Fender Super Champ XD SCXD mods

[xtian]

PREAMBLE: I wanted a lightweight 10" combo, but couldn't find a Princeton for less than $600. But I finally got one of the last SCXDs from MF, as new, for $173.

This amp has a solid-state preamp with digital FX and modeling. Then the signal goes to the tube section, which is one half of a 12ax7 as a gain stage, the other half as a PI, and a pair of 6V6 as power section.

As expected, the digital front end exhibits a lot of white noise, plus crappy digital artifacts and aliasing as notes decay into silence. Fine for loud rock, but poor for sensitive playing.

I followed the lead of others <http://www.thegearpage.net/board/showth ... p?t=628217>, and installed a line-in jack just following the digital preamp. As I hoped, this cut all of the crappy noise from the preamp, and let me play directly into the tube stages. However, the signal from my guitar is obviously very low for this stage in an amp. It sounded nice and clean, but as if the Gain control was down around 1 or 2 (obviously, this mod bypasses all of the controls--I'm just trying to give an idea of the volume level).

QUESTIONS: How much, in dB or mVac or something useful, does my guitar's signal need to be boosted to equate to the signal leaving the preamp of a dimed Princeton?

I pulled out my mod, because I haven't drilled the chassis yet, so I can't test this idea: I just ordered an OCD pedal, which advertises 30dB of boost. Would that make a good preamp?

Any other ideas for bypassing the crappy preamp and making this SCXD a poor-man's Princeton (while leaving said crappy preamp intact and available)?

[xtian]

Well, I put the power-amp-in jack back in, this time permanently, drilling a hole in the chassis for the jack. Got out my clean boost pedal and cranked it up. EXCELLENT! Sounds great.

Now that I know I can completely bypass the digital front end and run directly into the pure-tube section, I'm very happy about keeping this killer, little, CHEAP, multipurpose amp in the house.

Photos below. I put some painters tape inside the chassis to catch the metal shavings as I drilled:

[IMG765]http://www.superconductormusic.com/pub/pix/scxd1.jpg[/img]
[IMG765]http://www.superconductormusic.com/pub/pix/scxd2.jpg[/img]
[IMG765]http://www.superconductormusic.com/pub/pix/scxd3.jpg[/img]

[dorrisant]

Thanks for posting... Gonna do this for a customer soon.

Any more thoughts since you've done this? Did you try anything else, like an opamp change?

Tony

[xtian]

I played it for a year, mostly in church services in a large theater, miked up through the PA. It did a great job with the Ragin' Cajun speaker. The noise floor was always bothersome at home, but on stage it wasn't noticeable. I rarely used The line in mod I created. Eventually I got bored and sold it.

[keysmank]

Any instructions for this mod?

[maxkracht]

I got one of these in for repair, client has been unresponsive so I haven't made changes yet. There's some kinda parasitic on V3, my guess is it is a pcb design issue, not lead dress or component failure. Might not show up on all, but i'm guessing it's not just this one. Tacking in 100pf plate to cathode got rid of the issue. I'm hoping adding grid stoppers will be a better fix but not pulling the board until I get the OK from its owner.

[xtian]

Any instructions for this mod?

All info is above at the top of this thread.