Atomic Energy Commission tube DI preamp

Yet another golden oldie project, shot on real film. Former Peavey TB Raxx bass preamp, cut down and rebuilt as a 2 channel tube DI preamp, using RCA output transformers of unknown origin. 'Atomic Energy Commission' badge added for authority; I pulled a bunch of those off of gear I scrounged in Los Alamos. Input has parallel jacks to feed an amplifier (never use them) and 1M ohm input pot feeding fixed gain stages. I roughed this in with a simulator way back when, then did a lot of listening tests and small changes. Revisited with simulator later and came up with a better solution that I've still never implemented. This gets stereo keyboard feeds and acoustic guitar pickups most frequently. Built it originally to take on tour with a band I was recording who used two acoustics with pickups.

Very nice. I'd love more info on your build.

Nice, I rather like my TB-Raxx and use it as my Bass pre

( after fitting some decent valves and having a "tweak" & a re-cap )

MM.

I'd love to find the info too! :razz:

I think I did this in '97, so memory is a bit dim. I think it was originally 12AX7 single gain stage with cathode follower output, then I changed to double gain stage after 15k:600 output transformers were added. But it might still be CF driving transformers. I intended to rewire for a proper 12AU7 2nd stage driving the outs, but it's not happened. There's a plan on paper somewhere around here that was done in sim, which I'll probably toss when I revisit.

Apologies to Peavey.....

Hey Doug. Nice! How do this thing sound?...

Fairly colored 12AX7 sound. Perfect for acoustic pickups. Tends to help crappy sounding keyboard outputs. Clips very nicely. Gets used as a fuzzbox during mixing at times. I'm reminded that I must have done away with the CF stage as I recall messing with overall feedback loop values, and opting to have none.

Gotta pull it back apart and re-hack it sometime soon.

[quote author="MartyMart"]Nice, I rather like my TB-Raxx and use it as my Bass pre

( after fitting some decent valves and having a "tweak" & a re-cap )

MM.[/quote]
I'm with you on the injustice done to the TB-Raxx :wink:
Used one for various years as well, not a bad pre.
These seem to go cheap though in the US, so can understand that when in need of a case it gets slaughtered.

[quote author="emrr"]There was really absolutely no one at the time (and not many even now, in the USA) who don't look down their noses at anything Peavey. Even painting over the name tag raises the value. :razz:[/quote]
Can completely understand how things went over there :thumb:

Not completely deserved though imho, poor poor Peavey preamp...
I mean, not completely satisfied with the preamp in my SWR SM-400 I ended up with the TB-Raxx-pre to replace the pre in the SWR-amp. The Peavey was more what I was looking for. After that it got replaced again with the Ampeg SVT-IIp which was even more what I was looking for, so actually my TB-Raxx is a bit dusty here as well. Hmmmm, what was your mod again ? :wink: :razz:

But if I understood it correctly these chrome Peavey Valverbs (tube-spring reverb & hybrid amplitude modulation) aren't really frowned upon, right ? ... would love to find one....


Bye,

Peter

Yes, the Valverb is an exception.

the AEC badge is the real kicker! :green: You could just tell people "I could show you the schematic, but then I'd have to kill you"

it just might be killing me already. It is pre-1974, after all, so who knows were it was. I haven't bothered with a Geiger counter.



:green: :?: :shock: