Modding my XTC :)

I have just return from the Marvel Amps HQ with my modded XTC. Totally new amp! The essential change was removing all polypropylene coupling and tone caps for dirty channels and replacing them with TAD/Mojo Dijon polyester film-to-foil caps. Man, WHAT A CHANGE!! The amp is now hairy, aggressive and crunchy, not losing Bogner flavour by the way . Now I know why Bogner put these to the 20th Ann amp. I felt polypro FKP3 caps sounding harsh since they allows more highs to pass. Polyester caps tend to round the highs off a bit and smooth out the tone. I can strongly recommend that change.

Second big part of the "new" tone are NOS ERO Roederstein MKT1813 cathode bypass caps - the best for what I wanted to get. Very clear, detailed, with a bit much upper spike, treblyish and very Marshally-sounding. I tried NOS Ero caps and current 1813's made by Vishay. That second cap was much thinner sounding and noticeably brighter. I like Ero caps much better, fuller sounding.

Third part of all that mess are new values in cathodes for 1st and2nd stage. That change gave me more open tone, with more crunchy mids, more Marshally-sounding. I ended up with these values:
- 1st stage: 1.5K//1uF - NOS MKT1813 bypass cap (as in Splawn QR, Marshall JVM, etc.)
- 2nd stage: 2.7K//1.5uF - NOS MKT1813 bypass cap piggybacked (as in XTC 20th Ann, Splawn QR 3rd gear - but 1uF bypass cap)
- Structure R43: 12K - giving 2.2K overall resistance in 2nd stage if needed (C2 Structure cap removed) - I chose that value because using 1.5K in 1st cathode it gives more Bogner flavour than 2.38K stock value

BTW, for bypass caps I have also tried these:
- Mallory 150 - the best "drive" (distortion) but too much low-end. Good thing for some as such (for Marshalls), but as I try to take away some of it from my amp it could eventually be used as 2nd bypass only
- Wima MKS4 - sounds good, but only "good". Quite out-of-character. Transparent but a bit backed-off. Same impression with Siemens&Halske MKT and MMK Rifa stock XTC caps... good all-around caps though
- tantalum - boomy and unclear, very compressed. I wonder why Bogner put it as 2nd bypass. Don't like it at all... Changing tantalum to polyester cap in Structure circuit was the first mod I've done to my XTC
- axial BC electrolytic (small blue Philips axial caps remake) - quite interesting, nice drive but a bit backed-off and boomy

It now looks like this:



So, as for now end of modding, time for some giging with a "new" amp .

Regards, Andy

clips

Further mods done to my amp. Changed 1st CC to 2.2nF (TAD/Mojo Dijon) and output caps to 22nF (Mallory 150). The flubby bass was reduced quite a lot I must say. But I'm gonna give it some time to get used to it. Eventually I will raise 1st CC to 3.3nF or return to 4.7nF. But no way back to 100nF output caps for sure!!

I like "new" tone in general, especially those last mods drastically reduced "blanket effect" and made the tone much more "in-front". I can even reduce volume a bit and my tone is hearable in the mix exactly the same way as before doing the last mods. Now there's much more classic Marshall crunch in my amp.

I also switched to RFT/Siemens EL34 powertubes. A bit more clarity in lows than using =C='s.

But the biggest part of the overall tone improvement was changing polypropylene coupling and signal caps to film-to-foil TAD/Mojo Dijon mustard clones. Strongly recommended change.

Will post some clips further on...

Regards, Andy

Clips:

RFT/Siemens: https://www.soundclick.com/player/single ... 84552&q=hi
=C='s: https://www.soundclick.com/player/single ... 84553&q=hi

Don't mind my crappy playing but hopefully You'll get how the amp sounds after the mods.

Regards, Andy

It's a shame you didn't do before and after clips under "controlled conditions" (i.e., same cab, mic placement, etc.).

Impossible to please everyone...

I thought that everyone knows how "regular" XTC sounds, tons of clips on YT, and that is why I recorded my amp modded only.

rlord1974":31gyj0ek said:

It's a shame you didn't do before and after clips under "controlled conditions" (i.e., same cab, mic placement, etc.).

Click to expand...

I agree that it would have been very interesting to hear a pre and post mod clip. There are plenty of pre mod clips but thats a different player, guitar, cab, mic,etc...

that aside, very cool info and thanks for the mod description. I think I remember you from the Bogner forum. You are constantly tweaking your 101b!

Hi!

You're right, I am the very same Setneck from Bogner forum. Shame that it is dead for a very long time...

As for the clips, the modding trial took me nearly a few months, I have worked on my amp step by step, changing parts and testing the tone, with a few things that was reversed. It was simply impossible to record pre and post clips in the very same conditions.

