XTC 101b clean channel?

[Setneck]

yea all these things are tough, one tweak here, changes everything down the line

And that's the greatest thing in modding amps . You not only have to predict the impact the particular mod has on the tone but - while modding the amp in a few places - predict the correlation between all mods done. That is why I had to reverse some mods I've done. And that is why the modding process took me nearly 2 years .

I can see where a lot of the amp makers, just put it in the middle, to satisfy the masses and sell the most amps. Bogner did a great job with all the little adjustments he added IMHO

I totally agree - XTC is one af the best examples of what You've said. It is extremely versatile amp, covering lots of grounds, having its own individual - great - tone, that "Bogner nasally sound" as I name it. That is why some love it as it is and some don't and sell it. And some of the users don't like it stock, but keep it and mod it .

my tweaks are great for only me. Tweak on

Most of the tweaks are good only for those who do it. It especially depends what music do You play. You are great example of that, and so is a friend of mine who is fusion guitarist and for whom stock XTC tone is more than perfect (the only mod done in his amp was removing post2004 R12 factory mod). He played my amp and said the thing which was actually totally obvious: "if I'd play rock, I'd steal that amp from You ". But he doesn't, so it would be harder for him to achieve the tone he needs. He is able to use it stock and get great sounds, "HIS" sounds. My mods were designed to make my XTC more a strictly hardrock amp, taking away some of the versatility. I don't need my amp to be good in fusion or blues, the same as You need Your amp to be bluesy and not metal.

One thing is worth mentioning: XTC is a great platform for tweaking, when You: 1) like it in general, 2) know what do You want from Your tone, 3) know what to do to achieve it with modding XTC (what mods to do to get the tone You need).

That is why there was only one moment I started to think about reversing the mods and sell the XTC. It was before I finally decided to switch to TAD/Mojo Dijon signal caps and 22nF PI output caps, and during the days a friend of mine bought himself Splawn Quickrod. Man, what an amp!! Rude, nasty and dirty tone machine. I liked that very much, but after I did above mods the unconditional love to my XTC returned . The main point for that was the feel of an XTC. Any other amop doesn't have such soft, smooth and meaty feel.


Regards, Andy

 

[jamme61]

to me the feel of the xtc is just perfect. It makes me want to play more and it effects the way I play (in a good way) I had a PT-100 which many people love(I don't) it was cold and hard compared to the XTC and there was a lot less versatility to the sounds. The clean channel on the pt-100 does not want to crunch at all and the chn 2 and 3 do what they do and don't try to change it. don't mean to bash the pt-100 great amp and john suhr is a super nice guy (great support) it's great at what it does just not for me. XTC just has that vintage feel and sound, that I love.

 

[Setneck]

Hear Ya bro, same with me about the feel of XTC. That is why I decided to mod it instead of selling it. And that is why some day I'll buy myself another stock XTC to have it at home and play for myself

My modded "Setneck XTC" will always remain my main gigging amp . I feel unarmed without my baby on stage .


Best Regards, Andy

 

[_actual time_]

update: take the 470pf out of the circuit. its part of the negative feedback of the amp. IMHO the amp sounds a lot better without it. it's the red cap C40 mounted right behind the excursion B switch .

can you school me on this C40 mod? (didn't it used to have its own thread? i can't find that thread...)

is there any way to make it switchable without taking out the amp circuit board to solder onto the bottom side? (like how the mod of removing the unboost cap C224 can be made switchable without pulling the circuit board because you can solder onto the resistor that's in parallel with it.)

i'd love to try it, but only if i can put it back to stock without having to pull the board.

 

[jamme61]

the 470pf sends all those high frequencies back into the amp, which kills all those highs.

 

[_actual time_]

What I did was clip the cap out and then I ran two alligator clips off the 1 meg resistor (which is in parallel with the 470pf cap). then I could play the amp with the 470pf cap on and off (using the aligator clips) to see what I liked. ... If you like it better with the 470 pf in there, you can easily attach it to the 1 meg that is on the board. this way you don't have to remove the board.

perfect! thanks. yes, the resistor in parallel means i can definitely put it back to stock without pulling the board, just like C224.

this resistor is R62, right? like Setneck talks about modding, in a similar way, here: viewtopic.php?f=59&t=116020&p=1619875#p1524117

 

[Setneck]

Remove that C40 sucker and You'll never want to have it back in the amp. Don't even test the tone with and without the cap. I should have start with this mod before I modded anything else. The amp is now truly open, very in-front and aggressive as hell.

