Rogue Audio Dark Upgrade.

My amp became darker sounding. :)

Which amp, specifically? They do it on ST100, M180, Apollo, and even old Zeus.

I went from stock 2010 Apollos to 2017 Apollo Dark. To be quite honest, I feel the stock Apollo were a better value. If I could have this back, I would have stuck with the old Apollos. But everyone is different, and you will find others gushing about what the upgrade did for them.

Two caveats to my circumstances:

1. I had already rolled excellent NOS small tubes into my old Apollos. Which negates the biggest sonic upgrade from the "Dark" model (which usually comes with RCA clear tops and Telefunken smoot plates - there are better vintage tubes than this).
2. I don’t think I like the premium Mundorf EVO coupling caps that go into the Dark models (standard models use plain white M-Caps). I wish Rogue offered a couple choices of premium caps.

The best upgrade would be to move up to the next bigger amp model, culminating in the Apollo monos. It does make a difference over the M180, even if you don't need the power (I have 96dB Tannoys). Unfortunately, I think they only offer the Apollo in "Dark" form now. But Apollo and Zeus amps are a GREAT deal used, if you can deal with shipping / transport issues.

That upgrade is $$  and shipping damages are always possible not to mention $$

Id say maybe conciser Some excellent NOS Input tubes and have a tech install some Sweet Coupling caps

Good reading

Please Click                       " Capacitor Check"

In the last link for a good read

@mulveling thank you 1st and foremost with your experience and recommendations.  I have a ST-100 and wondered exactly what you brought up. Would I even like the upgraded caps. Caps probably make a big difference but which one would be preferred. Hiend2 also brings up a good point and that is to purchase caps and have a tech install but again which ones?  In addition,  shipping back and forth isn't cheap plus the possibility of damages if shipped to Rogue for the Dark Upgrade. 

NOS tubes are another recommendation but which 12AX7 are considered popular for the ST-100?  I have several 12au7 to experiment with.  I  prefer a neutral to slightly warm sound. 

Lastly, the only downside of changing caps is it could hurt resale value because some buyers do not want to purchase a modified component unless it was performed by the factory.