NAD: Bogner XTC 20th

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
 
Thanks! I owned a 20th shiva also and it’s better than the original but I’m just not a fan of Shiva’s. I’ve owned many trying to convince myself and they just don’t do it for me.
 
that's the thing with the 20th - they had to mess with the blue to change the red - they're connected, so no way around it, I guess? On the clean channel the only change i saw was the first cathode cap being a .68 - what else did you see there? also the NFB was changed a lot - its been awhile - I just didn't like what the blue channel turned into - liked the rest of the changes but you're right the Friedman plexi channel is a lot better.
 
jamme61":187hj8kh said:
that's the thing with the 20th - they had to mess with the blue to change the red - they're connected, so no way around it, I guess? On the clean channel the only change i saw was the first cathode cap being a .68 - what else did you see there? also the NFB was changed a lot - its been awhile - I just didn't like what the blue channel turned into - liked the rest of the changes but you're right the Friedman plexi channel is a lot better.

Blue/Red are connected but you can raise the gain in 1 of the 3 stages of the blue and counter act it by lower the gain in the 1 stage of the red that blue doesn't use if that makes sense.

.68uf is the 100 and Classic clean. The 20th is 1uF like the Shiva but the Shiva plate is 220k and cathode RK is 1.8k vs 100k plate 1.5k RK. 101B if I remember correctly is a 22uF like the normal black face amps.

NFB I didn't venture into that area other than the excursion values changed. What did you see that changed? 101 I believe was a 100k to the 8ohm if I remember correctly. Presences is still a 25k but kicks in highs around 1:00 which I believe is how the presence is reacting due to the new updated design.
 
jamme61":35s302rx said:
that's the thing with the 20th - they had to mess with the blue to change the red - they're connected, so no way around it, I guess? On the clean channel the only change i saw was the first cathode cap being a .68 - what else did you see there? also the NFB was changed a lot - its been awhile - I just didn't like what the blue channel turned into - liked the rest of the changes but you're right the Friedman plexi channel is a lot better.

I updated my reply.
 
Great write-up, Brent. Best I've seen.

20th Anniversary with 6L6s is the best all-around amp I've ever owned - should have never sold it to get the Helios. The clean was simply GLORIOUS.

I hear what you are saying about the Blue channel. I liked the Blue on the 6L6 version better, and the Red on the EL34 version better. The power amp filtering was an interesting choice, and wonder what it would sound like with the 101b values (more '68 rather than '69) and the 6L6s.
 
BrentSP":25kuqzfv said:
I pulled the chassis of course to see what was going on under the hood and how it compares to the other XTCs

....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.
great post!!! thanks for all the great specific info.

in my 101B i put a Structure mod switch a few years ago, inspired by Setneck's posts here about his experimentation with Structure values from the 20th Annv schematic. i forget the details but my notes say "a Structure mod switch soldered across R11, with 6k2//1.5 uF, so with Structure set to L, I can switch the mod on and have the circuit be 20th Structure 2k7//1.5 uF. And with the mod off, I can then set Structure to H and have stock 101B H." it makes my 101B sound a bit brighter and clearer and less compressed.

now your info on R12 makes me want to wire a resistor and .47 uF on R12 that turns it into the 20th 2.7k//.47uf. :)

although in the last couple years, i've been modding it to make the gain lower, like with a resistor across C224 in un-boosted mode. i can always crank the gain knob for more when i need it, but if i turn the gain down to get old AC/DC, the tone gets thin.

you say "the last gain stage is a 1k resistor with no bypass cap." do you know the resistor number on the board for that 1k? in case i ever want to fiddle with that?

thanks again for the awesome post!
 
_actual time_":2n4vj0ux said:
BrentSP":2n4vj0ux said:
I pulled the chassis of course to see what was going on under the hood and how it compares to the other XTCs

....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.
great post!!! thanks for all the great specific info.

in my 101B i put a Structure mod switch a few years ago, inspired by Setneck's posts here about his experimentation with Structure values from the 20th Annv schematic. i forget the details but my notes say "a Structure mod switch soldered across R11, with 6k2//1.5 uF, so with Structure set to L, I can switch the mod on and have the circuit be 20th Structure 2k7//1.5 uF. And with the mod off, I can then set Structure to H and have stock 101B H." it makes my 101B sound a bit brighter and clearer and less compressed.

now your info on R12 makes me want to wire a resistor and .47 uF on R12 that turns it into the 20th 2.7k//.47uf. :)

although in the last couple years, i've been modding it to make the gain lower, like with a resistor across C224 in un-boosted mode. i can always crank the gain knob for more when i need it, but if i turn the gain down to get old AC/DC, the tone gets thin.

you say "the last gain stage is a 1k resistor with no bypass cap." do you know the resistor number on the board for that 1k? in case i ever want to fiddle with that?

thanks again for the awesome post!