After You remove C40, Excursion circuit become nfb adjustment circuit. The higher the NFB resistor the lower the feedback signal, that makes for a more aggressive amp.

Note that without the cap it'd be difficult to use L Excursion, especially for dirty channels. It is 1M resistor in parallel with nfb 100k resistor. I had a 1M pot soldered to R62 slot and after turning it full up the amp was simply too loud, way too much buzzy highs. In M position You'll have 1M//220k, which gives 180k in series with nfb resistor. And that is the best setting if You have fixed Excursion, at least for distorted tones. I lowered the pot resistance to 250K and now have it nearly half-way, so it is additional 120-130k.

If You want to have more flexible adjustment - and don't have class A/AB switch - remove R62 and put a linear 250K pot in this slot. Set Your both Excursions to L and set an amount of nfb with a pot. Forget about caps I have, I don't remove them only because I don't want to have a hole in a chassis.

Here You have a pic of a board.




Regards, Andy

 

[jamme61]

setneck is the best! he's a great resource and has helped me find my xtc tone. Big thanks

NFB? so stk values without cap are M = 90K L= 180k what does T=? Thanks again

 

[Setneck]

In T position the Excursion filter is completely bypassed so You have bare 100k nfb resistor in circuit. In M and L positions it’s added in series with the 100k nfb resistor.

So, in stock XTC, in L position you have the 1M//470pF combo in series with 100k, in M position the 220k is added in parallel to 1M//470pF, which results in a 180k//470pF in series with nfb resistor.

So basically in M position You have 280k total nfb resistance and in L - 1.1M (resistance added in series sums up, contrary to capacitance).

You can imagine the Excursion switch and resistors like a 1M log pot with 3 positions - 0 (T), middle (M) and max (L).


Regards, Andy

 

[_actual time_]

Setneck is the best!

yes, he totally is!

the Excursion filter is...

so this exact Excursion resistor network takes the signal for both Excursion A and Excursion B? what i mean is, if you remove C40, is it removed for both Excursion A and Excursion B?

and you say, a few posts above this, that without C40, it's difficult to use the L setting of Excursion. do you mean that the L Excursion's 1.1 M resistance of nfb doesn't sound good without C40 in the circuit too? was that when it sounded buzzy with too much highs?

(and in that post a few posts above, when you say "It is 1M resistor in parallel with nfb 100k resistor", that "parallel" is a typing mistake, right; it should be "series"?)

while thinking about all of this, your power amp mods schematic in this post has been a big help: viewtopic.php?f=59&t=116020&p=1619875#p1569564

thanks for helping me understand.

 

[Setneck]

Setneck is the best!

yes, he totally is!

Thanks guys . As I've said many times - always a pleasure to help Bogner bros .

so this exact Excursion resistor network takes the signal for both Excursion A and Excursion B? what i mean is, if you remove C40, is it removed for both Excursion A and Excursion B?

That is correct. Every change done to Excursion circuit affects both A & B pots.

and you say, a few posts above this, that without C40, it's difficult to use the L setting of Excursion. do you mean that the L Excursion's 1.1 M resistance of nfb doesn't sound good without C40 in the circuit too? was that when it sounded buzzy with too much highs?

Yes it was, as the cap removes big amount of highs and mids out of the nfb. Even with C40 if You switch from L to M there a noticeable drop in volume. Without the C40 none of the freqs is blocked so if You remove it the amp became too loud in L. Try for Yourself and You'll see. In my amp it is even more noticeable than in Yours because of the mods done to remove unneccessary lows out of my XTC's tone. So there's even more highs and hi-mids that are allowed to pass.

That is why I soldered 330k resistor in parallel with 1M pot to make it ~250K, which is enough to control the amount of signal being fed back. While having 1M pot I didn't even turn it up more than to 9 o'clock, so it had 250K resistance in that position (pot is linear) or the amp was becoming hard to control. Now I set the pot halfway, so it has ~125k.

So if any of You will decide to replace R62 resistor with a pot, 250K linear one is more than enough.

(and in that post a few posts above, when you say "It is 1M resistor in parallel with nfb 100k resistor", that "parallel" is a typing mistake, right; it should be "series"?)

