Nobelium low headroom

P

Paceman

New member
Hi! New member here. I’ve built a 40+ pedals at this point so I’m not a complete beginner but I can’t say I understand enough to be an efficient troubleshooter. Finished my Nobelium kit from Das Musikding a couple of days ago
2 questions:

1: I had to flip the polarity on my audio device (Audient ID4) to get the XLR output and the 1/4” outputs to play in phase. I’ve never seen that mentioned in any of the Nobelium threads. Not a huge issue

2: This is supposed to be a really clean DI, right?

I had to set the trimpot no higher than a quarter of it’s travel to prevent some pretty ugly distorsion from the XLR out. I thought I might be overdriving the transformer but the 1/4” had the same distorsion around noon and upwards.
I’m pretty confident I’m not overdriving the input of the device or amp.
Tubes are JJ ECC82. Could be those? I don’t have any more ECC82s lying around, possibly a couple of 12AX7s and 12AT7s
I did ask Klaus about the silver mica for C6 that was marked 270J (=27pF ?) in the kit and he said that it was fine. Since it is a Silver mica cap it would be labelled differently. My DMM doesn’t have a Farad setting
If It was labelled conventionally after all, would a 27pF cap lower the headroom a lot?

The power supply is a One spot 1700mA

Bass is a Sandberg California active bass with a P style pickup and a MM humbucker. I stay mainly on the P pickup. The distorsion is present also in passive mode if I play a little harder. I did try another bass with a ridiculously hot Billy Sheehan P pickup in it. Same result

It does sound nice enough if I keep these pots low. Seems weird though…

Any help is appreciated

Cheers!

/Mattias, Stockholm Sweden

270J.jpg Inside.jpg
 
The XLR uses only tube 1 that's on the left when you look from the back, the one that is above the Nobelium writing.
The 1/4" output uses both tubes.
Swap your tubes around and see if it is any better on the XLR output, or try another 12AU7 tube in Tube 1 position.
The 12AU7 has a gain of about 19, and all other tubes in the 12##7 range has higher gain then that so trying other type of tubes wont prove anything except give you more breakup.

Some small caps are marked with their actual PF value instead of the correct code, so yours might actually be 270pF or 27pF, the only way to know for sure is to test it.

The Nobelium uses a standard Fender tone stack so it is easy to work out what it does, here is a link to one like the Nobelium with a 270pF cap:

And here it is with a 27pF capacitor:

You can move the RB and the RT pots around but leave RM on 10 all the time, the mid pot RM is replaced with resistor R21 so it is not adjustable. (Unless you stick a 5k pot in there)

If you leave the Bass and the Treble pot on 0 you end up with a fairly flat response, if you move both up you get a mid dip in the response.

I think you have a hot tube in V1 position or you are using a very hot signal going into the nobelium, have you tried turning the volume down on the guitar ?

Cheers
Mick (from Tungelsta a long time ago)
 
Thanks! I’ll try swapping the tubes.
My pickups are pretty hot, clipped my oc2 so I built a clone that I run on 18v which gives enough headroom.
I think I can borrow a vintage style p bass to try more traditional pickups

(Tungelsta, huh? Grymt!)
 
Yes, just look at the schematic. Only the DI out volume, though. The output jack one is before the second tube that acts as a line driver (cathode follower). The trimmer is also linear, so you should expect different behaviour from the output jack volume.
I would check all the resistor values and if the transformer is mounted correctly.
 
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