which is closer to the 101b. It can be aggressive and rude or soft and polite. Has much more gain available compared to Friedman HBE (without SAT or C45).
Here's a quick explanation of how cathode resistors and caps work in a tube amp. The resistor dams up the gain flowing through the signal path, lower the number/value (ex. 2.7k) the more gain passes through. Higher the number/value (ex. 10k) the less gain passes through. The value cap chosen will boost certain frequencies. A big cap like a 250uf would boost high and low frequencies. A 1uf cap would boost only mid to high frequencies filtering out the low end. So with that said....every gain stage has a bypass cap boosting frequencies (if in M mode) and gain unlike the other XTCs. For you that are in the know of the R12 mod. The 101B and Classic R12 via the red channel cathode has a single 10k, no bypass cap..........the Post 2004 has a .47uf and 2.7k in series, paralleled to the 10k on the board. The 20th replaces the 10k entirely in favor of a 2.7k and bypasses it with a .47uf boosting a crap ton of hi mid and high frequencies. Also on both the 101 and classic the last gain stage is a 1k resistor with no bypass cap. On the 20th that is vintage mode on the structure. When switched to Modern mode it engages a 1uF (SLO/Cameron) bypass cap again boosting gain but in the more thicker mid range frequencies.
The excursion or resonance switch is redone with different values. 101B and Classic has a 470p boosting low mids with L and M giving you different variation of how much boost and T with no boost. The 20th is a little different. It has two choices of frequencies to boost with T being no boost. M is .0047uf like Soldano, Friedman, Cameron (I've seen Cameron using a .0022uf also). Boosting the low end. The L is something I haven't seen before. Its value cap is .01uf which is boosting the really low frequencies. The result is a massive subsonic almost 3D undertone. I like it. But with that said I tend to use M more than anything. Still a nice touch.
The coupling caps in between the stages (particularly the 1st stage) are bigger (.01uf 20th compared to .0047uf 101B and .0022uf Classic) allowing more bass to travel through the preamp (still not as big as JCM800 .022uf coupling caps) but is counter acted sorta speak with more high end, openness through out the preamp. To big of a cap with more bass can sometimes result in boomy congested tone. He has it dialed in right. One thing left untouched on the XTC line is the 1st gain stage (cathode, plate, grid) of the lead channels. Its the signature tone of the XTC and if changed wouldn't sound like an XTC. It's reminisce of the 67/68 plexi first stage where its pushing a lot of gain in its first stage compressing the signal.
Power amp is borrowed from the Classic 50/50uf filtering which is classic late 60s to 80s Marshall.
Damn good amp. Would I personally change anything on it. Yeah possibly. A little more gain on the blue and a little less gain on the red but that's about it. Its near perfect the way it is and I can certainly live with it.
XTC 20th using a 412 Greenback loaded cab via UA Ox.
Leads were with a Friedman BE100.
Guitars were both Charvel SoCal w/ Duncan distortion and ProMod w/ Duncan JB.
https://soundcloud.com/brentsp/ua-ox