Yes, that is a mistake, sorry. R62 resistor is IN SERIES with R64 nfb resistor.

while thinking about all of this, your power amp mods schematic in this post has been a big help: viewtopic.php?f=59&t=116020&p=1619875#p1569564
thanks for helping me understand.

No problem, always feel free to ask any questions .

Regards, Andy

 

[jamme61]

I wonder if the 20th xtc made these changes?

 

[Setneck]

Excursion circuit is somehow modded in 20th Ann. but I don't know which way.

470pf C40 cap, alongside with audio treble pot, are mainly responsible for "blanket effect" in 101B. Getting rid of C40, alongside with changing dirty Treble pot to linear, was the most important mods in my amp.

I clipped out C224 too, but still the drop in gain is too much for me. I stay with bare 500k 2nd stage grid resistor.


Regards, Andy

 

[_actual time_]

In T position the Excursion filter is completely bypassed so You have bare 100k nfb resistor in circuit. In M and L positions it’s added in series with the 100k nfb resistor.

So, in stock XTC, in L position you have the 1M//470pF combo in series with 100k, in M position the 220k is added in parallel to 1M//470pF, which results in a 180k//470pF in series with nfb resistor.

so C40 is not in the circuit when Excursion is set to the T position?

which means the remove-C40 mod only affects M and L Excursion?

interesting. i'm designing a switchable mod for it that would let me switch it back to stock, and maybe to some other value too. hmm...

 

[jamme61]

In T position the Excursion filter is completely bypassed so You have bare 100k nfb resistor in circuit. In M and L positions it’s added in series with the 100k nfb resistor.

So, in stock XTC, in L position you have the 1M//470pF combo in series with 100k, in M position the 220k is added in parallel to 1M//470pF, which results in a 180k//470pF in series with nfb resistor.

so C40 is not in the circuit when Excursion is set to the T position?

which means the remove-C40 mod only affects M and L Excursion?

interesting. i'm designing a switchable mod for it that would let me switch it back to stock, and maybe to some other value too. hmm...

 

[_actual time_]

You should hear what 470pf does, it sounds like crap IMHO. you might not want to put it back once you hear it.

i need it switchable so i can give it a good test. and maybe i can find a cool other thing to put on the other side of a DPDT switch...

I like T setting on clean and M setting on blue and red, unless playing at home at low volumes. Then I use T on Blue and red.

i use T on the Red, for tighter metal lows, and M on the Blue, for looser rock. so it seems like C40 would brighten my Blue rock sound but not change my Red metal sound. which is totally cool. i'm stoked to try it.

 

[Setneck]

so C40 is not in the circuit when Excursion is set to the T position? which means the remove-C40 mod only affects M and L Excursion?

According to the schem, in T position You have bare 100K nfb resistor in circuit. I had an subjective impression that removing C40 changed slightly T voicing too, but I tested it for a short time, as I have a pot in place of L R62 resistor and both Excursions are set to L in my amp.

interesting. i'm designing a switchable mod for it that would let me switch it back to stock, and maybe to some other value too. hmm...

That is how I got it in my amp. I have a spdt switch with 470pF and 2.2nF cap soldered to the nfb adjustment pot. But I don't use any of the cap. You will not too .

But You may feel better with having a possibility to switch back to stock voicing. What will never happen .

i need it switchable so i can give it a good test. and maybe i can find a cool other thing to put on the other side of a DPDT switch...

The coolest thing here is a nfb adjustment pot. The only other thing You may use with a dpdt switch here is a different cap or different resistor. But You already have a 220k M resistor on board.

Regards, Andy

 

[_actual time_]

But You may feel better with having a possibility to switch back to stock voicing.

exactly. my C224 switchable mod came out of the amp later, when i was OK to never have the stock voicing there (and needed the mount hole for another mod ).

The only other thing You may use with a dpdt switch here is a different cap or different resistor. But You already have a 220k M resistor on board.

yeah, i'm thinking about another resistor. which, combined with the stock 220k and 1M resistors, would give me other NFB resistances higher than 100k (the T Excursion resistance) but lower than 1.1M (the L Excursion resistance). still designing...

 

[Setneck]

i'm thinking about another resistor. which, combined with the stock 220k and 1M resistors, would give me other NFB resistances higher than 100k (the T Excursion resistance) but lower than 1.1M (the L Excursion resistance). still designing...

You may try to use additional resistor in range between 220-470k. Higher values would tend the amp to get too loud and fizzy.

Still You might consider 250K linear pot in place of R62...

Regards, Andy