Thanks. R11 is a 220k to ground for the Clean channel. Structure on the 101 is R21, R24 and C23. The switch is SW11. It effects the 2nd gain stage of the lead channels. Structure on the 20th is V4 the last gain stage of the lead channels. The 2nd gain stage lead channels on the 20th is exactly like the Classic 1.5uF/2.7k.

You can try R12 with 2.7k//.47uf but it might be too much because on the 20th he's pulling back some gain early in the preamp (unlike the 101) then boosting it back up quite a bit on Red's 3rd gain stage. I did try that mod with the Classic and it was pretty good.

R33 is the 1k cathode.

Edit: Make sure and check the values with a meter to be sure because there was a board change done some time but not sure when. So my point is R33 may be something else now. Just check the values. If it reads 1k on R33 then you're good to go.
 
BrentSP":n4zq0sgv said:
Thanks. R11 is a 220k to ground for the Clean channel. Structure on the 101 is R21, R24 and C23. The switch is SW11. It effects the 2nd gain stage of the lead channels.
then mine must be the old board or something, because Setneck directed me to R11 and my R11 mod definitely changes the Structure, not the Clean channel.

BrentSP":n4zq0sgv said:
You can try R12 with 2.7k//.47uf but it might be too much because on the 20th he's pulling back some gain early in the preamp (unlike the 101) then boosting it back up quite a bit on Red's 3rd gain stage. I did try that mod with the Classic and it was pretty good.

R33 is the 1k cathode.

Edit: Make sure and check the values with a meter
all good to know. thank you!
 
Very nice commentary! I use my 20th anniv.xtc for modern country and way beyond.Lately been running it with my rev green uber.Quite a deadly combination.
 
that's the thing with the 20th - they had to mess with the blue to change the red - they're connected, so no way around it, I guess? On the clean channel the only change i saw was the first cathode cap being a .68 - what else did you see there book of ra
? also the NFB was changed a lot - its been awhile - I just didn't like what the blue channel turned into - liked the rest of the changes but you're right the Friedman plexi channel is a lot better.
 
Congratz and awesome write up!! :thumbsup: :rock:

I love both the 101B and the EL34-20th, and prefer the 20th for its subtleties. As for the commonly cited "Blue is too glib, Red is too hot" in the gain structure; one thing that became very apparent to me is volume changes everything. Sure, the Plexi sounds dark, and the Blue could use more push, and the Red has too much gain - at low volumes. But get these volume knobs pointing closer to noon and the amp takes on a totally different feel and its seamless and glorious to say the least. IMHO, YMMV.

I just found with solid SPL, the Red opened up and was amazing for all styles of heavy; and the Blue ended up getting all the grit and grind it needed to become beastly, WITH volume. Even the Plexi mode - totally became exactly what it was meant to be - at volume.

Love my 20th. Glad you're digging yours, and thanks for the technical run-down. Have you messed with the New/Old switch on the rear to change the powertubes from pentode to triode operability? There's a slight hum there, but it's primarily due to the tubes sensitivity being run in that mode; I found there was always a slight hum, minimal, tolerable - but as my tubes got more worked over, the hum increased in its noticeability. Fortunately I don't resort to the New/Old or even Class A/AB switch much at all. I leave it on New and Class AB, done.

Killer amp - and one that's stayed the course since I managed to get one of the first ones off the line from Bogner.

Enjoy that monster amp - it'll do everything (and gawd YES the clean with just a hint of break-up is something else... :inlove: )

Peace,
Mo
 
Mo, I’ve had the 20th for a good while now and you’re correct that volume does help. FRYETTE PS helps a lot but it has such a great Master it doesn’t need it. Really I’ve grown to appreciate those two “quirks” of too little and too much gain in the channels now. Classy blue channel and trashy (in a good way) red channel. Kinda how I like my wife, Lady in the streets and freak in the sheets.
 
BrentSP":848tznl3 said:
Kinda how I like my wife, Lady in the streets and freak in the sheets.
:rawk:

Awesome man... Ya, volume - that thing we're supposed to utilize when owning 100W heads. Funny how it changes things. Glad you dig. And loved the anology :LOL: :LOL:

Keep it loud and pound it out Braddah!! :rock:
 
Excellent post, Brent. :thumbsup: Lot of great information on the different versions of the XTC

Per our conversations, I'm super interested in the 20th but still not sure I'm ready to dump the Classic. When it's loud it seems to come alive like no other amp I've owned and I love the Blue channel as is. I just don't have the opportunity to open it up as often as I'd like to. Plus, I still don't have a Bogner cab and feel that I'd be doing an injustice if I traded or sold before grabbing at least a 212. I keep thinking the Helios 212 would pair up nicely.
 
I've spent a fair bit of time on the EL34-20th lately.

It's one amp of very few that simply never gets old. It's just flat out addictive. Glorious.

/end love rant
 
After having played three different XTCs over the years, I'm waiting for my first Friedman amp, the BE100 DLX. Only the EL34 20TH Anniversary XTC is still on my bucket list. Do you think, they are comparable and cover the same spectrum?


Cheers, Stefan
 
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