But I am very happy with the final result. The final mods are:
- 1st stage: 1.5K//1uF - NOS MKT1813 bypass cap
- 2nd stage: 2.7K//1.5uF - NOS MKT1813 bypass cap
- Structure R43: 12K - giving 2.2K overall resistance in 2nd stage if needed (C2 removed)
- all dirty CC's and dirty tone caps changed to TAD/Mojo Dijon film-to-foil caps
- 1st dirty CC: .0022uF
- PI output caps: .022uF (Mallory 150)

Also here are the samples how the amp sounds in band context with both =C='s and RFT's. Clips aren't too clear but hopefully You can catch the point. The amp settings and recording conditions are the same. Also clips are recorded without bass guitar but it is by purpose to hear the difference better:
Svetlana: https://www.soundclick.com/player/single ... 04852&q=hi
RFT: https://www.soundclick.com/player/single ... 04853&q=hi

My amp is backing for the first solo and I play second solo. The difference is IMO very audible between those two tubes. RFT's maybe don't have as much "balls", but are clearer and more forward. They are focused in upper mids to my ears and have very singing tone.

Regards, Andy

Question, why did you increase the PI caps and what was the result?

I changed PI output caps to remove most of the muddying low-end, which caused "blanket effect". 100nF is way too much, lets too much bass go thru. It is a value which was put by Marshall to JMP bass amps.

The main cause of a change (actually of all mods done) was that I was getting lost in the mix, my tone was "cardboard". Now it's more hi-mid thing. The Bogner flavour is still there, but it's more "marshall-ish".

Here are the short clips:
100nF: https://www.soundclick.com/player/single ... 06063&q=hi
22nF: https://www.soundclick.com/player/single ... 06064&q=hi


Regards, Andy

But wouldnt that be basically making your 101b a classic xtc? or am i dumbing it down?

It is partially similar to Classic and partially to 20th Ann. It has 1st dirty CC .0022uF, 2nd gain stage 2k7//1.5uF and Structure circuit removed as it is in Classic. Also dirty signal and coupling caps are now all film-to-foil polyester caps like in 20th Ann.

My ideas are: 1k5//1uF in 1st gain stage and .022uF PI output caps.

Regards, Andy

Hi guys!

Some time of gigging with my modded XTC confirmed, that the direction of modding is right . The amp started to sound more "proper" . So time for further mods .

I plan to:
- change dirty Middle & Treble and both Presence pots to linear (as they are linear in Marshalls)
- replace 1M Excursion resistor to 1M linear pot to have pot-adjustable Resonance Control - in XTC we have fixed resonance resistors: 1M is Resonance all way up, 1M paralleled with 220k is the pot in a half way and bare 100k nfb cap (220k M position resistor will be most probably removed from the circuit)
- add a DPDT switch to 470pF Resonance cap adding in parallel 2.2nF and 4.7nF caps - as single 470p cap adds too much bottom IMO. Resonance cap in most amps and most mods is 4.7nF
- 1st gain stage will be now DPDT switchable between stock values 820R/.68uF and modded values 1.5K//1uF - above mods would remove much of the muddying bottom (sepecially pots), so it may be possible to return to stock 1st stage values (which I actually quite liked ).

Any thoughts apreciated

Andy

Did these mods take any of the chewy goodness of the blue channel?

My mods are designed to take away some (quite big I must say) amount of bottom, which may make an impression of taking away some chewiness and woodyness out of the overall tone also. But that Bogner flavour is definitely still there, the mods didn't make my XTC a different amp, but only a more "Marshall-esque" one.

I have a feeling that my mods have bigger impact on Red channel than a Blue, which - especially thanks to 22pF PI caps, 2.2nF CC1 cap and Mojo/TAD tone caps - is now only more close to classic JMP/JCM800 tone. But it still holds the XTC signature tone.

Regards, Andy

Right on. Thank you.

You're more than welcome Greg.

Andy

You may decrease the Presence pot's resistance down to 5-10k. Stock it's a 25k pot, which isn't too effective. You got to turn it up quite much to achieve any effect. When You make it 5-10k it'll start to function more hearable earlier, thus the highs should appear in more pleasant way

Regards, Andy

Andy, I think Reinhold need's to hire you!! I think at this point you know the XTC better then him, you could give him a few pointer's

Thanks Greg . That would be great indeed to become a part of Reinhold's gang, but I doubt He'd like my ideas, since they are actually quite opposite to his view on the XTC amp . He's darkened its tone and I am bringing it back to Marshall territory, with XTC "Setneck Edition" as a result .

After doing mods described above I'll record clips comparing my friend's stock XTC and my amp, using same tubes and similar settings. I am curious about the results myself .

Regards, Andy